Friend or Foe: Dietary Restriction and Its Protective Effects on Responses to Ionizing Radiation

1.1. Dietary Restriction: Biological Foundations and Systemic Adaptation

Dietary restriction (DR) broadly describes nutritional strategies that reduce overall caloric intake, selectively limit specific macronutrients or amino acids, or modify feeding schedules, while preserving essential micronutrient sufficiency and preventing malnutrition. This framework encompasses caloric restriction (CR), protein restriction (PR), amino acid restriction (AAR), and fasting-based approaches including intermittent fasting (IF) and time-restricted feeding (TRF).^1,2 Since the pioneering experiments by McCay and colleagues in the 1930s first demonstrated lifespan extension in rodents subjected to reduced caloric intake, ³ DR has become the most robust and evolutionarily conserved non-pharmacological intervention shown to extend lifespan and improve healthspan across diverse species. Research spanning yeast, invertebrates, rodents, and non-human primates indicates that DR does more than reduce energy consumption; it induces systemic remodeling of nutrient-sensing and stress-response pathways, leading to improved metabolic efficiency, enhanced cellular maintenance, and delayed progression of age-associated pathologies.^4-6

Mechanistically, DR modulates conserved metabolic signaling networks. Central features include suppression of insulin/insulin-like growth factor-1 (IGF-1) signaling and the mammalian target of rapamycin (mTOR) activity, together with activation of AMP-activated protein kinase (AMPK) and sirtuin pathways.^7-9 These coordinated shifts reorient cellular physiology away from growth and biosynthesis toward repair, stress adaptation, and quality control. Such reprogramming intersects with several hallmarks of aging, particularly mitochondrial dysfunction, genomic instability, impaired proteostasis, and chronic inflammation, thereby positioning DR as a systemic regulator of longevity-associated biology.^10,11

1.2. Dietary Restriction as a Modulator of Ionizing Radiation Responses

Exposure to ionizing radiation (IR) provokes complex biological injury characterized by DNA double-strand breaks, oxidative damage, mitochondrial disruption, inflammatory cascades, and regulated cell death. These processes contribute to both acute tissue toxicity and delayed consequences such as fibrosis, degenerative changes, and carcinogenesis.^12,13 Notably, many of these radiation-induced alterations overlap with molecular features of aging, including genomic instability, impaired protein homeostasis, mitochondrial dysfunction, and sustained inflammation. This convergence suggests that interventions enhancing cellular resilience and maintenance may influence radiation responses. Within this framework, DR represents a metabolic intervention with potential to reshape IR outcomes through several complementary mechanisms: reduction of baseline oxidative stress, reinforcement of antioxidant defenses, enhancement of DNA repair and cellular quality-control pathways, and modulation of inflammatory and immune signaling that drives late radiation injury.^14-16 Importantly, DR effects appear context-dependent. Under nutrient limitation, normal cells often adopt a quiescent and stress-tolerant phenotype, whereas cancer cells—frequently constrained by oncogenic signaling and metabolic rigidity—may lack equivalent adaptive capacity.^17,18 This divergence underlies the concept of differential stress resistance, whereby DR may confer protection to normal tissues while simultaneously increasing tumor susceptibility to radiation-associated stress.

1.3. Purpose, Scope, and Novelty of This Review

Although studies linking DR to radiation biology are expanding rapidly, findings remain fragmented across aging research, metabolism, oncology, and radiobiology. The present review integrates these domains by positioning DR as a systems-level metabolic intervention with emerging relevance to IR. We (i) outline principal DR regimens and their shared conceptual basis, (ii) synthesize molecular and systemic mechanisms through which DR reinforces cellular maintenance programs, and (iii) critically evaluate available evidence for both radioprotective and radiosensitizing effects in normal and malignant contexts. By connecting nutrient-sensing regulation with radiation injury and therapeutic response, we propose DR as a metabolic framework capable of enhancing radiation resilience while improving therapeutic index. Key knowledge gaps and priorities for translational development are also discussed. A schematic overview is provided in Figure 1.OPEN IN VIEWER

2.1. Overview of Dietary Restriction Regimens

Dietary restriction (DR) encompasses a spectrum of nutritional interventions that reduce energy intake, modify nutrient composition, or alter feeding patterns without causing malnutrition. Major DR paradigms include caloric restriction (CR), protein or amino acid restriction (PR/AAR), and fasting-based approaches such as intermittent fasting (IF) and time-restricted feeding (TRF). Although these strategies differ in implementation, they consistently induce overlapping metabolic and cellular adaptations associated with improved stress resistance and metabolic homeostasis.

CR, typically defined as a sustained reduction in caloric intake while maintaining adequate micronutrient supply, remains the most extensively studied DR modality and has been associated with lifespan extension and delayed onset of age-related disorders across multiple experimental systems.^4,19 In contrast, PR and AAR primarily target nutrient composition rather than total energy intake, highlighting the importance of amino acid signaling in regulating metabolism, stress responses, and longevity-associated pathways.^20,21 Restriction of specific amino acids, particularly methionine and branched-chain amino acids, has been shown to reproduce several metabolic adaptations observed under CR, including improved insulin sensitivity, reduced oxidative stress, and altered nutrient-sensing signaling. These findings emphasize that modulation of amino acid availability itself, particularly through mTOR- and insulin/IGF-1–related nutrient-sensing pathways, can independently influence metabolic adaptation and stress resistance.^22-24

Fasting-based regimens, including IF and TRF, differ from continuous dietary restriction by emphasizing periodic cycles of feeding and fasting. These approaches promote metabolic switching from glucose utilization toward fatty acid oxidation and ketone body production, thereby activating adaptive stress-response pathways and enhancing metabolic flexibility. This adaptive metabolic reprogramming is thought to contribute to enhanced cellular resilience and improved tolerance to metabolic and oxidative stress.^25-28 Importantly, several beneficial effects of IF and TRF appear to occur independently of overall caloric reduction, suggesting that temporal regulation of nutrient availability itself exerts significant biological effects. ²⁹

In addition to restrictive paradigms, emerging nutrient-directed strategies aimed at restoring metabolic balance and supporting tissue recovery have also gained interest. Such approaches, including “dietary inversion” concepts involving selective replenishment of amino acids, micronutrients, and antioxidant-associated nutrients, may complement restrictive interventions by mitigating treatment-associated metabolic dysfunction and normal-tissue injury.^30-33

Despite their methodological differences, these dietary and nutrient-directed interventions converge on several conserved biological responses, including suppression of insulin/IGF-1 and mTOR signaling, activation of AMPK and sirtuin pathways, enhancement of autophagy and mitochondrial quality control, and attenuation of oxidative and inflammatory stress. Because these interconnected nutrient-sensing and stress-adaptive pathways critically influence radiation-induced tissue injury and recovery, they provide an important mechanistic framework for understanding how DR modulates responses to ionizing radiation.

2.2. Integrated Nutrient-Sensing and Stress-Response Networks Relevant to IR

Dietary restriction (DR) exerts its biological effects through coordinated modulation of conserved nutrient-sensing and stress-response pathways that regulate cellular metabolism, energy balance, and adaptive stress responses. ³⁴ Rather than functioning independently, signaling networks involving insulin/IGF-1 (IIS), mTOR, AMPK, and sirtuins operate as an integrated regulatory system that dynamically adjusts cellular priorities according to nutrient availability.^35-37 Under nutrient-rich conditions, IIS and mTOR signaling promote anabolic metabolism, protein synthesis, and cellular proliferation.^38-40 In contrast, nutrient limitation suppresses growth-promoting pathways while activating AMPK- and sirtuin-dependent programs associated with metabolic adaptation, autophagy-mediated quality control, mitochondrial maintenance, and cellular stress resistance.^41-44

Collectively, these signaling adaptations shift cellular physiology away from growth-oriented processes toward maintenance and repair. Reduced IIS and mTOR activity limit anabolic demand and enhance cellular quality-control mechanisms, whereas AMPK activation promotes energy conservation, fatty acid oxidation, and mitochondrial homeostasis.^41,45,46 Concurrently, increased NAD⁺ availability during nutrient limitation enhances sirtuin activity, linking metabolic status to transcriptional reprogramming, antioxidant defense, and genomic maintenance.^47,48 These adaptive responses also contribute to preservation of genome integrity and enhanced tolerance to oxidative and genotoxic stress.^49,50 Extensive crosstalk among these pathways coordinates cellular responses to energetic and oxidative stress and contributes to improved metabolic flexibility and stress tolerance. ⁸

Importantly, many of these pathways directly intersect with biological processes implicated in ionizing radiation (IR) responses.^51,52 Radiation exposure induces oxidative stress, mitochondrial dysfunction, inflammatory signaling, and DNA damage, all of which are influenced by nutrient-sensing networks regulated during DR. ⁵³ This mechanistic overlap provides a biological basis for the capacity of DR to modulate radiation sensitivity, tissue recovery, and long-term radiation-associated pathology.

2.3. Cellular Maintenance and Stress-Adaptive Processes Influencing Radiation Responses

The coordinated nutrient-sensing adaptations induced by DR ultimately converge on a set of cellular maintenance and stress-response processes that are highly relevant to radiation biology. These include regulation of oxidative stress, preservation of mitochondrial integrity, modulation of inflammatory signaling, enhancement of DNA damage surveillance and repair capacity, and activation of autophagic quality-control pathways. Together, these mechanisms promote cellular resilience under conditions of metabolic and environmental stress. ¹¹

One of the most consistent consequences of DR is improved redox homeostasis. Nutrient limitation enhances mitochondrial efficiency, reduces excessive reactive oxygen species (ROS) production, and strengthens endogenous antioxidant defenses through activation of stress-responsive transcriptional programs.^54-57 At the same time, DR supports mitochondrial quality control through enhanced mitophagy and metabolic remodeling, thereby limiting accumulation of dysfunctional mitochondria that contribute to oxidative injury and inflammatory activation.^58-61 DR also modulates inflammatory and immune signaling pathways implicated in both aging and radiation injury. Reduced nutrient availability suppresses chronic pro-inflammatory signaling, partly through inhibition of NF-κB activity and improved metabolic regulation, while promoting cellular programs associated with stress adaptation and tissue maintenance.^62,63 In parallel, DR enhances genomic stability by supporting DNA damage surveillance and repair pathways and by reducing oxidative burden that contributes to DNA lesions.^64-67 These protective adaptations are closely linked to activation of autophagy, a conserved cellular recycling process that removes damaged proteins and organelles while maintaining metabolic homeostasis under stress conditions. ⁶⁸

Because oxidative stress, mitochondrial dysfunction, chronic inflammation, impaired DNA repair, and defective autophagy are central determinants of radiation-induced tissue injury and carcinogenesis, ⁶⁹ these DR-responsive pathways provide a mechanistic framework through which dietary interventions may influence radiation sensitivity and therapeutic outcomes. These mechanistic interactions form the basis for growing evidence that DR can differentially modulate radiation responses in both normal and malignant tissues, as discussed in the following sections.

3.1. Classical Findings of Diet–Radiation Interactions

Early diet–radiation studies provided foundational evidence that nutritional state modulates radiation tolerance, tissue recovery, and late carcinogenic outcomes. In the 1970s, studies in irradiated rodents indicated that dietary composition could strongly influence survival, as exemplified by marked survival differences under altered electrolyte balance regimens. ⁷⁰ Clinical observations also suggested a dietary role in modulating radiation injury. In a cohort of 44 children who received whole-abdominal radiation therapy at the Institut Gustave-Roussy between 1961 and 1972, 5 of 14 long-term survivors (36%) developed severe delayed radiation enteritis with small bowel obstruction. Histological findings included villus blunting, lymphatic dilatation, and inflammatory infiltrates. Remarkably, all affected patients showed sustained clinical and radiologic recovery under a fractionated, low-residue, low-fat, gluten-free, and milk-free diet, with no recurrence of enteritis. ⁷¹ Parallel work in animal models established that DR influences hematopoietic outcomes following radiation exposure, including bone marrow death and recovery. Regarding tumorigenesis, the most consequential late effect of radiation, the classical studies of Tannenbaum and colleagues in the 1940s provided convincing evidence that CR suppresses spontaneous tumor development.^72-76 However, it was not until the 1980s that Gross and Dreyfuss demonstrated that restricting food intake could also suppress radiation-induced tumors in animal models, marking a major milestone.

In Sprague-Dawley rats subjected to fractionated total-body X-irradiation (1.5 Gy × 5 weekly), tumor incidence rose dramatically, from 22% to 93% in females and from 5% to 59% in males. ⁷⁷ In rats fed ad libitum (AL) (5–6 pellets/day), all irradiated animals (14 females, 9 males) developed tumors or leukemia (100%), with average onset at 13.7 months in females and 13.4 months in males. By contrast, in rats maintained on a restricted diet (2 pellets/day), only 9/29 females (31%) developed tumors at 18.2 months, and 1/15 males (6.7%) developed a tumor at 9 months. In full-fed females, most tumors were benign, whereas in males, 1 leukemia and 8 tumors developed, 6 malignant and 1 benign. In the restricted group, female tumors were 4 malignant and 5 benign, and the single male tumor was a sarcoma. These findings clearly demonstrated that DR strongly suppressed radiation-induced tumorigenesis in both sexes. ⁷⁸ Two years later, the same group extended their work to C3H(f) mice, a strain in which spontaneous leukemia is rare (<0.5%) but markedly increased by total-body irradiation. ⁷⁹ Under the same fractionated gamma-irradiation regimen (1.5 Gy × 5 weekly), AL-fed mice (4.5–5.4 g/day) exhibited a high incidence of leukemia: 31/58 females (53.4%) and 24/50 males (48%), with an average onset at 8 months. In contrast, restricted-fed mice (2 g/day, then 3 g on alternate days) showed dramatically lower incidence, with only 2/55 females (3.6%) and 1/36 males (2.8%) developing leukemia at average ages of 9 and 12 months, respectively. Leukemia was predominantly lymphatic or lymphoblastic, with extensive infiltration of the thymus, lymph nodes, spleen, liver, kidneys, and bone marrow, and frequent leukemic involvement of the peripheral blood. Together, these results demonstrated that DR can strongly suppress both radiation-induced tumorigenesis and leukemia in rodents, although the underlying mechanisms remain to be elucidated.

These classical findings led to later experimental studies that expanded the scope of DR-mediated radiation effects beyond classical DR, including CRD, LHF, and ORA interventions. Emerging evidence indicates that dietary composition, restriction timing, and intermittent fasting protocols can influence radiation sensitivity in both normal and cancerous tissues. These studies reveal context-dependent effects, showing that DR can either mitigate or, under specific conditions, enhance IR-induced cellular damage, emphasizing the importance of diet type, duration, and biological context. These studies also lay the groundwork for subsequent mechanistic studies.

3.2. Calorie-Restricted Diets (CRD) and IR

3.3. Other Restriction Approaches (ORA) and IR

3.3.2. Main Achievements

Research on ORA, encompassing fasting-based strategies, targeted nutrient restriction or supplementation, microbiome-modulating diets, and bioactive dietary compounds, has yielded several key advances in understanding how dietary modulation intersects with RT efficacy and toxicity. Collectively, these studies demonstrate that ORA can influence radiation responses at multiple biological levels, including tumor metabolism, normal tissue resilience, immune regulation, and host–microbiome interactions.

3.3.2.1. Feasibility, Safety, and Patient-Centered Outcomes

Across clinical and translational studies, ORA interventions have generally demonstrated acceptable feasibility and safety when implemented during RT or chemoradiotherapy. Systematic evaluations indicate high patient acceptability and completion rates for dietary interventions overall, although adherence varies substantially depending on intervention intensity and clinical context. ¹¹² While survival benefits have not been consistently demonstrated, multiple studies report improvements in treatment tolerance, symptom burden, and quality-of-life parameters, supporting ORA as supportive adjuncts rather than replacements for standard oncologic care. Fasting and FMD protocols have emerged as particularly promising within this category. Reviews of early clinical studies indicate that short-term fasting or FMD cycles are feasible and generally well tolerated, with evidence of reduced treatment-related toxicity and preserved patient well-being.^110,113 These findings establish a practical foundation for further clinical investigation of metabolically restrictive strategies during RT. Notably, while fasting-mimicking diets (FMD) are supported by consistent preclinical evidence, the available clinical data remain encouraging but heterogeneous. This apparent contrast reflects differences in evidence maturity rather than inconsistency: preclinical studies consistently demonstrate metabolic reprogramming and tumor-selective radiosensitization, whereas clinical studies are still limited by small cohort sizes, variable protocols, and mixed endpoints. Accordingly, current clinical findings should be interpreted as preliminary, highlighting translational potential while underscoring the need for well-controlled, radiotherapy-specific trials.

3.3.2.2. Tumor-Selective Radiosensitization Through Metabolic Restriction

A major achievement of ORA research is the demonstration of tumor-selective radiosensitization via metabolic stress. Short-term starvation has been shown to enhance radiation-induced DNA damage and clonogenic cell death in metastatic cancer cells while sparing non-malignant cells, providing direct experimental evidence for differential stress resistance. ¹¹⁴ This principle has been reinforced by fasting and FMD studies, which consistently show that nutrient deprivation suppresses growth signaling and antioxidant defenses in tumor cells that are unable to appropriately downregulate oncogenic pathways. Targeted amino acid restriction represents another important advance. Restriction of serine and glycine impairs nucleotide synthesis, redox homeostasis, and central carbon metabolism, thereby amplifying radiation-induced oxidative stress and DNA damage across multiple tumor models.^115,116 Similarly, methionine restriction disrupts one-carbon metabolism, enhances sensitivity to RT and chemotherapy in resistant tumors, and induces systemic metabolic changes in humans that mirror preclinical findings. ¹¹⁷ These studies provide mechanistic proof that selective nutrient limitation can be leveraged to overcome tumor radioresistance.

3.3.2.3. Protection of Normal Tissues and Mitigation of Treatment-Related Toxicity

A second major achievement of ORA research lies in its contribution to normal tissue protection. Preclinical models demonstrate that dietary fiber accelerates intestinal crypt regeneration, preserves epithelial barrier integrity, and prevents bacterial translocation and chronic inflammation following irradiation. ¹¹⁸ Although clinical evidence for fiber modification during pelvic RT remains inconsistent and of low certainty,^119,120 these mechanistic insights highlight the therapeutic relevance of diet–microbiota interactions in radiation injury. Strongest clinical support within ORA is observed for interventions targeting oral and mucosal toxicity. Meta-analyses show that zinc supplementation and amino acid–rich elemental diets significantly reduce the incidence and severity of oral mucositis, particularly in GI and esophageal cancers.^121,122 Probiotic supplementation further reduces severe mucositis without increasing GI adverse events, supporting both efficacy and safety. ¹²³ Glutamine supplementation consistently improves mucosal repair and symptom control across multiple anatomical sites. ¹²⁴ Together, these findings establish ORA as a viable strategy for mitigating dose-limiting toxicities that compromise treatment continuity and quality of life.

3.3.2.4. Immune Modulation and Microbiome-Mediated Effects

ORA studies have substantially advanced understanding of immune and microbiome-mediated modulation of RT response. Metabolic dysfunction and nutrient deficiencies are increasingly recognized as contributors to immune suppression and radiation resistance, particularly in vulnerable patient populations, highlighting metabolic correction as a potential strategy to improve therapeutic index. ¹⁰⁸ At the tumor level, intratumoral bacteria such as Fusobacterium nucleatum have been identified as drivers of radioresistance through suppression of oxidative stress and inhibition of radiation-induced cell death pathways. Notably, dietary leucine restriction reduced bacterial burden and restored radiosensitivity in vivo, providing a compelling example of diet-driven modulation of tumor–microbe–radiation interactions. ¹¹¹ In parallel, intermittent fasting and other metabolically restrictive strategies have been shown to enhance antitumor immune responses while reducing systemic toxicity.^109,113

3.3.2.5. Context-Dependent Effects of Dietary Bioactives and Lipid Metabolism

Finally, ORA research has clarified that dietary interventions can exert highly context-dependent effects. Modulation of lipid metabolism through PPARα activation enhances RT efficacy and antitumor immunity, whereas excessive lipid availability may negate these benefits. ¹²⁵ Bioactive dietary compounds, including soy isoflavones and xanthophylls such as lutein and zeaxanthin, demonstrate anti-inflammatory, antioxidant, and radiosensitizing or radioprotective properties by influencing redox balance, DNA damage responses, and immune signaling.^126,127 Taken together, ORA studies represent a major conceptual advance by demonstrating that rational dietary manipulation can simultaneously enhance tumor radiosensitivity and protect normal tissues through coordinated metabolic, immune, and microbiome-mediated mechanisms (Table 1). While preclinical evidence is strong and early clinical data are encouraging, heterogeneity in study design and intervention protocols underscores the need for rigorously controlled clinical trials to define optimal ORA strategies, timing, and patient selection.

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Table 1.

Calorie Restriction (CR) and Responses to Ionizing Radiation (IR)

CR category	Specific intervention	Model / Population	Radiation context	Study design	Main achievements / Outcomes	Normal tissue effects	Tumor / Carcinogenesis effects	Key limitations / Notes	Representative citations
Lifelong / Adult-Onset CR	20–40% calorie restriction without malnutrition	Mouse models (B6C3F1, ApcMin/+)	Whole-body γ-irradiation (early-life or adult)	Lifespan analysis, histopathology, carcinogenesis modeling	Extended lifespan; reduced late-occurring solid tumors	Lower oxidative stress; improved mitochondrial quality	Reduced intestinal, liver, lung tumors; limited effect on thymic lymphoma	Tissue- and mutation-pathway dependence	81,82
Pre-Irradiation CR	CR initiated before IR exposure	Mouse hematopoietic models	γ-irradiation	Timing-controlled intervention studies	Suppressed initiation of radiation-induced leukemia	Reduced HSC proliferation; preserved marrow function	Lower myeloid leukemia incidence	Protection highly timing-dependent	88,90
Post-Irradiation CR	CR initiated after IR exposure	Mouse leukemia and solid tumor models	γ-irradiation; high-LET radiation	Delayed-intervention carcinogenesis studies	Delayed tumor promotion and progression	Reduced delayed genomic instability	Delayed leukemia onset; reduced solid tumors	Less effective against early lymphoid malignancies	89,91
CR During Radiotherapy	Short-term CR concurrent with therapeutic IR	Triple negative breast cancer mouse models; breast cancer patients	Fractionated radiotherapy	Preclinical + translational studies	Enhanced radiosensitivity; improved survival	Improved treatment tolerance	Reduced metastasis; increased apoptosis	Clinical validation still limited	85,86

3.3.3. Main Conclusions

Overall, restriction-based metabolic interventions can modulate both tumor and normal tissue responses to RT/chemoradiotherapy(Tables 1 and 2), with generally acceptable feasibility and metabolic safety when appropriately implemented.^112,128 While definitive survival gains remain unproven, improvements in quality of life and toxicity endpoints support continued evaluation as adjuncts.^112,128 Mechanistically, ORA strategies exploit tumor–normal metabolic asymmetries to increase tumor radiosensitivity (oxidative stress amplification, impaired redox homeostasis, glycolysis suppression, lipid/amino-acid rewiring) while engaging stress-resistance/repair programs in normal tissues.^{109,110,129,130} Key supporting studies include tumor-selective radiosensitization by short-term starvation ¹¹⁴ and radiosensitization by amino acid restriction (serine/glycine, methionine),^115-117 as well as lipid-metabolism–dependent effects. ¹²⁵

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Table 2.

Other Restriction Approaches (ORA) and Responses to Ionizing Radiation (IR)

ORA category	Specific intervention	Model / Population	Radiation context	Study design	Main achievements / Outcomes	Normal tissue effects	Tumor / Carcinogenesis effects	Key limitations / Notes	Representative citations
Fasting-Based Strategies	Short-term starvation	Metastatic cancer cell lines; normal cell controls	Single high-dose IR	In vitro mechanistic study	Enhanced radiation-induced DNA damage and reduced clonogenic survival selectively in cancer cells	Normal cells spared from excess DNA damage	Tumor-selective radiosensitization	In vitro only	114
Fasting-Based Strategies	Intermittent fasting	Preclinical tumor models; early clinical studies	Fractionated radiotherapy	Preclinical + clinical synthesis	Improved tumor control and reduced toxicity	Improved systemic stress resistance	Enhanced radiosensitivity via metabolic and immune modulation	Optimal timing unresolved	113
Fasting-Mimicking Diets	Cyclic fasting-mimicking diets	Breast cancer patients; mouse models	Chemotherapy ± radiotherapy	Phase II + translational	High pathological complete response rates	Preserved normal tissue tolerance	Downregulation of glycolysis and growth signaling	Radiotherapy-specific trials limited	131
Amino Acid Restriction	Serine/Glycine restriction	Colorectal cancer and breast cancer models	Fractionated radiotherapy	Preclinical	Increased reactive oxygen species and impaired nucleotide synthesis	Minimal toxicity reported	Potent radiosensitization	Human feasibility unknown	115
Amino Acid Restriction	Methionine restriction	Patient-derived xenograft models; human feeding study	Radiotherapy and chemotherapy	Preclinical + human	Enhanced radiotherapy sensitivity via one-carbon metabolism	Systemic metabolic adaptation	Tumor-selective vulnerability	Diet adherence	117
Microbiome-Targeted	Leucine restriction	Nasopharyngeal carcinoma models with Fusobacterium nucleatum	Fractionated radiotherapy	Translational preclinical	Restored radiosensitivity via mTORC1 suppression	No direct toxicity reported	Overcomes microbiome-driven resistance	Tumor-specific	111
Supportive Nutrition	Dietary fiber modulation	Pelvic radiotherapy patients; mouse models	Pelvic radiotherapy	Review + animal studies	Reduced late intestinal inflammation	Improved epithelial repair	Indirect tumor effects	Low clinical certainty	120
Supportive Nutrition	Probiotics	Cancer patients	Chemo/radiotherapy-induced mucositis	Meta-analysis of randomized controlled trials	Reduced mucositis severity	Improved mucosal integrity	Supportive care benefit	Strain heterogeneity	123
Bioactive Compounds	Soy isoflavones	Preclinical + early clinical studies	Radiotherapy across tumor types	Mechanistic + translational	Enhanced tumor radiosensitivity	Radioprotection of normal tissues	Multi-target modulation	Standardization lacking	126

On the normal-tissue side, evidence supports roles for fiber, probiotics, elemental diets, glutamine, dietary nitrate, and micronutrients in mitigating GI toxicity, mucositis, xerostomia, and skin injury, with zinc and probiotics showing the most consistent mucositis benefits to date.^{118-123,132,133} Emerging data also emphasize immune and microbiome regulation—including intratumoral bacterial signaling—as integral mediators of dietary effects on RT response.^111,134,135

However, limitations include heterogeneous clinical evidence, small cohorts, protocol variability, and adherence challenges during intensive therapy, favoring individualized, supervised implementation over uniform prescriptions.^112,130 In addition, unsupervised supplementation—particularly antioxidants—may risk attenuating therapeutic efficacy, reinforcing the need for evidence-based guidance. ¹³⁶ Future progress will require adequately powered trials incorporating mechanistic biomarkers, stratification by metabolic/immune status, and clinically meaningful endpoints.^110,128,131

3.4. Mechanistic Insights of Dietary Interventions (DI) and IR

DI, encompassing CRD and ORA, modulate biological responses to IR through interconnected effects on metabolism, redox homeostasis, DNA damage responses, immune regulation, and tissue microenvironments. A unifying mechanistic principle emerging from preclinical and translational studies is that DI amplify intrinsic metabolic and stress-response differences between tumor and normal cells, thereby enhancing the therapeutic index of RT while attenuating radiation-induced normal tissue injury.

3.4.5. Integrated Mechanistic Framework

Collectively, CRD and ORA converge on a shared mechanistic framework in which dietary modulation reshapes systemic metabolism, redox balance, DNA repair capacity, immune surveillance, and tissue microenvironments to influence radiation outcomes. CRD primarily reduces host susceptibility to radiation-induced damage and carcinogenesis by limiting proliferative and oxidative stress, whereas ORA strategies more directly exploit tumor metabolic vulnerabilities to enhance radiosensitization. Importantly, these mechanisms operate in a tissue-, timing-, and pathway-dependent manner, emphasizing the need for personalized, biomarker-driven application of dietary interventions in radiation oncology (Tables 3 and 4).

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Table 3.

Mechanistic Insights Into Caloric Restriction (CR) and Responses to Ionizing Radiation (IR)

Mechanistic domain	Specific molecular / Cellular processes	Radiation context	Biological consequences	Normal tissue protection	Tumor / Carcinogenesis modulation	Strength of evidence	Representative citations
Oxidative Stress and Mitochondrial Function	Reduced mitochondrial reactive oxygen species, enhanced antioxidant defenses, increased mitophagy	Acute and chronic ionizing radiation	Lower oxidative DNA and protein damage	Protection of hematopoietic, intestinal, hepatic tissues	Reduced fixation of radiation-induced mutations	Strong (animal and lifespan studies)	95,98,100
DNA Damage Response and Repair	Enhanced base excision repair and non-homologous end joining, faster γ-H2AX resolution	Whole-body γ-irradiation	Improved genomic stability after IR	Reduced late radiation injury	Delayed tumor initiation	Strong	101,102
Growth Factor and Nutrient Signaling	Suppression of IGF-1/insulin–PI3K–AKT–mTOR, activation of AMPK	Therapeutic and environmental IR	Reduced proliferative signaling under stress	Normal cell stress resistance	Tumor radiosensitization	Strong	85
Inflammation and Immune Regulation	Reduced NF-κB signaling, preserved immune balance	Fractionated and chronic IR	Lower chronic inflammatory damage	Protection from late tissue toxicity	Enhanced antitumor immunity	Moderate–Strong	86,104
Stem Cell Homeostasis	Reduced hematopoietic stem cell cycling	Radiation-induced leukemogenesis models	Lower fixation of IR-initiated lesions	Hematopoietic protection	Reduced leukemia incidence	Strong	88,90
Metabolic Microenvironment	Suppression of lipogenesis and PPARγ–Cd36 signaling	Early-life IR with long-term follow-up	Reversal of pro-tumorigenic metabolic niches	Liver protection	Delayed hepatocellular carcinoma	Strong	81,96
Genomic Instability Pathways	Reduced copy-neutral loss of heterozygosity, suppressed proliferation-driven rearrangements	Radiation-induced thymic lymphoma	Selective genomic stabilization	Partial normal tissue protection	Limited efficacy in mutation-driven lymphomas	Moderate	94

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Table 4.

Mechanistic Insights Into Other Restriction Approaches (ORA) and Responses to Ionizing Radiation (IR)

Mechanistic domain	Specific molecular / Cellular processes	Radiation context	Biological consequences	Normal tissue protection	Tumor / Carcinogenesis modulation	Strength of evidence	Representative citations
Fasting / Fasting-Mimicking Diets-Induced Stress Responses	Downregulation of IGF-1, mTOR, AKT; activation of AMPK; induction of autophagy and DNA damage tolerance pathways	Radiotherapy, chemotherapy + IR, experimental irradiation	Differential stress resistance between normal and tumor cells	Enhanced cellular stress resistance; reduced apoptosis and oxidative injury	Increased tumor radiosensitivity via failure to downregulate oncogenic signaling	Strong (preclinical), Emerging (clinical)	110,113,114
Amino Acid Restriction (serine, glycine, methionine, leucine)	Impaired one-carbon metabolism, redox imbalance, reduced nucleotide synthesis, altered mTORC1 signaling	Radiotherapy and chemoradiotherapy models	Accumulation of oxidative DNA damage and replication stress	Context-dependent; may spare normal tissue via metabolic flexibility	Selective radiosensitization and suppression of tumor growth	Strong (preclinical), Limited (clinical)	111,115-117
Dietary Fiber and Microbiota Modulation	Enhanced short-chain fatty acid production; epithelial regeneration; immune homeostasis; reduced bacterial translocation	Pelvic and abdominal radiotherapy	Improved mucosal integrity and reduced chronic inflammation	Protection against radiation-induced enteropathy	Indirect modulation via immune and inflammatory pathways	Moderate (preclinical), Weak–Moderate (clinical)	118-120
Probiotics and Synbiotics	Microbiome reconstitution; reduced NF-κB signaling; enhanced barrier function	Head and neck and gastrointestinal radiotherapy	Reduced mucosal inflammation and infection	Lower incidence and severity of oral mucositis	Minimal direct tumor effects reported	Moderate–Strong (clinical)	107,123
Elemental Diets and Glutamine Supplementation	Support of epithelial proliferation, nucleotide synthesis, and antioxidant capacity	Chemoradiotherapy involving gastrointestinal tract	Accelerated mucosal repair	Reduced oral and intestinal mucositis	Generally tumor-neutral; potential risk if unsupervised	Moderate (clinical)	122,124
Dietary Nitrate and Micronutrient Modulation	Activation of EGFR–AKT–MAPK signaling; inhibition of apoptosis; redox regulation	Salivary gland and skin irradiation	Preservation of tissue structure and function	Reduced xerostomia and cutaneous toxicity	No evidence of tumor protection at tested doses	Limited–Moderate	132,133
Bioactive Compounds (soy isoflavones, lutein, zeaxanthin)	Antioxidant, anti-inflammatory, DNA damage modulation, immune signaling	Radiotherapy and experimental IR	Reduced oxidative stress and inflammatory injury	Radioprotection of normal tissues	Context-dependent radiosensitization of tumors	Strong (preclinical), Limited (clinical)	126,127
Lipid Metabolism Modulation (PPARα activation)	Enhanced fatty acid oxidation; immune metabolic reprogramming	Radiotherapy with metabolic intervention	Improved antitumor immune responses	Context-dependent; excess lipid intake may reverse benefits	Enhanced tumor control under controlled conditions	Strong (preclinical)	125

4.1. Key Findings and Shared Mechanisms

DI encompassing CRD and ORA, including fasting, FMD, ketogenic strategies, and targeted nutrient modulation, consistently emerge as powerful modifiers of biological responses to IR. Across preclinical, translational, and early clinical studies, these interventions influence both tumor and normal tissue responses, shaping radiation sensitivity, therapeutic efficacy, toxicity profiles, and long-term carcinogenic risk.

At the phenotypic level, a robust and reproducible observation is that DR improves tolerance to IR while, in many contexts, enhancing tumor control. In normal tissues, CRD and ORA attenuate acute and chronic radiation injury, particularly in metabolically active and rapidly renewing organs such as the GI tract, hematopoietic system, skin, and salivary glands. These protective effects manifest as reduced oxidative damage, preserved tissue architecture, improved regenerative capacity, and diminished inflammatory sequelae, translating into improved functional outcomes and quality of life in clinical settings. In parallel, multiple tumor models demonstrate that DR can sensitize cancer cells to radiation, suppress metastatic progression, and enhance RT efficacy, particularly in aggressive solid tumors.

Mechanistically, these divergent effects on tumor versus normal tissues are unified by the concept of differential stress resistance. CRD and ORA induce systemic metabolic reprogramming characterized by reduced circulating glucose, insulin, and IGF-1 signaling, activation of AMPK, suppression of mTOR, and shifts in mitochondrial substrate utilization. Normal cells respond to these changes by entering a protected, stress-resistant state marked by reduced proliferation, enhanced mitochondrial quality control, improved redox homeostasis, and more efficient DNA damage surveillance and repair. In contrast, cancer cells, constrained by oncogenic signaling, high biosynthetic demand, and limited metabolic flexibility, fail to fully engage these adaptive programs, resulting in heightened oxidative stress, impaired redox buffering, disrupted nucleotide and lipid metabolism, and increased susceptibility to radiation-induced DNA damage and cell death. A central mechanistic axis linking DR to radiation response is the modulation of oxidative stress and mitochondrial function. CRD and related interventions lower basal mitochondrial ROS production, enhance antioxidant defenses, and promote mitophagy in normal tissues, thereby limiting fixation of radiation-induced damage. In tumors, however, restriction of glucose, amino acids, or specific metabolic pathways (e.g., serine–glycine–one-carbon metabolism, methionine metabolism, fatty acid oxidation) compromises redox balance and biosynthetic capacity, amplifying radiation-induced oxidative and genotoxic stress. Mutation-spectrum analyses and reporter assays further demonstrate that DR selectively suppresses oxidative stress–linked mutations and proliferation-associated genomic instability, providing a mechanistic basis for reduced long-term carcinogenic risk.

DR also exerts profound effects on DNA damage responses and genome stability. CRD enhances DNA repair capacity and checkpoint control in normal tissues, facilitating resolution of double-strand breaks and limiting delayed genomic instability. At the organismal level, multistage carcinogenesis modeling indicates that CRD primarily acts by increasing the number of rate-limiting steps required for tumor development, thereby lowering age-specific cancer mortality independent of radiation exposure, whereas IR accelerates transitions between steps. This conceptual distinction explains why CRD robustly suppresses many late-occurring solid tumors while exhibiting limited efficacy against early-onset, mutation-driven lymphoid malignancies that rely less on proliferative or metabolic contexts.

Beyond cell-intrinsic effects, DR reshapes the immune and inflammatory landscape that critically determines radiation outcomes. CRD and ORA suppress chronic inflammation, reduce NF-κB signaling, and modulate cytokine profiles, mitigating late radiation injury. Simultaneously, these interventions can enhance antitumor immunity by increasing CD8⁺ T-cell activity, limiting regulatory T-cell expansion, and improving immune–metabolic fitness within the tumor microenvironment. Emerging evidence further implicates the gut and intratumoral microbiome as intermediaries of dietary effects on radiation response, with dietary fiber, fasting, and targeted nutrient restriction influencing microbial composition, immune signaling, and even tumor radioresistance mechanisms. Importantly, these benefits are context-dependent and mechanistically constrained. Tissue type, age at exposure, timing and intensity of restriction, genetic background, and dominant oncogenic pathways all influence outcomes. Early occurring lymphoid malignancies driven by point mutations or complex structural alterations show relative resistance to CRD-mediated protection, underscoring the need for complementary strategies targeting mutation-centric pathways. In clinical settings, adherence, tolerability, and the risk of malnutrition necessitate careful patient selection and medical supervision.

In conclusion, CRD and ORA define a coherent class of dietary interventions that modulate responses to IR through integrated effects on metabolism, redox biology, DNA repair, immune regulation, and tissue homeostasis. By simultaneously protecting normal tissues and, in many contexts, sensitizing tumors, these interventions have the potential to enhance the therapeutic index of RT and reduce long-term radiation-associated cancer risk. Future progress will depend on rigorously designed clinical trials, incorporation of mechanistic biomarkers, and stratification by metabolic, immune, and microbiome profiles to translate these biologically compelling phenomena into safe, personalized, and evidence-based clinical applications.

4.2. Integrative Themes and Emerging Paradigms

Across decades of investigation, DI, spanning classical CRD and more recent ORA, have revealed a set of convergent biological principles governing responses to IR. Early studies, grounded primarily in lifespan analysis, tumor incidence, and gross physiological outcomes, established the empirical observation that reduced nutrient availability profoundly alters radiation sensitivity, carcinogenesis, and tissue resilience. Contemporary work now provides mechanistic resolution to these phenomena, reframing dietary modulation as a systems-level regulator of radiation response rather than a simple modifier of energy balance.

A central unifying theme is differential stress adaptation between normal and malignant cells. Classical CRD studies demonstrated reduced radiation-induced tumor burden and delayed carcinogenesis, long before the molecular basis of these effects was understood. Modern data now show that CRD, fasting, ketogenic strategies, and targeted nutrient restriction converge on conserved nutrient-sensing pathways, AMPK, mTOR, insulin/IGF-1, and NAD⁺-dependent networks, that promote cellular maintenance, genomic stability, and metabolic efficiency in normal tissues, while simultaneously exposing the inflexibility of tumor metabolism. This framework reconciles early observations of tumor suppression and lifespan extension with current evidence for selective tumor radiosensitization and normal-tissue protection. A second integrative insight is the shift from mutation-centric to host-context–centric models of radiation carcinogenesis. Historically, radiation-induced cancer risk was viewed largely through the lens of DNA damage and fixed mutations. CRD studies challenged this paradigm by demonstrating profound reductions in radiation-associated cancer incidence without eliminating initial mutational events. Mechanistic analyses now clarify that DR primarily suppresses promotion and progression by limiting proliferative drive, oxidative stress, inflammatory signaling, and stem-cell cycling, processes required for clonal expansion of initiated cells. This host-level modulation explains why CRD is highly effective against late-occurring solid tumors but less so against early, mutation-driven lymphoid malignancies, and highlights the importance of tissue context and timing. Third, both old and new studies converge on metabolic regulation as a master determinant of radiation response. Early CR experiments implicitly altered mitochondrial function and redox balance; contemporary work explicitly demonstrates that dietary interventions remodel mitochondrial quality control, ROS handling, lipid and amino acid metabolism, and one-carbon flux. These metabolic shifts influence DNA repair capacity, epigenetic regulation, immune cell function, and microbial ecology, integrating tumor-intrinsic and host-mediated mechanisms. Importantly, newer ORA strategies, such as FMD, amino acid restriction, and ketogenic regimens, can reproduce many CRD-associated benefits with greater temporal precision and potential clinical feasibility. A fourth emerging paradigm is the integration of immunity and the microbiome into radiation–diet interactions. Earlier CRD studies noted changes in immune competence without mechanistic clarity. Recent evidence demonstrates that dietary modulation reshapes antitumor immunity, alters regulatory versus effector T-cell balance, and influences radiation-induced inflammation. In parallel, gut and intratumoral microbiota have emerged as diet-sensitive regulators of radioresistance, normal tissue injury, and immune tone. These insights extend classical concepts of “radioprotection” into a broader ecological framework involving host–microbe–immune crosstalk.

Collectively, these themes underscore a conceptual evolution: dietary interventions are no longer viewed as nonspecific modifiers of radiation damage, but as precision tools capable of reprogramming systemic and cellular states that determine radiation outcomes. By integrating historical phenomenology with modern molecular, metabolic, and immunological insights, the field now recognizes that effective modulation of IR responses depends on when, how, and in whom DR is applied. This integrative perspective provides a foundation for rational design of next-generation dietary strategies that complement RT, reduce long-term radiation risk, and advance personalized radiation medicine.

5.1. Outstanding Questions and Conceptual Gaps

Despite substantial progress over several decades, critical gaps remain in our understanding of how DI, including CRD and ORA, interact with IR across biological scales. One major unresolved issue concerns context specificity: the magnitude and direction of DI effects vary markedly by tissue type, developmental stage, radiation quality and dose, and underlying genetic background. While CR robustly suppresses many late-onset solid tumors, its limited efficacy against mutation-driven lymphoid malignancies underscores the need to delineate mechanism-dependent boundaries of protection, particularly where carcinogenesis is dominated by early, irreversible genomic lesions.

Another key gap lies in defining the temporal dimension of dietary modulation. Evidence indicates that the timing of restriction relative to radiation exposure, pre-exposure, peri-exposure, or post-exposure, critically influences outcomes by differentially affecting initiation, promotion, and progression phases of carcinogenesis. However, systematic frameworks integrating timing, duration, and intensity of restriction with radiation biology are lacking. Relatedly, the long-term consequences of intermittent versus sustained restriction, especially under chronic or fractionated radiation exposure, remain insufficiently characterized. At the mechanistic level, important questions persist regarding how DI reshape DNA damage processing, mutational spectra, and clonal selection following IR. While CR consistently suppresses proliferation-associated genomic instability and oxidative base damage, alternative mutation-driven pathways can persist or even be selected under restricted conditions. How dietary modulation influences clonal competition, stem-cell hierarchy, and tissue repopulation after radiation injury is only beginning to be understood. In parallel, the roles of the microbiome, intratumoral bacteria, immune-metabolic crosstalk, and cancer stem cell niches introduce additional layers of complexity that demand integrative, systems-level investigation.

Finally, translational uncertainty remains substantial. Most clinical data derive from small or early-phase studies, with heterogeneous protocols and limited biomarker integration. Identifying predictive markers of responsiveness, defining safe boundaries to avoid malnutrition or impaired treatment efficacy, and distinguishing beneficial metabolic stress from harmful catabolism are essential prerequisites for broader clinical adoption.

5.2. Translational Horizons Across Radiation-Exposed Settings

The expanding mechanistic foundation of dietary modulation of IR responses opens multiple translational avenues spanning medicine, occupational health, and extreme environments. In radiation oncology, DI hold promises as adjunct strategies to improve the therapeutic index of RT by simultaneously enhancing tumor radiosensitivity and protecting normal tissues. Carefully designed, time-limited interventions, such as short-term fasting, FMD, or metabolically targeted restriction, may offer clinically feasible alternatives to chronic CR, particularly when guided by metabolic and immune biomarkers.

In radioprotection, especially for occupational or accidental exposures, dietary modulation represents a non-pharmacological approach to reduce long-term cancer risk and late tissue injury. The ability of CR to suppress radiation-associated leukemias and solid tumors even when initiated after exposure suggests potential relevance for exposed populations where prophylactic interventions are no longer possible. Integrating dietary strategies with conventional countermeasures could enhance resilience without the toxicities associated with many radioprotective drugs.

The implications extend further to space biology, where astronauts experience chronic low-dose and high-linear energy transfer radiation in combination with metabolic stressors such as microgravity and circadian disruption. Dietary interventions that stabilize mitochondrial function, limit oxidative stress, and preserve immune competence may represent practical countermeasures for long-duration missions, provided their effects on muscle mass, bone density, and overall performance are carefully balanced.

From a public health perspective, the intersection of nutrition, metabolism, and radiation risk is particularly relevant for populations exposed early in life, individuals with metabolic syndrome or obesity, and aging societies with heightened vulnerability to both cancer and radiation injury. Tailored dietary guidance, informed by mechanistic insights rather than generalized restriction, could contribute to risk mitigation strategies following medical, environmental, or occupational radiation exposure.

Looking forward, progress will depend on integrative clinical trial designs, incorporation of mechanistic biomarkers (metabolic, genomic, immune, and microbiome-based), and cross-disciplinary collaboration among radiation biologists, nutrition scientists, oncologists, and epidemiologists. Rather than a universal prescription, dietary interventions should be viewed as precision modifiers of radiation response, whose optimal application will vary by context, mechanism, and individual susceptibility.

5.3. Personalized Dietary Interventions: Toward Precision Translation

DI, including CR, fasting regimens, time-restricted feeding, LHF, and nutrient-directed strategies such as dietary inversion, which strategically supplements or increases intake of selected amino acids, vitamins, minerals, and antioxidant-rich foods, are increasingly recognized as adaptable adjuncts to cancer therapy because of their capacity to reprogram systemic and cellular metabolism. Conventional modalities, including chemotherapy, RT, and immunotherapy, remain limited by variable efficacy and substantial normal-tissue toxicity. RT, in particular, frequently compromises nutritional status, especially in GI and head-and-neck malignancies, where anorexia, mucosal injury, and GI dysfunction contribute to malnutrition, treatment interruptions, and reduced tolerance. ¹³⁷ Within this clinical landscape, appropriately designed DI offer an integrated strategy to enhance therapeutic effectiveness while supporting patient resilience across radiation-exposed settings.

Mechanistically, CR, intermittent fasting, and pharmacological CR mimetics enhance tumor sensitivity to RT and chemotherapy by suppressing glycolytic dependence, improving insulin sensitivity, inducing autophagy, and attenuating inflammatory and angiogenic signaling. In parallel, nutrient-enriching approaches, such as dietary inversion, may mitigate radiation-induced normal-tissue injury, restore metabolic homeostasis, and facilitate recovery following treatment. ¹³⁸ Together, these complementary strategies illustrate how DI can simultaneously preserve normal-tissue integrity and exploit tumor-specific metabolic vulnerabilities, thereby improving the therapeutic index of radiation-based treatments.

The biological rationale for personalized DI is reinforced by the observation that aggressive and treatment-resistant tumors often display heightened glycolysis and metabolic inflexibility, features that overlap substantially with pathways targeted by CR and carbohydrate restriction. Systemic metabolic dysfunction, such as obesity, insulin resistance, and diabetes, is frequently associated with poorer oncologic outcomes and radioresistance, underscoring the importance of host metabolic state in shaping radiation response. Preclinical and early clinical studies suggest that integrating CR or CR mimetics with anticancer therapies can suppress tumor growth, enhance cancer-cell death, and potentially permit dose de-escalation of cytotoxic treatments, thereby reducing toxicity. Notably, cyclic FMD have demonstrated clinical feasibility, and early reductions in intratumoral glycolysis have emerged as candidate biomarkers predicting response to nutrient-based interventions.

Despite these advances, successful translation of DI requires careful personalization. Patient-specific factors, including age, baseline nutritional status, comorbidities, treatment intensity, and radiation field, critically influence safety, adherence, and efficacy. Overly restrictive or poorly timed interventions risk exacerbating frailty, impairing immune competence, or undermining treatment tolerance. Moreover, heterogeneity in dietary protocols, tumor biology, metabolic phenotypes, and combination treatment strategies contributes to variability in clinical outcomes, limiting the generalizability of existing evidence.

5.4. Clinical Caution and Malnutrition Risk Management

Implementation of restrictive dietary interventions during radiotherapy demands strict nutritional surveillance and multidisciplinary supervision, particularly in patients with head-and-neck or gastrointestinal malignancies who are highly vulnerable to treatment-associated malnutrition. Recent American Society for Parenteral and Enteral Nutrition (ASPEN) clinical recommendations emphasize that all oncology patients must undergo regular malnutrition risk screening before and throughout radiation treatment using validated tools such as the Malnutrition Screening Tool (MST), Malnutrition Universal Screening Tool (MUST), Nutritional Risk Screening 2002 (NRS-2002), or Patient-Generated Subjective Global Assessment (PG-SGA). ¹³⁹ Particular caution is warranted in patients receiving concurrent chemoradiotherapy, where treatment-related mucositis, dysphagia, and gastrointestinal toxicity can rapidly accelerate metabolic deterioration. ¹⁴⁰ To ensure patient safety and prevent severe cachexia during radiotherapy, clinicians should establish clear thresholds for modifying or immediately discontinuing restrictive regimens (such as Fasting-Mimicking Diets). Based on consensus clinical guidelines for oncology nutrition, it is recommended to discontinue restrictive DI if any of the following parameters are met:

• Unintentional Weight Loss: A cumulative weight loss exceeding 5% within 1 month, or more than 10% over 6 months. ¹⁴¹

Incorporating these practical thresholds into clinical oncology workflows allows for individualized surveillance, ensuring that the metabolic stress induced by restrictive DI remains within a safe therapeutic window without driving the patient into harmful catabolism.

Accordingly, future research must prioritize precision nutrition frameworks that tailor dietary strategies to individual metabolic, immunologic, and tumor-specific characteristics. Well-designed clinical trials that incorporate mechanistic biomarkers, spanning metabolic flux, immune profiling, microbiome composition, and circadian regulation, are essential for defining optimal nutrient composition, timing, duration, and safety parameters. Aligning DI with patient-specific vulnerabilities and therapeutic contexts will be critical for realizing their translational potential across oncology, radioprotection, and other radiation-exposed environments.