Letter re: BMI is Inadequate in Proposing an Immunological Effect of Excess Adipose Tissue

To the Editor,

We read with great interest the review article by Zhang et al ¹ on the association between body mass index (BMI) and mortality rates in patients with sepsis. In this retrospective study, the authors found that lower BMI correlated with a higher 28-day mortality rate in sepsis patients, while higher BMI (≥35 kg/m²) correlated with a reduced risk. This article provides valuable insight into risk-stratifying sepsis patients and provides a basis for more careful management, particularly in patients with low BMI.

The authors propose an interesting mechanism by which adipose tissue releases immune-modulating properties that may act as a buffer in sepsis, potentially improving survival rates in obese patients. However, they do not account for the fact that BMI does not incorporate body fat percentage in its calculation. Studies have shown that BMI is not a reliable indicator of health outcomes as it fails to differentiate between lean body mass and fat mass.^2-4 This limitation is particularly pronounced in specific populations, such as pregnant individuals, athletes, and the elderly. ² Furthermore, current BMI classifications are primarily based on data from Caucasian populations, despite significant variations in body fat and muscle mass distribution across different racial and ethnic groups. ⁴ For example, the World Health Organization (WHO) has recommended different cutoffs for people of Asian descent, as the standard classifications of BMI underestimate metabolic risk in these populations. ⁵ Some studies have even suggested waist-to-hip ratio may be a more accurate indicator of adiposity than BMI. ⁶

While the authors acknowledged various limitations in their study, not considering the inherent shortcomings of utilizing BMI as a measurement tool may have also contributed to the inconsistent conclusions found in their research. We believe utilizing additional methods to identify body fat percentages may help address this issue in future studies and could provide a more accurate understanding of the relationship between adipose tissue and mortality rates in sepsis.