A systematic review of evidence that environmental contaminant exposure impedes weight loss and glycemic control during calorie-restricted diets in humans.

Calorie-restricted diets cause weight loss and can drive type 2 diabetes remission. However, many patients struggle to achieve clinically relevant weight loss, and the reasons are not well understood. Chemical exposure is associated with obesity and type 2 diabetes development, and some evidence from preclinical experiments suggests it can limit the clinical benefits of calorie restriction. We systematically reviewed the evidence for the effects of environmental chemical exposure on mass loss and glycemic control during diet-induced weight management in humans (PROSPERO: CRD42022339993). Of 222 unique citations, only six papers directly examined this question. Only one targeted people with type 2 diabetes. One linked phthalates and parabens, but not bisphenols, with slower fat loss. Two showed per- and polyfluoroalkyl substances were not associated with mass loss, but with faster subsequent mass regain. One linked impaired adiposity improvements with air pollutants. Two papers reported weight loss-induced elevation in plasma organochlorines associated with altered glycemic control. The risk of bias largely arose from the potential for deviation from the intended diet, and statistics and reporting. The role of chemical exposure in impeding the effectiveness of weight management programs needs to be better understood to provide suitable support to people living with obesity and type 2 diabetes.