Fasting Impacts Metabolism and Immune Function Differently in Individuals with Obesity

Fasting has gained popularity as a method for weight loss and health improvement, but new research from the University of British Columbia indicates that its effects vary significantly depending on body type. Particularly, individuals with obesity respond differently to fasting compared to lean individuals, especially regarding immune system activity and metabolic changes.

The study focuses on the common practice of fasting, often in conjunction with ketogenic, very low-carbohydrate diets aimed at promoting fat burning through ketone production. Dr. Hashim Islam, an assistant professor at UBCO, explains that while fasting and low-carb diets can be beneficial for many, they may produce different outcomes in those living with obesity.

Fasting is believed to push the body from burning sugar to burning fat, creating ketones that can potentially fortify immune health and decrease chronic inflammation—a common link to many chronic diseases. However, the recent investigation revealed that in people with obesity, this shift is less pronounced. Participants with obesity showed sustained levels of pro-inflammatory T cells and produced inflammatory signals even after fasting, unlike lean participants whose immune cells adapted by increasing fat burning and generating more ketones.

Researchers measured various biological markers, including hormones, metabolites, and white blood cell activity, at different stages during a 48-hour fast. The findings, published in iScience, indicated that while fasting prompts lean individuals to shift towards an anti-inflammatory state, this response is weaker and less effective in those with obesity.

Dr. Helena Neudorf, the lead author, highlights that immune responses in lean participants became more balanced and anti-inflammatory. Conversely, people with obesity experienced increased inflammation and less metabolic flexibility, with smaller rises in ketone levels and reduced immune regulation. Dr. Islam stresses that although fasting can yield health benefits, obesity appears to dampen its positive effects.

The research underscores a complex relationship between nutrition, immune function, and metabolism, suggesting that fasting’s benefits may be limited or altered in individuals with obesity. More studies are needed to understand whether fasting could serve as a therapeutic strategy tailored to different body types and health conditions.

Source: [https://medicalxpress.com/news/2025-08-fasting-affect-metabolism-immune-response.html]