Fasting is often promoted as a way to burn fat, boost metabolism and reduce inflammation. But new research suggests it may not have the same effects for everyone.
A University of British Columbia Okanagan study compared how people with obesity and lean individuals responded to a 48-hour fast. Researchers measured changes in metabolism, immune activity and inflammation before, during and after the fast.
Both groups switched from burning sugar to burning fat and producing ketones, but the shift was smaller in participants with obesity. Their immune systems also stayed more active in ways linked to inflammation, and they didn’t show the same fat-burning changes in immune cells that were seen in lean participants.
“We also found the immune cells in lean participants adapted to fasting by burning more fat. This didn’t happen in those living with obesity,” said lead author Dr. Helena Neudorf.
Dr. Hashim Islam, senior author and assistant professor in UBCO’s School of Health and Exercise Sciences, said the findings highlight how body type may influence the benefits of fasting.
“People living with obesity may respond differently to an isolated two-day fast compared to those who are leaner, but we don’t yet know if this is good or bad,” he said.
The study, published in iScience, does not suggest that fasting is ineffective for people with obesity. Instead, the authors say it shows the complexity of the relationship between nutrition, metabolism and immune function, and the need for more research to guide personalized fasting recommendations.
This study was conducted by researchers at the University of British Columbia Okanagan’s Centre for Chronic Disease Prevention and Management. Specific funding details were not provided in the publicly available materials.