While fasting has become a popular trend, especially among those hoping to lose weight, new research from the University of British Columbia (UBC Okanagan) shows that fasting affects different body types in different ways.
Fasting as part of a ketogenic — very low-carbohydrate — diet is gaining popularity as people seek to burn stored fat for energy when carbohydrate levels in the body drop.
Dr. Hashim Islam, Associate Professor in the School of Health and Exercise Sciences and the Centre for Chronic Disease Prevention and Management at UBCO, says that fasting and low-carb meals can be beneficial for many people, but their effects may differ in those with obesity.
“These dietary trends continue to grow in popularity,” says Dr. Islam. “But our research shows that people with obesity may respond to fasting differently than leaner individuals, particularly in how their immune system reacts.”
Fasting has become fashionable thanks to media coverage, but, as lead study author Dr. Helena Neudorf notes, scientists value it for switching the body from burning sugar to burning fat, producing ketones in the process.
She added that fasting can improve health by altering metabolism, strengthening the immune system, and reducing chronic inflammation associated with many diseases.
“However, we wanted to determine whether fasting affects metabolism and the immune system differently in people with obesity compared to those who are lean.”
The research team asked people with obesity and their lean peers to abstain from food for 48 hours. Participants gave blood samples before, during, and after fasting so the researchers could measure hormone levels, metabolites, metabolic rate, inflammation, and T-cell activity — white blood cells that fight infections but can also cause chronic inflammation.
The study, conducted by Dr. Islam’s group and Professor Jonathan Little’s team at the UBCO Centre for Chronic Disease Prevention and Management, and recently published in iScience, found that people with obesity had more pro-inflammatory T cells and continued producing inflammatory signals even after fasting. This group also showed smaller increases in ketone levels and lower levels of key chemical reactions linked to immune regulation, such as the binding of ketones to amino acids or proteins.
“We also found that the immune cells of lean participants adapted to fasting by burning more fat. This didn’t happen in people with obesity,” says Dr. Neudorf. “Overall, their shift toward a more balanced, anti-inflammatory state was weaker.”
Dr. Islam notes that while fasting can be beneficial, obesity appears to reduce its positive effects on metabolism and the immune system.
“People with obesity may respond differently to a two-day fast compared to lean individuals, but we don’t yet know whether that’s good or bad,” he adds. “Our study highlights the complex relationship between diet, metabolism, and immune function, and shows that more research is needed to understand how to use fasting as a therapeutic approach for people with different body types.”
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