Body Type Influences How Fasting Affects Metabolism, Study Finds

A recent study led by researchers at UBC Okanagan has explored the effects of fasting on metabolism and the immune system, revealing important differences between people living with obesity and those who are lean.

The research, published in iScience, focused on how fasting as part of a ketogenic, very low-carbohydrate diet impacts the body’s ability to switch from burning sugar to fat, and its effect on inflammation and immune cell activity.

The team conducted a controlled 48-hour fasting experiment with participants from both obese and lean groups. Blood samples were collected before, during, and after the fast to measure hormones, metabolites, metabolic rate, inflammation, and the activity of T cells—white blood cells that fight infection but can also contribute to chronic inflammation.

Results showed that people with obesity had higher levels of pro-inflammatory T cells and continued to produce inflammatory signals even after fasting. This group also experienced a smaller increase in ketones compared to lean participants, indicating a reduced metabolic response. Interestingly, immune cells in lean individuals adapted to fasting by burning more fat, shifting toward a balanced, anti-inflammatory state. However, this shift was weaker in people living with obesity. Dr. Hashim Islam, lead author, suggested that while fasting offers health benefits, obesity might dampen these positive effects on metabolism and immunity. He emphasized that more research is needed to understand whether these differences are ultimately beneficial or harmful.