Fasting is often seen as a quick way to lose weight, especially when paired with a low-carb, high-fat ketogenic diet.
But new research from the University of British Columbia Okanagan (UBCO) suggests that fasting may not affect everyone the same way.
People with obesity, in particular, might not see the same benefits as those who are lean.
Dr. Hashim Islam, an Assistant Professor at UBCO’s School of Health and Exercise Sciences and the Centre for Chronic Disease Prevention and Management, says that although fasting and low-carb meals can help many people, they may have different effects on people living with obesity.
He notes that fasting is popular both in the media and among those seeking to burn fat for energy once the body runs out of carbohydrates.
Fasting changes how the body works. According to lead researcher Dr. Helena Neudorf, when people fast, the body switches from using sugar for fuel to using fat.
This process produces substances called ketones, which can help improve metabolism and reduce chronic inflammation.
These changes are believed to support a stronger immune system and overall better health. However, Dr. Neudorf and her team wanted to know if fasting affects people with obesity differently than it does those who are lean.
To find out, they asked both lean individuals and those with obesity to fast for 48 hours. Blood samples were collected before, during, and after the fast.
The researchers then measured hormones, metabolism, inflammation, and the behavior of immune cells, especially T cells. These cells are important for fighting infection but can also cause inflammation if not regulated properly.
The study, recently published in the journal iScience, found important differences between the two groups. People with obesity had more inflammatory T cells and continued to release signals that promote inflammation—even after the fast.
In contrast, lean individuals showed a bigger rise in ketones and had more chemical reactions that help regulate the immune system. One such reaction is when ketones attach to amino acids or proteins, which seems to support a healthier immune response.
Another key finding was how the immune cells used energy. In lean participants, immune cells adapted to fasting by burning more fat. This didn’t happen in people with obesity. Instead, their immune systems did not shift as much toward a healthier, less inflamed state.
Dr. Islam explained that while fasting still offers health benefits, it seems those benefits are reduced in people with obesity. He emphasized that the results don’t mean fasting is bad for people with obesity, but rather that their bodies may respond in more complex ways.
This study shows just how closely connected our nutrition, metabolism, and immune system really are. It also shows that we need more research to understand how fasting might be tailored to fit different body types.
What works well for one person might not work the same for another, especially when it comes to improving health through diet and fasting.
If you care about nutrition, please read studies about 9 signs you have inflammation in your body. Could an anti-inflammatory diet help? and high-salt diet strongly changes your kidneys.
For more about diet, please read studies that fiber is your body’s natural guide to weight management and diet and nerve damage in diabetes: a novel insight.
The study is published in iScience.
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