Does Fasting Affect Obese and Lean Individuals Differently?

Obese and lean individuals may respond differently to a 2-day fast, but its health effects remain uncertain.

Although fasting has gained popularity as a weight-loss strategy, new research from UBC Okanagan indicates that its effects can vary depending on body type ().

Fasting and Keto: A Powerful Combination for Metabolic Health?

Many people are now combining fasting with a ketogenic diet—a very low-carbohydrate eating plan—hoping to trigger fat burning by forcing the body to switch from carbohydrates to stored fat as its primary energy source.

Intermittent Fasting: A Key To Good Health
Intermittent fasting is a complete or partial abstinence from food and caloric drinks for a particular period. It reduces the caloric intake of the person.

TOP INSIGHT

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Dr. Hashim Islam, Assistant Professor in UBCO’s School of Health and Exercise Sciences and the Centre for Chronic Disease Prevention and Management, says fasting and low-carbohydrate meals can benefit many people, but the effects might be different for people living with obesity.

“These diet trends continue to grow in popularity,” says Dr. Islam. “But our study found that people with obesity may respond to fasting differently than leaner individuals, especially in how their immune systems react.”

Fasting has become trendy due to coverage in popular media, but lead author Dr. Helena Neudorf, says scientists also value it because it makes the body switch from burning sugar to burning fat while producing ketones.

Health Benefits of Ketogenic Diet
Ketogenic diet is a diet where you load up on protein and fat and drop your carbohydrate intake. Here’s how you get started on a ketogenic diet.

She adds that fasting may improve health by changing metabolism to strengthen the immune system and reduce chronic inflammation, which is linked to many diseases.

“However, we wanted to find out if fasting affects metabolism and the immune system differently in people living with obesity compared to those who are lean.”

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Studying the Effects of Fasting on Metabolism and Immunity

The research team had people with obesity and their lean counterparts fast for 48 hours. Participants gave blood samples before, during and after the fast, so the researchers could measure hormones, metabolites, metabolic rate, inflammation and activity of T cells—white blood cells that fight infections but can also cause chronic inflammation.

The study, led by Dr. Islam and Professor Jonathan Little’s research groups at UBCO’s Centre for Chronic Disease Prevention and Management, was recently published in iScience. It found that people living with obesity had more pro-inflammatory T cells, and kept producing inflammatory signals, even after fasting. This same group also had a smaller increase in ketones and lower levels of important chemical reactions linked to immune regulation—such as ketones attaching to amino acids or proteins.

From Plate to Platelets: How Intermittent Fasting Reduces Blood Clot Risk
Intermittent fasting, a simple dietary habit, inhibits platelet activation and reduces the risk of blood clots (thrombosis).

“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,” says Dr. Neudorf. “Overall, their shift toward a more balanced, anti-inflammatory state was weaker in this particular group.”

Dr Islam notes that fasting can have health benefits, but obesity seems to reduce its effects on metabolism and the immune system.

“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 adds. “Our study shows the complex relationship between nutrition, metabolism and immune function, and that more research is needed to see how fasting can be used as a therapeutic tool for people with different body types.”

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