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Intermittent Fasting ‘No Magic Bullet for Weight Loss’

A new study challenges intermittent fasting, also known as alternate day fasting or the ‘5:2’ as an effective way to lose weight. 

Published on June 16 in the journal Science Translational Medicine, the new research from a team of physiologists at the University of Bath provides evidence indicating nothing special about ‘intermittent fasting’ (Templeman et al., 2021).

Intermittent fasting is no magic bullet, and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow.
Professor James Betts

In the last few years, intermittent fasting—skipping food for few days in a week has become popular, supported by celebrities and photos of many people’s magnificent weight changes.

However, current evidence about ‘intermittent fasting’ effectiveness is limited compared with a more traditional way of dieting to reduce calorie intake.

In their randomized control trial, the researchers found that the participants in intermittent fasting lost less weight than the traditional way of dieting, even when the total calorie intake was at the same level.

Study Design

The research team from the University’s Centre for Nutrition, Exercise & Metabolism (CNEM) designed the study protocol. They recruited 36 lean, healthy adults (Body mass index 20-25 kg/m2) during 2018-2020. The researchers assigned the participants randomly into three groups after four weeks of the baseline monitoring phase.

Group 1: alternate day fasting, the fasted day is followed by a day of eating, 50% more than usual (energy intake, 0:150%).

 Group 2: Control, non-fasting, reduced calorie intake by 25%, every meal, every day, (energy intake, 75%:75%).

 Group 3: alternate day fasting, the fasted day is followed by the day of eating 100% more than usual (energy intake, 0:200%).

At the beginning of the study period, participants across all three groups consumed a typical diet of around 2000-2500 kcal per day. After a three-week monitoring period, the two energy-restricted groups reduced the calorie intake between 1500-2000 kcal on average. 

Groups 1 and 2 had the same amount of calorie intake but in different ways. Whereas group 3’s diet saw them fast without reducing overall calories.

Major Findings

The researchers found that participants in the non-fasting group (Group 2) lost 1.9 kg in three weeks. DEXA body scans revealed that this weight loss was almost entirely due to reduced body fat content.

On the other hand, the first fasting group (Group 1) experienced the same reduced calorie intake. After fasting on every alternate day and eating 50% more on non-fasting days, they lost 1.6 kg, half of which came from reduced body fat, and the remaining amount was from the muscle mass.

In group 3, fasting without energy restriction (0:200%) did not significantly reduce body mass. 

The results showed that alternate-day fasting less effectively reduces body fat mass than those with an energy-restricted diet. 

Also, analysis of cardiometabolic health and gut hormones and the expression of key genes in subcutaneous adipose tissue showed no significant changes between the fasting and energy-restricted groups.

intermittent fasting

Intermittent fasting stimulates lipolysis and ketogenesis to support energy requirements while the cell functions and maintains integrity. It also efficiently recycles the limited nutrients available with increased autophagy (de Cabo et al., 2019).

“Many people believe that diets based on fasting are an effective way for weight loss or that these diets have particular metabolic health benefits even they don’t stimulate weight loss.”

“But intermittent fasting is no magic bullet, and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow”, says Professor James Betts, Director of the Centre for Nutrition, Exercise & Metabolism at the University of Bath.

Intermittent fasting less effectively reduces body fat than a daily calorie-restricted diet and does not show any evidence of fasting-specific outcomes on metabolism, or cardiovascular health—the study concluded.

Related Publications

de Cabo, R. and M. P. Mattson (2019). “Effects of Intermittent Fasting on Health, Aging, and Disease.” N Engl J Med 381(26): 2541-2551. 10.1056/NEJMra1905136.
Templeman, I., H. A. Smith, et al. (2021). “A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults.” Science Translational Medicine 13(598): 10.1126/scitranslmed.abd8034.




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