New research released this week challenges the popular belief that intermittent fasting diets like the alternate day fast or the “5: 2” diet are the most effective ways to lose weight.
In recent years, diets where people fast a few days a week have grown in popularity, reinforced by images of people’s miraculous weight changes and endorsed by celebrities.
So far, however, there is limited evidence of the effectiveness of fasting compared to more traditional diets that aim to reduce caloric intake over a full week.
The new study by a team of physiologists at the University of Bath, published in the prestigious journal Science Translational Medicine, supports this evidence and shows that fasting is “nothing special”.
The participants in their randomized control study lost less weight while fasting compared to those who followed a traditional diet – even if their caloric intake was the same overall.
In the study, organized by a team from the University’s Center for Nutrition, Exercise and Metabolism (CNEM), participants were divided into one of three groups:
- Group 1, who fasted on alternate days with their fasting day, followed by a day on which 50% more than usual was eaten.
- Group 2, who reduced calories by 25% at all meals each day.
- Group 3, who fasted on alternate days (like Group 1) but ate 100% more than usual on one day after their fasting day.
Participants in all three groups ate a typical diet averaging around 2000-2500 kcal per day at the start of the study. During the three-week observation period, the two energy-restricted groups reduced this to an average of 1500-2000 kcal. While Groups 1 and 2 reduced their caloric intake by the same amount in different ways, they saw the Group 3 diet quickly without reducing total calories.
Their results showed that the fasting group (Group 2) lost 1.9 kg in just three weeks, and DEXA body scans showed that this weight loss was almost entirely due to a reduction in body fat.
In contrast, the first fasting group (Group 1), who experienced the same reduced caloric intake by fasting on alternate days and eating 50% more food on non-fasting days, lost almost as much body weight (1.6 kg), but only half that weight loss consisted of reduced body fat, the rest of muscle mass.
Group 3, who fasted but increased their energy intake by 100% on non-fasting days, did not need to rely on their body’s fat stores for energy and therefore the weight loss was negligible.
Professor James Betts, director of the Center for Nutrition, Exercise & Metabolism at the University of Bath, who led the research, explains, “Many people believe that fasting diets are particularly effective, or even special, for weight loss Having metabolic health benefits when not losing weight.
“But intermittent fasting is not a silver bullet, and the results of our experiment suggest that fasting is nothing special compared to the more traditional, standard diets that people might follow.
Most importantly, when following a fasting diet, it pays to think about whether longer fasts actually make it harder to maintain muscle mass and physical activity, which are known to be very important factors in long-term health. “
These results focused on participants who were defined as “lean” (ie body mass index 20-25 kg / m2). 36 people took part in the study, which was carried out between 2018-2020 and funded by the University of Bath.
Reference: “A Randomized Controlled Trial to Isolate the Effects of Fasting and Energy Restriction on Weight Loss and Metabolic Health in Lean Adults,” June 16, 2021, Science Translational Medicine.
DOI: 10.1126 / scitranslmed.abd8034
