People who fasted lost less weight than conventional dieters


A study challenges a popular belief that people who fasted such as alternative day the ‘5:2’ would be the most effective ways to shed weight.

Over recent years, diets which see people fast a couple of days each week have increased in popularity, bolstered by pictures of people’s miraculous weight transformations, and endorsed by celebrity endorsements.

However, evidence so far concerning the effectiveness of fasting compared with more conventional diets which aim to reduce calorie intake over the course of a full week was limited.

Released in the prestigious journal Science Translational Medicine, the new study by a group of physiologists at the University of Bath assembles this proof and indicates that there is ‘nothing special’ about fasting.

Participants within their randomized control trials lost less weight when fasting in contrast with those after a traditional diet – even when their caloric intake was the same overall.

The trial, organized by a team in the University’s Centre for Nutrition, Exercise & Metabolism (CNEM), watched participants allocated to one of 3 groups:

Group 1 which fasted on alternate days with their fast day followed by a day of eating 50 percent more than usual.

Group 2 which reduced calories across all meals regular by 25%.

Group 3 which fasted on alternative days (in the same way as Group 1) nevertheless followed their fast day with one day consumption 100% more than normal.

Participants across all three groups were consuming a typical diet of about 2000-2500 kcal on average at the onset of the study. Over the span of the three-week tracking period, the two energy restricted groups decreased this to be between 1500-2000 kcal normally. Whereas groups 1 and 2 reduced their calorie consumption by the same amount in different ways, category 3’s  diet watched them fast without reducing overall calories.

Their results found that the non-fasting dieting group (Group 2) Dropped 1.9 kg in just three months, and DEXA body scans demonstrated this weight loss was almost completely because of reduction in body fat content.

By comparison, the first group (Group 1) who underwent the same decreased calorie consumption by fasting on alternative days and eating 50% more on non-fasting times, lost almost as much body fat (1.6 kg) but only half this weight loss was from reduced body fat using the remainder from muscle mass.

Group 3, who intermittently fasted but increased their energy intake by 100 percent on non-fasting days, did not need to draw their body’s fat stores for energy and therefore weight loss was insignificant.

Professor James Betts, Manager of this Centre for Nutrition, Exercise & Metabolism In the University of Bath who headed the research clarifies: “Many people believe that diets based on fasting are especially effective for weight loss or that these diets have particular metabolic health benefits even if you don’t lose weight.”

“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.”

“Most significantly, if you are following a fasting diet it is worth thinking about whether prolonged fasting periods is actually making it harder to maintain muscle mass and physical activity levels, which are known to be very important factors for long-term health.”

These outcomes focused on participants who were defined as ‘lean’ (i.e. body mass indicator 20-25 kg/m2). 36 individuals participated in the Research Which was conducted involving 2018 – 2020 and financed by the University of Bath.

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