Time to ditch the 5:2? Fad fasting diets don’t help you lose weight quicker, and limiting daily calories is more effective, experts claim 


  • UK-based scientists say intermittent fasting is ‘no magic bullet for weight loss’
  • Fad diets involve switching between periods of fasting and eating normally.
  • A variation is the 5:2 diet – eating normally for five days and then fasting for two days

One study shows that diets that involve intermittent fasting — switching between periods of fasting and periods of eating normally — do not help you lose weight quickly.

In trials at the University of Bath, participants lost less weight during fasting than those following a traditional diet — even when their calorie intake was about the same overall.

The study’s authors believe that intermittent fasting – which has been endorsed by celebrities including Jennifer Aniston, Reese Witherspoon and Twitter CEO Jack Dorsey – are ‘no magic bullet for weight loss’.

A traditional diet, which involves consistently limiting calorie intake over a certain period of time, is therefore probably a better option for people who want to lose weight.

Intermittent fasting involves switching between fasting days and normal eating days. A variation is the 5:2 diet – eating normally for five days and then fasting for two days. But experts at the University of Bath have revealed that it may not work as well as normal dieting – consistently limiting the amount of calories consumed over a certain period of time.

intermittent fasting

Intermittent fasting involves switching between fasting days and normal eating days.

Intermittent fasting diets generally fall into two categories – daily time-restricted eating, which limits eating times to 6-8 hours per day, and 5:2 intermittent fasting.

5:2 involves eating normally for five days and then reducing calorie intake to a quarter of your daily needs.

Johns Hopkins Medicine neuroscientist Mark Mattson previously claimed that intermittent fasting ‘can be part of a healthy lifestyle’.

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The study is led by Professor James Bates, director of the Center for Nutrition, Exercise and Metabolism at the University of Bath.

“Many people believe that diets based on fasting are particularly effective for weight loss or that these diets have particular metabolic health benefits, even if you do not lose weight,” he said.

‘But intermittent fasting is no magic bullet and the findings of our experiment suggest that there is nothing special about fasting compared to more traditional, standard diets that people can follow.’

One of the best-known intermittent fasting diets is the 5:2, which involves eating normally for five days and then reducing calorie intake to a quarter of your daily needs—typically 600 for men or 600 for women. 500 every two days.

The 5:2 diet was popularized in the UK by British broadcaster and former doctor Michael Mosley around 2012.

Another form of intermittent fasting is the 16:8 diet, which is favored by ‘Friends’ actress Jennifer Aniston.

Followers of this diet fast for 16 hours a day, and eat whatever they want for the remaining eight hours – usually between 10 a.m. and 6 p.m.

According to the University of Bath, these diets have increased in popularity, reinforced by images of miraculous weight changes and backed by celebrity endorsements—but they may be less effective than many believe.

The team tested intermittent fasting, although they did not specifically use 5:2 or 16:8 in their experiments.

Famous diets you need to limit what you eat aren't 'better for weight loss' than eating in general, from the likes of Jennifer Aniston (pictured) and Reese Witherspoon

Famous diets you need to limit what you eat aren’t ‘better for weight loss’ than eating in general, from the likes of Jennifer Aniston (pictured) and Reese Witherspoon

The research, conducted by a team from the university’s Center for Nutrition, Exercise and Metabolism (CNEM), allocated 36 participants to one of three groups.

three groups

The trial allocated participants into one of three groups:

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

• Group 2 that reduced calories by 25 percent at all meals per day.

• Group 3 who fasted on alternate days (same as group 1) but followed their fasting day with a day that was 100 percent longer than normal.

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Group 1 fasted on alternate days. His fasting day was followed by a day of eating 50 percent more than his daily life.

Group 2 — a proxy for a traditional diet plan — reduced the calories in all meals per day by 25 percent.

Meanwhile, Group 3 fasted on alternate days (in the same way as Group 1) but followed their fasting day with one day eating 100 percent more food than they usually did in their daily lives.

Participants in all three groups were consuming a typical diet of approximately 2000–2500 kilocalories (kcal) per day on average at the start of the study.

During the three-week monitoring period, the two energy-restricted groups (Groups 1 and 2) reduced it to an average of between 1500–2000 kcal.

While Groups 1 and 2 reduced their caloric intake by the same amount in different ways, Group 3 fasted without reducing overall calories.

Their results showed that the non-fasting dieting group (Group 2) lost 1.9 kg in just three weeks.

Dual energy X-ray absorptiometry (DEXA) body scans showed that this weight loss was almost entirely due to a reduction in the amount of body fat.

In contrast, the first fasting group (Group 1) who experienced a lower caloric intake by fasting on alternate days and eating 50 percent more on non-fasting days lost nearly as much body weight (1.6 kg). .

But only half the weight loss was from body fat, with the remainder from muscle.

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

These results focused on participants who were defined as ‘lean’, meaning that their body mass index (BMI) was between 20 and …

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