New research suggests intermittent fasting is unlikely to aid weight loss more than simply cutting back on high calorie foods.
According to the researchers, regimes that include fasting have increased in popularity because some people report finding them easier to follow than a conventional diet, which would involve reducing calories all week and opting for healthier food choices.
But the study found that both methods have similar results.
Fasting diets come in many forms, such as the popular 5:2 diet - where dieters are instructed to eat only 500 calories per day for two days of the week and eat whatever they want for the other five - and the Every Other Day Diet - which works on a similar principle, but with a 500 calorie restriction on alternate days.
The benefits of fasting diets have been widely reported, with some linking 5:2 to reducing symptoms of chronic diseases, such as type 2 diabetes.
But the scientists sought to assess the weight loss benefits of such plans, focussing specifically on the impact of fasting every other day.
The clinical trial, by the University of Illinois, compared the effects of alternate-day fasting with daily calorie restriction on weight loss, weight maintenance and indicators of heart disease risk.
A total of 100 obese patients were assigned to one of three groups for one year: alternate-day fasting, daily calorie restriction or no intervention.
The alternate day fasting group consumed 25% of their calorie needs on ‘fast days’ (approximately 500 kcal) and were permitted to eat what they wanted on alternating ‘feast’ days (usually 125% of calorie needs).
The daily calorie restriction group consumed 75% of calorie needs every day.
All participants were instructed not to change their physical activity habits throughout the trial.
After one year, those on the fasting diet had lost 6% of their body weight, which was not significantly different from the daily calorie restriction group, who lost 5.3% body weight.
The study also did not find any significant differences in heart disease risk indicators, such as high blood pressure, among the fasting group.
In addition, the drop out rate was highest among those in the fasting group, with 38% of participants failing to stick to the plan compared to 29% in the calorie restricted group.
The study concludes: “The results of this randomised clinical trial demonstrated that alternate-day fasting did not produce superior adherence, weight loss, weight maintenance or improvements in risk indicators for cardiovascular disease compared with daily calorie restriction.”
The authors did note that the findings of the study were limited, as participants were only followed for six months after the initial diet phase to see whether the diet could be maintained. A longer follow up period would be needed to accurately asses the longterm benefits of each diet plan.
The study is published in the journal JAMA Internal Medicine.