Randomized Trial Suggests There is "Nothing Special" About Effects of Intermittent Fasting

James Betts, PhD

Results of a recent randomized trial indicate the purported benefits of intermittent fasting may not be as robust some studies have suggested in the past.

Assessing the impact of 3 different dietary approaches in healthy individuals, investigators found an approach incorporating fasting resulted in less weight loss when compared to a traditional diet, even when caloric intake was balanced between the groups.

"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,” said study lead investigator James Betts, PhD, Director of the Centre for Nutrition, Exercise & Metabolism at the University of Bath, in a statement. “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.”

With a slew of different dietary approaches gaining mainstream attention in recent years, Betts and a team of colleagues conducted a study to determine whether intermittent fasting provided metabolic benefits compared to a traditional diet. Funded by the University of Bath, the randomized 36 healthy individuals in a 1:1:1 ratio to different dietary groups for 3 weeks after a 4-week baseline monitoring period where investigators assessed habitual diet and physical activity of participants.

The first group served as a control group—patients in this group were prescribed 75% of their habitual energy intake each day, which represents a 25% daily energy restriction (75:75). The second group was prescribed a matched degree of dietary energy restriction that was to be achieved through alternating 24-hour periods of complete fasting (0:150). The third group was prescribed a matched pattern of complete fasting every other 24 hours but consuming 200% of their habitual energy intake on eating days (0:200). The primary outcome of the randomized controlled trial, which was conducted from 2015-2018, were body composition, components of energy balance, and postprandial metabolism.

All patients included in the study volunteers and had a BMI between 20.5-and 24.9 kg/m2. Additionally, patients were required to be aged 18-65 years and be considered weight stable for the prior 6 months. Participants were excluded if their body mass exceeded 120 kg, if they had engaged in fasting practices within the 3 months prior to start date, and if they had undergone or planned a change in diet or physical activity habits.

Upon analysis, 25% daily energy restriction was associated with a mean reduction in body mass of -1.91±0.99 kg, which investigators noted was driven mainly by reductions in fat loss (-1.75±0.79 kg). The fasting followed by 150% energy intake was also associated with decreased body mass (-1.60±1.06 kg; P=.46 vs 75:75) but this was associated with lesser body fat reductions than were observed in the daily 75% energy intake group (-0.74±1.32 kg; P=.01 vs 75:75).

Investigators pointed out fasting without energy restriction did not significantly reduce either body mass (-0.52±1.09 kg; P ≤.04 vs 75:75 and 0:150) or fat mass (-0.12±0.68 kg; P≤ 0.05 vs 75:75 and 0:150). In assessments of postprandial metabolism, results indicated indices of cardiometabolic health and gut hormones, as well as expression of genes in subcutaneous adipose tissue, were not statistically different between the study groups (P >.05).

This study, “A randomized controlled trial to isolate the effects of fasting and energy restriction on weight loss and metabolic health in lean adults,” was published in Science Translational Medicine.