Intermittent fasting and weight loss: Does it work?

The prevalence of overweight and obesity is dramatically increasing, along with the risk of chronic disease, and the efficacy and safety of time-restricted eating for weight loss has not yet been researched. In a study conducted by D.A. Lowe, PhD et al., researchers aimed to answer the question, "What is the effect of time-restricted eating on weight loss and metabolic health in patients with overweight and obesity?" The objective of the study was to determine the effect of 16:8 hour time restricted eating (or intermittent fasting) on weight loss and metabolic risk factors.

A previous study determined that time-restricted feeding without a decrease in caloric intake prevented weight gain and reduced metabolic outcomes in obese mice.

In a randomized clinical trial, participants were divided into two groups: the consistent meal timing (CMT) group who ate 3 structured meals a day, and the time-restricted eating (TRE) group who were instructed to eat ad libitum (as much or as often as they wanted) from 12:00 pm until 8:00 pm and fast from 8:00 pm until 12:00 pm the next day. The study lasted 12 weeks and gathered participants from all over the United States via mobile app on the Eureka Research platform, where they received surveys and connected to a bluetooth scale. There was also a subset of 50 participants in San Francisco who were able to do in-person comprehensive metabolic testing. The participants were men and women aged 18-64 with a BMI between 27 and 43 kg/m^2.

The primary outcome of the study was weight loss. The secondary outcomes (derived from the 50 in-person participants) were changes in body composition, blood lipids, fasting glucose and insulin, HbA1C levels, estimated energy intake, total energy expenditure, and resting energy expenditure.

In the 116 participants who completed the protocol, time-restricted eating was associated with a 1.17% decrease in weight, but this result was not significantly different from weight loss in the consistent meal timing group (0.75%). There was a significant difference in appendicular lean mass (ALM) between groups but there were no significant differences in any of the other secondary outcomes within or between groups.

A limitation to the study is that the researchers did not obtain self-reported measures of energy or macronutrient intake. They also didn’t measure changes in protein intake, given the loss of ALM in the time-restricted eating group and the possibility that protein intake was altered by TRE in the study. Also, the DEXA analysis of lean mass didn’t factor in muscle hydration, so there is a possibility that hydration status is also a confounding variable. The study is also limited in that physical activity level was not assessed and controlled in the participants within nor between the groups. Physical activity plays a major role in weight loss and metabolic risk factors.

In conclusion, the results of the study did not support the hypothesis that TRE is efficient for weight loss and improved metabolic markers, however, they did highlight the importance of control interventions, and also created a new concern and an area for future research on the potential effects of time-restricted eating on protein intake and appendicular lean mass. Future research should also focus on the same concept, but with physical activity level fully accounted for.

Interested in learning more? Visit: https://pubmed.ncbi.nlm.nih.gov/32986097/