Time-Restricted Diets Effective for Losing Weight, Study Finds

Krista Varady, MD

In recent years, intermittent fasting and time-restricted feeding have exploded in popularity and become a subject of debate among many clinicians.

Now, a new study from the University of Illinois at Chicago is shedding light on the specific cardiometabolic impact of a 4-hour time-restricted feeding diet compared to a 6-hour time-restricted feeding diet in patients over a 10-week period.

“The findings of this study are promising and reinforce what we’ve seen in other studies — fasting diets are a viable option for people who want to lose weight, especially for people who do not want to count calories or find other diets to be fatiguing,” said Krista Varady, MD, professor of nutrition at the UIC College of Applied Health Sciences, in a statement.

With popularity of time-restricted feeding as a weight-loss regimen continuing to increase, Varady and a team of clinicians sought to conduct the first human trial comparing the effect of 4-hour and 6-hour time-restricted feeding diets on body weight and cardiometabolic risk factors. Investigators designed their study as a 10-week randomized parallel-arm trial comparing the 2 diet approaches.

The trial consisted of a 2-week baseline period for weight stabilization, followed by an 8-week intervention period. Patients randomized to the 4-hour group were instructed to eat between 3-7 p.m. daily and those randomized to the 6-hour group were instructed to eat ad libitum between 1-7 p.m. daily.

Investigators pointed out monitoring caloric intake was not required and participants were not limited to specific types of food during the feeding periods. Investigators also included a group of controls in their study who were instructed to maintain their weight throughout the trial, and not to change their eating or physical activity habits. These controls did not receive dietary advice but visit the same research center as the intervention groups.

The primary outcome measure for the study was change in body weight. Secondary outcome measures included insulin resistance, blood pressure, plasma lipids, inflammatory cytokines, oxidative stress, and diet adherence.

In total, 58 patients were identified for inclusion in the investigators’ study. Of these 58, 19 were randomized to the 4-hour group, 20 were randomized to the 6-hour group, and 19 were randomized to the control group. At the end of the 10-week study, 16 patients, 19 patients, and 14 patients, respectively, from the 3 groups had completed the trial.

Upon completion of the study, patients in both the 4-hour group (-3.2±0.4%) and 6-hour group (-3.2±0.4%) experienced significantly more weight loss than those in the control group (P <.001). Investigators highlighted reductions in insulin resistant and oxidative stress were similar for both the 4-hour and 6-hour groups compared with controls. Additionally, patients randomized to a time-restricted feeding group experienced a 550 kcal/day reduction in energy intake.

Investigators pointed out neither of the time-restricted feeding groups had significantly different blood pressure, LDL-C, HDL-C, or triglycerides compared to the control group after the 8-week intervention period.

“It’s also telling that there was no added weight loss benefit for people who sustained a longer fast—until we have further studies that directly compare the two diets or seek to study the optimal time for fasting, these results suggest that the 6-hour fast might make sense for most people who want to pursue a daily fasting diet,” Varady added.

This study, “Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity,” was published in Cell Metabolism.