Not so fast!
Over the course of a year, study participants who ate only from 8:00 a.m. to 4:00 p.m. did not lose significantly more weight than individuals who ate whenever they wanted, nor did they achieve significantly greater improvements in other obesity-related health measures like body mass index (BMI) or metabolic risk, reported lead author Deying Liu, MD, of Nanfang Hospital, Southern Medical University, Guangzhou, China, and colleagues.
“[Daily fasting] has gained popularity because it is a weight-loss strategy that is simple to follow, which may enhance adherence,” Dr. Liu and colleagues wrote in the. However, “the long-term efficacy and safety of time-restricted eating as a weight-loss strategy are still uncertain, and the long-term effects on weight loss of time-restricted eating as compared with daily calorie restriction alone have not been fully explored.”
To learn more, Dr. Liu and colleagues recruited 139 adult patients with BMIs between 28 and 45. Individuals with serious medical conditions, such as malignant tumors, diabetes, chronic kidney disease, and others were excluded. Other exclusion criteria included smoking, ongoing participation in a weight-loss program, GI surgery within the prior year, use of medications that impact energy balance and weight, and planned or current pregnancy.
All participants were advised to eat calorie-restricted diets, with ranges of 1,500-1,800 kcal per day for men and 1,200-1,500 kcal per day for women. To determine the added impact of fasting, participants were randomized in a 1:1 ratio into time-restricted (fasting) or non–time-restricted (nonfasting) groups, in which fasting participants ate only during an 8-hour window from 8:00 a.m. to 4:00 p.m., whereas nonfasting participants ate whenever they wanted.
At 6 months and 12 months, participants were re-evaluated for changes in weight, body fat, BMI, blood pressure, lean body mass, and metabolic risk factors, including glucose level, triglycerides, blood pressure, and others.
Caloric intake restriction seems to explain most of beneficial effects
At one-year follow-up, 118 participants (84.9%) remained in the study. Although members of the fasting group lost slightly more weight on average than those in the non-fasting group (mean, 8.0 kg vs. 6.3 kg), the difference between groups was not statistically significant (95% confidence interval, −4.0 to 0.4; P = .11).
Most of the other obesity-related health measures also trended toward favoring the fasting group, but again, none of these improvements was statistically significant. Weight circumference at 1 year, for example, decreased by a mean of 9.4 cm in the fasting group versus 8.8 cm in the nonfasting group, a net difference of 1.8 cm (95% CI, –4.0 to 0.5).
“We found that the two weight-loss regimens that we evaluated had similar success in patients with obesity, regardless of whether they reduced their calorie consumption through time-restricted eating or through calorie restriction alone,” Dr. Liu and colleagues concluded.
Principal investigator Huijie Zhang MD, PhD, professor, chief physician, and deputy director of the department of endocrinology and metabolism at Nafang Hospital, noted that their findings are “consistent with the findings in previous studies.”
“Our data suggest that caloric intake restriction explained most of the beneficial effects of a time-restricted eating regimen,” Dr. Zhang said.
Still, Dr. Zhang called time-restricted eating “a viable and sustainable approach for a person who wants to lose weight.”
More work is needed, Dr. Zhang said, to uncover the impact of fasting in “diverse groups,” including patients with chronic disease like diabetes and cardiovascular disease. Investigators should also conduct studies to compare outcomes between men and women, and evaluate the effects of other fasting durations.