Time-restricted eating for weight loss: The jury is still out

Time-restricted eating (TRE) could provide a modest 1–4 percent weight loss without cutting calories, says an expert. But whether the evidence on hand supports its use is still debatable.

TRE allows a specific time window for eating during the day, the more popular schedule of which is 16:8 which means a 16-hour window for fasting, followed by an 8-hour window for eating.

Presenting at ADA 2021, Dr Courtney Peterson, an associate professor from the University of Alabama, Birmingham, US, said TRE is known to induce weight loss and promote better metabolic health.

“This type of intermittent fasting is not just actually linked to weight loss … it may also help improve blood glucose, blood pressure, and oxidative stress,” she continued. Now, this is what obese, hypertensive people who are experiencing prolonged blood sugar spikes find really interesting.

Benefits come with caveats

In a systematic review of 23 trials, TRE induced an average weight loss of 3 percent and a loss of fat mass without having to restrict calories, reported Peterson. [Nutrients 2020;12:3770]

Similarly, a meta-analysis of 19 studies identified from PubMed, EMBASE, and the Cochrane Library, showed there was a reduction of body weight (mean difference (MD), −0.90; and fat mass (MD), −1.58), while preserving fat-free mass (MD, −0.24), in overweight or obese individuals following TRE vs a regular diet. Beneficial effects were also seen on cardiometabolic parameters such as blood pressure (systolic BP, MD, −3.07), fasting glucose concentration (MD, −2.96), and triglycerides (MD, −11.60). [Nutrients 2020;12:1267]

The caveat, Peterson said, was that both analyses had no control treatment.  

More evidence, or no evidence

A separate study of TRE using an 8-hour window for eating showed that compared with control, TRE was as effective as alternate day fasting for weight loss in patients with nonalcoholic fatty liver disease (NAFLD).

At 4 and 12 weeks, adults in both treatment groups lost more weight than those in the control group. However, Peterson said this was not a fair comparison as no meal was provided in the control group whereas healthy meals were provided in the TRE and IF groups. [BMC Gastroenterol 2019;19:219]

TREAT or trick

Meanwhile, in the 12-week TREAT trial of overweight or obese individuals, TRE from noon to 8 pm did not confer greater weight loss vs three structured meals throughout the day nor cardiometabolic benefits. [JAMA Intern Med 2020;180:1491-1499]

TRE was associated with a modest reduction (1.17 percent) in weight, but it was not significantly different from the reduction in the control group (0.75 percent).

However, as the study didn’t report the macronutrient composition or caloric intake of the two groups, including the baseline metabolic conditions of the cohorts, drawing a definitive conclusion is difficult, according to Peterson.

Promising, but more data needed

There are studies showing that TRE can curb binge eating and compulsive overeating which can contribute to an unhealthy lifestyle. Proponents of TRE also believe diets that limit when you can eat work better than eating willy-nilly throughout the day.

In a 4-day crossover trial, although TRE had no impact on 24-hour energy expenditure, it decreased swings in subjective hunger, improved appetite hormones including ghrelin, and increased fat oxidation. [Obesity 2019;27:1244-1254] Another study reported that TRE improved one or more cardiometabolic endpoints. [J Transl Med 2016;14:290]

“I think TRE is promising because of its simple message and noted weight loss benefit,” commented session chair Dr Lisa Chow from the University of Minnesota in Minneapolis, US. “But more data are needed to provide definitive evidence.”