Early Time-Restricted Eating Ups Weight Loss, but Jury Still Out

Miriam E. Tucker

August 09, 2022

Time-restricted eating during the earlier part of the day (eTRE) may promote weight loss and reduce blood pressure, new findings suggest.

Previous studies have produced mixed results regarding the weight-loss potential for intermittent fasting, the practice of alternating eating with extended fasting, and the "time-restricted eating" format, where eating is restricted to a specific, often 10-hour, time window during the day.

In a new randomized clinical trial of 90 people with obesity in which that time window was 7 AM through 3 PM, so 8 hours long, researchers report that "eTRE was more effective for losing weight and lowering diastolic blood pressure than was eating over a period of 12 or more hours at 14 weeks. The eTRE intervention may therefore be an effective treatment for both obesity and hypertension." The study, by Humaira Jamshed, PhD, of the Department of Nutrition Sciences, University of Alabama at Birmingham, and colleagues, was published August 8 in JAMA Internal Medicine.

In an accompanying invited commentary, Shalender Bhasin, MBBS, points out that the study findings differ from those of a previous trial published in April of 139 adults conducted in China, which did not find a significant weight loss benefit with TRE versus ad lib eating.

"The scientific premise and the preclinical data of the effects of TRE are promising, but the inconsistency among studies renders it difficult to draw strong inferences from these well-conducted but relatively small trials," notes Bhasin, of Harvard Medical School, Boston, Massachusetts.

Need for Larger and Longer Trials of TRE

Bhasin says — and the study authors also acknowledge — that much larger randomized clinical trials of longer duration are needed "to comprehensively evaluate the hypothesized benefits and risks of long-term TRE of calorically restricted diets in adults."

Commenting on the study for the UK Science Media Centre, Simon Steenson, PhD, nutrition scientist, British Nutrition Foundation, said "one of the strengths of this new study is the trial design and the number of people who were recruited compared to many of the previous trials to date."

However, Steenson also pointed to the prior Chinese research as evidence that the inconsistencies across studies highlight the need for larger and longer trials, with cardiovascular as well as weight-loss endpoints.

Still, Steenson said, "For individuals who may find that this pattern of eating fits better with their lifestyle and preferences, time-restricted feeding is one option for reducing overall calorie intake that might be a suitable approach for some. Ultimately, it is about finding the best approach to moderate calorie intake that works for each person, as successful and sustained weight loss is about ensuring the diet is feasible to follow in the long-term."

Differences in Weight Loss, Diastolic BP, but Not All Measures

The study population included 90 adults seen at the Weight Loss Medicine clinic at the University of Alabama at Birmingham between August 2018 and December 2019. Participants had a body mass index of 30-60 kg/m2, and none had diabetes. 

They were randomized to eTRE with the 7 AM to PM eating window or a control schedule with eating across 12 hours or more, mimicking US median mealtimes, at least 6 days a week. All participants received 30-minute weight-loss counseling sessions at baseline and at weeks 2, 6, and 10 and were advised to follow a diet of 500 kcal/day below their resting energy expenditure and exercise 75-150 minutes per week.

The eTRE group adhered with their schedule a mean of 6 days per week, lower than the 6.3 days among controls (P = .03), and adherence declined by about 0.4 days per week in the eTRE group over the 14 weeks (P = .001).  

At 14 weeks, both the eTRE group and controls had lost clinically meaningful amounts of weight, at –6.3 kg and –4.0 kg, respectively, but the –2.3 kg difference was significant (P = .002).

However, there was no difference in absolute fat loss (P = .09) or ratio of fat loss to weight loss (P = .43). There were also no significant differences in changes in other body composition parameters including visceral fat and waist circumference.

Diastolic blood pressure was lowered by an additional 4 mmHg in the eTRE group compared with controls at 14 weeks (P = .04), but there were no significant differences in systolic blood pressure, heart rate, glucose, A1c levels, insulin levels, measures of insulin resistance, or plasma lipids.

There were no differences between the two groups in self-reported physical activity, energy intake, or dietary macronutrient composition either. However, weight-loss modeling in 77 participants with at least two weight measurements indicated that the eTRE group reduced their intake by about 214 kcal/day compared with controls (P = .04).

Those in the eTRE group also showed greater improvements in measures of mood disturbance, vigor-activity, fatigue-inertia, and depression-dejection. Other mood and sleep endpoints were similar between groups.

In a secondary analysis of just the 59 participants who completed the study, eTRE was also more effective at reducing body fat (P = .047) and trunk fat (P = .03).

About 41% of the eTRE completers planned to continue the practice after the study concluded.

The study was supported by grants from the National Center for Advancing Translational Sciences of the National Institutes of Health and the National Institute of Diabetes and Digestive and Kidney Diseases. Jamshed has reported no relevant financial relationships. Bhasin has reported receiving grants to his institution for research on which Bhasin is the principal investigator from AbbVie and MIB, receiving personal fees from OPKO and Aditum; and holding equity interest in FPT and XYOne. Steenson has declared funding in support of the British Nutrition Foundation that comes from a range of sources.

JAMA Intern Med. Published online August 8, 2022. Abstract, Commentary

Miriam E. Tucker is a freelance journalist based in the Washington, DC, area. She is a regular contributor to Medscape, with other work appearing in The Washington Post, NPR's Shots blog, and Diabetes Forecast magazine. She is on Twitter: @MiriamETucker.

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