Calories, not fasting, identified as primary for weight loss

A recent study casts doubt on the widely held belief that intermittent fasting, also known as time-restricted eating, is an effective weight loss strategy. Contrary to popular assumptions about its metabolic benefits, the study suggests that the key to weight loss may simply lie in reducing overall calorie intake, rather than any special effects of intermittent fasting on metabolism or circadian rhythms.

Calories, not fasting, identified as primary for weight loss

Published in the Annals of Internal Medicine, the study presents findings from a randomized-controlled trial comparing the weight loss outcomes of individuals following a time-restricted diet with those adhering to a non-restricted diet. Led by Nisa Marisa Maruthur, an internal medicine specialist at Johns Hopkins University, the study sheds light on the mechanisms behind time-restricted eating (TRE).

The research, though limited in scope, addresses a gap in existing TRE studies, which have often been criticized for small sample sizes and methodological flaws. Maruthur’s team acknowledges the study’s limitations but emphasizes its contribution to understanding TRE. The trial involved 41 participants, primarily Black women with obesity and either pre-diabetes or diet-controlled diabetes. Both groups received controlled meals with identical nutritional content and were instructed to maintain their current exercise levels.

Participants in the time-restricted group were restricted to a 10-hour eating window, consuming 80 percent of their daily calories before 1 pm. Meanwhile, the control group followed a standard eating pattern, with meals distributed throughout the day. Both groups demonstrated high adherence to their respective eating schedules. After 12 weeks, both groups experienced similar weight loss, averaging around 2.4 kg (5.3 pounds), with no significant differences in other health markers like glucose homeostasis and blood pressure.

Maruthur and her colleagues conclude that when calorie intake is matched, time-restricted eating does not offer additional benefits for weight loss. They acknowledge the potential for variations in outcomes based on different populations and shorter eating windows. Experts weigh in on the study, noting its alignment with expectations. Adam Collins, a nutrition expert at the University of Surrey, emphasizes the lack of magical effects associated with time-restricted eating. Similarly, Naveed Sattar, a professor at the University of Glasgow, praises the study’s rigorous methodology.

Krista Varady and Vanessa Oddo from the University of Illinois view the findings as a practical approach to weight loss, particularly for individuals who struggle with traditional calorie-counting methods. They emphasize the simplicity and accessibility of time-restricted eating as a viable dietary strategy for diverse populations. The study emphasizes the significance of calorie reduction in achieving weight loss goals, challenging assumptions about the exclusive efficacy of intermittent fasting. It underscores the importance of adopting practical approaches, such as time-restricted eating, which simplifies dietary strategies and enhances accessibility for diverse populations.

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