Study finds that time-restricted eating without cutting calories does not improve metabolic health

Contrary to common assumptions, a new study from the German Institute for Human Nutrition Potsdam-Lebrücke (DIfE) and the Charité University of Berlin shows that intermittent fasting (time-restricted eating), where caloric intake remains unchanged, does not lead to measurable improvements in metabolic or cardiovascular parameters, but does change the body's internal clock. Professor Olga Ramić and her team published Results of ChronoFast research published in journal scientific translational medicine.

Time-restricted eating (TRE) is a type of intermittent fasting characterized by a daily eating period of 10 hours or less and a fasting period of at least 14 hours. TRE is becoming increasingly popular as a simple dietary strategy for weight management and improved metabolic health. In rodents, TRE protects against diet-induced obesity and associated metabolic dysfunction.

Similarly, TRE studies in humans suggest a number of positive cardiometabolic effects, including improved cardiometabolic effects. insulin sensitivityglucose, triglycerides, and cholesterol levelalso a moderate decrease body weight and body fat. Therefore, TRE is considered a promising approach to combat insulin resistance and diabetes.

Inconsistent initial situation

Results from previous TRE trials have been partially contradictory, and it is not yet clear whether metabolic improvements are due to restriction of daily meal times, voluntary calorie restriction, or a combination of both factors. In fact, most previous studies did not carefully monitor energy intake or other potential confounders.

In the ChronoFast trial, Professor Ramic, Head of the Department of Molecular Metabolism and Precision Nutrition at DIfE and Professor at the Charity Medical University Berlin, and his team investigated whether an 8-hour meal period could improve insulin sensitivity and other cardiometabolic parameters in a tightly controlled isocaloric environment.

The researchers conducted a randomized crossover design involving a total of 31 women who were overweight or obese. Each participant ate a regular meal over a 2-week period during the early hours of 8:00 AM to 4:00 PM (eTRE) or the late hours of 1:00 PM to 9:00 PM (lTRE). The calorie and nutrient composition remained approximately the same (isocaloric).

During my 4 visits, blood sample are collected, Oral glucose tolerance test was performed to examine the effects of TRE on glucose and fat metabolism, as well as other metabolic markers. During the meal phase, continuous glucose monitoring was used to observe 24-h glucose levels and simultaneously record food intake. Physical activity was controlled using motion sensors. DIfE researchers, in collaboration with Professor Achim Kramer of the Charitable University of Berlin, also studied the circadian clock in isolated blood cells.

Insulin sensitivity and other metabolic values ​​do not improve

In contrast to previous studies suggesting positive effects of TRE, the ChronoFast study found no clinically relevant changes in insulin sensitivity, blood sugar levels, blood fats, or inflammatory markers, at least after this relatively short two-week intervention. “Our results suggest that the health benefits observed in earlier studies are likely due to unintentional calorie reductions, rather than shortening meal duration per se,” Professor Ramich explains.

Although participants did not show significant metabolic improvements, studies of blood cell internal clocks revealed that TRE influences blood cell circadian phasing and sleep timing. The body clock was delayed by an average of 40 minutes after the lTRE intervention compared to the eTRE intervention, and participants went to bed and woke up later after the lTRE intervention. “The timing of food intake acts as a cue for our behavior. biological rhythm“It's like light,'' says lead author Beek Peters.

Negative energy balance and chronotype may be important

This result highlights that calorie reduction plays a central role in the health benefits of intermittent fasting. “People who want to lose weight or improve their metabolism need to pay attention not only to the clock, but also to their energy balance,” Professor Ramić summarizes.

Future research should determine whether timing TRE in combination with reduced caloric intake confers additional benefits, and how individual factors such as chronotype and genetics influence these effects.

Background: Determination of circadian rhythms

The human body follows individual rhythms generated by molecular mechanisms. This rhythm roughly corresponds to the length of the day (Latin: circa, dia), so it is also known as the circadian clock. Following the day/night rhythm, it reliably controls almost all physiological and biochemical processes in the body, including sleep and metabolism.

Almost every cell in the body has a biological clock that is influenced by light and other factors such as exercise and nutrition. To objectively determine an individual's internal body rhythm (circadian phase), Professor Kramer developed the BodyTime assay. The test requires only one blood sample. This method was used in the ChronoFast study, which showed that meal times influence human body clocks.

Provided by the German Institute for Nutritional Research, Potsdam-Lebrücke