If you don’t engage in intermittent fasting, you probably know someone who does. Timed diets have become a popular way to lose weight and improve metabolic health—but how effective is it, really?
In a paper published in October in the journal Science Translational Medicine, a team of researchers investigated the effects of time-restricted eating (TRE, a type of intermittent fasting) in obese women over a two-week period. Their results revealed that TRE without changing the number of calories consumed does not actually improve body or heart variables in a measurable way, but it does change our internal clocks.
Eating within a set time
Timed eating involves eating all meals within a daily window of no more than 10 hours, followed by meals lasting at least 14 hours. People do TRE to control their weight and improve their health the body (how we convert food and drink into energy and carry out important chemical processes in our cells). In fact, human studies show that TRE leads to beneficial cardiometabolic effects, including improved glucose, triglyceride, and cholesterol levels; insulin sensitivity; and weight loss and fat loss. As such, TRE can be an effective tool in the fight against diabetes and insulin resistance.
However, the previous TRE tests were not completely consistent, and were not revealed if the metabolic benefits come from people who eat in a short period of time, they naturally eat less, or both. In this context, researchers conducted a two-week trial with 31 overweight or obese women in which each person ate their normal caloric and nutritional (isocaloric) meals between 8 am and 4 pm (eTRE) or between 1 pm and 9 pm (lTRE).
Every two weeks, the researchers measured the women’s metabolic parameters, glucose levels, food intake, physical activity, and internal clock. Our bodies are governed by biological day-night rhythms (circulating clocks) driven by cellular processes. Many cells in our bodies have an internal clock that is sensitive to influences such as light, exercise, and diet.
There is no obvious metabolic improvement
The results can be bad news for limited time eaters. After a two-week period, the researchers found no significant changes in insulin sensitivity, blood sugar levels, blood fats, or inflammatory markers. In other words, they did not see any clear metabolic benefits.
“Our results suggest that the health benefits observed in previous studies may be due to unintended calorie reduction, rather than a shorter meal time itself,” said Olga Ramich, co-author of the study and Head of the Department of Molecular Metabolism and Precision Nutrition at the German Institute of Human Nutrition Potsdam-Rehbruecke. statement by the German Center for Diabetes Research.
Changes in internal clocks and sleep
However, Ramich and colleagues found that TRE affects the sleep cycle and rhythm of individual blood cells. On average, the lTRE schedule followed an internal clock delay of 40 minutes compared to the eTRE schedule. In addition, women who participated in the lTRE program went to bed later and woke up later.
“The timing of food intake serves as an indicator of our biological rhythms-like light,” explains Beeke Peters, first author of the study and the Department of Molecular Metabolism and Precision Nutrition.
Ultimately, research highlights that the health benefits of intermittent fasting are focused on eating less. “Those who want to lose weight or improve their body should not only pay attention to the clock, but also measure their energy,” said Ramich.
