Intermittent fasting and time-restricted eating have become popular ways to structure meals, but most questions about these approaches remain unanswered, including whether it matters when the eating window falls during the day. A new study from German researchers suggests that earlier meal timing may influence fat metabolism at the molecular level, even when calories and nutrients are the same.
The study, part of the ChronoFast project and published in Science Translational Medicine, included 31 women with overweight or obesity who completed two different eating schedules: an early window from 8 a.m. to 4 p.m., and a later window from 1 p.m. to 9 p.m. Each phase lasted two weeks and calories were kept nearly identical. Researchers collected blood samples before and after each phase and also took a small fat-tissue biopsy from the abdomen.
Using lipidomics, a technique that measures hundreds of different fat molecules, the research team identified clear differences between early and late eating. Only the early schedule led to significant changes in lipid metabolism. Levels of more than 100 types of lipids decreased, including ceramides and phosphatidylcholines, which have been linked to type 2 diabetes and cardiovascular disease. The activity of certain fat-metabolizing enzymes shifted as well.
“We see that the timing of meals has an influence on the regulation of fat metabolism,” said study leader Olga Ramich, Heisenberg Professor at the German Institute of Human Nutrition Potsdam-Rehbrücke (DIfE). “Eating early — in line with internal circadian rhythms — leads to measurable changes in the lipid profile and enzyme activity, while eating late does not have this effect.”
To understand how these molecular differences arise, the researchers also analyzed gene activity in participants’ fat tissue. They found that several genes involved in regulating fatty acids and cell-membrane remodeling responded differently to early versus late eating. One pathway related to glycerophospholipid metabolism, central to inflammation and cell structure, was especially affected.
Despite these shifts in lipid biology, classic health markers such as cholesterol and triglycerides did not differ between the early and late eating windows. The researchers say this highlights an important point: time-restricted eating may influence metabolism in subtle ways long before changes show up on standard lab tests.
“Our data opens up new perspectives on the concept of chrononutrition in obesity and diabetes prevention,” Ramich said. “The data suggests that synchronizing nutrition with the circadian rhythm could be an effective strategy for optimizing fat metabolism and preventing metabolic diseases.”
Experts note that meal timing is just one factor in metabolic health, and the study was small and short-term. Still, the findings add to growing evidence that eating earlier in the day may work with the body’s internal clock, a pattern that could support healthier fat metabolism over time.
This research was supported by several German and European scientific organizations, including the German Center for Diabetes Research, the German Research Foundation, the European Association for the Study of Diabetes and the German Diabetes Association.