The notion behind intermittent fasting is supposedly simple: eat less for a time and improve your metabolism, but the reality is more complex, suggest German scientists, whose recent study found that some forms of intermittent fasting do not alter markers of metabolic or cardiovascular health.<\/p>\n
Science Alert reports that the team, led by the German Institute of Human Nutrition Potsdam-Rehbruecke (DIfE), put 31 women\u00a0who were overweight\u00a0or obese on two different intermittent fasting schedules for two weeks each.<\/p>\n
The schedules were 8am to 4pm or 1pm to 9pm, a particular kind of intermittent fasting known as time-restricted eating (TRE).<\/p>\n
While the timing of the schedules differed, the diet parameters were the same: participants could eat\u00a0as they normally did, and therefore take in the same amount of total calories (making this what’s known as an isocaloric study).<\/p>\n
Although the women lost some weight, other benefits that might be expected based on\u00a0previous research\u00a0\u2013 including lower blood sugar levels, lower blood pressure, and\u00a0lower cholesterol\u00a0\u2013 didn\u2019t show up in the data, raising questions about just how effective these timed fasting routines are.<\/p>\n
\u201cThe beneficial cardiometabolic effects described previously might be induced by TRE-mediated calorie restriction and not by the shortening of the eating window itself,\u201d\u00a0write\u00a0the researchers in their published paper.<\/p>\n
\u201cIn this nearly isocaloric trial, no improvements in metabolic parameters were observed after two weeks of TRE.\u201d<\/p>\n
The findings suggest it may be\u00a0calorie reduction\u00a0rather than time-restricted eating itself that boosts key indicators of health inside the body, although it\u2019s important to bear in mind this was a relatively small-scale, short-term study.<\/p>\n
In addition to the study\u2019s modest reductions in body weight, researchers observed changes in participants\u2019 body clocks. The timing of their\u00a0circadian rhythms, including those that nudge the body towards sleep, was shifted based on the TRE schedule.<\/p>\n
It\u2019s more evidence that our internal clocks can be partially controlled by when we drink and eat, as well as through other triggers (such as when\u00a0the sun goes down). This could play into health problems associated with eating late at night, for example.<\/p>\n
\u201cThose who want to lose weight or improve their metabolism should pay attention not only to the clock, but also to their energy balance,\u201d said biologist and nutritionist Olga Ramich, from the DIfE.<\/p>\n
Improving metabolic health is particularly important when tackling insulin resistance and\u00a0diabetes. Future findings like these may change how diets are structured for people with conditions like these or who are\u00a0at risk of developing\u00a0them.<\/p>\n
The researchers are keen to continue investigating the relationship between calorie consumption and calorie timing. It\u2019s possible that in hypocaloric scenarios (when calories are restricted), timing may have some influence on biological markers of health.<\/p>\n
Various types of intermittent fasting continue to be analysed by researchers, but studies\u00a0can differ substantially\u00a0in terms of the diets that are allowed, the participants, study duration, and the health benefits measured.<\/p>\n
\u201cOur findings suggest the importance of calorie restriction for metabolic improvements in TRE,\u201d\u00a0write\u00a0the researchers.<\/p>\n
\u201cWhether the timing of eating under the hypocaloric conditions can additionally contribute to metabolic changes and whether the optimal eating timing differs between individuals warrants investigation in future studies.\u201d<\/p>\n
The research was published in\u00a0Science Translational Medicine.<\/p>\n
Study details<\/p>\n
Intended isocaloric time-restricted eating shifts circadian clocks but does not improve cardiometabolic health in women with overweight<\/p>\n
Beeke\u00a0Peters\u00a0,Julia\u00a0Schwarz,\u00a0Bettina\u00a0Schuppelius\u00a0et al.<\/p>\n
Published in Science Translational Medicine on 29 October 2025<\/p>\n
Abstract<\/p>\n
Time-restricted eating (TRE) is a promising strategy to improve metabolic outcomes. However, it remains unclear whether TRE has cardiometabolic benefits in an isocaloric setting and whether its effects depend on the eating timing. We conducted a randomised crossover trial in 31 women with overweight or obesity to directly compare the effects of a 2-week early TRE (eTRE; eating from 8:00 to 16:00) and a 2-week late TRE (lTRE; eating from 13:00 to 21:00) on insulin sensitivity, cardiometabolic risk factors, and the internal circadian phase. During the restricted 8-hour eating period, participants were asked to consume their habitual food quality and quantity. Insulin sensitivity did not differ between (\u22120.07; 95% CI, \u22120.77 to 0.62;\u00a0P\u00a0=\u00a00.60) or within (eTRE: 0.31; 95% CI, \u22120.14 to 0.76;\u00a0P\u00a0=\u00a00.11; lTRE: 0.19; 95% CI, \u22120.22 to 0.60;\u00a0P\u00a0=\u00a00.25) interventions. Twenty-four\u2013hour glucose, lipid, inflammatory, and oxidative stress markers showed no clinically meaningful between- or within-intervention differences. Participants demonstrated high timely adherence (eTRE, 96.5%; lTRE, 97.7%), unchanged dietary composition and physical activity, minor daily calorie deficit (eTRE, \u2212167\u00a0kilocalories\/day), and weight loss (eTRE, \u22121.08\u00a0kilograms; lTRE, \u22120.44\u00a0kilograms). In lTRE, the circadian phase in blood monocytes (24 minutes; 95% CI, \u22125 to 54 minutes;\u00a0P\u00a0=\u00a00.10) and sleep midpoint (15 minutes; 95% CI, 7 to 23 minutes;\u00a0P\u00a0<\u00a00.001) occurred later compared with eTRE. Overall, in an intended isocaloric setting, neither eTRE nor lTRE improves insulin sensitivity or other cardiometabolic traits, despite a shift of internal circadian clocks.<\/p>\n
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Science Translational Medicine article \u2013\u00a0Intended isocaloric time-restricted eating shifts circadian clocks but does not improve cardiometabolic health in women with overweight (Open access)<\/a><\/p>\n \u00a0<\/p>\n Science Alert article \u2013 Study Raises Serious Questions About The Benefits of Intermittent Fasting (Open access)<\/a><\/p>\n \u00a0<\/p>\n See more from MedicalBrief archives:<\/p>\n \u00a0<\/p>\n Evidence review: Intermittent fasting for weight loss and lower cardiometabolic risk<\/a><\/p>\n \u00a0<\/p>\n The pros and cons of intermittent fasting to lose weight<\/a><\/p>\n \u00a0<\/p>\n