Time-restricted eating without calorie cuts doesn't improve metabolic health, study finds

Contrary to common assumptions, a new study  shows that intermittent fasting (time-restricted eating) with an unchanged calorie intake does not lead to measurable improvements in metabolic or cardiovascular parameters but does shift the body's internal clocks. Prof. Olga Ramich and her team published the results of the ChronoFast study in the journal Science Translational Medicine.

Time-restricted eating (TRE) is a form of intermittent fasting characterized by a daily eating period of no longer than 10 hours and a fasting period of at least 14 hours. TRE is increasingly popular as a simple dietary strategy for weight control and metabolic health improvement. In rodents, TRE protects against diet-induced obesity and related metabolic dysfunctions.

Similarly, TRE studies in humans have suggested numerous positive cardiometabolic effects, such as improved insulin sensitivity, glucose, triglyceride, and cholesterol levels, as well as moderate reductions in body weight and body fat. Consequently, TRE is considered a promising approach to combat insulin resistance and diabetes.

Results of previous TRE trials have been partly contradictory and have not yet clarified whether the metabolic improvements are due to the restriction of daily eating duration, due to spontaneous calorie restriction, or due to the combination of both factors. In fact, most previous studies have not carefully monitored energy intake or other potential confounding factors.

Therefore, this new study investigated whether an eight-hour eating period could improve insulin sensitivity and other cardiometabolic parameters in a tightly controlled isocaloric environment in the ChronoFast trial.

Contrary to previous studies suggesting positive effects of TRE, the ChronoFast study shows no clinically relevant changes in insulin sensitivity, blood sugar levels, blood fats, or inflammatory markers, at least following this relatively short two-week intervention. These results suggest that the health benefits observed in earlier studies were likely due to unintended calorie reduction, rather than the shortened eating period itself, explain the researchers. 

Although the participants showed no marked metabolic improvements, the study of the internal clock in blood cells revealed that TRE influenced the circadian phase in blood cells and the sleep timing. The internal clock was, on average, shifted back by 40 minutes after the lTRE intervention compared to the eTRE intervention, and participants who followed the lTRE intervention went to bed and awaked later. The timing of food intake acts as a cue for our biological rhythms—similar to light, the researchers say. 

The results underscore that calorie reduction plays a central role in the health benefits of intermittent fasting. 

Beeke Peters et al, Intended isocaloric time-restricted eating shifts circadian clocks but does not improve cardiometabolic health in women with overweight, Science Translational Medicine (2025). DOI: 10.1126/scitranslmed.adv6787

Demystifying a visual illusion: Why we see color that's not there

A new discovery has unraveled why we sometimes see colors that aren't there. The phenomenon of "color afterimages" is when you see illusory—or false—colors after staring at real colors for a longer time. Through this, the brain can be tricked into seeing color in a black and white image.

The cause of this illusion is the mechanism that allows us to see colors the same throughout the day, independently of light changes. Without it, the color of the world would change as we are under yellow sunlight, a green canopy, or in a bluish shadow.

Scientists have long debated what causes color afterimages, and how the brain creates them.

Researchers found the missing link between the illusory colors we see and the neural mechanisms that produce them. The answer is in the cone cells in our eyes.

We've finally got a conclusive answer—color afterimages are not opposing colors as everybody had thought. Instead, those illusory colors reflect precisely what happens in the cone photoreceptors.

Across all the experiments, researchers found the same thing—afterimages are not caused by opposing colors, as many scientists have thought. Instead, they match what we'd expect if they were caused by how cone cells in the eye adapt to light.

So,  now it is certain that afterimages come from cone cells and not from other parts of the visual system.

Christoph Witzel, The non-opponent nature of colour afterimages, Communications Psychology (2025). DOI: 10.1038/s44271-025-00331-5

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Fixate on the cross and you will see the moving grey circle become purple. Credit: Communications Psychology (2025). DOI: 10.1038/s44271-025-00331-5