Researchers Asked Women to Eat Within 9 Hours a Day. One Result Had Nothing to Do With Weight

Women in a six-month weight-loss study were asked to cut about 500 calories from their daily diets. Some received one more instruction: fit all their food into less than nine hours each day.

Both groups lost about the same amount of weight, around 15 pounds on average. The unexpected difference showed up in cognitive testing. Women with the shorter eating window performed better on tests of spatial planning and problem-solving, according to findings presented at NUTRITION 2026, the American Society for Nutrition’s annual meeting.

The result comes with an important limit. This was a pilot study of just 47 women with overweight or obesity, ages 50 to 79. The findings are preliminary and don’t show that time-restricted eating prevents dementia.

Women Cut Their Eating Window From About 12 Hours to 8

Twenty-six participants were assigned to time-restricted eating in addition to calorie reduction. Most ate between about 10 a.m. and 6 p.m., producing an average eating window of 8.2 hours.

Women in the comparison group continued to eat across an average of 12.3 hours each day. The intervention lasted six months.

The difference wasn’t a matter of one group following a weight-loss diet while the other ate without restrictions. Everyone received guidance to reduce daily calorie intake by about 500 calories.

Both Groups Lost About 15 Pounds

If the shorter eating window had produced far greater weight loss, that could have complicated the cognitive comparison. That isn’t what happened.

Average weight loss was about 15 pounds after six months, with no significant difference in weight loss between the two groups. Related Rutgers data from the intervention report weight changes of about 6 kilograms in the calorie-restriction group and 7.6 kilograms in the group that combined calorie restriction with time-restricted eating.

The researchers were left with another difference to examine: performance on some of the cognitive tests.

Problem-Solving Scores Showed a Difference

Women eating within the shorter window showed greater improvement in spatial planning and problem-solving than women eating across about 12 hours.

Memory and learning tests pointed in the same direction, with the time-restricted group tending to make fewer errors. That result, however, did not reach statistical significance. Researchers found no significant group differences in reaction time or multitasking.

Study principal investigator Sue Shapses, a Rutgers professor whose research includes metabolism, obesity, circadian rhythm, sleep, and cognition, described the cognitive effect as modest.

Eating Time Could Be Part of the Question

The study doesn’t establish why shortening the eating window might affect cognitive performance. Researchers plan to examine several possible mechanisms, including circadian rhythms, inflammation, metabolic health, and pathways involved in nutrient sensing.

Meal timing is of interest because eating and fasting interact with biological systems that follow daily rhythms. Shapses’ Rutgers research program includes ongoing work on time-restricted eating, circadian rhythm, metabolic health, sleep, and cognition.

That doesn’t mean an eight-hour window should now be treated as a prescription for protecting the brain.

47 Women Aren’t Enough to Set a New Eating Rule

The narrow study population matters. All 47 participants were women between 50 and 79 who had overweight or obesity, so the findings can’t be assumed to apply to men, younger adults, or people in other weight categories.

The size of the trial is another reason for caution. Larger studies are needed to determine whether the cognitive differences hold up and whether they translate into meaningful long-term changes.

Broader evidence also doesn’t establish time-restricted eating as a superior weight-loss method. A 2026 Cochrane review covering 22 randomized trials and 1,995 participants found intermittent fasting produced weight-loss results similar to conventional dietary approaches.

For now, the intriguing part of the Rutgers experiment isn’t that eating within eight or nine hours caused more weight to come off. It didn’t. It’s that after comparable weight loss, researchers still detected a difference in one area of cognitive performance.