Confining mealtimes and snacks to a nine-hour window and avoiding food for four hours before bed may help stave off cognitive decline in older age, researchers say.

A pilot study of older women living with overweight or obesity found hints of improvement in mental skills among those who ate within the restricted period compared with those who spread their meals over a longer time.

The finding is preliminary given the numbers in the trial, but if confirmed in larger studies, the work suggests people could help to protect their cognitive abilities by eating within a relatively narrow window and not eating late into the night.

Losing weight alone can help slow cognitive decline in older age, said Prof Sue Shapses, a nutritional scientist at Rutgers University in New Jersey, US, but there may be “additional benefits” for people who do not eat outside an eight to nine-hour window, and stop eating four hours before going to sleep.

Dementia is the leading cause of death in the UK and the seventh worldwide, leading to nearly 2 million deaths globally each year. Some risk factors are unavoidable, such as age and genetics, but experts believe nearly half of cases could be prevented or delayed through changes to lifestyle. Obesity in middle age can raise the risk of dementia in later life by 30%.

Shapses ran a small clinical trial in which 47 women aged 50 to 79, who were living with overweight or obesity, were encouraged to cut 500 calories from their daily diet for six months. Within the group, 26 were advised to eat only within a nine-hour window. Typically, this meant eating between 10am and 6pm, while the rest of the volunteers spread their meals over about 12 hours.

At the end of the trial, both groups had similar weight loss averaging about 7kg (15lbs). But cognitive tests revealed that those who confined their eating to the narrow window performed better than the others on spatial planning and problem solving tests. There were also hints that they made fewer errors on memory and learning tests, though on some multitasking and reaction time tests both groups performed the same.

Shapses called the effects “modest” but said they suggested time-restricted eating may improve people’s ability to remember information for everyday tasks and reduce mistakes linked to memory, attention and problem solving. Details were presented at Nutrition 2026, the annual meeting of the American Society for Nutrition in Maryland.

The researchers now plan to investigate why it may be important to consider when we eat as well as what we eat. The benefits could be driven by a complex interplay of circadian rhythms, metabolism and inflammation.

In many countries, the UK and US included, it is common to eat over a 14-hour period, leaving only 10 hours overnight without food. But research points to clear health benefits from extending overnight fasting. A review published in January found that finishing eating before 7pm was associated with significant improvements in body weight, BMI, waist circumference, blood pressure and markers of metabolic health.

Prof Wendy Hall, the head of nutritional sciences at King’s College London, who was not involved in the study, said confining mealtimes to a narrow window may have benefits for the brain.

“Time-restricted eating is a plausible approach to supporting cognitive health in midlife and older adults with overweight, not only because it may help with weight management but also because avoiding large meals late in the evening may improve blood sugar control, vascular function and inflammation,” she said.

Hall cautioned that the findings were preliminary and that it was important to see the full peer-reviewed study to determine whether any improvements were clinically meaningful.