In men with metabolic syndrome - a combination of metabolic disorders that raise the risk of heart disease, diabetes and memory decline - a month of eating only in the morning and afternoon coincided with improved memory test results and a slight reduction in "brain age" according to MRI data. This is reported in the journal Frontiers in Aging. The study was small and had no control group, so its results should be considered preliminary.
The experiment involved 23 men aged 25 to 55 (average about 35 years) with clinically confirmed metabolic syndrome. First they lived for a month on their usual schedule to establish baseline measures. Then for a month they ate only within an eight-hour window from 8:00 to 16:00, without restricting the types or amount of food, and during the remaining 16 hours they drank only water. To check adherence to the schedule, participants wore a continuous glucose monitor that transmitted data to the doctor and daily sent photos of their meals to a chat with the researchers.
Before and after the intervention, the men were measured for weight, body mass index (BMI - an indicator of the ratio of height and weight), blood measures including glucose, insulin and lipids (fats), and also underwent brain MRI. Memory was assessed using a word-list recall test: immediate and delayed recall were checked. "Brain age" was calculated using machine learning: an algorithm trained on images from 3477 healthy adults predicted age from the structure of gray matter - tissue rich in nerve cell bodies. The difference between predicted and actual age is called the "brain age gap": a positive value means the brain looks older than it should.
On average participants lost about 4.4 kg, and their BMI fell from about 31.4 to 30. Triglyceride levels (one type of blood fat) fell by about 29%, fasting glucose by 10%, and insulin and insulin sensitivity measures also improved. Changes in total cholesterol and its fractions were not statistically significant.
Memory test results improved: immediate recall rose by about 19% (from 45 to 54 points), and delayed recall from 9.4 to 11.3 points. The brain age gap was on average 2.8 years at the start and 2.0 years after the month, that is, it shrank by about nine months. Gray matter volume also increased in four regions of the left hemisphere: the thalamus, hippocampus, substantia nigra and red nucleus. The hippocampus and thalamus are linked to memory, while the substantia nigra and red nucleus are involved in movement and the reward system.
The authors note that they did not measure the calorie content of the diet. People who restrict meals to eight hours often eat less, so the effect of meal timing cannot be separated from the effect of reduced calories and weight loss. In addition, without a control group, the influence of constant medical observation or a practice effect from retaking the test cannot be ruled out. The researchers emphasize: a lower "brain age" score does not mean the brain has biologically become younger, and does not prove that such a schedule prevents dementia. The sample was small and included only men, so the results cannot be automatically transferred to women or older people. Future work should include more participants, including women, account more precisely for calories and follow people for longer.