But the key seems to be how sleepy you're feeling rather than the actual hour when you sit down to eat your last meal of the day.
People who are overweight seem to eat closest to the time when their body is getting ready for sleep, say researchers from the Brigham and Women's Hospital in Boston. Interestingly, the actual time when lean and overweight people eat their main meal may be the same, but the body clock of the overweight person seems to be set differently, and is already telling them it's time for bed.
The researchers tracked the eating habits of 110 people, who were aged between 18 and 22 and had different body weights, for 30 days. Those with the highest amounts of body fat were consuming most of their calories within an hour or so before their melatonin levels rose, a chemical signal that the body is getting ready to sleep and its metabolism begins to slow.
This had a far bigger impact on weight gain than the amount or type of food being eaten, or the level of activity or exercise, or how long the person slept, the researchers discovered.
Food spacing—the intervals between meals—also had a part to play in weight gain. Eating meals too close together, or even waiting too long between meals, also sends out the wrong signals to our metabolism, and blocks the healthy processing of food. Ideally, there should be around a four-hour gap between meals, the researchers say.