Does the timing of meals throughout the day affect your weight?

Eating later in the day is associated with a higher risk of overweight, insulin resistance and other metabolic problems. This appears to be due not only to people eating more at that time, but also to the fact that late eating disrupts the internal biological clock. The body processes carbohydrates and fats differently in the morning than in the evening.

Eating early, with all meals before around 15:00, produced noticeably better blood sugar levels, lower blood pressure and less oxidative stress after five weeks in a small but carefully designed study in men with prediabetes. Notably, the participants did not lose weight. The timing of eating therefore affected metabolism independently of body weight. This is a preliminary finding from a small-scale study, but it is biologically well explained.

Intermittent fasting in the form of 16:8 (eating between 12:00 and 20:00) did not produce more weight loss than simply eating three meals a day in a large randomised study, the TREAT trial. That puts the popular claim that this schedule automatically leads to weight loss into perspective. Alternate-day fasting, however, does appear to: studies observed weight loss of 3 to 7% and a reduction in blood lipids, although these are studies of three to twelve weeks and long-term effects remain unknown.

How often you eat, whether two, three or five times a day, makes little difference to your weight when you do not exercise and your total calorie intake stays the same. More eating occasions can dampen the feeling of hunger to some extent, but the evidence for this is limited.

Whether eating early works for everyone is not yet certain. Whether you are naturally a morning or an evening person influences when your metabolism functions best. General advice about meal timing overlooks this. Large long-term studies that take such individual differences into account do not yet exist.