"We should now seriously start to consider the timing of food -- not just what we eat, but also when we eat," said study co-author Frank Scheer, from Brigham and Women's Hospital and Harvard Medical School in Boston.
His group's research included 420 people attending nutrition clinics in southeast Spain. Along with going to regular group therapy sessions with nutrition and exercise counselling, dieters measured, weighed and recorded their food and reported on their daily physical activity.
Participants were on a so-called Mediterranean Diet, in which about 40pc of each day's calories are consumed at lunch. About half said they ate lunch before 3pm and half after. Over 20 weeks, early and late lunchers ate a similar amount of food and burned a similar amount of calories through daily activities.
However, early eaters lost an average of 10kg (22lbs) while late eaters dropped 7.7kg (17lb).
What time dieters ate breakfast or dinner wasn't linked to ultimate weight loss.
One limitation is that the researchers didn't randomly assign people to eat early or late, so it's possible there were other underlying differences, for example certain gene variants have been linked to obesity were more common in late lunchers.
People who eat later may have extra food in their stomach when they go to sleep, which could mean it ends up being stored as fat, said Yunsheng Ma, a nutrition researcher from the University of Massachusetts Medical School in Worcester.
How often people eat during the day and whether they bring food from home or eat out may also contribute to weight loss, added Ma.