By Mary MacVean, Los Angeles Times

Some popular diets advise against late-night snacking or even eating after 6pm. Now, there’s some research to confirm that when you eat could matter as well as what you eat if you’re trying to shed pounds.

A study in Spain followed 420 men and women on a diet for 20 weeks. They were grouped into early eaters — those who had their main meal before 3pm – and late eaters – those who had it after. (The participants followed the Mediterranean diet, in which the main meal was lunch.)

Researchers looked at what the participants ate, their activity, their sleep habits and other characteristics. The dieters also attended weekly group therapy sessions.

It turned out that the late eaters lost less weight — 17 pounds — and at a slower rate than the early eaters, who lost almost 22 pounds, the researchers wrote Tuesday in the International Journal of Obesity.

“Recent studies link energy regulation to the circadian clock … emphasizing that the timing of food intake itself may have a significant role in weight regulation,” wrote the authors, led by M. Garaulet of the University of Murcia in Spain.

“No significant differences were found in age, gender distribution, obesity-related variables and metabolic syndrome characteristics between the early and late lunch eaters,” the researchers said. But they said the late eaters had small breakfasts or skipped breakfast — and that long period from the first meal to the second might be at work.

The researchers noted that their study was based on observing the dieters, and that more work is needed to figure out the cause of the difference between the groups.