When you eat could play an important role in weight loss, a new study suggests.

Researchers looked at the role of meal timing in 420 men and women in southeast Spain participating in a 20-week weight-loss treatment following several studies in animals showing a relationship between the timing of feeding and weight regulation.

"Our results indicate that late eaters displayed a slower weight-loss rate and lost significantly less weight than early eaters, suggesting that the timing of large meals could be an important factor in a weight loss program," Frank Scheer, director of the medical chronobiology program at Brigham and Women's Hospital in Boston, said in a release.

Of the participants, 51 per cent were early eaters who ate their main meal, lunch, before 3 p.m. The other 49 per cent had lunch after three.

The researchers found energy and nutrient intake, estimates of calories burned, appetite hormones and hours of sleep were similar between both groups.

"Nevertheless, late eaters were more evening types, had less energetic breakfasts and skipped breakfast more frequently than early eaters," Scheer and his co-authors wrote in Tuesday's issue of the International Journal of Obesity.

They suggested that new weight loss strategies should incorporate the timing of food as well as the classic look at calorie intake and distribution of carbohydrates, fats and protein.

Evening types or "night owls" like to stay up late at night and sleep late in the morning while early birds feel they perform best when they go to bed early and rise at dawn.

Timing has metabolic consequences

The researchers said that changes in these "chronotypes," genetic background and how the circadian system functions may be implicated.

Recently, fat tissue has been found to have an active circadian or body clock. The study's authors suggested that timing of feeding, for high energy meals in particular, could have metabolic consequences such as the development of obesity and weight loss.

A previous U.S. study showed that eating after 8 p.m. was associated with increased body mass index independently of sleep timing and duration.

In the study, late eaters had a lower estimated insulin sensitivity, a risk factor for Type 2 diabetes.

Study participants were given recommendations about the number of portions they should eat from each food group. They were free to eat those portions when they wished.

Most studies of shift workers also suggest they are more prone to obesity than day workers, even when they have the same energy intake, the researchers said.

The study was funded by grants from Tomás Pascual and Pilar Gómez-Cuétara Foundations, Spanish Government of Science and Innovation, Séneca Foundation from the Government of Murcia, the U.S. National Heart, Lung, and Blood Institute grants, U.S. National Institute of Diabetes and Digestive and Kidney Diseases, and the U.S. Department of Agriculture Research.