Previous studies suggest that people who make lunch the main meal of the day lose more weight and have lower BMIs.
If you consistently work through lunch and find yourself scarfing something down late in the afternoon, your schedule could be secretly damaging your weight loss efforts. A recent study published in the American Journal of Clinical Nutrition examined the effectiveness of a weight loss program among more than 1,200 overweight and obese people in Spain and found that eating lunch later than 3 p.m. resulted in less weight lost.
The study looked specifically at the perilipin protein, which is found in human cells and is essential in moving and burning fat throughout the body. People with a specific genetic variation of this protein lost less weight when they ate lunch later than 3 p.m. compared to people who ate lunch earlier. (Lunch timing didn't make much difference for people with other genetic variations.)
Although this study focused on people with specific genetic makeups, a similar study published in the International Journal of Obesity in 2013 also found that eating lunch late was associated with less weight loss success.
So why does the timing of your lunch make a difference? Just like feeling sleepy is governed by our circadian rhythms, so is feeling hungry, says Marie-Pierre St-Onge, Ph.D, an assistant professor at Columbia University who studies the impact of lifestyle behaviors on weight control at the New York Obesity Nutrition Research Center.
"[Metabolism] differs among individuals, and the timing of food consumption in relation to circadian rhythm may influence weight loss," she says. Circadian rhythms also control insulin secretion in the body, she adds. If you're eating at a time when your body is less sensitive to insulin, you might have a harder time mobilizing fats and losing weight.
Although the timing of lunch might affect some people's waistlines, the researchers didn't find any differences in weight loss when they looked at the timing of breakfast or dinner. That could be due to the fact that the study was conducted in Spain, where nearly half of the day's calories are consumed at lunch.
In fact, people who eat a larger lunch may already have a leg up: Previous studies suggest that people who make lunch the main meal of the day lose more weight and have lower BMIs. According to the World Obesity Federation, about 40 percent of American women are obese, while in countries where the midday meal is traditionally larger, such as Spain (21.4 percent), Germany (23.9 percent), and Hungary (31.3 percent), those numbers are much lower.
Here in the U.S., we're also more likely to skip breakfast, which may contribute to weight gain, too, St-Onge says. "If you look at the breakdown of food intake in the U.S. population, there are fewer calories being consumed for breakfast and lunch. (This is what happened when one writer tried eating a huge breakfast every day.)
If you add breakfast and lunch together that would be about 40 percent of calories, and dinner and snacks make up the other 60 percent," she says. She still thinks more research needs to be done on the impact of meal timing, but if you find yourself eating healthy yet struggling to shed pounds, making lunch your main meal—and eating it before 3 p.m.—could be a good place to start.