You've heard the dieting advice to eat breakfast like a king, lunch like a prince and dinner like a pauper? Well, there's mounting evidence that there's some truth to it.
A new study published in the International Journal of Obesity builds on previous studies that suggest it's best not to eat too many calories late in the day.
The Spanish study finds that dieters who ate their main meal before 3 p.m. lost significantly more weight than those who ate later in the day. This held true even though the early eaters were eating roughly the same number of calories during the five-month weight-loss study as their night-owl counterparts.
The study included 420 overweight and obese volunteers who lived in the Mediterranean seaside town of Murcia, Spain. Their average age was 42. Half were men, half women. Their midday meal constituted about 40 percent of their diet of roughly 1,400 calories a day, on average. Right — that's not a lot of calories. The average nondieting American eats about 2,700 calories a day, according to the U.S. Department of Agriculture.
On average, the early eaters in the Spanish study lost 22 pounds, compared with the late eaters who lost 17 pounds.
Both the early eaters and late eaters had similar levels of physical activity and got similar amounts of sleep, so researchers ruled out these factors as possible explanations for the differences in weight loss.
"The study suggests that it's not just what we eat but when we eat is important," says study author Frank Scheer, who directs the Medical Chronobiology Program at Brigham and Women's Hospital in Boston.
So what's at play here? Well, Scheer says recent animal studies have shown that the timing of eating can have a powerful influence on weight regulation and metabolism. This new study, he says, is among the first to suggest it's also key in people.
"Only in recent years are we trying to study this and tease apart what the underlying mechanisms might be," says Scheer.
In the study, the people who ate late and didn't lose as much weight also tended to skip breakfast or eat just a little in the morning.
Scheer says that because eating seems to send a signal to our body clocks, it's possible that when people delay eating a big meal until late in the day, things get out of whack: The master clock in the brain gets out of sync with the mini clocks in the cells of the body that regulate metabolism.
"When the timing of meals do not match with the sleep-wake cycle well, there's a disconnect between the different clocks that we have in basically all the cells of our body," explains Scheer.
And with this disconnect, the complex systems that regulate weight don't work as well, he says.
Not everyone is convinced by the findings of this study. Madelyn Fernstrom of the University of Pittsburgh Medical Center says she's skeptical that the timing of meals can influence weight loss so significantly. The study shows an association between the timing of meals and weight loss, says Fernstrom, but "it's not [proving] cause and effect."
Weight loss is complicated. But Fernstrom says as we learn more about the many factors that may influence weight regulation, it's important for dieters not to lose sight of the big picture.
"The greater importance is what you are eating," Fernstrom says. If you want to lose weight, "you need to eat fewer calories and exercise more."
That, of course, is something you likely already know.