In contrast to the lunch findings, there was no evidence that the timing of people's breakfast or dinner affected their weight loss. (Half of the group ate their dinner after 9:30 p.m.)
So in a culture where the biggest meal of the day is dinner, would it matter if you ate it at 9 p.m. or 6 p.m.? "It's hard to say, based on these data," Scheer said. Further research is needed to answer that question, he added.
For now, the current findings are in line with animal research showing that meal timing seems to affect weight, Scheer said.
It may have to do with effects on the body's circadian rhythms, which influence a range of functions, including the sleep-wake cycle and metabolism. There is a "master clock" in the brain that coordinates those rhythms, but there are also "peripheral clocks" in tissue and cells throughout the body, Scheer explained.
[See Best Heart-Healthy Diets]
In animals, unusual feeding times seem to disrupt some of those peripheral clocks and throw them out of sync with the master clock. In theory, that clock "decoupling" could affect weight control.
More research is still needed, though, to see whether the timing of a person's main meal directly influences weight -- and how important that influence really is, Scheer said.
"We need to know if this has clinical relevance," he said.
Diekman said the findings support the notion that meal timing matters, but she agreed that the ultimate importance to weight loss remains to be seen.
"As a registered dietitian, this study helps me feel comfortable with recommendations about the importance of meal spacing," she said. "But it does not give an answer to why or what impacts that might have on weight."
Learn more about weight-loss dieting from the U.S. National Institutes of Health.
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