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We all know that eating badly, and eating too much, are associated with gaining weight.
New research suggests that another factor is also important: the time of day you eat.
A new study, published in The American Journal of Clinical Nutrition, found that eating later in the evening was associated with a higher percentage of body fat.
But it also found that the overall effects all came down to a person’s personal biological clock rather than the actual time.
Researchers collected data from 110 college students over 30 days to observe their sleep times and eating habits. They also looked at when subjects released melatonin – the sleep hormone – to determine where their circadian rhythm (body clocks) was at.
They then examined the relationship between body clock setting, body mass index, and the timing of food consumption.
The team expected to see that people who ate closer to their melatonin onset – which usually occurs just before sleep – would have a higher percentage of body fat.
Results showed that they were right and that those with a high body-fat percentage consumed most of their calories shortly before going to bed, when melatonin levels were high.
But this didn’t mean they found a relationship between eating later and gaining weight; rather, the timing of when you consume calories, relative to your own biological timing, may be an important factor for your health.
“We believe that our findings highlight that when you eat may be just as important as what you eat,” lead author Andrew W. McHill, a researcher with the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital in Massachusetts, told Business Insider.
“We actually hypothesise that the mechanism driving this result is a lower amount of energy expended to break down food that is consumed during the night, as we have shown that to be true during controlled laboratory studies.”
As with every study, there were a few limitations, such as the fact that participants may have underreported how many calories they consumed or may have changed their eating habits while they knew they were being tracked.
Also, melatonin levels were assessed on only one night, so slight changes could not be identified.
Still, the researchers are confident that the results provide evidence that eating food during the circadian evening plays an important part in body-fat percentage.
“To show cause and effect, randomized controlled trials that include altering the timing of meals of the exact same food content in relation to melatonin timing (e.g., providing meals within 4 hours of melatonin or restricting calories to when melatonin concentrations are low) are needed,” McHill said. “Further, examination of the timing of caloric consumption relative to melatonin onset in non-college-aged populations is also needed to extend our findings.”