Eating In Sync With Your Body Clock May Help Curb Fat Gain

NEW YORK - Timing meals relative to your own body clock, rather than to the time of day, may affect how lean you are, researchers suggest. Studies have shown that eating later in the day ups your risk of weight gain. However, the impact of a person’s body (biological) clock - independent of the time of day - has not been tested until now, according to Dr Andrew McHill of Brigham and Women’s Hospital in Boston and colleagues.

“Our findings could be considered a reason not to eat right before going to sleep, but they’re also a reason not to eat later in the evening, even if you are planning to go to bed at a later time,” McHill told Reuters Health by email.

The team recruited 110 college students ages 18 to 22 (about 60% male) for a 30-day study of sleep times and food intake. The students completed questionnaires about their sleep habits at the outset of the study, as well as daily electronic sleep-wake and exercise diaries. They also wore motion monitors throughout the study to help track sleep-wake timing.

For one week during the study, participants used a cellphone app to time-stamp, document and record their food intake during their regular routines.

It comes down to when your body releases melatonin, which marks the onset of sleep

Your body clock could be more responsible for weight gain than you thought, a new study has found. 

Different people have different approaches to timing your meals if you want to lose weight or stay healthy. Some argue you shouldn’t eat less than two hours before bed, and others advocate waiting until lunchtime to eat your first meal of the day, thus giving your body a fasting period overnight.

But little research has been conducted into how our eating habits can be affected by our sleeping patterns - until now. The study by the Brigham and Women’s Hospital in Boston, Massachusetts, US, has discovered how mealtimes affect your weight gain, based on what time you wake up and go to sleep.

They analysed data from 110 adults aged 18 to 22 to document sleep and circadian behaviours within their regular daily routines.  Using an app, all their food intake was logged for seven consecutive days during their regular daily routines. Body composition and timing of melatonin release (which marks the onset of sleep) was assessed in a laboratory.

The researchers found that the most important thing is to wait a few hours after eating before going to bed, so your body has time to digest. The participants with the highest body fat percentages consumed most of their calories shortly before bed, when their levels of melatonin were high. In contrast, those with lower percentages of body fat tended to go to bed a few hours after finishing eating.

Our metabolism is affected by our circadian rhythm, and this varies greatly from person to person, whether due to irregular work shifts or simply natural preference for rising early or staying up late. “We found that the timing of food intake relative to melatonin onset, a marker of a person’s biological night, is associated with higher percent body fat and BMI, and not associated with the time of day, amount or composition of food intake,” lead author Andrew McHill, Ph.D., researcher with the Division of Sleep and Circadian Disorders at BWH, said.

“These findings suggest that the timing of when you consume calories, relative to your own biological timing may be more important for health than the actual time of day,” he added. The researchers accepted that university-aged students may not be representative of the population as a whole, but they concluded that the study’s results provide evidence that the consumption of food during the circadian evening plays an important role in body composition.

They were also evaluated for one night at the hospital to see what time their level of the hormone melatonin began to rise - which marks the beginning of a person’s biological night - and to assess their body composition (i.e., muscle mass and fat). Melatonin onset timing was similar for both lean participants and those with a higher percentage of body fat, according to the American Journal of Clinical Nutrition study, online 6 September.

However, those with a higher percentage of body fat - 8.7% higher in women and 10.1% higher in men - ate most of their calories about an hour closer to the time of melatonin onset than did lean participants. There was no relationship between body composition and when (clock hour) they ate, how many calories they consumed, what kind of food they had, their exercise or activity level or sleep duration.

“While it’s not possible to know the timing of your melatonin onset without having it measured very precisely in dim lighting, we tend to think that melatonin levels rise about two hours prior to habitual sleep onset,” McHill explained.

What about waking up and eating a snack in the middle of the night?

“This would also be a time when melatonin is high and your body clock is promoting sleep and fasting,” he said, “so we would consider that a time that food consumption could lead to higher body fat if done repeatedly over a long period of time.”

McHill cautioned that the findings don’t show cause and effect. To do that, he said, “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 four hours of melatonin onset or restricting calories to when melatonin concentrations are low) are needed.”

It’s also important to study groups other than college students, and the team has already begun to track meal timing in older and ill populations. Dr Eric Feigl-Ding, a nutritional epidemiologist at Harvard Chan School of Public Health in Boston who was not involved in the study, told Reuters Health he agrees that “the takeaway is that eating earlier before bed may be better” - perhaps as much as 4 to 5 hours earlier.

However, “actual experiments to show direct long-term weight loss and health benefits from consistently eating earlier before bed are needed,” he added by email. “Be vigilant of your food intake as the time to sleep approaches,” Dr Jocelyn Cheng, a neurologist at NYU Langone Health in New York City urged in an email to Reuters Health.

“If you notice yourself eating more during this period compared to earlier in the day, consider redistributing your meals, snacks included,” said Cheng, who was not involved in the study.