News, Culture & Society

When you eat is key to weight loss

The food we eat has a huge impact on our body, and our general health. 

But experts warn many of us do not think about the time we consume our meals. 

While some of us may eat extremely healthily, research shows we face ruining all that progress if we eat too close to bedtime, or cram all our meals together, or wait too long between eating. 

It all boils down to metabolism, giving the body enough time to digest.  

However, while the internet is full of specific plans for dieters saying what time of day to eat, none of those take into account how it could be affected by different schedules. 

Our metabolism is affected by our circadian rhythm (i.e. body clock). For some, our body clock is the standard night-day. But for others who work night shifts or burn the candles at both ends, it is not so simple.  

Now, researchers at Brigham and Women’s Hospital have conducted the first study showing how meal times affect your weight gain, depending on what time you rise and sleep.

Hacking your body clock: Researchers say our meal times are almost as important as our nutrition. A new study has tested this theory in a real-world setting for the first time


If you wake up at… 7am

And you go to bed at… 11pm

  • BREAKFAST: 8am
  • LUNCH: 12pm
  • SNACK: 3-4pm
  • DINNER: no later than 8pm

If you wake up at… 10am

And you go to bed at… 2am 

  • BREAKFAST: 11am
  • LUNCH: 3pm
  • SNACK: 6-7pm
  • DINNER: no later than 10pm

If you wake up at… 12pm

And you go to bed at… 4am 

  • BREAKFAST: 1pm
  • LUNCH: 5pm
  • SNACK: 8-9pm
  • DINNER: no later than 1am

Previous research has shown an unconventional body clock leads to poor metabolism and obesity – no matter what meal time schedule you follow. 

Ultimately, the most important factor is waiting a few hours after your last meal before going to bed.  

In the study, published this week in The American Journal of Clinical Nutrition, researchers at Brigham and Women’s Hospital examined body fat, body mass index and the timing of food consumption.

They compared these with the time of day and the person’s circadian rhythm (i.e. body clock). 

This is the first time that the timing of meals has been studied in real world settings, in relation to melatonin onset, which marks the onset of sleep.

‘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 Dr Andrew W. McHill 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.’

Dr McHill, a researcher with the Division of Sleep and Circadian Disorders, led a team in analyzing data collected from 110 college-age participants.

They were enrolled in a 30-day observational study to document sleep times and daily meal intake. 

A mobile phone app was used to time-stamp, document and record the participants’ food intake over seven consecutive days of their regular routines. 

For one night during the 30-day study, participants were studied at the BWH Center for Clinical Investigation to assess the timing of their melatonin onset, marking onset of sleep, and their body composition.

Researchers found that individuals with high body fat percentages consumed most of their calories shortly before going to sleep when melatonin levels were high.

Individuals with lower percentages of body fat tended to go to bed a few hours after their last bite. 

Researchers note that they were unable to detect a relationship between the clock hour of food intake, caloric amount, meal composition, activity/exercise level, or sleep duration, and either of these body composition measures. 

The researchers acknowledged several limitations that need to be considered for future work, including the fact that the population of college-aged individuals may not be representative of the entire population in terms of food choice and circadian or body clock rhythm.

Researchers concluded that these results provide evidence that the consumption of food during the circadian evening plays an important role in body composition.