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Weight Loss: The Time You Eat Matters

The data is in on late-night eating. Traditional weight loss approaches focused on diet and physical activity. However, current evidence shows factors like meal timing and sleep deprivation as barriers to weight loss.1,2,3 While there is no best weight loss program, eating late may be your cause of weight gain.3,4

Meal-timing matters

Recently, scientists from Harvard Medical School explored how eating late at night can cause weight gain. Their question was whether or not “the time that we eat matters” when other factors known to affect weight, like sleep, physical activity, and calorie intake, are kept consistent.5

To answer whether meal-timing matters, overweight or obese participants were grouped into an early or late eating protocol. All participants switched their eating habits from early to late or vice versa after their first time period was up. There was a break in between the switch to allow their bodies to adjust to their normal states.

The researchers kept the following the same for both groups:

  • caloric intake
  • sleep-wake cycle
  • exercise
  • lighting
  • temperature

Each person chose a wake period according to their habit. For 2 to 3 weeks before admission into the laboratory suite, they spent 8 hours in bed and kept to the sleep schedule.

Before admission and throughout the inpatient period, the subjects ate a standardized meal at specific times. The amount and composition of food eaten in both protocols were identical. 

During the early eating protocol, the participants ate at 1 hour, 5 hours, and 9.5 hours after waking. During the late eating protocol, they at at 5 hours, 9.5 hours, and 13.5 hours after waking.  Furthermore, during the late protocol, subjects ate 2.5 hours before sleep.

The results are in

At the end of the study, most participants subjectively felt hungrier when they ate late. Additionally, there were quantitative health measures that changed when eating late as well. Hormones like leptin and ghrelin that help manage hunger and appetite were negatively thrown off balance. This dysregulation means being hungry more often and at a more insatiable rate.

What else did they find?

Energy expenditure decreased during the wake period following late eating conditions. In addition, the participants’ core body temperature was also lower after the late eating protocol. Finally, late eating affected gene expression to reduce fat loss capabilities.

These findings add up to a tendency for weight gain. However, these findings need real world evidence in real-life circumstances. 

With further studies, suggestions can be made for controlling weight gain in those who cannot avoid eating late, i.e., shift workers. This research is also helpful in reminding people they may have more control over lifestyle factors affecting their weight and fat mass.


  1. Vujović N, Piron MJ, Qian J, et al. Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity. Cell Metabolism. 2022;34(10):1486-1498.e7. doi:10.1016/j.cmet.2022.09.007
  2. Cooper CB, Neufeld EV, Dolezal BA, Martin JL. Sleep deprivation and obesity in adults: A brief narrative review. BMJ Open Sport & Exercise Medicine. 2018;4(1):e000392. doi:10.1136/bmjsem-2018-000392
  3. ‌Garaulet M, Gómez-Abellán P, Alburquerque-Béjar JJ, Lee Y-C, Ordovás JM, Scheer FAJL. Timing of food intake predicts weight loss effectiveness. International Journal of Obesity. 2013;37(4):604-611. doi:10.1038/ijo.2012.229
  4.  Allison KC, Hopkins CM, Ruggieri M, et al. Prolonged, controlled daytime versus delayed eating impacts weight and metabolism. Current Biology. 2021;31(3):650-657.e3. doi:10.1016/j.cub.2020.10.092
  5. Late-Night Eating Impact. Accessed October 25, 2022.



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