Sleep. People who report sleeping less (usually 6 or less hours a night) are more likely to gain weight over the years than those who sleep more (7 or 8 hours). But does less sleep cause weight gain?
To find out, researchers deprive people of sleep to see if they put on pounds. In a recent study, scientists allowed nearly 200 people to sleep from only 4 a.m. to 8 a.m. for the five consecutive nights they lived in the research lab. Thirty others were allowed to sleep anytime from 10 p.m. to 8 a.m. during their stay in the lab.
The results: on average, the sleep-restricted people ended the study two pounds heavier. Data from a subgroup suggested that they ate an extra 550 calories between 10 p.m. and 4 a.m. In contrast, those whose sleep was not limited gained no weight.
Why might less sleep make people eat more? “We’re currently examining the effects of sleep loss on changes in brain activity in areas related to reward and impulse control,” says lead author Andrea Spaeth of the University of Pennsylvania.
Other studies have found that lack of sleep raises blood sugar, makes insulin less effective, or boosts ghrelin, a hormone that stimulates appetite.
Night eating. Researchers are just starting to look at whether it matters when you eat.
For example, scientists kept 160 people in a research lab with unlimited free access to food from a vending machine for three days. Those (roughly a third) who ate between 11 p.m. and 5 a.m. on at least one night gained an average of 14 pounds over the next three years. Those who didn’t eat during those hours gained only 4 pounds.
“It’s not necessarily the timing of the eating that mattered, because those who ate at night consumed about 300 more calories than the others,” explains lead author Marci Gluck of the National Institute of Diabetes and Digestive and Kidney Diseases in Phoenix.
“There’s a lot of media attention paid to the idea that if you eat more late at night, you don’t burn off those calories,” notes Gluck. “I don’t know of studies showing that. In our study, the night eaters burned the same number of calories as those who didn’t eat at night.” They just ate more food.
We need more research to know if eating at night causes weight gain, says Gluck. But, she cautions, “from a psychological perspective, nighttime is a trigger for some people to eat when they’re alone.”
Sources: Am. J. Epidemiol. 2013. doi:10.1093/aje/kwt180; Sleep 36: 981, 2013; Diabetes 59: 2126, 2010; Ann. Intern. Med. 141: 846, 2004; Am. J. Clin. Nutr. 88: 900, 2008; Obesity 19: 319, 2011.
Other relevant links:
- Is one diet more effective than others for weight loss? See: New Clues to Diet and Weight Loss
- You may be able to change your metabolism with your mind. See: Can Your Mindset Boost Your Metabolism?
- Trying a gluten-free diet might delay the correct diagnosis. See: Is Weight Gain a Common Sign of Gluten Sensitivity?