You might already know that good shut-eye plays a key role in dropping unwanted pounds. Research has consistently connected a lack of sleep to weight gain and, conversely, research shows that good sleep typically helps weight loss.
But a new study flips this connection on its head, finding that if you're trying to lose weight through diet, a high-protein eating plan might stand above the rest because it actually improves the quality of your sleep.
"Our research suggests that what you eat while losing weight can influence whether or not sleep improves," said the study’s author, Wayne W. Campbell, a professor of nutrition science at Purdue University. "And consuming a higher-protein diet improved sleep."
Campbell and his team conducted two studies to determine that a high protein diet improved sleep. One study found that the source of protein, whether vegetable or animal, did not affect sleep as much as the proportion of calories coming from protein did. The second study -- one of the longest of its kind to look at the effect of protein intake on sleep -- showed higher rates of improvement in sleep for individuals on a high protein diet compared with those consuming lower amounts of protein.
Protein source doesn't matter, but the amount does
The first study included 34 overweight or obese adults who consumed diets in which protein came from either beef and pork or soy and legumes. For each group, the dieters were further split into three subsets, eating diets that were 10 percent protein, 20 percent protein, or 30 percent protein.
Researchers measured participants' sleep quality based on their self-reported global sleep scores, which, in addition to measuring how long you sleep, also incorporate other sleep quality factors like whether or not you use sleep aids, how often you wake during the night, how deep you sleep, and how long it takes you to fall asleep.
While the type of protein didn't seem to affect sleep quality -- both the beef-and-pork and soy-and-legume consumers had similar scores -- sleep was improved for those whose diets consisted of 20 percent protein compared to the 10 percent-protein dieters. (Sleep did not further improve for those whose diets consisted of 30 percent protein.)
Higher protein means sweeter sleep
To further investigate how the amount of protein dieters ate affected their sleep, the researchers set up a second study that only compared sleep quality in high-protein versus normal-protein dieters.
The second study included 44 overweight or obese adults were randomized to follow either the high- or normal-protein diet for four months. The foods in the diet were consistent for each group, except that the high-protein diet included added milk protein powder, while the normal-protein dieters got carbohydrate powder. Protein intake for each dieter was assigned based on their body weight, and high-protein dieters were assigned about twice as much protein as the normal-protein dieters.
Researchers again used global sleep scores for the participants, but this time had the participants update their scores at monthly benchmarks. The number of high-protein dieters reporting a poor sleep score decreased throughout the study period, with only half as many dieters reporting a poor sleep score at the end of four months as at the start of the study. While the number of normal-protein dieters in the normal-protein group who reported being poor sleepers jumped throughout the study, it had increased by the end of the four months.
Why your sleep likes protein
So why does a high-protein diet encourage better sleep? Previous research suggests brain neurotransmitters or other biomarkers associated with the sleep-wake cycle may be influenced by what we eat. More specifically, findings have also hinted that higher protein intake may change the body’s insulin and circulating amino acids, both of which affect levels of serotonin and melatonin, which in turn affect sleep. Even though Campbell’s research did not measure those biomarkers, he says this might be the explanation behind his study's findings, too.
We'll leave it to the experts to determine why sleep and protein seem to mix well. But the data so far build a pretty good case for making protein a key part of your diet if you're trying to lose weight, both to shed those pounds and catch your Zs.
Sarah DiGiulio is The Huffington Post's sleep reporter. You can contact her at firstname.lastname@example.org.