The simple rule for millennia was eat to survive, but our modern lifestyle seems to have it flipped.
Now, with obesity rates on the rise and affecting more than one-third of Americans, according to the Centers for Disease Control and Prevention, it seems humans survive so they can eat.
What we should eat has long been debated as diet recommendations have changed over the decades from fat free to high protein to low carb. As has the simplest of factors—how much we should eat—with calories occupying the central role. But what aboutwhen? If your goal is weight loss, should you eat throughout the day or is there value in reserving meal times for certain segments of the day? It turns out that answer is personal.
“The recommendations for eating patterns (including the number of times you eat throughout the day as well as when you eat) needs to be approached on an individual basis taking individual goals into consideration,” says Jessica Bachman, Ph.D. and professor in the Department of Exercise Science at the University of Scranton.
One long-running, popular approach to promote general health and weight maintenance has been to spread calories throughout the day in the form of several small meals. In doing so, the concept is that you’ll feel less hungry at any particular time and, therefore, less likely to consume an excess of calories during meals.
There is some data to support this. Bachman led a study that appeared in the Journal of the Academy of Nutrition and Dietetics, in which people who were of normal weight or those who were maintaining their weight reported eating more often than individuals who were obese.
Another study, this one from the University of Murcia in Spain, found timing may be a factor as well. Over a 20-week test period, those who consumed the majority of their calories later in the day lost weight at a slower rate weight than those who were early eaters. Diet, energy expenditure, and sleep were consistent between both groups, but the early eaters tended to eat breakfast more often than late eaters.
“The hypothesis is that if you eat small meals and snacks throughout the day, you never allow yourself to get overly hungry,” says Bachman. “We know that people tend to eat more when they are very hungry, so by avoiding this greater level of hunger, maybe people can limit overeating and therefore control their calorie intake and, ultimately, weight.”
Bachman followed up her original study with a six-month weight-loss intervention with two groups of 25 overweight and obese adults. One group was told to eat all of their calories in three meals a day and the other group was told to eat meals and snacks at 2-3 hour intervals throughout the day. Both groups lost weight. But the group that ate three times a day ate fewer calories and lost more. “What we found was contrary to observational research. It appeared that eating less often, and therefore being exposed to fewer opportunities to overeat, may help people with losing weight.”
However, this doesn’t necessarily hold true for weight loss programs that offer a set amount of calories and predetermined meal sizes.
A study at the Salk Institute in La Jolla chose to look at time-restricted eating instead of focusing on specific types of diets or the number of meals. Their hypothesis was that how efficiently the body handles calories is more closely related to the circadian rhythms of active and rest periods than the food consumed. The researchers at Salk, led by Associate Professor Satchidananda Panda, tested 400 mice. The mice were given a range of diets, from high fat to just sucrose or fructose, and found those that were restricted to an 8-12 hour feeding window lost weight and were healthier than those allowed food all day.
Even the mice that had 24-hour access to a high-fat diet, and became obese, lost weight once their diet was confined to the feeding time frame. This held true for diets high in fat or sugar, even if they consumed the same number of calories as the all-day eaters. Those fed in the 9-12 hour window were leaner. “It highlights the temporal aspect of feeding more than the calorie content and shows it is important to eat during your active phase which is when your body is tuned to energy expenditure and not energy storage,” says Circadian Biology Ph.D. Amandine Chaix, who participated in the study and felt these results could have further positive effects, when tested on humans.
“One set of the population is already obese,” Chaix said. “So already being obese and switching to a time-restricted feeding, you can lose weight? That was really powerful.”
Bachman said research is moving in the direction of meal timing and may have further benefits for the aging population in addition to those overweight, especially as it relates to the consumption of protein.
“This has potential important applications for older adults who are commonly plagued with muscle loss as they age but, also, for anyone trying to lose weight,” Bachman said. “With weight loss, you are losing not only fat but also lean muscle mass and this way of eating may help prevent some of the loss in muscle mass.”
But all of this may come down to a numbers game—calories. Baschman says, “If someone is trying to lose weight, the individual needs to create a calorie deficit, ideally by eating fewer calories and exercising more.”
And that science is simple.
