We have all heard the age-old weight loss advice to eat less and exercise more. But a number of recent studies suggest that the key to dieting success is not just in how many calories you eat, or don’t, but in when you eat them.
“There has been so much energy on what we eat and on carbohydrates and it’s only very recently that there have been studies to say that we have been ignoring timing and timing might be as important,” said Ruth Patterson, professor of family medicine and public health at the University of California, San Diego.
One twist on the typical three-square-meals schedule that is gaining traction is fasting. A recent study found that avoiding food for 12 or 15 hours a day was associated with less weight gain over time and better control of blood sugar level, which could reduce diabetes risk.
However, the study was done in mice, and it is unclear whether people could benefit from limiting their hours of eating. “The really strong evidence is in rodent studies mostly where [timing calories] is a huge powerful predictor of overall metabolic health and chronic disease prevention,” Patterson said.
Studies are starting to trickle in suggesting that fasting, as well as other strategies such as eating the bulk of your daily calories early in the day, could pay off in terms of weight loss.
“If you are interested in modest weight loss over time or better metabolic health, then this could be the way to go, [but] if you really want to lose a lot of weight fast then you’re still going to have to cut way back on what you eat overall,” Patterson said.
Cut out midnight snacks
Patterson and her colleagues are carrying out some of the first work to see whether the benefit of fasting that was reported in rodent studies holds true in people. So far, they have found in a large cohort study that women who reported going more hours at night without eating have better control of blood sugar levels.
Although it is only a guess at this point, Patterson believes that it would improve weight loss if we did away with eating between about 8 at night to about 8 in the morning. She and her colleagues are doing a pilot study to test this schedule in a small group of older women. It is too soon to say how it affects weight loss and overall daily calorie intake, but Patterson said that the women report that the schedule is simpler to follow than the usual dieting strategy of counting calories.
“We think that nighttime fasting is a feasible lifestyle [while] something like diet is not,” Patterson said. Other fasting methods, such as severely cutting calories two days a week to only a few hundred, known as 5-2 fasting, may be less feasible, she said.
And like with diets, the rules of nighttime fasting are not absolute, and cheating once in a while with a late-night dinner with friends is probably not a big deal, Patterson said.
Early to dine
A couple of recent studies suggest that eating the bulk of calories in the first part of the day could lead to greater weight loss. One study of a weight loss intervention in Spain found that adults who ate their largest meal of the day before 3 p.m. lost more weight over a 20-week period than those who ate their largest meal after 3 p.m.
The benefit of frontloading calories seems to stem from the fact that we are programed to burn more energy at the beginning of the day. A region of our brain acts like our body’s internal clock and sets our circadian rhythms; it controls the activity level of the tissues in our body and also seems to make us metabolize meals in the first part of the day better than meals later in the day, said Frank Scheer, director of the medical chronobiology program at Brigham and Women’s Hospital in Boston and one of the authors of the study in Spain.
“We need more research, but to me, you can try [frontloading calories] if you don’t have any medical issues,” said Joan Salge Blake, clinical associate professor of nutrition at Boston University. People who have diabetes or hypoglycemia and need a more steady supply of glucose might not be good candidates for this strategy.
Nibbling or pigging out?
A study of just seven men way back in 1989 propped up the long-held belief that many smaller meals throughout the day trump three big ones. It found that men who ate 17 snacks a day had lower levels of cholesterol than those who ate the same diet concentrated into three meals.
The jury is still out on the effect of noshing instead of gorging on weight loss, and one recent study found that two large meals a day were better for weight loss than six smaller ones, at least in diabetics. There have not been many studies on the topic because there is so much focus instead on the types of calories you eat, Blake said. A new study is underway that will compare the effects of three and six meals a day on appetite as well as markers of heart disease risk.
“I think there could be a benefit to weight loss if you break up the meals, as long as the calories are controlled, [because] you are less likely to be starving and eat everything in front of you,” Blake said.
Breakfast, not the most important meal of the day
Despite what your mom told you, breakfast might not be the most important meal of the day. A study of college students found that skipping a meal, whether breakfast or lunch, did not lead the students to eat more later in the day compared with the students who did not go hungry. As a result, the meal skippers ate fewer calories overall.
“I’m a strong believer, our data and others’ suggest it, that humans do not accurately compensate for calories, which means that if you skip a meal or eat less, you’re not going to eat more on subsequent occasions. That’s a good sign,” said David Levitsky, a professor of nutritional sciences and psychology at Cornell University and co-author of the study.
If you are thinking of skipping breakfast, make sure that you still get enough nutrients from the other meals, Levitsky said. Most Americans get the bulk of their fiber from cereal, which could be problematic for those banishing breakfast, he added.
However, Patterson warned, it might not be worth skipping breakfast, even if it does help keep your total calorie intake down.
“In kids, we know breakfast really affects academic performance, and you would think perhaps the same thing would apply to adults,” she said.