What you eat matters most. (Probably.) But, more and more, researchers are finding when you eat also affects your risk for obesity and several other serious—and seriously common—health problems.
“When you look at the world’s healthiest populations, none of them are eating the way most people do in the United States,” says Valter Longo, Ph.D., a professor of biological sciences at the University of Southern California.
Even if you’re eating healthy foods, “eating five or six times a day is a problem,” he says. Other experts agree.
“Human beings are not genetically engineered to eat all day long,” says Mark Mattson, Ph.D., chief of the Laboratory of Neurosciences at the National Institute of Aging. “But most people are putting something caloric in their mouths throughout their waking hours, and I think the evidence of the harm this causes is how many people are overweight or obese.”
Put simply, three meals bridged with snacks and smoothies is not a healthy plan of attack. So what does an ideal eating schedule look like?
Here are some easy-to-follow, not-extreme rules that could help you dodge weight gain while lowering your risk for cardiovascular disease, diabetes, and other deadly health issues.
Stick to Three Squares - Or Two and a Snack If You’re Overweight
Even if you’re careful about what you eat and your total calorie intake, snacking between meals can keep your blood sugar levels elevated, which can increase your risk for weight issues and metabolic diseases like diabetes, Longo explains.
“When you’re always eating, the message you’re sending to your body at an endocrinological level is that it needs to stay in a state of increased metabolism, which promotes fat storage,” he explains.
Setting aside your weight status, Longo says eating all the time may also harm some “intercellular regenerative processes” that protect you from disease, including cancer.
At the same time, he says there’s not enough good, human-based research to support the so-called “intermittent fasting” fad, or trying to cram all your daily calories into a 6- or 8-hour window.
“A lot of those findings come from studies in mice, but so far I don’t think it’s translated to humans,” he explains. (He says there’s better evidence to support the benefits of longer fasts every now and then, but that’s a different story.)
His advice: If you’re not overweight, stick to three meals a day, and try to keep them within a 12-hour window. “Based on the clinical studies I’ve conducted, I think 12 hours - not the 6 or 8 you hear - is an appropriate amount of restriction.”
If you ARE overweight or obese, he recommends a two-meals-plus-one-snack approach to eating. Whether you choose breakfast, lunch, or dinner for your snack-sized meal, keep it to around 100 calories, and limit your intake of proteins and added sugars, he advises.
He says a healthy snack could be a salad with nuts and olive oil, an apple with nut butter, or vegetables with olive oil and hummus.
Depending on your current eating habits, making the switch may be difficult at first. But stick with it for 30 days, and you should find it easy to maintain, he adds.
Eat Those Meals Between 8am and 7pm (Approximately)
In a recent University of Pennsylvania study, one group of healthy 20-somethings spent 8 weeks eating all their meals inside that 8-to-7 window. A second group ate later in the day - between noon and 11pm. After taking a break, the groups switched schedules.
When eating during the early shift, the study participants lost weight and improved their blood sugar, cholesterol, and triglyceride levels. Just the opposite happened when the same people ate later in the day—even though the study team made sure the participants’ diets and exercise habits stayed the same.
“What we found was that eating later and closer to bed was associated with adverse changes to the subjects’ weight and metabolism,” says the study’s lead author Namni Goel, Ph.D., a research associate professor of psychology at Penn’s Perelman School of Medicine.
Previous research has also linked “delayed eating” - or eating later in the day - to greater risks for obesity and metabolic diseases like diabetes.
Why is eating later a problem? It likely has something to do with your body’s circadian rhythms and the hormones they regulate, Goel says. In oversimplified terms, your body just may not manage food as well when you eat it later in the day.
“If you wake up really early, like four or five in the morning, I don’t think you need to wait until eight to eat,” she adds. “I’d say try to eat an hour after you wake up, and then finish your eating 11 or 12 hours later when you still have a few hours before bed.”
All this research is evolving. But sticking to three squares and fitting them inside that early-ish 12-hour window seems like a safe, science-backed approach to healthy meal timing.