Does how often you eat impact metabolic health?
Intermittent fasting can improve metabolic markers for some, but what you eat is still more important than when.
When it comes to meal frequency, everyone has their preferences. Some religiously eat three times daily, while others prefer intermittent fasting and eating just one or two meals. Then there are the grazers who snack consistently throughout the day. But which eating schedule is the best for our bodies?
USDAÂ guidelines acknowledge meal frequency as a critical component of health but state that there is insufficient evidence to firmly link any particular schedule to obesity, diabetes, or cardiovascular disease. Having said that, strategically spacing meals may help some people improve their metabolic flexibility or manage their weight.
What happens when we eat?
To understand why meal frequency matters, consider what happens in your body after you eat. First, the body breaks down digested macronutrients into smaller pieces: for example, fats become fatty acids, proteins become amino acids, and carbs become glucose (blood sugar). As glucose levels rise, the pancreas releases insulin to help the body process this influx of sugar. Insulin, in turn, helps shuttle glucose into cells for energy and, if there is extra, tells the body to build up its glucose reserves. This means transforming excess blood sugar into glycogen (stored glucose) and fat.
As circulating glucose moves from your blood into cells, levels in the bloodstream drop, and you may begin to feel hungry again. Indeed, the frequency with which you might want to eat has a lot to do with the amount of glucose in your blood. When glucose levels are sufficient, you tend to feel satiated, your mood improves, and you have plenty of energy to perform mental or physical work. When it drops—as it often does after the sharp rise of eating something sweet or carby—you may feel hungry, moody, or tired.
A healthy eating schedule allows you to avoid these dips in blood sugar. At the same time, you don’t want to eat so frequently and in such a way that your glucose repeatedly spikes and plummets or remains elevated all day—dynamics that can lead to insulin resistance and chronic illness. Through a combination of food choices and meal timing, you should aim for a plan that allows you to maintain stable glucose levels in a healthy range.
“You want your blood sugar level to vary across the course of a day, but not too much,” says Natasha Eziquiel-Shriro, MS, a registered dietitian nutritionist and certified diabetes care and education specialist at Brookdale Hospital in New York City. “I like to explain it as a roller coaster—it’s supposed to go up and down, but you want it to be a baby roller coaster, not a big scary grownup one.”
How often should I eat?
A 3-meal day can be convenient because it aligns with social structures like lunch breaks at work and restaurant hours. From a strictly physiological point of view, however, little evidence supports the superiority of the three-meal day. On the other hand, there doesn’t seem to be any harm in this schedule either.
If your energy and glucose levels are stable with a 3-meal schedule and you find this plan convenient, there’s no need to switch it up. But if you’re struggling to meet your health or performance goals, changing your meal frequency may help. Competitive athletes, for instance, may benefit from eating more than three times each day; people trying to lose weight often find infrequent meals more effective.
Small, frequent meals
According to a 2015 study, the average American eats 5.7 times a day. Appropriately done—with a mix of macronutrients, micronutrients, and an appropriate number of calories—this can be perfectly healthy. More often than not, however, frequent eating means _ove_reating.
Research doesn’t conclusively support the once-popular theory that frequent eating helps you lose weight by increasing your metabolic rate. And though increased meal frequency may seem like a good strategy to control hunger, the research doesn’t bear this out. One study found that, compared to participants eating three times a day, those who ate the same total calories in six meals experienced greater hunger levels.
Still, eating frequently has no serious drawbacks as long as your eating habits are otherwise healthy. In research studies where scientists can precisely control the total calories consumed, the distribution of calories throughout the day doesn’t seem to matter much. In the real world, however, increasing meal frequency may, in fact, increase the desire to eat.
When researchers observe participants’ existing habits (rather than prescribing a set number of meals and calories), they tend to find a link between increased meal frequency and risk of overweight or obesity. For example, one study found that eating more than three times per day predicted an increase in body mass index (BMI). Similarly, a study of meal frequency in 50,000 people showed that people who ate once or twice a day were likely to lower their BMI over a year, while those who ate more than 3 times a day were likely to increase their BMI.
It’s important to note that there are also counter-examples, like this study, which showed that higher meal frequency lowered obesity risk. The best a 2020 meta-analysis of meal frequency studies could say is that eating two meals a day instead of three “probably slightly reduces body weight.”
What certainly matters is what you eat during these meals. The more often you consume foods high in sugar and refined carbohydrates, the more frequently your blood sugar spikes, and this high glycemic variability can increase your risk of diabetes, heart disease, and metabolic dysfunction.
However, high meal frequency can support metabolic health and satiety for some groups of people. In particular, those whose diet contains less protein (e.g., some vegetarians) may experience shorter satiation periods, so a higher meal frequency with sufficient protein at each may help.
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Inside Levels
Infrequent meals and fasting
Most people have some kind of extended fast built into their daily routine: even if you snack all day, your body gets a break from food while you’re sleeping. Some people may find that extending this fast—for example, by only eating between 11:00 am and 7:00 pm—provides health benefits. Known as intermittent fasting or time-restricted eating, this strategy may increase your metabolic flexibility and overall metabolic health.
Two recent small studies have found that time-restricted eating can improve insulin sensitivity in people with prediabetes. Other research in people observing Ramadan, which entails fasting from sunup until sundown, or about 14-15 hours, every day for a month, found it may provide anti-inflammatory and antioxidant benefits.
Additionally, for people hoping to lose weight, some small studies suggest intermittent fasting may be an effective tool. One study of 23 people with obesity found that keeping eating to an 8-hour window slightly decreased weight and calorie intake. Another study of 11 people with overweight found that a similar eating period reduced levels of ghrelin, the so-called hunger hormone. Finally, in another study, 7 healthy adults ate breakfast 1.5 hours later than usual and dinner 1.5 hours earlier for 10 weeks—with no restrictions on what they ate—still took in fewer calories than a control group that ate normally.
“For a lot of people who have a hard time with just general caloric restriction, time-restricted eating can be an easier way to get there,” says Kyle Murray, a Registered Dietitian and Certified Diabetes Educator. “It just makes it much easier to control what is eaten in terms of the quality of the diet and the number of calories consumed.”
What is the fasted state? And what are its benefits?
Recall that after you eat, your cells either use your meal’s glucose or store it as glycogen and fat. As a result, your blood glucose levels may begin to drop, and you may start feeling hungry again. At this point, you can either eat, replenish your glucose, and remain in a “fed” state; or you can hold off on your next meal and enter a “fasted” state.
In the fasted state, low insulin levels prompt the body to switch from “build” mode to “break down” mode. Without fresh glucose entering the bloodstream, the body must tap into its reserves. First, it turns to glycogen for energy; as that decreases, it begins breaking down fat.
Your cells’ ability to switch energy sources—from glucose to glycogen to fat and back again—is called metabolic flexibility, and it’s a good indicator of metabolic health. A metabolically flexible body can more effectively regulate blood sugar levels and maintain insulin sensitivity, reducing the risk for short- and long-term health consequences of unstable blood sugar and insulin resistance.
There is, of course, a downside to prolonging the amount of time we spend in a fasted state: it doesn’t always feel great. As Murray explains, our bodies are accustomed to being fed at certain times, so when we deviate from that routine, we feel hungry and cranky and may not perform our best. However, he notes, the body is highly adaptable.
“It’s like quitting smoking—it starts out really hard because you have a dependency,” he says. “But your metabolism is highly adaptable, and after a couple of weeks, you will adapt to fasting. I haven’t eaten breakfast in four and a half years.”
The benefits of fasting for metabolic health
Nutrition
“If you eat on a consistent schedule, ghrelin will be produced at your normal eating times, making you feel hungry at those times,” adds nutritionist Kelly LeVeque. “Some people think they need to eat more often, but it’s really because they have eaten at those times historically.”
Still, fasting isn’t for everyone. Pregnant women should never fast, as it can promote the release of ketones, which are toxic to the fetus. For people who are underweight and don’t have any excess fat to burn, fasting may prompt the body to start consuming valuable muscle. And fasting may trigger unhealthy habits in people who struggle with binge eating or other forms of disordered eating.
Frequency versus timing
You can achieve metabolic health following many meal frequency schedules. But that doesn’t mean that timing is irrelevant. On the contrary, syncing meals with your circadian clock—a practice known as chrononutrition—may be an essential element in maintaining or achieving metabolic health.
Chrononutrition follows the premise that your hormone levels and other physiological factors fluctuate over the day and in response to light. For example, at night, levels of melatonin rise and insulin levels fall, which can lead to higher-than-normal glucose levels after you eat. For this reason, timing your meals to occur during daylight hours can positively impact your hormone levels, glucose levels, and metabolic function. Chrononutrition can also be a valuable tool for weight loss: while dieting, “top loading” the bulk of one’s calories in the first half of the day, rather than eating later, can lead to fewer feelings of hunger.
The bottom line
Whether you choose to eat one, three, or six times a day is likely of less consequence than ensuring that you eat a quantity of food that supports your activity level and a quality of food that helps you meet your nutritional needs. Sugary, processed meals will negatively affect metabolic health, regardless of timing, and even if you’re an adept faster, you can’t optimize your health unless you also get adequate doses of micronutrients in your diet. Still, particular meal schedules may help you eat the right quantity of food, control your hunger, and improve your metabolic flexibility.
