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Don't Buy Into These Persistent Myths About Eating and Your Metabolism

Does eating more frequently boost your metabolism or cause you to burn more calories? Will going too long between meals cause you to go into starvation mode? Nutrition Diva has the facts on these widely held metabolism myths.

By
Monica Reinagel, MS, LD/N, CNS
5-minute read
Episode #614
The Quick And Dirty
  • Your body will not go in to "starvation mode" if you don't eat for several hours. It takes about three days of serious caloric restriction for your body to respond with any sort of metabolic adjustment.
  • Your body does burn calories digesting food, but eating more frequently does not cause your body to burn more calories.
  • Eating earlier in the day and eating more protein can increase the amount of calories you spend digesting food, but the effect is modest.

Despite the recent popularity of intermittent fasting, there's still a widespread belief that eating several small meals a day promotes weight loss by stoking your metabolism. Or that going too long between meals will cause your metabolism to slow down. I think one of the reasons that these notions have gotten so much traction is that people haul out some very scientific-sounding explanations that seem, well, very scientific and, therefore, believable.

There are two basic arguments and we’ll tackle them one at a time:

Does your body go into "starvation mode" and slow your metabolism?

THE MYTH

Your body, when deprived of food for a period of time, will go into “starvation mode” and slow your metabolism. The prevailing nutrition myth suggests that eating smaller, more frequent meals will prevent this.

WHY THE MYTH EXISTS

"Starvation mode" is when the body burns fewer calories in order to conserve energy, just in case the food shortage continues. During a famine, you’d need to live on your stored fat. Down-regulating your metabolism is a way to make those fat stores go a bit further.

We've come to believe that the trick to keeping our metabolisms reved up is to reassure our bodies that there is no shortage of food by eating every few hours.

It’s similar to the way your laptop adjusts its energy usage when it’s running on batteries, by making the screen a little dimmer, for example. When food is plentiful again, your metabolism goes back to normal, just the way your screen gets brighter when you plug your laptop back in.

If there were actually a famine, you’d be glad your body is designed this way. But, if you’re trying to lose weight, the last thing you want is increased fuel efficiency. You want to be burning through stored fat like an RV burns through a tank of gas.

So, we've come to believe that the trick to keeping our metabolisms reved up is to reassure our bodies that there is no shortage of food by eating every few hours. Your body will oblige you by continuing to burn calories with reckless metabolic abandon. Or so the story goes.

THE NUTRITION FACTS

This idea that you should eat more frequently so your body doesn't react by slowing your metabolism makes sense, doesn’t it? And it's rooted in at least some truth. Your body does respond to a prolonged fast by slowing your metabolism to conserve energy.

Your body doesn’t go into starvation mode if you go four hours without food. In fact, it takes about three days of fasting or serious caloric restriction for your body to respond.

Here’s the thing, though: your body doesn’t go into starvation mode if you go four hours without food. In fact, it takes about three days of fasting or serious caloric restriction for your body to respond with any sort of metabolic adjustment.

Not only is there no harm in going a bit longer between meals, but there may be some benefits, which I talked about in episode 32: How Often Should You Eat?

Can the thermic effect of food help you burn more calories?

THE MYTH

Because digesting food burns calories, eating more often will cause you to burn more calories.

WHY THE MYTH EXISTS

The second argument, which sounds even more technical and is, therefore, even more impressive, has to do with something called the thermic effect of food (TEF). This is a term scientists use to describe the energy your body expends releasing energy from your food.

The prevailing myth is that if you go too long between meals, you will be missing out on this calorie-burning opportunity.

Think of this thermic effect as a sort of transaction tax that your body charges you to convert the energy in your food into a form of energy your cells can use. If a meal contains 300 calories worth of food energy, converting that food energy into cellular energy might use up 30 calories or so. So you’d end up with just 270 calories worth of energy when it’s all over. It’s a little like changing money in a foreign country. In order to convert your dollars into euros, you have to pay the money-changer a fee.

Some people have interpreted the thermic effect of food to mean that if your body is constantly digesting food, it will also constantly burn calories. The prevailing myth is that if you go too long between meals, you will be missing out on this calorie-burning opportunity.

THE NUTRITION FACTS

Once again, there's some real science behind this myth. The problem lies in the interpretation.

The thermic effect of food is based on how much you eat, not when you eat it.

Just like at the money-changer, the fee to exchange food energy into body energy is simply a percentage of how much you’re changing. It doesn’t matter whether you exchange all your money in one lump sum at the beginning of your trip or change small amounts of money three times a day. The fees will be based on how much money you convert. And the thermic effect of food is based on how much you eat, not when you eat it.

Evidence-based nutrition: 3 ways to increase TEF and burn more calories

1. Eat your biggest meals early in the day

Eating more often won't necessarily affect the TEF. But eating earlier in the day might. Although the research is limited, you might use 30% more calories digesting a meal eaten in the morning than you would if you ate the same meal in the evening. In one study, that amounted to 90 extra calories a day. And this may be one of the reasons that people who eat more of their calories earlier in the day lose more weight. However, most of us follow the opposite pattern, eating most of our calories in the second half of the day. 

2. Eat more protein and less fat

The balance of macronutrients (protein, fat, and carbs) in a meal also affects TEF. It takes more energy to digest protein than it does to digest carbs or fat. In other words, the metabolic money changer levies a higher transaction tax to exchange protein into energy, much the way you might pay a surcharge to exchange traveler's checks rather than cash. As a result, you'll burn more calories digesting a high protein meal than you would digesting a low protein meal that has the same number of calories. 

Protein is definitely king when it comes to TEF.

Protein is definitely king when it comes to TEF, but is there any meaningful difference between carbs and fat? Again, the research is quite limited, but some studies suggest that a meal that is higher in carbohydrates and/or fiber will have a higher TEF than one that is high in fat. 

3. Eat less processed foods

One interesting study found that more highly-processed foods have a lower TEF than more minimally-processed foods. It's more costly for your body to release the stored energy in whole grains, vegetables, or legumes than it is to release the same amount of stored energy in chips, doughnuts, and energy drinks. 

The bottom line

In terms of the thermic effect of foods, it doesn't matter how often you eat. If you want to maximize the effect of diet-induced thermogenesis, eat earlier and increase your protein. It may also help to avoid meals that are high in fat and/or highly processed foods.

But rest assured that going 4—or even 12—hours between meals will have virtually no effect on your metabolism. It’s also not necessary to eat every few hours in order to keep your blood sugar steady. In fact, spacing your meals out more can have some very beneficial effects on your blood sugar and on other aspects of your health, as well. 

Citations +

About the Author

Monica Reinagel, MS, LD/N, CNS

Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes' most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation's leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.