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Can You Out-Exercise a Bad Diet?

Can You Out-Exercise a Bad Diet?

You’ll learn how much exercise it takes to eat what you want within reason—and whether you’re even capable of that.


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We’ve all probably heard you can’t “out exercise” a bad diet.

But some new science and common-sense observations suggest that’s not quite right.

Yet, as with all things around physiology, it’s a bit complicated. And we need to use the implications carefully.

Today, we’re diving into:

  • Whether you can “out exercise” a bad diet.
  • A few quick words on how exercise alters your metabolism.

Why it matters: This information can help the average person determine just how much exercise contributes to their weight status.

Note: If you just want the takeaways, scroll down to the takeaways section.

Let’s roll …

Can you out-exercise a bad diet?

In short

Probably, but it requires a lot of exercise.

The details

“You can’t out-exercise a bad diet” is a popular quip in the fitness world.

But as Adam Campbell—a fitness savant and my old editor at Men’s Health—used to say, “You see high school athletes out-exercise a terrible diet all the time.”

You also see it in the ultra-running community. Many ultra-runners eat a lot of junk food—they simply can’t get enough calories if they eat only “health foods.” Consider Courtney Dauwalter’s love of Cinnamon Toast Crunch and straight sugar.

Of course, we like to believe high schoolers have a magic metabolism and that ultra-runners are freak specimens.

A more relevant question is whether the average person can exercise enough to eat what they’d like within reason and not become obese.

So researchers in Australia looked at the weights of 13,000 masters (older) athletes. These are everyday people who competed recreationally in various sports.

They found that the masters athletes had significantly lower BMIs (a useful but imperfect measure of weight status). Their average BMIs tended to fall in the “normal” category while the general public tipped into the “overweight” category.

You see it, too, at the starting lines of marathons. Marathoners, to the naked eye, appear lighter than a group of people you’d see at, say, the starting line of a Black Friday store opening.

And scientists have indeed discovered that recreational runners have a lower-than-average BMI.

This approach probably won’t make you look ready to be on the cover of a fitness magazine—that takes diet and exercise—but seems to keep many in a healthy zone.

Issues with exercise and weight studies

In short

Studies showing exercise doesn’t lead to weight loss don’t have people exercise that much.

The details

Some research shows exercise alone doesn’t help overweight people lose weight. But there’s a catch:

  • These people were following the government’s exercise guidelines.
  • The guidelines call for 150 minutes a week (or about 20 minutes a day) of moderate exercise.

I.e., It’s not “enough” exercise. You can’t expect a 20 minute brisk walk to “make up for” a giant slice of pie.

But exercising far more than the guidelines recommend seems to lead to weight loss. For example:

  • People who exercised an hour a day but didn’t change their diet lost more than 15 pounds in three months. That was the same as a group who crash dieted.
  • Another study had obese people burn either 400 or 600 calories a day with exercise. They didn’t change their diet. Both groups lost weight, but the 600-calorie burn group lost more.

The researchers wrote:

This demonstrated a clinically significant weight loss for both men and women. However, the amount of activity to achieve this weight loss was again greater than the general exercise recommendations for health.

Most important: In those studies, the exercisers got healthier than those who only dieted. They burned more fat, maintained muscle, and also increased their VO2max.

Other research suggests that exercise is particularly helpful for maintaining weight.

Can the average person exercise enough to lose weight?

In short

Humans are all capable of amazing amounts of exercise. It’s part of our wiring.

The details

Ultra-runners are an excellent case study of out-exercising an imperfect diet. And you might think ultra-runners are freaks who do things you can’t.

But consider a paper titled “Extreme endurance and the metabolic range of sustained activity is uniquely available for every human not just the elite few.” The researchers explained:

Modern humans have unique physiological capabilities to perform sustained exercise in a wide range of environmental extremes (heat, cold, high altitude).

In other words, we’re all capable of tremendous amounts of exercise. Consider that everyday people in the past were about 14 times more active than we are today.

The innate human ability to endure helped our ancestors persist on long hunts and searches for food. If we couldn’t do that, we’d have all died off.

Our incredible endurance ability has been civilized out of many of us. But it’s always there, waiting to be accessed with dedication and training.

The scientists pointed to regular people with full-time jobs who poured themselves into training and completed events like an Ironman and 100-mile ultramarathons.

These people all burned fantastic amounts of energy in training and the event.

Their average weight—and it was a group of 10 men and 6 women—was 155 pounds.

You don’t have to exercise that much to help with weight loss or maintenance.

Just know that you are indeed capable of fantastic physical feats. And the more you exercise, the more room for error you’ll have around what you eat.

Exercise and diet isn’t an either/or

In short

Exercise and diet often run in tandem—one good habit leads to another. Lean into that.

The details

Some of the exercise and weight studies are noisy. For example, people who exercise are also more likely to watch what they eat. So it’s hard to say whether it was the exercise or the diet.

But who cares? If one good habit is associated with another, let’s lean into that. Exercise makes you more likely to start eating healthier, and vice-versa.

We see this in the real world. One study looked at recreational runners who ran distances ranging from 10Ks to ultra-marathons. It showed that 37 percent of them were vegan. That’s 12 times more than the general public. (Veganism isn’t magic for weight control. The point is that they were more likely to watch what they eat.)

On Changing Metabolism

In short

As you exercise more, your body adapts and spends less energy on other bodily processes. This lowers your overall daily calorie burn, stalling weight loss.

The details

In 2016, Duke researcher Herman Pontzer released a paper that shook the exercise world.

His theory suggests that as you ramp up your exercise, you don’t burn calories in a linear fashion. There isn’t a one-to-one relationship between exercise and calorie burn.

Your metabolism adapts elsewhere to constrain your daily calorie burn into a narrow range. This puts a ceiling on the total energy you burn.

This is actually a feature, not a bug. Pontzer told NPR:

And for most of us, that's a really good thing, because if we spend less energy, for example, on inflammation, we reduce our inflammation levels. If we spend less energy on stress reactivity, for example, our cortisol levels don't go up as high and our adrenaline levels don't go up as high, we achieve lower levels of stress response. And it seems that that exercise might also help keep testosterone for men or estrogen levels for women at a slightly healthier level. So that adjustment, that metabolic adjustment that we make is one of the reasons exercise is so good for us.

As you exercise more, you’ll eventually hit a plateau of calorie burn.

But that’s a good thing—it improves health. Cement the habit, and you’ll have a healthy lifestyle.

Big takeaway

Exercise alone can lead to meaningful weight change, and it’s great for weight maintenance.

It just takes far more exercise than modern people are used to and than the government’s guidelines recommend.

You may need to exercise an hour a day to see a meaningful effect. This might seem like a lot, but it’s far less than our ancestors exercised.

But once you adopt an exercise habit, you’ll likely adopt better eating habits. It’s a positive feedback loop. One good thing leads to another.

Have fun, don’t die, exercise.


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