Why Exercise Can Cause Weight Gain

Does gaining muscle make you gain weight? Is there anything to that old saying that "muscle weighs more than fat?" Here's what you need to know if you're exercising your butt off but the scale numbers seem to be moving in the wrong direction.

Brock Armstrong
8-minute read
Episode #506
The Quick And Dirty
  • Calories are deceptive—counting calories really isn't all that useful.
  • Gaining muscle can also make you gain weight.
  • Stress (even from a workout program) can make you gain weight.
  • We often eat more because we have exercised.
  • Not all forms of exercise are effective for weight loss.
  • Exercise is not for weight loss, but it does have many other amazing benefits.

A listener named Marcia sent an email asking about weight loss and exercise. This is what she asked:

I've been doing resistance training and some cardio for a couple of months now and I've noticed that I've been gaining weight, mainly around my belly. Do you have any way to explain this?

Why yes, Marcia, I do have a few different ways to explain what kind of things might cause you to gain weight even if you’re exercising. And of course, I won't leave you hanging. I will also tell you what you can do to avoid this issue.

Exercise isn’t for weight loss

I don’t know where the idea first came from but I do know that the majority of people I have met and coached in my life hold this idea that the most important factor in losing weight is exercise. Well, despite how ingrained this belief may be, it is not true. Here's one important reason why: The extra calories you burn when you exercise only account for a small portion of your total energy expenditure. In fact, there are three main components to your overall energy expenditure:

  1. basal metabolic rate (the energy your body uses to stay alive) makes up 60 to 80 percent of your energy expediture,

  2. the energy used to break down and metabolize food makes up about 10 percent,

  3. the energy used to make your body move makes up 10 to 30 percent.

While the food you eat accounts for 100% of the energy you bring into your body, the exercise and movement you do only uses up about 10 to 30% of it. So, exercising away your food intake would take some real heroic efforts. Decreasing your food intake (while exercising for the other wonderful benefits exercise bestows) would be much more effective.

While the food you eat accounts for 100% of the energy you bring into your body, the exercise and movement you do only uses up about 10 to 30% of it.

Before we move on, I want to make sure you know that I'm not suggesting you leave exercise out of your healthy weight loss regimen—I'm just tempering your expectations. Although exercise alone isn't an effective way to lose weight, it's been shown to be great for maintaining weight. The vast majority of your weight loss should be focused on, and will come from, the changes you make to your relationship with food.

This is exactly why the Weighless Program, which I co-founded with Nutrition Diva Monica Reinagel, includes both movement and dietary interventions but spends much more time focusing on what, when and why we eat, rather than crushing the Workout of the Day.

But there is another weight loss elephant in the room.

The issues with calories

Along with the exercise myth, we have been beaten to death with the idea that we need to measure calories. But here's the thing: Technically, a calorie is just the amount of energy it takes to raise one gram of water by one degree Celsius.

Wait, what? That's right. It has nothing to do with our biology.

Technically, a calorie is just the amount of energy it takes to raise one gram of water by one degree Celsius. It has nothing to do with our biology.

In her podcast episode called Can You Trust Your Calorie Counter?, licensed nutritionist Monica Reinagel (who also has a Master’s of Science in Human Nutrition), explains it like this:

In broad strokes, you submerge a chamber in a bucket of water and put a thermometer in the water. Inside the submerged chamber, you set something on fire. The heat generated by the combustion raises the temperature of the water in the bucket, which you can measure with the thermometer. You can then calculate the amount of energy or calories that were in the thing you set on fire.

And the mental hurdles don't end there! Let’s talk about the act of counting calories. It turns out, that's not as useful as we have been told, either. Not only is it an extremely tedious endeavor, but the calorie counts on foods are notoriously unreliable (A variation of +/- 10%) and calorie measurements on activity trackers are even worse (some studies show a 93% inaccuracy). So trying to carefully balance your MyFitnessPal account with your FitBit readout is not worth the effort.

Does all this mean that we should stop paying attention to calories altogether? Probably not, since it's all we have to go on (at the moment). But hopefully, you get the idea that just because the treadmill at the gym is showing that you burned more calories than your meal tracker says you ate, and you still aren’t losing weight, you aren't doomed or experiencing some freak anomaly.

Why exercise can cause weight gain

You're gaining muscle mass

The problem:

Muscle gain is the most common reason for weight gain caused by exercising. Muscle is comprised of small dense fibers while fat is comprised of larger, less dense droplets. This means that even if you lose fat, you may notice a weight gain if you’re simultaneously putting on some lovely muscle mass.

But this is nothing to complain about! Along with this muscle weight gain comes a tighter waistline, more definition, and a positive change in your overall physical appearance. Not to mention a boost in your resting metabolic rate—win-win!

The solution:

Since being able to tell the difference between losing fat and putting on muscle can be tricky, this is a good reason to keep an eye on the way your favorite pants or t-shirt fit. You can also use weekly (or bi-weekly) full-body photos to monitor changes in your body shape (if not size). Or you can monitor your body fat using a fancy scale rather than simply tracking your weight.

The old fitness cliché we often hear says "Muscle weighs more than fat." But that's a bit silly—a pound of muscle and a pound of fat both weigh, well ... a pound. What the saying likely means is that it takes less muscle tissue to make a pound than it does fat tissue. Because muscle tissue is more compact, it also takes up less space.

Stress can cause weight gain

The problem:

When you begin a serious exercise program or begin to work out more, you may sacrifice sleep, have less time to get important tasks done, and also require your body to push itself much more than it is used to. This can create a perfect storm for a significant stress response.

When you're stressed, your adrenal glands can increase the production of a hormone called cortisol. Think of this as your fight-or-flight stress hormone—an evolutionary adaptation that would come in quite handy if you were running from a lion and you needed to increase your heart rate, sweat rate, blood pressure, or body temperature.

When you're stressed, your adrenal glands can increase the production of a hormone called cortisol.

But if an increase in exercise changes up your schedule and your life to the point where you feel as if you're constantly running from the lion, then you may overstimulate your adrenal glands and produce excessive cortisol.

By making you retain sodium and fluid, cortisol causes an increase in blood pressure and a stronger contraction of your heart. Since you aren’t running from a lion while you’re sitting at your desk at work, not only do you not really need this constant blood pressure elevation, but you also don’t need all the fluid retention and weight gain that comes with it.

The solution:

If you are constantly feeling stressed, and not taking enough recovery or rest from your workout days, then you can experience weight gain due to fluid retention. The solution is to make adjustments that decrease stress, such as getting to bed earlier, substituting a workout day with a yoga day, or rearranging your schedule to make getting some extra movement into your day less stressful. Check out my 8 Ways to Get More Movement into Your Day article for more on that.

You eat more to compensate for working out

The problem:

Studies have shown that if you do a hard workout early in the day, you’ll very likely to compensate and overeat later in the day. This is the case for two reasons:

  1. You feel entitled to eat more because you did such a good job exercising
  2. Your metabolism is temporarily elevated and your appetite is greater

In that same study, the researchers summed it up by saying "Exercise-induced changes in the hedonic response to food could be an important consideration in the efficacy of using exercise as a means to lose weight." Yes, they used the word "hedonic." Nice work, science!

Even without getting into the dreaded calorie conversation again, it is obvious that if you're increasing food intake more than you're increasing movement, then you’re going to gain weight even if you’re exercising a lot.

The solution:

Here are some tips to avoid compensatory eating:

  • Don't worry about trying to refuel beyond your hunger level. In most cases, especially if weight loss is your goal, waiting until your next scheduled meal to eat is absolutely appropriate (despite what Powerbar may tell you).

  • Remember that the magic "feeding window" you may have heard about is not as short or as simple as it seems. And it is only truly important if you are planning a hard workout later that same day.

  • Drink lots of fluids. Often appetite cravings after a workout are due to slight dehydration, and not a true need for calories.

  • Write down what you eat. The simple act of logging your food (for a few days, not forever) can help you be a little more honest without yourself, especially on your most active days.

You don't use the most effective exercises

The problem:

As I already mentioned, you can't exercise yourself thin—trying to can be a frustrating reason for weight gain. But when we dig into this phenomenon in more detail, it may be that your weight gain with exercise is a result of not working out in an effective way to maximize energy usage.

I'm not saying that you aren't working out in a way that will make you stronger, more stable, more capable, and healthier overall. It's just that your workout may not be adding to your weight loss efforts in the most effective way.

There is no perfect, one-size-fits-all exercise routine that results in maximum fat loss.

I most often observe this phenomenon in people who are not exercising at a high enough intensity, only focussing on low-level cardio, not doing any resistance or weight training, or simply not being physically active for the portion of the day (or the week) outside of their dedicated exercise time (we call this the Couch Potato Athlete: you crush a workout and then hit the couch for the remainder of the day).

The solution:

Because every body is different, there is no perfect, one-size-fits-all exercise routine that results in maximum fat loss. But there are four characteristics of every successful fat loss program.

  1. Consistently convenient. You can do it anywhere, without being forced to spend two hours at a gym or access special equipment or expensive gadgets. Convenience will help you be consistent with your workouts, even when time is tight.

  2. Full-body. Hit as many muscles in your body as you can to get the maximum metabolic boost. This means combining upper and lower body workouts, cardio and resistance training, sprints, and yoga.

  3. Heart-rate-stimulating. You want to raise your heart rate (a little or a lot) and for maximum cardiovascular stimulation, the workout should require that you move from exercise to exercise with minimal rest.

  4. Heavy enough. When you lift weights, to maximize fat loss, you should not be able to do more than 12 repetitions of an exercise with the weight you choose. You don't have to go all the way to failure (not being able to lift the weight again) but you should get close.

If the number on your scale has you feeling down and discouraged about continuing to include exercise in your life, well ... get the heck off the scale and spend some time assessing the amazing benefits you've gained from extra movement, instead. I bet you have more energy, and you feel stronger, happier, more motivated, and less stressed. Not only that, but you're healthier overall. These are just a few of the benefits you get from exercise. To me, they matter more than the number of pounds you have or haven't lost.

This article was originally written by Ben Greenfield. It has been substantially updated by Brock Armstrong.

All content here is for informational purposes only. This content does not replace the professional judgment of your own health provider. Please consult a licensed health professional for all individual questions and issues.

About the Author

Brock Armstrong Get-Fit Guy

Brock Armstrong was the host of the Get-Fit Guy podcast between 2017 and 2021. He is a certified AFLCA Group Fitness Leader with a designation in Portable Equipment, NCCP and CAC Triathlon Coach, and a TnT certified run coach. He is also on the board of advisors for the Primal Health Coach Institute and a guest faculty member of the Human Potential Institute.