Gaining Weight While Working Out? Don’t Panic! Here Are 7 Potential Causes

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Most people who start working out expect to experience certain things after the first few workouts: muscle soreness, perhaps stiffness in our joints, and fatigue. Another thing we usually hope to see is weight loss.

However, some people who begin a new exercise routine step on the scale after their first few workouts and are shocked to find that instead of seeing that number trending downward, they appear to be gaining weight after working out.

In fact, one of the most common questions beginners ask—albeit often with a bit of panic in their voice is—“Why am I gaining weight while working out?”

In other words, what is happening if you are working out yet still gaining weight?

In this article, we will discuss potential reasons why you may be gaining weight despite exercising or why you might be gaining weight while working out.

We will cover: 

  • Why Am I Gaining Weight While Working Out? 7 Possible Causes

Let’s get started! 

A scale pointing at 235.

Why Am I Gaining Weight While Working Out?

There are several potential reasons why you might be gaining weight after working out. Here are some of the primary causes of weight gain despite working out.

#1: Post-Workout Muscle Inflammation

The most common cause for gaining weight after working out, particularly during the first few weeks of a new training program or after a particularly intense workout, is due to water retention.

This is temporary weight gain rather than a true increase in body fat.

Whenever you perform some type of stressful exercise such as running, heavy resistance training, or an interval workout, there is some amount of structural muscle damage that occurs.

A runner with closed eyes, exhausted from running.

Overloading your muscles causes microtears in the muscle fibers. This initiates a reparative process that will ultimately rebuild and strengthen your muscles. However, it also triggers a cascade of inflammation.

The body retains excess water to help facilitate the muscle reparative process. 

Therefore, if your weight gain after exercise coincides with delayed-onset muscle soreness (DOMS), the start of a new workout routine, or follows a particularly strenuous workout, the most likely reason that you are seeing your weight creep up on the scale post-workout is simply water retention from muscle inflammation.

Before you panic, the important question becomes, “How long does temporary weight gain after exercise last?”

In most cases, unless you caused pretty severe damage to your muscles, with proper fueling, hydration, and recovery, any temporary weight gain after working out from water retention should subside in about 72 hours.

The word carbs with carb-filled foods around it, such as pasta, fruit and grains.

#2: Your Diet Is High In Carbohydrates

Another common cause for gaining weight after working out is also due to water retention, but rather than the body holding onto water because of muscle damage and inflammation, the body is storing more water due to your diet.

Many athletes fuel with carbohydrates. Carbohydrates supply the glycogen your muscles need when producing energy during high-intensity exercise.

For this reason, endurance exercise such as running and high-intensity cycling, as well as strenuous strength training workouts, require fueling with carbohydrates before and during longer workouts to support energy production.

For every gram of carbohydrates that your body stores as glycogen, another 3 to 4 grams of water are also stored because glycogen has to bind with water in order to be metabolized by the muscles for energy.

A person doing a bicep curl at the gym.

#3: You Are Increasing Your Muscle Mass

Depending on the type of training that you are doing and the diet that you are following, you might be gaining weight despite exercising because you are building muscle.

If you are engaging in hypertrophy training or intense strength training workouts and consume an adequate number of calories and grams of protein per day to support muscle growth, your body will respond favorably to your workouts by increasing your lean muscle mass.

You can monitor body recomposition changes and changes in your overall body composition with a body fat scale or another form of body fat analysis.

It is possible to lose fat and gain muscle at the same time, which would result in no net weight gain or weight loss, but this is often fairly tricky and requires discipline in your diet and training program.

Note that muscle does not weigh more than fat. One pound of muscle and one pound of fat weigh the exact same: one pound. 

However, the volume taken up by one pound of muscle and one pound of fat is different.

Muscle tissue is denser than fat, so if you gain muscle and lose fat at the exact same rate, your overall body size (or the size of clothes you wear) will go down. Your circumference measurements will drop, and you’ll look leaner, but your weight on the scale will remain unchanged.

A person holding out a glass of water.

#4: You Are Dehydrated

Probably the most counterintuitive but common reason that you may be gaining weight after exercise is dehydration. 

When you exercise, your body sweats, and you also lose more water through increased exhalation, which increases the amount of expired respiratory water vapor.

Therefore, unless you are taking in enough fluids before, during, and after your workout, you can easily become dehydrated, especially during longer endurance workouts or when exercising in a warm environment.

On the one hand, when you are dehydrated, your total body water levels drop, which would result in a decrease in your weight on the scale.

However, dehydration actually causes the body to retain more water, as water is viewed as a scarce resource.

Although immediately after a very sweaty workout, it will appear that you have lost weight if you do not rehydrate adequately, the following day, you may find that you have gained weight on the scale because your body is now holding onto more water.

A person with six plates of food in front of him, eating pasta.

#5: You Are Overeating

Although working out does burn calories, some people overestimate the number of calories they have burned, which leads to overcompensation in terms of how many calories you consume. 

You may also “reward yourself“ with food after a workout. 

Compensatory overeating can negate the caloric deficit you generated by doing the exercise in the first place and lead to a net caloric surplus. This will result in true weight gain because you are consuming more calories than you are burning.

Studies suggest that exercise, such as running, may help control appetite.

However, even if it’s not deliberate, some people also find that they have a compensatory spike in appetite after exercise that is disproportionately higher than the amount of work they did. 

In other words, imagine a scenario where you perform a cardio workout on an elliptical machine and burn 400 calories.

 If you feel incredibly hungry in the hours following your workout, you might consume at least 400 extra calories over what you would have had you not exercised or what you would otherwise need to maintain your weight. 

This will result in a net surplus of calories, which will cause you to put on weight. Excess energy that you take in is converted to triglycerides and stored in adipose or fat tissue. 

A person tired bent over a gym machine.

#6: You Are Overtraining

If you’re doing a lot of exercise, it’s natural to assume that you’d lose weight or at least not be gaining weight.

However, overtraining or doing too much exercise can overstress the body.

Overtraining and physically taxing workouts can increase your levels of cortisol, which is the primary stress hormone.

High levels of cortisol have been associated with increased appetite and an increased risk of weight gain, particularly in the abdominal region.

Therefore, it’s possible that if you’re not allowing your body enough time to recover and you’re red-lining your efforts day after day, you’re gaining weight because your hormones are imbalanced and your cortisol levels are too high.

A person doing a lateral raise.

#7: You Just Started Working Out

Beginners who have just started a workout program are most apt to gain weight after working out. 

As mentioned, the body retains water to help the muscles repair damage after exercise, and if your body is unaccustomed to working out, there’s a greater chance that any type of physical activity will cause some amount of damage.

Your body retains fluid to help bring healing nutrients and amino acids to the site of any structural damage to heal your muscles.

But, how long does temporary weight gain after exercise last, in this case, you ask?

This type of water retention may last for 48-72 hours after a workout, but if you’re working out several days per week, you’ll keep triggering the inflammatory process, making it appear that you’re gaining weight that won’t go away.

As your body adapts to your workout routine, the post-workout DOMS and muscle swelling should decrease, so your weight should drop a couple of weeks into your workout routine. 

Stay patient and re-examine your diet to make sure you’re maintaining a caloric deficit if you are indeed trying to lose weight yet still gaining weight even though you are working out consistently.

If you are trying to lose weight and would like some more information on maintaining a caloric deficit, check out our guide: What Is A Calorie Deficit, And Is It The Best Way To Lose Weight?

A person doing dumbbell bicep curls.
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Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, as well as a UESCA-certified running, endurance nutrition, and triathlon coach. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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