Why Do I Gain Weight When I Exercise?

There are many different reasons people start exercising. Some want to lose weight, some want to stay in shape, and some do it because they would like to improve their health. Whatever the reason for starting to work out, you should expect to gain weight at the very beginning of your exercise journey. Even though you are congratulating yourself for making that decision and sticking to it, you may be wondering: Why do I gain weight when I exercise?

There are a couple of reasons you may be noticing you’re gaining weight while hoping to shed some pounds. Let’s go through each.

Water Retention Weight Gain After Exercise

When you start to exercise, you expose your body to a lot of stress. Micro-tears and inflammation are the first responses your body will have after starting to work out. Your body’s response to this kind of trauma is water retention. Let me break it down for you.

Right after your workout, you will feel soreness and slight pain in your muscles. That’s a sign of a micro muscle tear. Your body’s response to this trauma will cause the water to retain all over the tears, trying to heal.

How to get rid of water retention? The answer is simple—make sure you eat properly, drink a lot of water, and get a lot of rest so that your body can heal quickly.


Inflammation is your body’s main response to injury or trauma. If you are just starting your workout routine, inflammation is inevitable—but usually necessary and helpful. Yes, you read that right! 

Woman suffering from pain in leg after workout.
Muscle Inflammation Is Your Body’s Response To The Trauma And Injury And The Way That It Heals (Image Source: Shutterstock)

When your muscles are inflamed, they can start swelling and become red, warm, and painful. After a tough training, you’ll probably feel all of these sensations. And since inflammation includes water retention, you’ll temporarily gain water weight after you exercise.

Muscle inflammation is your body’s response to the trauma and injury and the way that it heals. If it weren’t for inflammation, your muscles would never heal. The good news is that it usually lasts for only a couple of days.

Chronic inflammation, however, is not so helpful, as it can cause a lot of health issues as well as weight gain. When your body detects a threat, it releases substances called cytokines, activating the body’s immune response to the injury. Cytokines support inflammation, interfering with the body’s insulin response.

After the body has become insulin resistant, the pancreas needs to produce more of it, making your body store fat.

Inflammation can also interfere with how your body responds to leptin (the eating hormone), making it hard for your brain to get the information that you’re full, so you end up eating a lot more than necessary.

Using Post-Exercise Inflammation to your Benefit

Because post-exercise inflammation (and the accompanying water-weight gain) is categorized as a good thing for healing after your workout, it is good to know all the way you can induce the effect of post-workout inflammation. There are two techniques you can use to reap the benefits.

Athlete doing stretching exercises on running track.
Stretching Help You Relax Your Muscles And Make Them More Flexible So That Inflammation Ends Sooner (Image Source: Shutterstock)

Stretch: Stretching after intense training is an underestimated activity. You’re done with your workout, you’re already tired, and all you want to do is take a shower and lie down on your couch. Instead of doing that, try stretching out for 5–10 minutes. It’ll help you relax your muscles and make them more flexible so that the healing period (inflammation) can end sooner.

Rest: Although it might sound obvious, you’d be surprised how often people forget to rest after a demanding workout. Either take a rest day or do a slow-paced yoga class after an intense workout day. During an exercise, your body releases unstable molecules that damage your cells. Usually, your body in response will release antioxidants to neutralize those molecules. Pushing yourself every day will make these free radicals overwhelm your body’s defense system, creating oxidative stress. Oxidative stress is a condition that causes chronic inflammation—an injurious state that can cause bigger and more long-lasting tears of your muscles. If you’re feeling low on energy, are sleeping poorly, lack motivation, feel irritable, or experience frequent illness, you should probably take a break.

Fat vs. Muscle Weight Gain with Exercise

“Muscle weighs more than fat”—you have probably heard this before. But the truth is, it doesn’t! A pound of muscle equals a pound of fat. So what’s the real difference?

Why Am I Gaining Weight With More Exercise? – Dr. Beth Westie

The key is in the density of each.

Muscle has a much denser structure than fat, thus taking less space in your body for the same amount of weight. This is why, if you’re on your weight loss journey and you have just started to work out, a mirror is your best friend, not a scale, despite popular belief. However, if you feel like you need to measure results, then consider a BMI device like the FitTrack Dara Scale.

Another great thing about muscles is that they have better circulation, which makes them a calorie-burning machine, even when you’re resting or sleeping.

Gaining Muscle but Not Cutting Fat

If you’re gaining muscle but not losing fat, know that this is normal. So even though you’re making progress, you might be gaining weight as you add on muscle as you exercise. You probably need to make subtle changes to your diet in order to start losing fat.

The challenge here is that muscle gain requires more food, and loss of fat requires less food. Confusing, I know. But I want to let you know that it’s possible!

To start losing fat, you just need to start incorporating fuel for your muscles in your diet. Protein is known as food for your muscles. If you’re lifting weights, you’ll need 1.5 grams of protein per kilo of your body mass.

Avoiding processed food and consuming protein and carbs right after your training will help feed your muscles and make them stronger, ultimately making you lose fat and gain muscle.

One thing to remember, though, is that you have to reduce your calorie intake if you’re in the process of losing fat—but do not undereat! Undereating will cause your metabolism to slow down, sabotaging your weight loss goals.