Despite regular exercise, a person may gain weight for several reasons. These include increased muscle mass, water retention, and stress responses.

If a person’s goal is to lose or maintain weight, gaining weight despite exercising can be discouraging. It can feel as if their hard work during workouts is not paying off.

However, weight gain from exercise can sometimes indicate changes in body composition. A person’s weight may increase as they develop more muscle mass and become stronger.

This article looks at why weight gain may occur with exercise and how supplements and metabolism may affect weight. It also looks at how to balance weight gain and exercise and stay motivated, and when to seek help.

People may gain weight despite or because of exercising for the following reasons:

Muscle mass development

A person may lose fat during exercise, but still gain weight. This is because exercise can increase muscle mass, which is denser and heavier than fat mass. These changes in body composition can lead to a leaner, stronger physique.

The amount of muscle mass a person develops through exercise can depend on several factors, including:

  • Diet: Calorie and protein intake are key factors in building muscle mass. Research suggests that a protein intake of 1.5 or 1.6 grams (g) per kilogram (kg) of body weight per day can help develop muscle mass.
  • Exercise type: Resistance training, or strength training, is the most effective exercise type for muscle mass development.
  • Sex: Sex differences may affect how muscle mass develops from exercise, although research has produced mixed results. A 2020 review of research found that females improved their upper body strength more than males when following the same resistance training program.
  • Genetics: A person’s genetics play a role in many physical traits that influence muscle mass development, such as the fibers that compose muscles.

Water retention and hydration

Water retention may lead to weight gain during exercise. This is a buildup of fluid in areas of the body that leads to swelling. It can cause temporary weight gain that may fluctuate.

People may become dehydrated during exercise as they lose water through sweat. This can cause the body to retain water, which may lead to a buildup of fluid.

Water retention also often occurs due to hormone changes that occur throughout the menstrual cycle. A person’s weight may fluctuate as fluid retention increases and decreases during different phases of the cycle.

Cortisol and stress response

Excessive exercise can trigger a stress response in the body, elevating levels of the stress hormone cortisol.

Cortisol increases blood glucose, which can lead to higher insulin levels. When a person’s insulin levels remain high, they may develop insulin resistance. This means the cells in the body no longer respond properly to insulin signals. Weight gain may occur as a side effect.

High cortisol can also influence how the body produces other hormones, including those that help regulate appetite, such as corticotropin-releasing hormone (CRH). This could prompt a person to eat more than they otherwise would.

Medical Perspective

“Losing weight at any age can be challenging as our bodies are evolutionarily conditioned to hold on to weight. Decreasing muscle mass, hormonal changes, and slowing of metabolism as we age can make losing weight even harder.”

— Jillian Foglesong Stabile, MD, FAAFP, DABOM

Learn more about losing weight after 40.

Quotes represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Some people may be concerned that supplements, such as creatine or protein, may cause weight gain, but research does not support these claims.

Creatine is composed of amino acids, which the body stores to use as energy. The recommended intake is 3 to 5 g per day, or 0.1 g per kg of body mass per day.

It is a common misconception that creatine increases fat. Several studies suggest that, in conjunction with exercise, creatine may actually help reduce fat.

Individuals may experience water retention during the first few days of creatine use, which can cause a temporary weight increase.

Protein supplements are also made up of amino acids and can help build muscle and repair tissue.

Studies suggest that protein may help reduce weight and fat buildup. It may also improve insulin sensitivity, which could help prevent weight gain. The recommended daily allowance of protein for adults is 0.8 g per kg of body weight. People who exercise may require more protein — between 1.2 and 2 g per kg of body weight.

The following tips may help balance exercise and weight management:

  • Balancing types of training: If a person’s primary goal is weight loss, they may want to balance strength training with other types of exercise that focus less on building muscle mass, like cardio and flexibility training.
  • Allowing for rest and recovery: Adequate rest and recovery between workouts may help reduce stress responses in the body, which may lower cortisol levels.
  • Fuelling workouts without excess calories: Exercise can increase a person’s appetite. A person may want to speak with a healthcare professional about their caloric and nutritional needs during exercise.
  • Staying hydrated: Exercise may lead to dehydration. This can result in various health complications, including water retention. Drinking plenty of fluids during exercise can help prevent dehydration.

Remember to celebrate your successes

If your focus is on weight loss or maintenance, you may feel disheartened to see the numbers on the scale go up after exercising. Regular physical activity is hard work, and it can be challenging to keep a positive mindset.

However, weight does not have to be the only measurement of success.

Adjusting fitness goals and celebrating achievements can motivate you to keep exercising. Instead of focusing on weight, remember to celebrate your other gains from exercise, such as:

  • improved mental well-being
  • increased strength
  • more energy
  • better mobility and flexibility
  • better overall health
  • having clothes fit more comfortably
  • losing inches and feeling leaner

A dietitian or nutritionist can help develop an eating plan that suits a person’s goals and exercise routine.

In some cases, health issues may contribute to unintended weight gain after exercise. These can include:

A person should speak with a healthcare professional if symptoms of these conditions accompany unintended weight loss.

Certain types of exercise, such as resistance training, may increase muscle mass, which can cause weight gain. Extensive muscle development from excessive exercise may lead to weight gain.

Water retention typically resolves within a few days. If it worsens or does not improve, contact a doctor.

A person may want to adjust their approach rather than stop exercising if they gain weight.

Changes to their nutrition and the type of exercise they do may help them avoid weight gain. A person can also decenter weight loss as a fitness goal and measure their achievements in other ways, such as improvements in strength and energy.

A person can measure fat loss in the following ways:

  • measuring different parts of the body
  • taking photos to record progress
  • noticing how clothing fits differently
  • measuring strength increases
  • speaking to a healthcare professional about a body composition scan, such as DEXA

Weight gain can be frustrating if a person expects to lose or maintain weight through exercise. However, it can be a positive indication of changes in body composition, as exercise can help a person lose fat and develop more muscle mass.

Adjusting training type and diet may help a person avoid or minimize weight gain from exercise. They can also use measures of success other than weight to track and celebrate their achievements. These may include fat loss, increased strength, and higher energy.