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Reasons Why You Might Be Gaining Weight While Working Out

Jan 24, 2023
Reasons Why You Might Be Gaining Weight While Working Out

It’s January, and the gyms are jam-packed with people working out. Many people begin the New Year with resolutions to exercise daily, get in shape, and lose weight. After a few weeks, the gym crowd thins out. Why does this happen year after year? One reason is that most people do not see quick weight loss from working out and may even see weight gain.

How can you overcome this? While it can be discouraging not to see expected weight loss immediately, you will if you stick with it and combine exercise with a nutritious, low-calorie diet. Weight loss is not always linear. Stress, sleep habits, hormonal changes, and digestive factors can all cause weight fluctuations. In the meantime, focus on other goals, such as

  • Do you have more energy?
  • Has your waist circumference decreased?
  • Are you sleeping better?
  • Do your clothes fit better?
  • Do you look thinner in pictures?
  • Are you stronger?
  • Do you have better balance?
  • Are you losing body fat?

There are many potential causes for weight gain with exercise. To get the most benefit from your workout, ensure you are getting the macronutrients, vitamins, and minerals you need for maximum performance.

Why Do I Gain Weight After Working Out?

Short-term weight gain after working out is very common. You may notice this discouraging phenomenon for several reasons, many of which result from healthier changes in your body. You may be gaining muscle and changing your body composition, but you may also be over or under-training or not supplying your body with the best combination of nutrients to fuel your workout.

Too Much Cardio

Cardio is a favored exercise that improves aerobic capacity, cardiovascular function, and metabolic regulation. You can spend countless hours on the treadmill or elliptical and track the number of calories burned during your workout and not see a comparable weight loss. Calorie counts on tracker apps and fitness machines are estimates and are not usually as accurate as you would like. Aerobic exercise also increases hunger, which makes it easy to consume more calories than you burn.

It has long been thought that resistance or strength-building exercise builds muscle tissue, and cardio does not. However, newer ways to measure muscle fiber density show that muscle fiber hypertrophies after aerobic exercise as long as the duration and intensity are high enough.1 These changes are steps towards better health because they indicate increased strength but can cause temporary weight gain.

Excessive amounts of cardio also stress your body, stimulating the release of cortisol. Cortisol mobilizes glucose in your body to prepare for a threat. This was a valuable response in a time of physical threats that required fight or flight, but today it is not as useful, and it causes weight gain and increased abdominal fat.

A woman running on a treadmill

Water Retention

When you ramp up your workouts, your body prepares for the increased demand by storing more glycogen in your muscle fibers. Glycogen is how your body stores glucose (sugar) to fuel your muscles. Glycogen binds to water which can increase water retention. For each gram of glycogen stored, your body retains three grams of water (which can add up to as much as two to four pounds of body weight).2 As your muscle become better trained and efficient, they will back off on storing glycogen, and you will hold less water and lose weight.

A high sodium diet, hormone fluctuation, and gastrointestinal motility changes can all cause water retention. After eating salty foods, most people consume more water, but urine output does not increase proportionately, resulting in water retention and weight gain.3,4

Premenopausal women may notice fluctuations in their body weight throughout their menstrual cycle. Estrogen and progesterone have important effects on body fluid regulation. Estrogen increases water retention and increases blood volume.5 This may also contribute to temporary weight gain after working out.

Fiber-rich food is a great part of a healthy diet. As fiber moves through the gastrointestinal tract, it holds onto water, which can increase bloat and fluid retention. Drink plenty of water and continue eating high-fiber foods; bloating will improve as your body adjusts to the added fiber.


When you stress your muscle fibers, they develop small micro-tears and become inflamed. This can cause delayed onset muscle soreness. The inflammatory reaction brings blood rich in proteins and immune cells to the damaged tissue. To aid in this process, blood vessels become leakier, and more fluid from the bloodstream leaks into the surrounding tissue.6 This temporary increase in fluids around the injured muscles can cause a three to four-pound weight gain, which will go away after the muscle tissue heals.

Exercising moderately or ensuring adequate rest breaks if you exercise vigorously can help reduce inflammation. Drink plenty of fluids and eat a nutritious diet high in vitamins and minerals, or take supplements that can reduce inflammation in the body.

Why Do I Keep Gaining Instead Of Losing Weight With Exercise?

Weight gain after working out can sometimes last for a longer time. This is a good thing if you are undergoing body recomposition and gaining muscle mass. Stress, lack of sleep, consuming too many calories, and not working out enough can cause weight gain without any health benefits.

Building Muscle

You will build muscle as you do strength training and consume more protein. Genetic predisposition, dietary choices, and the type and amount of strength training you do will determine how much muscle you build. As you build muscle and gain strength, the number on the scale will probably increase. Muscle is denser than fat, so as you gain muscle and lose body fat, you will lose inches, and your clothes will fit better. You can track your body fat and muscle mass at home. Individual readings are notoriously inaccurate, but they can help you track trends.

Body recomposition, building muscle, and losing body fat, has a multitude of health benefits.7  Increased muscle mass increases your resting metabolic rate, which can help you burn calories throughout the day, even when you are not working out.

Eating Too Much

Engaging in a great aerobic workout makes you hungry. While it is important to fuel your body for exercise, you will gain weight if you consume more calories than you burn. Poor sleep, high stress, low protein intake, dehydration, and some medications can also cause excessive hunger.

Experiment with different combinations of proteins, fats, and carbohydrates and with meal timing to determine what food choices provide you with the energy you need to complete your workout without leaving you ravenously hungry afterward.

It’s also important to check with yourself to ensure you are hungry before eating. Sometimes people feel like they should eat after exercise whether or not they are hungry. Emotional stress, poor sleep, and other triggers can cause you to eat even when you are not hungry.

A person holding a large hamburger

Not Working Out Enough Or Intense Enough

For health and fitness benefits and to stabilize your weight, the Centers for Disease Control and Prevention (CDC) recommends choosing one of the following options:

  • Exercising at a moderate intensity for 30 minutes a day, five days a week (i.e., 150 minutes per week).
  • Exercising at a vigorous intensity for seventy-five minutes per week.
  • Doing a combination of moderate and vigorous-intensity walking.

According to the American College of Sports Medicine (ACSM), if you want to lose weight, increase your weekly exercise to 200 to 300 minutes per week. Researchers found that over a three-month period,8

  • Less than 150 minutes of weekly physical activity resulted in minimal weight loss.
  • Between 150 and 225 minutes per week resulted in a 4-to-6-pound weight loss.
  • Between 225 minutes per week and 420 minutes per week resulted in an 11-to-16.5-pound weight loss.

Use your heart rate to ensure you are in a fat-burning training zone.

Target Heart Rate by Age and Exercise Intensity

20114–126         128–152         154–190         192–200
30108–120121–144         146–180         182–190
40102–113115–137         139-171          173-190
  • Low Intensity: 57%-63%
  • Moderate Intensity: 64%-76%
  • Vigorous Intensity: 77%-95%)  
  • Maximum Intensity: 96%-100%*

*100% = 220- your age

Not Sleeping Enough

Sleep restriction also increases cortisol which can affect how your body loses weight. In one study, people who were sleep restricted lost the same amount of weight as the group that was not sleep-restricted, but they lost significantly more fat-free mass than body fat.9

The sleep-restricted group also had higher ghrelin and lower leptin levels. Ghrelin is commonly referred to as the hunger hormone because it increases appetite and the likelihood of weight regain.7 Ghrelin speeds up stomach emptying, increases glucose metabolism and fat storage, and tells your brain that eating food is pleasurable, which increases cravings. Proteins can suppress ghrelin release.10

A single night of poor sleep is all it takes to increase ghrelin secretion and hunger.11

High Stress

High stress causes increased cortisol secretion. Cortisol mobilizes glucose from the liver and makes it available for the brain and muscle cells to use as energy to fight the threat. Excessive cortisol secretion causes blood sugar spikes and rapid energy store depletion. Energy depletion stimulates hunger, so you consume carbohydrates to restore glycogen. Even psychological stress can cause excessive cortisol release and hunger. This is why stress is a common cause of sudden weight gain in women.

Not Recovering Properly

It seems logical that if you train more, you will lose more weight. However, vigorous exercise followed by inadequate recovery time increases inflammation and can cause weight gain. Your body will adapt to the demands you place on it, but you need to give your muscles enough time to repair microtrauma between sessions. Scientists have studied athletes and developed protocols for maximizing athletic gains and performance based on the science of performance and recovery for athletes.

Whether or not you consider yourself to be an athlete, you can use these same principles to maximize your workout results.

A chart says ways to lose weight: diet, exercise, better sleep, reduce stress, supplements, track progress, drink more water

How To Manage Weight With Exercise

Working out has so many health benefits. Try not to focus on one measurement of your progress—your weight. Continue with your workout plans and these other tips to help you meet your body recomposition and weight loss goals.

  • Make exercise a regular part of your daily routine.
  • Check your heart rate to ensure you exercise at a moderate to vigorous intensity.
  • Get 7 to 9 hours of restful sleep each night
  • Try spending time in nature, meditating, or doing yoga to reduce stress and cortisol levels.
  • Consume a nutritious diet full of colorful fruits and vegetables.
  • Prioritize strength-building exercises as part of your workout.
  • Watch your calorie intake to ensure you are not overcompensating for the calories you burn while working out.
While we strive to always provide accurate, current, and safe advice in all of our articles and guides, it’s important to stress that they are no substitute for medical advice from a doctor or healthcare provider. You should always consult a practicing professional who can diagnose your specific case. The content we’ve included in this guide is merely meant to be informational and does not constitute medical advice.

Reasons Why You Might Be Gaining Weight While Working Out

Leann Poston, M.D.

Dr. Leann Poston is a licensed physician in the state of Ohio who holds an M.B.A. and an M. Ed. She is a full-time medical communications writer and educator who writes and researches for Invigor Medical. Dr. Poston lives in the Midwest with her family. She enjoys traveling and hiking. She is an avid technology aficionado and loves trying new things.


  • Konopka AR, Harber MP. Skeletal Muscle Hypertrophy After Aerobic Exercise Training. Exercise and Sport Sciences Reviews. 2014;42(2):53-61. doi:10.1249/jes.0000000000000007
  • Fernández-Elías VE, Ortega JF, Nelson RK, Mora-Rodriguez R. Relationship between muscle water and glycogen recovery after prolonged exercise in the heat in humans. European Journal of Applied Physiology. 2015/09/01 2015;115(9):1919-1926. doi:10.1007/s00421-015-3175-z
  • Rakova N, Kitada K, Lerchl K, et al. Increased salt consumption induces body water conservation and decreases fluid intake. The Journal of Clinical Investigation. 05/01/ 2017;127(5):1932-1943. doi:10.1172/JCI88530
  • Bankir L, Perucca J, Norsk P, Bouby N, Damgaard M. Relationship between Sodium Intake and Water Intake: The False and the True. Annals of Nutrition and Metabolism. 2017;70(Suppl. 1):51-61. doi:10.1159/000463831
  • Stachenfeld NS. Hormonal Changes During Menopause and the Impact on Fluid Regulation. Reproductive Sciences. 2014/05/01 2014;21(5):555-561. doi:10.1177/1933719113518992
  • Cerqueira É, Marinho DA, Neiva HP, Lourenço O. Inflammatory Effects of High and Moderate Intensity Exercise—A Systematic Review. Systematic Review. Frontiers in Physiology. 2020-January-09 2020;10doi:10.3389/fphys.2019.01550
  • Barakat C, Pearson J, Escalante G, Campbell B, De Souza EO. Body Recomposition: Can Trained Individuals Build Muscle and Lose Fat at the Same Time? Strength & Conditioning Journal. 2020;42(5)
  • Donnelly JE, Blair SN, Jakicic JM, Manore MM, Rankin JW, Smith BK. American College of Sports Medicine Position Stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults. Med Sci Sports Exerc. Feb 2009;41(2):459-71. doi:10.1249/MSS.0b013e3181949333
  • Wang X, Sparks J, Bowyer K, Youngstedt S. Influence of Sleep Restriction on Weight Loss Outcomes Associated with Caloric Restriction. Sleep. 02/09 2018;41doi:10.1093/sleep/zsy027


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