Why You Might Gain Weight When You Start Exercising

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So you’ve started an exercise program, and to your dismay, you’ve put on a few pounds—the exact opposite of your goal to shed some of that extra weight. Not to worry. There are several reasons why people experience weight gain with exercise, but if you keep at it, the extra pounds won’t hang around for long. 

What’s With the Weight Gain?

Your Muscles Are Changing

When you first start exercising—or come back to it after being inactive for a while—your body naturally undergoes muscle mass changes that can affect your weight. The exercises put stress on your muscle fibers, causing small micro tears and inflammation, which can lead to water retention and weight gain.

When you exercise regularly, your body also retains water as it stores more glycogen (sugar that your muscle cells convert to glucose for energy). This can add weight, too. But after a few weeks, as your muscles adjust to the new routine and need less glycogen for the same energy level, that water weight will start to go down.

You’re Hungrier

For some people, increasing their activity level translates to a healthier appetite. Once you begin to lose weight, the body’s hunger hormones, leptin and ghrelin, tell your body that you don’t feel as full, and tell your brain that it’s time to refuel, causing you to eat more frequently. In addition, the part of your brain that regulates food restraint becomes less active. So while you’re eating more to feel full, you’re also less aware of overdoing it.

You Need More Sleep

When it comes to maintaining a healthy weight, adequate rest goes hand-in-hand with exercise and healthy eating. It helps boost your immune function, metabolism, memory, learning and other functions. Inadequate sleep can result in poor exercise performance and weight gain. It can also increase the risk of obesity, along with many other chronic diseases such as diabetes, heart disease and depression

The good news is, you may find that sleep comes easier when you’re exercising regularly. But if you’re skimping on the shut-eye, you may see it show up on your waistline. 

What You Can Do

To help prevent weight gain when you start exercising, be mindful and:

  • Get proper rest. This will give your body a chance to recover, and your workout the best chance of working. Individual sleep needs vary, but in general, the National Sleep Foundation recommends adults ages 26 to 64 get between seven and nine hours of sleep per night.

  • Watch what you’re eating. Stop to consider if you’re really hungry, or if you’re eating for other reasons—boredom, fatigue, stress. When it’s hunger you’re feeling, choose low-calorie, high-protein, and high-fiber foods that will fill you up, such as vegetables, low-fat dairy, and lean meats. Talk to your doctor, or use a tracking app, to determine how many calories you should be getting based on how many you’re burning in the gym.

  • Don’t overdo it. When you’re first starting a new exercise regimen, be sure to take it slowly. Start with ten minutes, once a week, and work up from there. It’s important to give your muscles a chance to rest and repair between workouts.

As always, talk to your doctor if you have any health concerns before starting a new exercise routine, or if you have concerns about weight gain after exercise. You may also want to consult a physical therapist or athletic trainer who can help you map out a program and understand more about the effects of exercise, rest and nutrition on your body.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Jan 27
  1. I Just Started Exercising — Why Am I Gaining Weight? Cleveland Clinic. https://health.clevelandclinic.org/just-started-exercising-gaining-weight/
  2. How Your Body Fights Weight Loss. Northwestern Medicine. https://www.nm.org/healthbeat/healthy-tips/how-your-body-fights-weight-loss
  3. Does Sleep Affect Your Exercise? Duke Diet & Fitness Center. https://www.dukedietandfitness.org/does-sleep-affect-your-exercise
  4. Benefits of Sleep. Healthy Sleep. Division of Sleep Medicine at Harvard Medical School. http://healthysleep.med.harvard.edu/healthy/matters/benefits-of-sleep
  5. How Much Sleep Do We Really Need? National Sleep Foundation. https://www.sleepfoundation.org/articles/how-much-sleep-do-we-really-need
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