Weight gain during exercise often reflects more muscle, not setbacks in your progress.
Muscle is denser than fat, so body composition can improve even if the scale doesn’t drop.
Fluid shifts, hydration and appetite changes may cause temporary weight fluctuations.

Have you started eating healthier and exercising more to lose weight, build muscle, improve your health or address some lab results? Yet when you step on the scale after weeks of putting in effort at the gym and in the kitchen, you might be shocked to see the number has gone up. Although this can feel defeating, it can actually be a positive sign. 

The No. 1 reason you might gain weight while working out and eating healthier is often due to gaining muscle mass. And that’s a good thing! 

Benefits of Increased Muscle Mass

When you begin exercising, your body composition starts to shift. The body is made up of fat, water and lean mass. Fat provides insulation, protects internal organs and stores energy. While some fat is essential, women generally need a higher percentage than men to support healthy hormones and reproductive function.

Lean mass—made up of muscle, organs and bones—forms the framework that keeps us upright, mobile and balanced. Over time, lean mass naturally declines, especially muscle, which can impact strength, independence and overall longevity. Preserving muscle is one of the best ways to support health as you age. 

Although a pound of muscle and a pound of fat weigh the same, they look very different. Muscle is denser and more compact, while fat takes up more space. That’s why you might see little change on the scale when building muscle and losing fat, yet notice more definition in your arms and legs or find it easier to carry heavy grocery bags.

Muscle also works harder for you than fat does. It’s metabolically active, meaning it burns more calories even at rest. The more muscle you maintain, the more energy your body uses throughout the day. and since natural muscle loss accelerates with age, building and protecting muscle is crucial for strength, bone health, mobility and long-term vitality.

More Reasons for Weight Gain

While gaining muscle mass is often the reason for weight gain during a new health journey, there are a few other reasons you might be gaining weight too:  

Exercise Induced Fluid Retention

Starting a new workout routine, or engaging in more exercise than you are used to, can cause temporary exercise-induced muscle damage. This leads to soreness, swelling and inflammation as your body works to repair itself. Edema or fluid retention and swelling in muscles can occur within one to two hours after exercise and peak around day 4 to 10. This inflammatory process can cause temporary weight gain.

You’re Drinking More Water

When you start breaking a sweat during workouts, you likely will start to feel a lot more thirsty. Increased intake of fluids, around and after workouts, can cause you to temporarily gain weight too. Two cups (16 ounces) of water—or another fluid—is equal to about 1 pound. If you drink a few cups after a sweaty gym session, you will likely see it reflected on the scale. For your most accurate weight, check it first thing in the morning after waking up. 

You’re Consuming More Sodium

We lose fluid and electrolytes in sweat, and both need to be replenished post-workout. The most abundant electrolyte in sweat is sodium. Replenishing electrolytes through an electrolyte beverage or food sources, like adding more salt to your food or grabbing a handful of salted nuts, may cause your body to retain fluid. may cause your body to retain fluid, which helps keep you hydrated but can also show up as weight gain. 

Your Appetite Is Increasing

Being more active often increases hunger. It’s important to have well-balanced meals and snacks ready, especially post-workout, to avoid overeating or making unhealthy food choices. A balanced meal should consist of complex carbs, proteins and fats to provide your body with nourishment and help you optimize and recover from your workouts. 

Remember, these changes are normal and healthy (and often temporary), so don’t let them derail your exercise routine or eating pattern. Drinking more water, increasing your salt intake and having a bigger appetite are common and other possible reasons why you may experience temporary weight gain. So if it causes you stress, ditch the scale and instead focus on how you feel and other non-scale victories like improved sleep, less stress, increased energy and better mood. Consistency and sustainability are key to achieving your long-term health goals. 

Our Expert Take

Weight gain during a new exercise or eating routine doesn’t always mean setbacks—it often reflects positive changes in body composition. Building muscle supports strength, mobility, bone health and longevity, even if the number on the scale goes up. Other short-term factors like fluid retention, higher water intake or increased appetite can also play a role. The key is to look beyond the scale and recognize that adding muscle is one of the best investments you can make for long-term health.Â