Why You May Be Gaining Weight After Working Out

It is more common than you think

Have you noticed that you're gaining weight after working out? If weight loss is your goal, seeing an increase on the scale when you've been making an effort to exercise can be frustrating. But there are several research-backed reasons why you might notice a slight weight gain after exercise. Possible explanations include muscle weight gain, water retention, post-workout inflammation, supplement use, or even undigested food.

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Muscle Weight Gain

It is likely that you will gain muscle when you start working out. How much muscle you gain depends on your diet and the type of workouts you do. But any increase in physical activity is likely to produce at least some improvements in strength and muscle mass, especially if you were mostly sedentary prior to the start of your program. If you are participating in strength training workouts and you're consuming adequate protein, you're likely to see greater increases in muscle mass.

Genetics also play a role in the amount of muscle mass you gain when starting an exercise program. Some people put on muscle more easily than others. If you tend to gain muscle easily, consider yourself lucky. Muscles help to shape a strong, healthy body.

But when you gain muscle, the number on the scale is likely to increase. In fact, even if you're also losing fat, you may see an increase on the scale. Muscle is more dense than fat, but it takes up less space. That means if you gain muscle, your scale weight may go up even as you're losing body fat.

If you've been working out regularly, it's possible for you to lose inches even if you're not losing weight. A higher number on the scale could mean that you are losing fat while gaining muscle—a positive trend that leads to a leaner, stronger body.

Water Weight Gain

Water retention is a common cause of temporary weight gain. Pre-menopausal women are especially prone to body-weight fluctuations throughout the month due to hormonal changes.

Women are likely to notice some degree of bloating immediately before and during their menstrual period. Exercise can help to reduce symptoms of PMS—so it's helpful to keep up with your workouts, though you may still see an increase on the scale.

Studies have shown that fluid retention peaks on the first day of menstrual flow. It is lowest during the mid-follicular period (the middle phase of your cycle) and then gradually increases over the 11 days surrounding ovulation. The degree to which you see an increase on the scale varies from person to person, but at least a slight increase in weight—even after exercise—is normal.

Another common reason for water weight gain is an increase in your sodium intake. According to research, consuming high salt foods ​can cause an increase in body weight. Studies have shown that after we eat salty foods, we increase our water intake but we do not necessarily produce more urine. The extra fluid in your body adds up to pounds on the scale. Some people are very sodium-sensitive and may retain more water.

Keep in mind that even if you aren't adding salt to your food, it may still be lurking in the processed foods and beverages that you consume. Even some healthy, nutrient-rich foods like soup, cottage cheese, and canned beans may contain excess sodium.

Post-Workout Inflammation

It's possible that your workout itself is causing weight gain—at least temporarily. But this increase may be an indicator that you are exercising hard enough to see real results.

Very simply put, exercise (especially weight training) damages muscle tissue. The repair process that occurs after exercise allows your muscles to grow and get stronger. But in the meantime, inflammation occurs in the tissues. Exercise physiologists call this exercise-induced muscle damage (EIMD).

EIMD is a temporary phenomenon that occurs after new or exceptionally challenging exercise patterns. It causes structural damage to myofibers (cells in muscle tissue); inflammation results due to a build-up of white blood cells in the damaged tissues. This inflammation and build-up of fluid may show up as temporary weight gain after a workout.

How do you know if your body is experiencing EIMD? You may feel delayed-onset muscle soreness, also called DOMS. You're likely to feel increased soreness the day after or even two days after your workout as a result of the inflammation and repair that is happening in the body.

Supplement Use

Post-workout nutrition or supplement use may also cause a certain degree of weight gain after working out.

Exercise—particularly prolonged endurance exercise like running or cycling—depletes the body of glycogen. It's very common for trained athletes to consume supplement beverages after exercise that contain carbohydrates. Carbs help to restore muscle glycogen. But for each gram of glycogen stored, the body retains three grams of water. The result? An increase in stored water and possible water weight gain following your workout.

Of course, this post-workout effect doesn't just apply to carbohydrate supplementation. Even carbs that you consume in meals and snacks following your workout will be stored as glycogen with water. This is a normal and healthy process of recovery—so it is not something you should try to avoid.

Other supplements can also cause post-workout weight gain. Creatine, a supplement used by many avid exercisers, may cause weight gain through an increase in muscle mass or fluid retention. Creatine has been studied extensively throughout the years. Evidence has been mixed regarding its effectiveness, but some early studies indicated that creatine supplementation can increase body mass and total body weight. Research scientists surmised that these increases were due to an increase in water retention.

More recent studies have investigated creatine's potential to increase muscular strength and muscle mass, with some evidence showing that it may provide a benefit. However, the mechanism by which it provides this benefit is not fully understood.

Undigested, Fiber-Rich Food

If your workouts make you hungry and you are refueling with healthy fiber-rich foods, the nutritious food you consume may lead to an increase in the scale as it works its way through your body.

Fiber is said to aid in water retention in the colon and results in stools that are less dry and easier to evacuate. Insoluble fiber, in particular, is known to increase stool weight. Before the stool is passed, you might notice an increase in weight after your workout, but fiber also decreases colonic transit time, so this is not a nutrient you should avoid.

So how much of a difference can it make? In one research study, investigators found that you might produce 125 to 170 grams of stool per day—or about a half-pound. However, other studies report average daily stool weight to be roughly 106 grams per day—less than a quarter-pound. Still, other sources report that your body may produce up to one ounce per day for every 12 pounds of body weight.

Should You Worry About Post-Workout Weight Gain?

In many cases, there is no reason to worry about an increase in weight after exercise. In fact, if the weight gain is the result of one of the common causes listed above, you should take it as a sign of success.

Of course, there are other reasons that you may see an increase on the scale. Some medications may cause weight gain or your calorie intake may have increased along with your hunger levels after exercise. It may be helpful to use methods other than the scale to measure your workout progress to figure out if changes if warranted.

Most basic bodyweight scales can't tell you if your weight gain is due to an increase in fat, muscle mass, or water retention. To measure actual fat loss, you can use a body fat scale or take measurements at different areas of the body on a regular basis. (If you're losing inches, you're likely on the right track.)

But there are also benefits to not focusing entirely on the numbers when measuring your progress toward your weight loss goals. How you feel mentally and physically, how your clothes fit your changing body, and your overall strength and health are all important parts of the process, too.

A Word From Verywell

Exercise provides countless physical and mental benefits. If you've started a workout program and you're sticking to it, you're likely to experience an increase in energy, a greater ability to move through activities of daily living with ease, and improved fitness levels. You're also likely to gain a boost in pride and confidence. These are real benefits that should take priority over the numbers on the scale.

If you've measured yourself in different ways and realized you really are going in the wrong direction, you can work with a qualified trainer, registered dietitian, or talk to your healthcare provider to see if there are other reasons for weight gain after your workouts. But in many cases, it's simply a sign that you're doing things right.

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