Why do you sometimes gain weight after exercising?

If you’ve ever started a particularly high-intensity exercise program with good faith and enthusiasm, only to be disappointed when the scales exceed the weight you started at, you may have asked yourself a question: Why does exercise make me gain weight? Is there a biological explanation or am I just unlucky?

The answer is many, an exercise expert told Live Science. Any post-workout weight gain is most likely the combination of several factors, but most importantly, it does not mean that you should stop exercising.

“People don’t understand that exercise is good even when you gain weight,” Corinne Caillaud, professor of physical activity and digital health at the University of Sydney, Australia, told Live Science.

Related: Why do some people never gain weight?

“While exercise does play a role in weight management, the other side of the coin is food intake,” said Caillaud. When a person notices their weight is gaining, it is worth checking the quantity and quality of the food they are consuming, she said. Your post-exercise weight gain could be explained by what and how much you eat.

“You might be thinking, ‘Well, I’ve been exercising and that’s why I can eat more,'” noted Caillaud. While there is nothing wrong with ingesting the occasional treat, exercise likely cannot offset the effect of increasing the frequency of consuming junk food.

But assuming your diet hasn’t changed, there are a few other biological quirks that could explain the weight gain. If you’re not used to a good workout and then go all out, you can end up straining your muscles more than you should. In other words, your muscle fibers suffer micro-tears, but that’s nothing to worry about because when this happens, your body sends nourishment to the muscles to repair the damage, according to University Hospitals in Cleveland, Ohio. This is why your muscles ache the next day, but over time it leads to muscle growth.

However, these microcracks can stimulate the body’s inflammatory process. “That means swelling,” said Caillaud. That swelling, in turn, can lead to extra water retention in the body, according to the Cleveland Clinic. In fact, this increased water may be another explanation for post-workout weight gain.

“But that may not really mean a significant increase in total weight since not all of the fluid comes from water retention,” said Caillaud. “Some of it simply comes from other parts of the body – for example from the plasma in the bloodstream.”

Exercise, especially weight lifting, can also help build muscle. “When someone does strengthening exercises, they can see an increase in their muscles,” said Caillaud. “But that takes pretty serious training, and it’s not going to happen in a few weeks. It takes months to increase muscle size and get to the point where you realize the change on the scale will take a year or more. “

The other possible explanation depends on the amount of blood in your body. “When you do aerobic exercise, at some point there may be an increase in blood volume, which is essentially an increase in aerobic capacity,” said Caillaud. Aerobic capacity is a measure of the maximum amount of oxygen your body can use up during exercise. Muscles need oxygen, which is supplied by the blood. The more oxygen a person can use, the better his endurance.

Neither of these components – minor dietary changes, inflammation, increased muscle mass, or increased aerobic capacity – matter individually, Caillaud said. “But when you add it all up, it can begin to explain things.”

Related: Can you “speed up” your metabolism?

The important thing is that people shouldn’t be leaving the gym too quickly if they experience weight gain. Water retention from inflammation is not permanent, and continued exercise will eventually help burn calories and therefore lead to weight loss.

All of this means, according to Caillaud, that people who have started exercising properly shouldn’t be deterred from moving on even if they gain a little, since pounds and ounces aren’t the only important metrics.

“People can increase their body weight a little after exercising because they have increased muscle weight, total blood volume, etc., but that doesn’t mean it isn’t successful,” to improve their health, she said. “It’s all [a] positive change to build healthy muscles and make them function better in terms of metabolism. “

Originally published on Live Science.