You are determined to make healthier choices so you begin an intense new workout routine. You are tired and achy, but decide to persevere so that you can lose weight and feel better. After several days of hard physical exertion, you step on the scale and can hardly wait to see the smaller numbers. The scale is not broken and you are reading the numbers correctly. You have gained weight.
Theory No. 1
If you ask your aerobics instructor what is happening, she may very well tell you that you are transforming your fat into muscle. Mike Boggs, certified strength-conditioning specialist, explains that this is close, but inaccurate. When your body becomes more fit, your fat cells shrink and your muscle cells expand. Because muscle weighs more than fat, this explains a slight weight gain after recently beginning a new exercise program.
Theory No. 2
Keri Glassman, nutritionist and author of "The O2 Diet," says exercise might cause weight gain for three reasons. First and foremost, exercise increases your hunger, causing you to eat more. Second, when you exercise, you have feelings of entitlement. You might feel as though you have earned an extra treat. And third, exercise usually does not burn as many calories as you think. These three factors combine when you begin a rigorous exercise plan, and it results in weight gain.
Theory No. 3
"Time" magazine's article, "Why Exercise Won't Make You Thin," suggests that many of conceptions of weight loss resulting from exercise are incorrect. A study done by the Public Library of Science actually showed that women who exercised for six months lost the same amount of weight as women in a control group who did not exercise at all. It appeared that their weight loss was more a result of writing down everything they ate for test purposes than from exercising.
Theory No. 4
Exercising causes you to sweat, and if you don't replenish the missing fluids fast enough, you may experience dehydration. Dehydration causes your body to hold on to its water and might result in a slight weight gain. Harvard Health suggests drinking up to three cups of water an hour, and even more if you're sweating excessively from your workout.