Lactic acid does not cause weight gain. Lactic acid buildup is caused by excessive exercise, which results in the production of a large amount of lactic acid, which cannot be completely metabolized by the body and accumulates in the body, resulting in symptoms such as muscle aches and stiffness in the limbs, which can be relieved after resting for the most part. The accumulation of lactic acid does not cause weight gain, weight gain and eating too much high-calorie food, too little exercise and other reasons. If weight gain occurs after excessive exercise and lactic acid buildup, it may be due to drinking or eating too much water or urinating too little after exercise, and is not directly related to lactic acid buildup.