I just started exercising to lose weight, but I have gained weight instead! Why?

Sometimes people can gain weight or not lose any weight when they first start an exercise routine. It is not uncommon for the first 4-6 weeks.  Why?  The extra weight is usually water because your body starts storing more fuel in the muscle cells so that it can be utilized during your workouts. The process of converting glucose(carbohydrates) into fuel that your muscles actually store and use(glycogen) requires three molecules of water for every molecule of glucose.  As your muscles are building up glycogen stores, your body has to retain extra water for this purpose.  That is what causes most of the initial weight gain or lack of weight loss. 

The extra water retention will stop once your body has adjusted to its new activity level.  At that point, you will start noticing the scale moving down.

The best advice is to stick with your exercise routine because every time you stop and restart exercising, (meaning you work out a few weeks consistently, then quit exercising-then start exercising again a few months later)you make it harder and harder for your body to respond to exercise in the form of weight loss. So every time you start back exercising, your body will not respond as well as it did previously.