Exercise is key to lose excess fat. Without it, even with proper eating, you may lose muscle, and lower your metabolism in the process. By exercising, you build muscle mass, which increases your metabolism. It is true muscles may weigh more than fat, but in comparison on the exterior of an individuals body, it looks slimmer, while having the same “weight” of fat will look bulkier, heavier. This doesn’t mean healthy eating isn’t important. Healthy eating in conjunction with exercise will give you very satisfying results.
Also, it’s not always true when they say that if you lose weight too fast, it will come right back on just as quick. As long as you continue a healthy lifestyle, you have nothing to worry about. I lost all the “baby” weight and some around 3-5 months postpartum. I’m even smaller now than I was before getting pregnant. It has been over 2 years and I have not gained any of the weight back.