By far the most common cause of putting on too much weight is simply eating too much, or the wrong foods, and exercising too little. For most people, balancing what they eat and the amount of exercise they do can determine their weight. If you fall into this category you can lose weight by cutting down what you eat, or cutting out certain foods, or exercising more.
Carbohydrates and especially fats are the main source of energy in our diet: if we do not draw on this energy that our food has provided (due to a sedentary lifestyle), then storing it as fat deposits is the body’s only solution.
With exercise, the demand for energy increases and the stores of fat are broken down. If you also increase the amount you eat, though, the balance will remain the same and you will not lose weight, only avoid gaining it.
There are several diets that are effective for this type of weight gain, because any regime that puts restrictions on your food intake will cause you to lose weight. In fact, the weight loss is often due to a simple change in what you eat, rather than the amount. The problem with most diets that treat this kind of weight gain is that they are not complete changes in eating habits and do not provide workable plan for maintaining your new lower weight once you have achieved it. Cutting down on say, sugar or fat or alcohol and doing some exercise has a beneficial effect, but once you stop and slip back into your old ways, the weight all starts piling on again.