Markets and Markets says the business is made up of three major parts. They are weight loss services; physical fitness and surgical equipment; and diets, including foods and drinks. There is a seemingly endless supply of ideas about how to lose weight. There are low-carbohydrate diets and low-fat diets, diets that limit calories and ones that let you eat as much as you want. And, there are thousands of different kinds of diet pills and programs.

So where does one begin? Which one is best? Experts say there is no single diet plan that works best for everyone. Many experts agree on one thing: that to lose weight, you must use or burn off more calories than you take in. When you eat more calories than your body needs, it stores that extra energy as fat.

Calories are a measure of energy in food. A pound of fat is equal to 453 grams or about 3,500 calories. To lose that fat in a week, you have to burn off at least that amount in calories or eat that much less. The best thing to do is to combine both ideas. Eat fewer calories and increase physical activity so that you burn off more.

America’s National Institutes of Health says eating plans that contain 1,000 to 1,200 calories each day will help most women lose weight safely. It says eating plans that contain 1,200 to 1,600 calories each day are right for men seeking to lose weight. Those calorie levels may also be right for women who weigh 75 kilograms or more or who often exercise.