Do they have proof that their program works, not just praise given by other people?
Keep in mind that quick weight loss methods that rely on diet aids (like drinks, prepackaged foods, or diet pills) will not keep weight off in the long run. The best way to lose weight is slowly, with a healthy diet and exercise. The good eating and exercise habits you develop by losing weight this way will last a lifetime, helping you to control your weight and be healthy.
