Dietary modulation is an essential part of weight loss and maintaining its reduction. Although simple in behavioral terms (eat less, exercise more), the tremendous difficulty of weight loss and maintenance has inspired many different diet regimens, in search of an easier, more efficient way to lose weight. Contemporary issues in this matter are the composition of diets (low fat versus low carbohydrate), the choice of carbohydrate (the glycemic index), and the role of calcium and dairy products. This article discusses the scientific evidence of the various dietary manipulations for weight loss and the challenges of maintaining a reduced obese state.