Figure 3. The daily energy and nutrient balance of a 70-kg man (20% body fat) in relationship to macronutrient energy stores, intake and oxidation. Each macronutrient intake and oxidation on a 2,500 kcal/day standard American diet (composition 40% fat, 40% carbohydrate, 20% protein) is shown on the left as absolute intake in kilocalories and on the right as a percentage of its respective nutrient store. Because carbohydrate and protein intake and oxidation rates are tightly regulated on a daily basis any inherent differences between energy intake and energy expenditure therefore predominantly impact body fat stores. During overfeeding (shown in red) the oxidation of carbohydrate and protein is increased to compensate for the increased intake at the expense of fat intake yet the increase in oxidation is not equally coupled with intake. Thus, if sustained fat kilocalories are stored, fat stores expand and body weight is gained.