That the composition of a diet can affect the way in which calories are expended is a fascinating concept. Hill and colleagues [1] state that the impact of diet composition on the thermic effect of food is not significant. They base part of their argument on what appears to be a miscalculation. Table 1 and the text state that the total thermic effect of food is 230 kcal for a person on a low-fat diet who consumes 2500 kcal/d. The total is, in fact, 310 if the numbers for the individual components are correct: carbohydrate (120), fat (90), and protein (100). This new total is significantly higher than the total for a person on a high-fat diet consuming the same number of calories; the difference is 110 kcal/d, not 30 as stated in the article. Over the course of a month, this difference would amount to 3300 kcal and could produce a weight loss of almost 1 pound (approximately 3500 kcal/lb of body fat). Many people who are trying to lose or maintain their weight do so by combining exercise with a low-fat diet. Daily aerobic exercise allows a person to intake more calories without gaining weight. The error in the article trivializes the significant caloric expenditure (through the thermic effect of food) that can be achieved by those who eat more calories but less fat than their nonexercising neighbors.