Two isocaloric diets (same total calories) differ only in carbohydrate source: Diet A emphasizes refined grains and sugar-sweetened beverages; Diet B emphasizes whole grains, legumes, fruits, and vegetables. Over several months, which outcome is most likely and why?

• A. Both diets will show identical outcomes on weight and metabolic health because carbohydrate quality is irrelevant if calories are equal; only macronutrient percentages matter
• B. Diet A will necessarily produce less weight gain because refined carbohydrates are easier to store and therefore require fewer calories overall to maintain body weight
• C. Diet B is more likely to produce better weight management and improved metabolic markers because whole-food carbohydrate sources increase satiety, slow glucose absorption, provide fiber and micronutrients, and reduce likelihood of excess caloric intake over time
• D. Diet B will cause greater weight gain due to the higher fiber and bulk increasing gastric emptying rates and signaling increased appetite, which reliably leads to overeating

Answer: (C)