Final answer:
Calorie restriction is a reduction in calorie intake below daily needs. Obese people might not lose weight even when reducing food intake. Correct option is A.
Step-by-step explanation:
Calorie restriction is known as a reduction in calorie intake below daily needs. It refers to eating a low-calorie diet while still maintaining proper nutrient intake. When the body perceives a decrease in calorie intake, it responds by becoming more efficient, making it difficult for obese people to lose weight even when cutting back on food.