How is a calorie restriction defined?

Calorie restriction: This usually means a restriction of the amount of foods eaten depending on its caloric content. E.G. A diet may be recommended that is a 1000 calorie per day diet, so foods are allowed up to that calorie amount each day.

Maintain nutrients: caloric restriction, or energy restriction, is a dietary regimen that reduces calorie intake without incurring malnutrition or a reduction in essential nutrients.