Define nutrient density.

Nutrient density refers to the amount of essential nutrients provided by a food relative to its calorie content. It emphasizes foods that offer a high concentration of vitamins, minerals, and other beneficial substances without an excessive amount of calories. Foods that are considered nutrient-dense typically provide more nutrients per calorie, making them healthier choices. This concept is crucial in promoting a balanced diet, as it encourages the selection of foods that contribute to overall health while avoiding those that provide empty calories, which offer little to no nutritional benefit.

In the context of the other options, while total calories are important for understanding energy content, they do not reflect the nutritional value of a food. Similarly, the variety of foods consumed provides a broader perspective on dietary patterns, but does not directly measure nutrient density. The weight of food served may relate to portion sizes but does not account for the nutrient-to-calorie ratio that defines nutrient density. Thus, option B accurately captures the essence of nutrient density by focusing on the relationship between nutrients and calories.