Which of the following best defines nutrition?

The correct answer, which defines nutrition, is that it is the study of food and nourishment. This definition encapsulates the broader scientific field that examines how food and its constituents affect health, growth, development, and overall well-being. Nutrition encompasses various aspects including dietary choices, nutrient composition, and how the body uses food for energy and cellular function.

The other options focus on narrower aspects related to food but do not capture the comprehensive nature of nutrition. Cooking food describes a method of preparing meals rather than analyzing food's role and impact on health. A meal preparation technique is a practical skill associated with food but does not relate to the scientific study of food's effects. Dietary restrictions pertain to limitations on certain food types or ingredients for health or ethical reasons, which is only a small part of the overall study of nutrition. Thus, B is the most accurate and encompassing definition.