What does "metabolism" refer to in nutrition?

Metabolism in the context of nutrition encompasses all the chemical reactions that occur within the body to convert food into energy. This process involves breaking down the macronutrients (carbohydrates, proteins, and fats) from the food we consume into simpler forms that can be utilized by the cells for energy, growth, and repair.

Metabolism is divided into two main components: catabolism, which is the breakdown of molecules to obtain energy, and anabolism, which is the synthesis of all compounds needed by the cells. This functional aspect of metabolism is crucial as it defines how efficiently the body can use the calories from food, affecting not only energy levels but also overall health and well-being.

Other choices may relate to aspects of nutrition but do not capture the full essence of metabolism. For example, digestion refers to the mechanical and chemical breakdown of food into smaller components, while absorption deals with how nutrients pass through the intestinal wall into the bloodstream. The impact of exercise, although significant in terms of energy expenditure and metabolic rate, does not define metabolism itself. Therefore, the correct answer highlights the comprehensive role of metabolism in the conversion of food into energy essential for bodily functions.