Final answer:
The preferred unit in metabolic studies and nutrition labels is the kilocalorie (kcal), which is a unit of measurement representing the energy content of food.
Step-by-step explanation:
The preferred unit in metabolic studies and nutrition labels is the kilocalorie (kcal). It is a unit of measurement used to represent the amount of energy provided by different foods. The kilocalorie, commonly known as the Calorie (spelled with a capital C), is equal to 1000 calories (1 kcal), and it is used to describe the energy content of food on nutrition labels.