Nutrition is the science of food, the nutrients and other substances it contains, and its actions within the body (including ingestion, digestion, absorption, transport, metabolism, and excretion).

Humans primarily eat food to nourish their bodies. This food contains nutrients for the maintenance of life and the growth and repair of tissue such as skeletal muscle.

Figure 1.Different foods contains different levels of nutrients.

Macronutrientsare nutrients that the body needs in relatively large amounts (many grams daily). Nutrients that we consider macronutrients arecarbohydrate,protein, andfat.

Micronutrientsare nutrients that the body needs in relatively small amount (milligrams or micrograms daily). Nutrients that we consider micronutrients arevitaminsandminerals.

微量元素是用来构建和修复组织s and to regulate body processes, while macronutrients are converted to and used for energy.

Essential nutrientsare nutrients that a person must obtain from food because the body cannot make them by itself in sufficient quantities.

References:

• Rolfes,S. Understanding normal and clinical nutrition 8th ed. Wadsworth, Cengage Learning,