Nutrition encompasses the processes by which organisms obtain and use food and nutrients to sustain life, as well as the scientific study of those processes. In humans, it concerns the relationship between food, energy, growth, tissue maintenance, and health. Nutritional science also examines eating behaviours and the social conditions that shape food choices. Its scope extends from the absorption of individual nutrients to dietary patterns and population health. (medlineplus.gov)
Nutrients and their functions
The principal nutrient groups in human nutrition are carbohydrates, proteins, fats, vitamins, mineral nutrients, and water. Carbohydrates, proteins, and fats are commonly grouped as macronutrients; vitamins and minerals are micronutrients. These categories distinguish the quantities required rather than their biological importance. Food supplies both energy and materials needed for the body to function. (medlineplus.gov)
Digestible carbohydrates supply sugars, including glucose, that can be used for energy or stored for later use. Carbohydrate-containing foods include grains, fruits, vegetables, legumes, and milk. Dietary fibre comprises carbohydrate components that the body cannot fully digest. It contributes to bowel function, and different forms have different effects on digestion and blood glucose. Thus, carbohydrate content alone does not describe a food’s nutritional properties. (medlineplus.gov)
Proteins provide amino acids for making and maintaining body tissues. Essential amino acids must come from food because the body cannot produce them. Both animal and plant foods supply protein, although their amino-acid composition differs. Fats provide energy and fatty acids used in tissue development, and they assist the absorption of certain vitamins. Saturated, monounsaturated, and polyunsaturated fats differ chemically and in their physiological effects. (medlineplus.gov)
Vitamins and minerals contribute to growth and the production or functioning of enzymes, hormones, and other substances. Water intake includes both beverages and moisture in foods. Mineral electrolytes, including sodium and potassium, participate in fluid balance and normal nerve and muscle function. (who.int)
Digestion, absorption, and metabolism
Digestion combines mechanical actions with chemical breakdown. Chewing and muscular movements mix and transport food, while digestive juices and enzymes break larger components into forms that can be absorbed. Proteins yield amino acids, fats yield fatty acids and glycerol, and digestible carbohydrates yield simple sugars. The pancreas supplies digestive enzymes, while bile produced by the liver assists fat digestion. (niddk.nih.gov)
Most nutrient absorption occurs in the small intestine. Absorbed substances enter the blood or lymphatic system and are transported to tissues. The liver processes, stores, and redistributes many nutrients. The large intestine absorbs water, and intestinal bacteria help break down remaining food components and produce some vitamins. (niddk.nih.gov)
Metabolism connects nutrient use with energy production, growth, and repair. Nutritional research examines how these processes vary across the life course and how illness, medicines, inherited characteristics, and the gut microbiome influence absorption and nutrient handling. Nutritional status therefore depends not only on what is consumed but also on how the body processes it. (medlineplus.gov)
Requirements and reference values
Nutrient requirements differ with age, sex, growth, and physiological circumstances. Energy needs also vary with physical activity. Reference values describe requirements for defined population groups; they are not exact measurements of every individual’s needs. (ods.od.nih.gov)
In the United States and Canada, Dietary Reference Intakes provide a framework for assessing and planning the nutrient intakes of healthy people. The Estimated Average Requirement meets the estimated needs of half a specified group. The Recommended Dietary Allowance covers nearly all healthy individuals in that group. An Adequate Intake is established when evidence is insufficient to calculate an allowance, while a Tolerable Upper Intake Level identifies an intake unlikely to cause adverse effects. (ods.od.nih.gov)
Daily Values on United States food labels serve a different purpose: they provide standardized benchmarks for comparing nutrient quantities in a serving. A label’s percentage Daily Value is consequently not an individualized estimate of nutritional need. (ods.od.nih.gov)
Malnutrition and dietary patterns
Malnutrition includes deficiencies, excesses, and imbalances of energy or nutrients. It encompasses undernutrition, micronutrient deficiencies or excesses, overweight, obesity, and associated diet-related conditions. In children, wasting denotes low weight relative to height, stunting denotes low height relative to age, and underweight denotes low weight relative to age. These indicators describe different aspects of nutritional status. (who.int)
Nutrition is also studied through whole dietary patterns rather than isolated nutrients. The World Health Organization characterizes healthy diets through adequacy, balance, moderation, and diversity, together with food safety. Their specific composition varies with individual characteristics, cultural practices, and locally available foods. Dietary patterns are relevant to both malnutrition and the risk of noncommunicable diseases. (who.int)
Population nutrition and research
Population nutrition is an area of public health concerned with food access, dietary intake, and nutritional outcomes across communities. Poverty, food prices, availability, and marketing can influence which foods people consume. Undernutrition and overweight may coexist within the same country or community, so population assessment cannot be reduced to food quantity alone. (who.int)
Nutrition policy includes food fortification, nutrition labelling, school food standards, and the monitoring of dietary intake. Research addresses nutrient requirements, absorption, energy regulation, and relationships between diet and disease. It also investigates how biological variation and the food environment interact, linking the study of individual physiology with the conditions under which populations obtain and consume food. (who.int)