Nutrient
Overview
A nutrient (營養素, nutrient) is a chemical substance that an organism must obtain from outside to grow and maintain life activities. Carbohydrates, proteins, and lipids are macronutrients that supply energy, while vitamins, minerals, and water are needed only in small amounts but play decisive roles in metabolic regulation and maintaining body composition. How much of which nutrient and in what proportion is consumed is treated as a key variable determining health status and risk of chronic disease.
Main Content
Definition and Classification
Nutrients are divided into essential nutrients, which are not synthesized sufficiently in the body and must be supplied through food, and nonessential nutrients, which can be synthesized conditionally. Based on intake, they are divided into macronutrients, needed in tens of grams or more per day, and micronutrients, needed in milligram or microgram units. By function, they are generally organized into three categories: energy sources, materials for body composition, and substances that regulate physiological functions.
Macronutrients
Carbohydrates are the main energy source, providing about 4 kcal per gram, and are classified into monosaccharides (glucose, fructose), disaccharides (sucrose, lactose), and polysaccharides (starch, cellulose). Indigestible dietary fiber becomes food for gut microorganisms, slowing the rise in blood sugar and helping cholesterol excretion.
Proteins are composed of 20 amino acids, 9 of which are essential amino acids that are difficult for the body to synthesize. They provide about 4 kcal per gram, but their main role is to serve as materials for muscles, organs, enzymes, hormones, and antibodies. Protein quality is evaluated using indicators such as DIAAS, which reflect digestibility, absorption rate, and amino acid composition; combining animal and plant sources can balance amino acids.
Lipids provide about 9 kcal per gram, the highest energy density. They are components of cell membranes and are necessary for absorption of fat-soluble vitamins and synthesis of steroid hormones. Linoleic acid and alpha-linolenic acid are essential fatty acids that cannot be synthesized in the body. The ratio of saturated, unsaturated, and trans fats is directly linked to cardiovascular health.
Water is a solvent making up about 60% of body weight, and is responsible for transporting nutrients, regulating body temperature, and excreting waste. It is recommended to consume at least 1.5–2 L of water per day, including water from beverages, food, and metabolic processes.
Micronutrients
Vitamins are organic compounds that act as coenzymes in metabolic reactions in the body. Water-soluble B vitamins and vitamin C are excreted in urine when in excess, but fat-soluble A, D, E, and K accumulate in the body and can be toxic when overconsumed. Vitamin D is synthesized in the skin from sunlight and is involved in calcium absorption and immune function.
Minerals are divided into major minerals such as calcium, phosphorus, potassium, sodium, and magnesium, and trace minerals such as iron, zinc, copper, iodine, and selenium. They are broadly involved in bone composition, acid-base balance, nerve transmission, enzyme activity, and oxygen transport.
Digestion and Absorption
Nutrients are mechanically and chemically broken down in the mouth and stomach, then mainly absorbed in the small intestine. At the villi surface of the small intestinal mucosa, monosaccharides and amino acids enter the liver through the portal vein, while lipids enter the circulatory system via lymphatic vessels. Absorption efficiency varies depending on the processed form of the food, cooking method, other nutrients consumed at the same time, and the individual's gut environment.
Intake Standards and Assessment
Each country establishes intake standards for each nutrient, consisting of average requirement, recommended intake, adequate intake, upper intake level, and acceptable macronutrient distribution range. The Dietary Reference Intakes for Koreans (KDRIs) present these by age, sex, and life cycle. Actual intake is assessed using the Daily Value on food labels and dietary intake surveys.
Deficiency and Excess
Deficiencies appear as iron deficiency anemia, vitamin D deficiency, thyroid disease due to iodine deficiency, night blindness due to vitamin A deficiency, and so on. Conversely, excessive sodium intake can cause hypertension, and excessive fat-soluble vitamins can cause liver damage or kidney stones, so balance is important.
Recent Trends
In 2024–2025, nutrition science is rapidly moving toward personalized nutrition. As genomic and metabolomic data and continuous glucose monitoring (CGM) confirmed that blood glucose responses to the same food differ from person to person, precision nutrition services and AI-based diet recommendations spread.
Gut microbiome research is accumulating evidence that dietary fiber and fermented foods are linked to immune and mental health. As large cohort studies on the association between ultra-processed food (UPF) consumption and risk of metabolic and mental disorders follow one after another, discussions have gained strength to use the degree of processing itself as a nutrition assessment indicator. The spread of GLP-1 obesity treatments has created a new nutrition task: combining protein and resistance exercise to prevent muscle loss.
The claim that protein intake higher than existing recommendations is needed to prevent sarcopenia in older adults has spread, and the alternative protein market for plant-based protein, cultured meat, and insect protein has grown. The impact of climate change on crop nutritional value, debate over the effectiveness of vitamin D supplementation, and research on the long-term effects of Mediterranean and plant-based diets remain major issues.
Related Topics
- [[Nutrition]]
- [[Protein]]
- [[Vitamin]]
- [[Dietary mineral]]
- [[Gut microbiota]]
- [[Metabolic syndrome]]
- [[Food safety]]