ESSENTIAL NUTRIENTS AND THEIR ROLE IN HUMAN HEALTH

By Constantine A. Dimopoulos Professor Emeritus of Biochemistry and Food Chemistry / Department of Chemistry, National and Kapodistrian University of Athens (NKUA)

Both practical experience and scientific data continuously confirm that nutrition is directly or indirectly linked to the onset and progression of various diseases.

To sustain life, our bodies require specific substances known as nutrients. For humans, there are approximately 40 essential chemical compounds (nutrients), categorized into the following classes: Proteins, Carbohydrates, Lipids, Minerals, Vitamins, and Water. While a human can survive without food for a month and without water for a few days, survival without oxygen lasts only minutes. However, oxygen is not traditionally classified as a nutrient because it is supplied through the lungs rather than the digestive system.

Nutrients are found in food, but no single food contains all essential nutrients in the necessary quantities (with the exception of milk for a specific period of life). The combination of various foods constitutes our diet.

1. Proteins (Albuminoids)

The term "protein" derives from the Greek word proteuo (to hold first place), signifying their primary importance for life. Proteins make up 85% of the body's non-water components. They are indispensable for all biological processes, including reproduction, nutrition, growth, and movement.

• Function: They replenish body tissues and synthesize enzymes and hormones. Excess protein is metabolized for energy (4 calories/g).

• Biological Value: Proteins are made of amino acids. Complete proteins contain all essential amino acids. For instance, cheese has a higher biological value (75) than bread (50). Combining foods can improve this; for example, a mix of bread and cheese enhances overall protein quality because the lysine in cheese compensates for the deficiency in bread.

2. Carbohydrates

Composed of sugar molecules, carbohydrates are classified into monosaccharides (glucose, fructose), disaccharides (sucrose, lactose), and polysaccharides (starch, glycogen, cellulose).

• Function: They are the primary energy source for the Central Nervous System. Energy is stored as glycogen in humans and starch in plants.

• Fiber: Although humans cannot digest cellulose (fiber), it is essential for regulating digestion.

3. Lipids (Fats)

Lipids include triglycerides (energy storage) and phospholipids (cell membrane components).

• Function: They provide concentrated energy (9 calories/g) and act as a protective cushion for organs. They carry fat-soluble vitamins and essential fatty acids while regulating biochemical signaling.

4. Vitamins

Vitamins cannot be synthesized by the body and do not provide energy. Instead, they act as coenzymes, facilitating almost all chemical reactions in the body.

• Water-soluble (C, B-complex, Biotin): Easily absorbed and stored in small amounts.

• Fat-soluble (A, D, E, K): Require dietary fat and bile for absorption and are stored primarily in the liver and adipose tissue.

• Note: While vitamin deficiency leads to disease (avitaminosis), excessive intake can result in toxicity (hypervitaminosis).

5. Minerals

• Macrominerals (Ca, P, Mg, Na, K, S, Cl): Required in larger quantities for bone structure and fluid balance.

• Trace Elements (Fe, Cu, Zn, I, Se, etc.): Needed in minute amounts for specialized roles, such as oxygen transport (iron) or thyroid function (iodine).

6. Water

Water constitutes approximately 50% of the human body. It serves as the universal solvent and transport medium for nutrients and waste. It is vital for digestion and temperature regulation. As a rule of thumb, every calorie of nutrient processed requires approximately 1g of water.