Nutrition Fundamentals: Nutrients and Their Roles
Diet and Nutrition
Nutrition
Concept: Nutrition is the science of food, nutrients, and their actions, interactions, and balance for health and disease. It also deals with the social, economic, cultural, and psychological aspects of food. It can be defined as an involuntary process that begins after food ingestion, providing energy, building and repairing body structures, and regulating metabolic processes.
Food: Food is the set of actions that provide the body with the raw materials necessary for life maintenance. It is a voluntary, conscious, and educable process, influenced by cultural habits and economic factors.
Factors in Food and Nutrition:
- Improving living standards, which encourages overeating.
- Transportation development facilitates food distribution.
- Development of conservation techniques.
- Proliferation of synthetic and refined foods, potentially harmful to health, reducing natural food consumption (e.g., constipation, intestinal diverticula).
- Advertising can cause consumer confusion and indiscriminate spending.
- Decline of traditional food habits considered outdated, despite their nutritional value.
- Sedentary lifestyles change nutritional needs; less food is required, but people often eat as if physically active.
Food Definition: Food is any substance taken from the environment by living organisms to synthesize new living matter, as an energy source, or to provide factors regulating life processes. Food should provide two types of nutrients:
- Those the body cannot synthesize.
- Those the body can synthesize.
The most common nutrients for most living things are water, carbohydrates, lipids, proteins, vitamins, and certain minerals.
Nutrients: Nutrients are the nourishing substances in food. There are two types:
- Organic or Bio: Found only in living things.
- Inorganic: Water, minerals, and other elements necessary for metabolic reactions, found in the surrounding physical environment.
Carbohydrates
Carbohydrates are organic compounds consisting of carbon, oxygen, and hydrogen. They play a crucial role in nutrition and are known as sugars due to their sweet taste. Most of the energy needed for movement, work, and life comes from carbohydrates. In Western countries, they constitute 50% of total energy requirements. They are easily digested, cheaper, and readily available fuel. While survival is possible on a diet of meat and fat with minimal carbohydrates, a daily intake of 100 grams is recommended.
They are classified into:
Usable Carbohydrates:
These can be used and metabolized by the body. They are divided into:
- Monosaccharides: Generally clear, colorless, sweet-tasting solids, soluble in water. The most important are:
- Glucose: The carbohydrate into which all others are transformed for body use.
- Fructose: Found in fruits, honey, and vegetables.
- Galactose: Usually occurs in food.
- Disaccharides: Composed of two monosaccharide units. The most abundant in foods are:
- Sucrose: Formed by a glucose molecule and a fructose molecule. Found in fruits and vegetables, but the largest contribution comes from table sugar and sweets.
- Maltose: Formed by two glucose molecules. It does not exist freely in nature and is produced by starch hydrolysis. Found in oil, starches, and beer.
- Lactose: Formed by a glucose molecule and a galactose molecule. It is the disaccharide found in milk.
- Polysaccharides: Composed of many monosaccharide molecules. The most notable is starch, found in cereals, legumes, and tubers.
Unusable Carbohydrates:
These are polysaccharides that form part of plant cell walls and are not usable by the human body.
Cellulose is not digested and is eliminated through feces. It aids stool formation and speeds up peristaltic movements.
Functions of Carbohydrates:
- Energy: Provide immediate energy for the body; they are the major fuel for cellular respiration.
- Structural: Part of the composition of nucleic acids (DNA and RNA) and cell membranes.
- Reserve: Glycogen stores a large amount of glucose molecules, which can be released when needed.
Daily Needs:
The minimum daily intake should be about 80-100 grams, with 50-60% of dietary calories coming from carbohydrates.
Lipids
Lipids are insoluble in water but dissolve well in organic solvents (ether, alcohol, etc.). They consist of carbon, oxygen, and hydrogen, forming molecules called fatty acids. Lipids are the body’s most important energy reserve, provide insulation against heat loss, and offer protection and support to viscera.
They are classified by molecular architecture into:
- Complex Lipids: Molecules include fatty acids, phosphoglycerides, sphingolipids, and waxes.
- Simple Lipids: Steroids and prostaglandins.
- Fatty Acids: Can be saturated (beef, lamb, milk) or essential unsaturated (e.g., linoleic acid, involved in skin growth).
They are categorized by their state of aggregation:
- Fat: Solid at room temperature.
- Oil: Liquid at room temperature.
Proteins
Proteins are macromolecules composed of carbon, oxygen, hydrogen, and nitrogen. They are grouped into units called amino acids. Molecules composed of two amino acids are called dipeptides, those with three are tripeptides, and longer chains are polypeptides.
Proteins are necessary for the body to produce its own substances. Essential amino acids are vital because the body cannot synthesize them.
Essential amino acids include isoleucine, leucine, lysine, methionine, phenylalanine, tryptophan, arginine, and histidine.
Proteins are classified by source into animal proteins (meat, milk, fish, eggs) and vegetable proteins (pulses, potatoes, fruits, vegetables).
Properties:
- Specificity: Each living organism has unique protein sets.
- Denaturation: Loss of protein structure due to agents like heat.
Functions:
- Structural: Basic elements of cell and organism architecture (cell membrane, mitochondria).
- Energy: Provide the same calories as carbohydrates but are used as fuel only after lipid and carbohydrate reserves are depleted.
- Enzymatic: Most chemical reactions in the body are facilitated by enzymes, which are protein substances.
- Transportation: Many substances in the blood bind to proteins for transport.
- Reserve: Some proteins, like casein in milk, are a source of amino acids and phosphoric acid for newborns.
- Hormonal: Insulin and glucagon have hormonal functions.
- Cell Recognition: Cell membrane glycoproteins allow cells to identify others of the same body or detect abnormal or foreign cells.
- Defensive: Immunoglobulins are proteins that target and facilitate the destruction of foreign cells.
Protein Requirements:
About 10-20% of dietary calories should come from protein.
- Male: 56 grams/day.
- Female: 44 grams/day.
These requirements may increase during pregnancy, adolescence, etc.