The Essential Nutrients: Water, Macros, and BMI

Food and Nutrition Fundamentals

Key Definitions

Nutrition

The study of nutrients in food, how the body uses them, and the relationship between diet, health, and disease. It involves taking in matter and energy to grow, survive, and reproduce; waste matter and waste energy are produced as by-products.

Food

Any solid or liquid substance consumed to provide nutritional support for an organism.

Nutrients

Compounds in foods essential to life and health, providing us with energy, the building blocks for repair and growth, and substances necessary to regulate chemical processes.

Types of Nutrients

Nutrients are classified into two main groups:

• Inorganic compounds: Water and mineral salts.
• Organic compounds: Carbohydrates, Fats (Lipids), Proteins, and Vitamins.

Water

In most organisms, almost 80% of the body is made up of water. Human beings hold about 65% of water relative to their total weight. Remember that the cytoplasm is a solution of many different substances in water.

Functions of Water

1. Metabolic reactions: Chemical reactions inside every living organism can only take place in water.
2. Solvent: Water is an important solvent.
3. Transport: Plasma, the liquid part of blood, contains a lot of water, and dissolved substances are transported around the body.
4. Temperature Regulation: Water regulates body temperature.
5. Waste Removal: Water is needed to get rid of waste products (urine).

Minerals (Inorganic Substances)

Minerals are inorganic substances needed in small amounts in the diet.

Essential Minerals and Their Roles

• Calcium:
  • Needed for: Bones and teeth structure; blood clotting.
  • Deficiency disease: Brittle bones and teeth, poor blood clotting.
  • Food sources: Dairy products, bread.
• Iron:
  • Needed for: Making haemoglobin (the red pigment in blood which carries oxygen).
  • Deficiency disease: Anaemia (tissues do not get enough oxygen delivered to them from red blood cells).
  • Food sources: Liver, red meat, egg yolk, dark green vegetables.

Carbohydrates (Glucids)

These molecules are made of long chains of smaller molecules or building blocks: glucose.

Types of Carbohydrates

1. Simple Carbohydrates (Sugars): They are soluble in water and taste sweet. They are also called sugars.
   • Monosaccharides: E.g., glucose and fructose.
   • Disaccharides: Two simple sugar molecules join together. E.g., sucrose, maltose, and lactose.
2. Complex Carbohydrates (Polysaccharides): Many sugars join together.
   • E.g., Starch and cellulose (plant cell walls). Animal cells often contain glycogen.

Functions of Carbohydrates

• Energy: Carbohydrates are primarily needed for energy.
• Structural purpose: Cell membranes contain carbohydrates.
• Dietary Fiber: Cellulose fibers are very strong, so the cell wall helps to maintain the shape of the plant cell. Fibers help human beings avoid constipation.

Fats (Lipids)

They are also known as lipids. They are insoluble in water. Fats that are liquid at room temperature are called oils. These molecules are made of long chains of smaller molecules or building blocks: fatty acids and glycerol.

Types of Fats

• Saturated fat: Found predominantly in foods from animals.
• Unsaturated fat: Found predominantly in foods from plants.

Functions of Fats

1. Energy Release: They can be used in a cell to release energy. Most cells use carbohydrates first when they need energy, and only use fats when all the available carbohydrates have been used. Adipose tissue stores drops of fat.
2. Insulation: They help to keep heat inside the body.
3. Hormone/Vitamin Production: Some vitamins and hormones are made of lipids.
4. Structural purpose: Cell membranes comprise lipids.

Proteins

These molecules are made of long chains of smaller molecules or building blocks: Amino acids. There are about 20 different kinds of amino acids. Any of these can be joined together in any order.

Functions of Proteins

1. Growth and Repair: Making new cells, which are needed for growing and for repairing damaged parts of the body.
2. Structural purpose: Cell membrane and cytoplasm contain a lot of protein.
3. Immunity: They are also needed to make antibodies. These help to kill bacteria and viruses inside the body.
4. Catalysis: Enzymes are also proteins.

Vitamins

Vitamins are organic compounds that people need in small quantities. Most vitamins need to come from food because the body either does not produce them or produces very little.

Classification of Vitamins

Fat-soluble vitamins (A, D, E, K)

The body stores fat-soluble vitamins in fatty tissue and the liver. Reserves of these vitamins can stay in the body for days and sometimes months. The body absorbs them through the intestinal tract.

Water-soluble vitamins (C and all B vitamins)

They do not stay in the body for long and cannot be stored; they leave the body via the urine. Because of this, people need a more regular supply of water-soluble vitamins than fat-soluble ones.

Body Mass Index (BMI)

Body Mass Index (BMI) is a person’s weight in kilograms divided by the square of height in meters. A high BMI can indicate high body fatness.