Food gives the body energy and the raw materials to build and repair tissue. Carbohydrates, proteins and fats supply energy, while vitamins, minerals and water keep the chemistry running.
Carbohydrates
Starches and sugars are broken down to glucose, the main fuel for the brain and red blood cells. Extra glucose is stored as glycogen in the liver and muscle, and the rest is turned into fat.
Proteins
Proteins are chains of amino acids used to build muscle, enzymes, antibodies and blood proteins such as albumin. The body has no real protein store, so a steady daily intake matters, especially during illness and healing.
Fats
Fats are the densest energy store and carry the fat-soluble vitamins A, D, E and K. They also form cell membranes and some hormones.
Vitamins, minerals and water
Vitamins and minerals are needed in small amounts for enzymes, bones, blood and nerves. Water is the largest part of the body and must be replaced every day.
| Nutrient | Energy per gram | Main use |
|---|---|---|
| Carbohydrate | 4 kcal | Quick fuel, stored as glycogen |
| Protein | 4 kcal | Building and repairing tissue |
| Fat | 9 kcal | Long-term energy store, cell membranes |
| Alcohol | 7 kcal | Energy with no nutritional value |
At the bedside
A nutrition assessment combines weight trend, BMI, diet history and signs of muscle loss. Unplanned weight loss of more than 5% in a month points to malnutrition.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).