The body needs three main nutrients to function properly—carbohydrate,
protein, and fat. These nutrients are digested into
simpler compounds. Breads, grains, vegetables, and sugary foods are
carbohydrate that is converted to glucose, one of many types of sugar molecules
produced when carbohydrate is digested in the stomach and intestines.
Similarly, the body breaks down protein into
amino acids and fat into fatty acids, all to store
energy for the body.
Nutrients needed by the body and what they are used for Type of nutrient | Where it is found | How it is used |
| Carbohydrate (starches and sugars) | - Breads
- Grains
- Vegetables
- Foods
with sugar
| Broken down into glucose, used to supply energy to
cells |
| Protein | | Broken down into amino acids, used to build muscle and to
manufacture other proteins that are essential for the body to function
|
| Fat | - Oils
- Butter
- Egg
yolks
- Animal products
| Broken down into fatty acids, used to manufacture cell
linings and
hormones and to serve as food stores for future
needs |
After a meal, the blood sugar (glucose) level rises as carbohydrate
is digested. This stimulates the beta cells of the
pancreas to release
insulin into the bloodstream. Insulin helps glucose
enter the body's cells to be used for energy. If all the glucose is not needed
for energy, some of it is stored in fat cells and in the
liver as glycogen. As sugar moves from the blood to
the cells, the blood glucose level returns to a normal between-meal
range.
Several hormones and processes help regulate the blood sugar level
and keep it tightly within a safe range (80 mg/dL to 120 mg/dL). When the blood
sugar level falls below the desirable range, which may happen between meals,
the body has at least three ways of responding:
- Cells in the pancreas release
glucagon, a hormone that stimulates the body to
produce glucose from glycogen in the muscles and liver and release it into the
blood.
- Once glycogen is used up, muscle protein itself is broken
down. The liver uses the resulting
amino acids to create glucose through a series of
biochemical reactions (gluconeogenesis).
- Fat stores are also used
for energy, forming compounds called
ketones.
Other hormones may also intervene to raise the blood sugar level,
including epinephrine (also called adrenaline) and
cortisol released by the
adrenal glands and growth hormone released by the
pituitary gland.