Food provides the body with the materials it needs for energy, growth, repair, and reproduction. These materials are called nutrients. Nutritionists divide nutrients into two main groups: macronutrients and micronutrients. Macronutrients, so called because the body needs more of them, include carbohydrates, fats, and proteins. These are the foods our bodies use for energy and growth. Micronutrients, or nutrients required in only small amounts, include vitamins and minerals. Most foods contain a combination of the two groups.

Macronutrients provide the body with the energy it needs to work, grow, reproduce, and repair. Carbohydrates and fats are the body's primary energy sources. Protein is essential to growth and maintenance. 

Here is a rundown of what each macronutrient does and some good sources. 

Carbohydrates: 
Carbohydrates include all starches and sugars. They are the body's main source of energy. Each gram of carbohydrate provides 4 calories. Most foods contain carbohydrates. The main sugar in food is sucrose, which is everyday white or brown sugar. Other sugars include lactose (found in milk) and fructose (found in most fruits and many vegetables). Starches are a more complex form of carbohydrate. They are more filling and contain more nutrients than foods with lots of sugars, fats, or oils. Foods containing starches include beans, breads, cereals, pasta, and potatoes.

Fat: 
Fats pack a lot of energy. Each gram of fat provides 9 calories. There are three kinds of fat: saturated, monounsaturated, and polyunsaturated. Animal and dairy fats, which remain solid at room temperature, are saturated fats. Saturated fat is often called "bad" fat. Unsaturated fats include vegetable fat and oils; they remain liquid at room temperature. 

Proteins: 
Proteins provide energy at 4 calories per gram, but they are more important as the body's building materials. Muscle, skin, bone, and hair are made up largely of proteins. In addition, every cell contains proteins called enzymes, which speed up chemical reactions in the body. Cells could not function without these enzymes. The body uses proteins to make antibodies, or disease-fighting chemicals, and certain hormones such as insulin, which serve as chemical messengers in the body. (Other hormones, such as the female hormone estrogen, are not made from proteins.) Meat, poultry, fish, dairy products, eggs, cereals, legumes, and nuts are all good sources of protein. 

What role do vitamins and minerals play in nutrition? 

Vitamins help the body turn food into energy and tissues. There are 13 vitamins in all: vitamin A; the vitamin B complex, which includes thiamine, riboflavin, niacin, vitamin B6, folic acid, vitamin B12 pantothenic acid, and biotin; and vitamins C, D, E, and K. 

Minerals are needed for growth and maintenance of body structures. They also help to maintain digestive juices and the fluids found in and around cells. 

Unlike vitamins, carbohydrates, fats, and proteins, minerals are not made by plants and animals. Plants get minerals from water or soil, and animals get minerals by eating plants or plant-eating animals. 

The minerals the body needs in large amounts include calcium, chlorine, magnesium, phosphorus, potassium, sodium, and sulfur. 

Other minerals, called trace elements, are needed in much smaller amounts. Trace elements include iron, copper, fluorine, iodine, selenium, zinc, chromium, cobalt, manganese, and molybdenum.