Six Nutrients the Body Needs

We need enough food to live and the right assortment of foods for optimal health. Foods provide energy (calories), nutrients, and other substances necessary for growth and health. People eat foods for many different reasons. The most compelling reason is the requirement for calories, nutrients, and other substances supplied by foods for growth and health.

The six categories of nutrients

A calorie is a measure of the amount of energy transferred from food to the body. Because calories are a unit of measure and not a substance present in food, they are not considered nutrients.
Nutrients are chemical substances in food that the body uses for a variety of functions that support growth, tissue maintenance and repair, and ongoing health. Mostly, every part of our body was once a nutrient consumed in food.

There are six categories of nutrients. Each nutrient except water consists of many different substances.

1. Carbohydrates
Carbohydrate often means any food that is particularly rich in complex carbohydrate starch (such as cereals, bread, and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts). Starch is a polysaccharide. It is abundant in cereals (wheat, maize, rice), potatoes, and processed foods based on cereal flour, such as bread, pizza, or pasta. Sugars appear in the human diet mainly as table sugar (sucrose, extracted from sugarcane or sugar beets), lactose (abundant in milk), glucose, and fructose, both of which occur naturally in honey, many fruits, and some vegetables. Table sugar, milk, or honey are often added to drinks and many prepared foods such as jams, biscuits, and cakes.

Carbohydrates perform numerous roles in living organisms; they are central to nutrition and are found in a wide variety of natural and processed foods. Sugar, fruit, starchy vegetables, and whole-grain products are good sources of carbohydrates. It also includes dietary fiber, which does not contribute food energy (calories) in humans. Dietary fiber generally helps maintain a healthy digestive system by facilitating bowel movements.

2. Fats (Lipids)
Fat is an essential foodstuff for many forms of life, and fats serve structural and metabolic functions. They are a necessary part of the diet of most heterotrophs (including humans) and are the most energy-dense, thus the most efficient form of energy storage. Most fats are composed of glycerol attached to three fatty acids. Oil, butter, fish, sausage, and avocado are examples of rich sources of dietary fats.

Essential fatty acids (EFAs) are fatty acids that humans and other animals must ingest because the body requires them for good health but cannot synthesize them. Only two fatty acids are known to be essential for humans: alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid).

3. Proteins
Proteins are essential nutrients for the human body. Proteins are polymer chains made of amino acids linked together by peptide bonds. Amino acids that cannot be synthesized in adequate amounts by humans and therefore must be obtained from the diet are also called indispensable amino acids. There are 9 amino acids that cannot be endogenously synthesized by humans: phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine.

Protein can be found in all cells of the body and is the major structural component of all cells in the body, especially muscle. When broken down into amino acids, they are used as precursors to nucleic acids, co-enzymes, hormones, immune responses, cellular repair, and other molecules essential for life.

Protein occurs in a wide range of foods. Dietary sources of protein include grains, legumes, nuts, seeds, beans, meats, dairy products, fish, eggs, edible insects, and seaweed.

4. Vitamins
A vitamin is an organic molecule that is an essential micronutrient for the proper functioning of its metabolism. Vitamins are classified as either water-soluble or fat-soluble. Vitamins are present in many foods and are essential components of the diet. Vegetables, fruits, and grains are good sources of vitamins. Humans require 13 vitamins in the diet:

• 9 water-soluble vitamins: vitamin B1 (thiamine), vitamin B2 (riboflavin), vitamin B3 (niacin), vitamin B5 (pantothenic acid), vitamin B6 (pyridoxine), vitamin B7 (biotin), vitamin B9 (folic acid or folate), vitamin B12 (cobalamins), vitamin C (ascorbic acid).
• 4 fat-soluble vitamins: vitamin A (as all-trans-retinol, all-trans-retinyl-esters, as well as all-trans-beta-carotene and other provitamin A carotenoids), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (phylloquinone and menaquinones).

5. Water
Water is the source of all life, and as far as we know, life cannot exist without it. Water is the perfect medium for body processes because it enables chemical reactions to occur. It forms the greatest component of the human body, making up 50% to 70% of the body's weight (about 10 gallons or 40 liters). Lean muscle tissue contains about 73% water. Adipose tissue is about 20% water. Depending on the amount of fat stores present, an adult can survive for about 8 weeks without eating food but only a few days without drinking water. This occurs not because water is more important than carbohydrates, fat, protein, vitamins, or minerals, but rather because we cannot conserve or store water as well as we can the other components of our diet.

6. Minerals
In the context of nutrition, minerals consist of 15 elements found in foods that perform particular functions in the body. Milk, dark, leafy vegetables and meat are good sources of minerals.  The 15 essential minerals for humans are potassium, chloride, sodium, calcium, phosphorus, magnesium, iron, zinc, manganese, copper, iodine, chromium, molybdenum, selenium. Additionally, cobalt is an essential component of Vitamin B12.

Essential and Nonessential Nutrients

Of the many nutrients required for growth and health, some must be provided by the diet, while others can be made by the body.

Essential Nutrients: Substances required for growth and health cannot be produced, or produced in sufficient amounts by the body. They must be obtained from the diet.
Nutrients the body cannot manufacture, or generally produce in sufficient amounts, are referred to as essential nutrients. Here essential means required in the diet. All of the following nutrients are considered necessary:

• Carbohydrates
• Certain amino acids (the essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine)
• Linoleic acid and alpha-linolenic acid (essential fatty acids)
• Vitamins
• Minerals
• Water

Nonessential Nutrients: Nutrients required for growth and health that can be produced by the body from other components of the diet.
Cholesterol, creatine, and glucose are examples of nonessential nutrients.
Nonessential nutrients are present in food and used by the body, but they do not have to be part of our diets. Many beneficial chemical substances in plants are not considered essential, for example, yet they play essential roles in maintaining health.