An essential part of organisms, proteins are made up of amino acids. Some amino acids can be synthesized by the human body while some must be obtained through food. Proteins are major contributors to cells' functions.
Protein is one of the nutrients that are needed in larger quantities (i.e., macronutrients) along with carbohydrates and fat. Proteins contain 17 kJ/g (4 cal/g) energy.
Sources of protein in the diet include nuts, legumes, grains, eggs, meats and dairy products. Proteins have a distinct behaviour in cooking compared to fats and carbohydrates. Proteins in general stiffen when heated, for example a egg yolk becomes more solid when heated, because it's rich in protein.
Some proteins are toxic for humans but become edible via cooking, for that reason some legumes must be boiled before they can be eaten.
The building blocks of protein molecules are called amino acids. There are only 20 amino acids, but these can be combined in a huge number of combinations. The proteins are digested in the intestine, and split up in amino acids. These amino acids are later recombined to new proteins in the cells of the body.
Carbohydrates, also known as carbs, refer to starches (complex carbohydrates) and to sugars (simple carbohydrates).
Strictly speaking, carbohydrates are not necessary for human nutrition because proteins can be converted to glucose, which the body uses for energy. The traditional diet of many peoples consists of nearly no carbohydrates, and these people have been shown to be perfectly healthy. However, carbohydrates require less water to digest than do proteins or fats.
Problems have been cited for the long term effects of a no-carbohydrate diet. These include reduced athletic performance, possible brain damage, and nephrotoxicity. The brain can only utilize carbohydrates for energy, and protein may not supply enough in many cases. The increase in protein means that more ammonia groups need to be removed from the blood.
Carbohydrates have a varying degrees of glycemic index. People with diabetes or hyperglycemia (elevated blood glucose levels) need to carefully monitor their carbohydrate intake to prevent complications related to prolonged high blood glucose levels or acute hypoglycemia (too little blood glucose), and avoiding foods with high glycemic indexes can help.
Vitamins are essential nutrients that must either be ingested or synthesised to maintain health. There are two main varieties: water-soluble and fat-soluble. Because some vitamins are only soluble in fat, a totally fat-free diet can be unhealthy.
- Vitamin A (also known as retinol) is a fat-soluble vitamin found in dairy products and in liver. Excessive vitamin A can poison you. The body can create vitamin A as needed from beta-carotine , which is water-soluble and not dangerous (large amounts can turn your skin and eyes orange, though). You can get plenty of beta-carotine from carrots, squash, and spinach. Vitamin A deficiency can affect the eyesight, so the popular belief that carrots help you see in the dark is not wholly false.
- The Vitamin B group of water-soluble vitamins contains a number of separate vitamins. An excess of these vitamins is not harmful.
- Vitamin B1 (or thiamine) can be found in beef, pork, legumes, yeast, egg yolks, milk, green leafy vegetables, and many grains, nuts, and seeds. Deficiency can cause beriberi.
- Vitamin B2 (or riboflavin) can be found in beef, dairy products, nuts, and green, leafy vegetables.
- Vitamnin B3 (or niacin) can be found in fish and poultry meats, liver, nuts, seeds, legumes, and green, leafy vegetables. Deficiency can lead to pellagra.
- Vitamin C (or ascorbic acid) is a water-soluble vitamin found in citrus fruits and green vegetables. A deficiency can lead to scurvy.
- Vitamin D (or calciferol) is a fat-soluble vitamin found in oily fish. With sufficient exposure to sunlight, most of the requirement can be met through the synthesis of vitamin D by the skin.
- Vitamin E (or tocopherol) is a fat-soluble vitamin found in vegetable oils, nuts and green leafy vegetables.
Minerals are inorganic chemicals, generally metallic, that are used by the body. Usually the body has a sufficient supply of minerals through eating a variety of foods in the correct amounts. Mineral distribution in the body falls into two categories: bulk minerals, and trace minerals (defined by the USRDA as greater than and less than 200 mg).
Calcium is the most abundant mineral in the human body, and is needed to form strong bones and teeth, and is also used for blood, muscle, nervous system transmission, and inter-cellular fluid. Calcium plays a part in the contraction of muscle cells and blood vessels, and the secretion of hormones and enzymes. Some typical sources of calcium include: dairy products (milk, cheese, yogurt), Chinese cabbage, kale, and broccoli.
Sodium is found together with chloride as sodium chloride or common salt. In the body, sodium helps to balance the fluids inside the body cells and outside them. A lack of sodium can cause cramps. However too much salt in the body is harmful as it can cause hypertension, a condition that affects the blood system
The fourth most abundant mineral in the body - half of which is found in bones, while the other half is distributed amongst tissues and organs. It is a vital component in muscle and nerve function, immune system function, bone strength, blood sugar and blood pressure, and metabolism and protein synthesis. Most sources of magnesium are green vegetables and whole or unrefined grains and nuts, as magnesium is the central component of chlorophyll molecules, which give the green color of vegetables.
A trace mineral that makes antioxidant selenoprotein enzymes, which prevent cellular damage from free radicals, regulate thyroid function, and play a role in the immune system. The amount of selenium in a particular food is related to the amount in the soil of the area the food was produced in. Typically it is found in grains and nuts, but also in the meats of animals that eat grain or plants from selenium-rich soil.
Iron is needed for the formation of hemoglobin in red blood cells which are responsible for carrying oxygen to all parts of the body. Most sources of iron are animal related (also called heme iron sources) and include beef, turkey, chicken, pork, oysters, crab, and tuna. Other sources, called nonheme iron sources, include beans, tofu, spinach, raisins, molasses, and some cereals and grains.
Zinc can be found in almost every cell in the body, and stimulates about 100 different enzyme reactions. It is used by the immune system, for DNA synthesis, for healing wounds, and for normal growth and development during hormonally active periods. Zinc is provided by oysters, beef, pork, chicken, fish, beans, tree nuts, and some dairy products.
Copper aids in the formation of Red Blood Cells. Copper excess also mimics zinc deficiency and can promote impotence.
- USDA National Nutrient Database
- USDA Food Guide Pyramid
- Harvard School of Public Health: Food Pyramids
-  National Institute of Health - Office of Dietary Supplements, Vitamin and Mineral Fact Sheet
- See http://www.hsph.harvard.edu/nutritionsource/protein.html