Vitamin A is a fat-soluble vitamin with multiple functions in the body. It helps cells differentiate, an essential part of cell reproduction. Cells that are not fully differentiated are more likely to undergo precancerous changes. It is a central component for healthy vision; vitamin A nourishes cells in various structures of the eye and is required for the transduction of light into nerve signals in the retina. It is required during pregnancy, stimulating normal growth and development of the fetus by influencing genes that determine the sequential growth of organs in embryonic development. It influences the function and development of sperm, ovaries, and placenta and is a vital component of the reproductive process.

Vitamin B1 is a water-soluble vitamin that the body requires to break down carbohydrates, fat, and protein. Every cell of the body requires vitamin B1 to form adenosine triphosphate (ATP). Vitamin B1 is also essential for the proper functioning of nerve cells.

Vitamin B12?is a B vitamin found mainly in animal foods, particularly liver and kidney. It is also found in rabbit, duck, pork, lamb, turkey, chicken, oysters and fish. Vitamin B12 helps make red blood cells and is also essential for nerve cell function.

Vitamin B2 is a water-soluble vitamin that helps the body process amino acids and fats, activate vitamin B6 and folic acid, and convert carbohydrates to adenosine triphosphate (ATP). Under some conditions, vitamin B2 can act as an antioxidant.

Vitamin B3 is required for cell respiration and helps release the energy in carbohydrates, fats, and proteins. It also supports proper circulation and healthy skin, functioning of the nervous system, and normal secretion of bile and stomach fluids. It is used in the synthesis of sex hormones, treating schizophrenia and other mental illnesses, and as a memory-enhancer.

Nicotinic acid (but not nicotinamide) supplementation improves the blood cholesterol profile, and has been used to flush the body of organic poisons, such as certain insecticides. People report more mental alertness when this vitamin is in sufficient supply.

A shortage of niacin may be indicated with symptoms such as canker sores, depression, diarrhea, dizziness, fatigue, halitosis, headaches, indigestion, insomnia, limb pains, loss of appetite, low blood-sugar, muscular weakness, skin eruptions, and inflammation.

Vitamin B5 is a water-soluble vitamin involved in the Kreb?s energy production cycle and is needed for the production of acetylcholine, a neurotransmitter. Vitamin B5 also triggers the adrenal glands, is essential in transporting and releasing energy from fats, and enables the synthesis of cholesterol, vitamin D, and steroid hormones. Pantethine, a vitamin B5 byproduct, has been shown to lower cholesterol and triglycerides in the blood.

Vitamin B6 is a water-soluble vitamin and is part of the vitamin B complex. Vitamin B6 plays a role in the synthesis of antibodies by the immune system, which are needed to fight many diseases. It helps maintain normal nerve function and also acts in the formation of red blood cells. Vitamin B6 is also required for the chemical reactions needed to digest proteins. The higher the protein intake, the more the need for vitamin B6.

Large doses of vitamin B6 can cause neurological disorders and numbness. Deficiency of this vitamin can cause mouth and tongue sores, irritability, confusion, and depression. Vitamin B6 deficiency is uncommon in the United States.

Vitamin B9, also known as folic acid, is a B vitamin necessary for cell replication and growth. Folic acid helps form building blocks of DNA, which holds the body's genetic information, and building blocks of RNA, needed for protein synthesis. Folic acid is most important, then, for rapidly growing tissues, such as those of a fetus, and rapidly regenerating cells, like red blood cells and immune cells. Folic acid deficiency results in an anemia that responds quickly to folic acid supplements.

The need for folic acid increases considerably during pregnancy. Deficiencies of folic acid during pregnancy are associated with low birth weight and an increased incidence of neural tube defects in infants. Most doctors, many other health-care professionals, and the March of Dimes recommend that all women of childbearing age supplement with 400 mcg per day of folic acid. Such supplementation may protect against the formation of neural tube defects during the time between conception and when pregnancy is discovered.

Vitamin C is an essential water-soluble vitamin that has a wide range of functions in the human body.

One of vitamin C's important functions is acting as an antioxidant, protecting LDL cholesterol from oxidative damage. When LDL is damaged, the cholesterol appears to lead to heart disease, but vitamin C acts as an important antioxidant protector of LDL. Vitamin C may also protect against heart disease by reducing the stiffness of arteries and the tendency of platelets to coagulate in the vein.

The antioxidant properties also protect smokers from the harmful effects of free radicals. Small doses of vitamin C taken by nonsmokers before being exposed to smoke have been shown to reduce the free radical damage and LDL cholesterol oxidation associated with exposure to cigarette smoke.

Vitamin C has a range of additional functions. It is needed to make collagen, a substance that strengthens many parts of the body, such as muscles and blood vessels, and plays important roles in healing and as an antihistamine. Vitamin C also aids in the formation of liver bile, which helps to detoxify alcohol and other substances. Evidence indicates that vitamin C levels in the eye decrease with age and that vitamin C supplements prevent this decrease, lowering the risk of developing cataracts.

Vitamin C has been reported to reduce activity of the enzyme aldose reductase, which theoretically helps protect people with diabetes. It may also protect the body against accumulation or retention of the toxic mineral lead. People with recurrent boils (furunculosis) may have defects in white-blood-cell function that are correctable with vitamin C supplementation.

Vitamin D is a fat-soluble vitamin that helps maintain blood levels of calcium, by increasing absorption from food and reducing urinary calcium loss. Both functions help keep calcium in the body and therefore spare the calcium that is stored in bones. Vitamin D may also transfer calcium from the bone to the blood, which may actually weaken bones. Though the overall effect of vitamin D on the bones is complicated, some vitamin D is certainly necessary for healthy bones and teeth.

Vitamin D is also produced by the human body during exposure to the ultraviolet rays of the sun. However, seasonal changes, latitude, time of day, cloud cover, smog, and sunscreen can all affect UV exposure. Vitamin D deficiency is more common in northern latitudes, making vitamin D supplementation more important for residents of those areas.

Vitamin D plays a role in immunity and blood cell formation and also helps cells differentiate?a process that may reduce the risk of cancer. From various other studies, researchers have hypothesized that vitamin D may protect people from multiple sclerosis, autoimmune arthritis, and juvenile diabetes. Vitamin D is also necessary to maintain adequate blood levels of insulin. Vitamin D receptors have been found in the pancreas, and some evidence suggests that supplements may increase insulin secretion for some people with adult-onset diabetes.

Vitamin E is an antioxidant that protects cell membranes and other fat-soluble parts of the body, such as LDL cholesterol (the ?bad? cholesterol), from damage. Several studies have reported that supplements of natural vitamin E help reduce the risk of heart attacks.

Vitamin E also plays some role in the body?s ability to process glucose. Some trials suggest that vitamin E may help in the prevention and treatment of diabetes.

In the last decade, the functions of vitamin E have been further clarified. In addition to its antioxidant functions, vitamin E has now been shown to directly affect inflammation, blood cell regulation, connective tissue growth, and genetic control of cell division.

Vitamin K is necessary for proper bone growth and blood coagulation. Vitamin K accomplishes this by helping the body transport calcium. Vitamin K is used to treat overdoses of the drug warfarin. Also, doctors prescribe vitamin K to prevent excessive bleeding in people taking warfarin but requiring surgery.

There is some evidence that vitamin K2 (menadione), not vitamin K1 (phylloquinone; phytonadione), may improve a group of blood disorders known as myelodysplastic syndromes (MDS). These syndromes carry a dramatically increased risk of developing acute myeloid leukemia. Comprehensive trials of K2 for MDS are needed to confirm these auspicious early results.

Some vitamins in nutritional supplements or fortified foods are not suitable for vegans as they are derived from animal sources. (See also Vitamin B12 and Vitamin D.)

The theory behind volumetrics is that people tend to eat the same weight (as in literal poundage) of food each day, regardless of the number of calories. For example, a pound of low-density carrots contains as many calories as an ounce of high-density peanuts. So if you fill your plate with foods that are less energy dense, meaning they have fewer calories per gram, then you'll be eating fewer calories without eating less food. It's about making smart swaps, like sweet potatoes for white potatoes.

This is more of an eating pattern than a structured diet. The Ultimate Volumetrics Diet book is a good guide, developed by the diet's original pioneer, Penn State University nutrition professor Barbara Rolls. The plan focuses on eating, and Rolls also recommends walking for 30 minutes most days of the week. This can be achieved by parking farther from the store, or getting off the bus a few stops early. The book costs about $15.

Excess fat around the waist and a larger waist size increase the risk of health problems linked to obesity. Women with a waist size of more than 35 inches or men with a waist size of more than 40 inches have a higher risk of developing health problems linked to obesity, such as diabetes, heart disease, and high blood pressure.