Vegetarian nutrition

Vegetarian nutrition is the set of health-related challenges and advantages of vegetarian diets.

Evidence suggests that vegetarians are generally healthier and live longer than non-vegetarians. They have lower rates of coronary heart disease, obesity, hypertension, type 2 diabetes and some forms of cancer. Vegetarian diets tend to be rich in carbohydrates, omega-6 fatty acids, dietary fibre, carotenoids, folic acid, vitamin C, vitamin E, potassium and magnesium. They are generally low in saturated fat, cholesterol, and animal protein.

However, vegetarian diets can sometimes be relatively low in protein, iron, zinc, vitamin B12, calcium and other nutrients. Nonetheless, well-planned vegetarian and vegan diets can meet all these nutrient requirements and are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence.

Benefits of a vegetarian diet
Vegetarian diets are usually rich in carbohydrates, omega-6 fatty acids, dietary fibre, carotenoids, folic acid, vitamin C, vitamin E, potassium and magnesium. They contain lower levels of saturated fat, cholesterol, and animal protein.

Evidence suggests that the health of vegetarians compares favourably with that of non-vegetarians. British vegetarians have lower death rates than non-vegetarians, although this may be due to non-dietary lifestyle factors, such as a low prevalence of smoking and the generally high socio-economic status of vegetarians, or to aspects of the diet other than the avoidance of meat and fish.

One review found that mortality from coronary heart disease was 24% lower in vegetarians than in nonvegetarians. Studies of cancer have not shown clear differences in cancer rates between vegetarians and non-vegetarians. There is evidence that vegetarians tend to have a lower body mass index, lower risk of obesity, lower blood cholesterol levels, lower homocysteine levels,, lower risk of high blood pressure,  and lower risk of type 2 diabetes. One large prospective study found that non-meat-eaters had only half the risk of meat eaters of requiring an emergency appendectomy.

Potential nutrient deficiencies
Poorly planned vegetarian diets can be relatively low in protein, iron, zinc, vitamin B12, calcium, omega-3 fatty acids, retinol (vitamin A), vitamin D, riboflavin (vitamin B2) and iodine. Vegans may have particularly low intakes of vitamin B12 and calcium. Nonetheless, well-balanced vegetarian and vegan diets can meet all these nutrient requirements and are appropriate for all stages of the life cycle, including during pregnancy, lactation, infancy, childhood, and adolescence.

Protein
The typical vegetarian gets adequate protein as long as caloric intake is adequate and a variety of foods is eaten. A typical vegetarian gets less protein than the typical non-vegetarian which may be beneficial. USDA's tables provide information about the protein content of most foods, and the Institute of Medicine's DRI tables show the amount of recommended protein intake.

Due to the lower digestibility of plant proteins, however, the American Dietetic Association (ADA) states "protein needs might be higher than the RDA in vegetarians whose dietary protein sources are mainly those that are less well digested, such as some cereals and legumes."

Combining Proteins
A widely held myth is the idea of protein combining: that vegetarians must eat grains and beans within a few hours of each other in order to make a 'complete' protein which contains all 9 "essential amino acids". While this myth is widely believed, it has never been substantiated by research.

The protein-combining theory was brought to popular attention in Frances Moore Lappe's 1971 bestseller Diet for a Small Planet. In later editions of the book, as early as 1981, Lappe withdrew her contention that protein 'combining' is necessary. John McDougall concurs with Lappe's 1981 conclusion, providing a table comparing amino acid requirements with the amino acids in common plant foods. McDougall says "many people believe that animal foods contain protein that is superior in quality to the protein found in plants. This is a misconception dating back to 1914, when Osborn and Mendel studied the protein requirements of laboratory rats. ... It has since been shown that the initial premise that animal products supplied the most ideal protein pattern for humans, as it did for rats, was incorrect."



Iron
Meat, fish and poultry are the only sources of heme iron; plants contain only non-heme iron, which is absorbed less efficiently by the human body. However, cereals, eggs, legumes (including peas, beans, chickpeas, lentils and soy foods) and nuts are significant sources of iron, so a well planned vegetarian diet should not lead to iron deficiency.

A study in the Journal of the American Dietetic Association found that while iron-deficiency anemia is not more common among vegetarians, "vegetarian children had ... reduced levels of haemoglobin and iron compared to omnivores" due "to the absence of animal iron sources with high utilizability".

Zinc
Western vegetarians and vegans have not been found to suffer from overt zinc deficiencies any more than meat-eaters. However, phytates in many whole-grains and fiber in many foods may interfere with zinc absorption and marginal zinc intake has poorly understood effects.

Vitamin B12
Vitamin B12 deficiency is potentially extremely serious, leading to pernicious anemia, nerve degeneration and irreversible neurological damage. A regular source of vitamin B12 is particularly important for those over the age of 50 years, and pregnant and lactating women (and for breastfed infants if the mother's diet is not supplemented).

Evidence suggests that vegetarians and vegans who are not taking vitamin B12 supplements do not consume sufficient servings of B12 and often have abnormally low blood concentrations of vitamin B12. This is because, unless fortified, plant foods do not contain significant amounts of active vitamin B12.

It is essential, therefore, that vegetarians consume adequate amounts of dairy products, eggs, dietary supplements or foods that have been fortified with B12 (such as certain yeast extracts, vegetable stock, veggie burger mixes, textured vegetable protein, soy milks, vegetable and sunflower margarines, and breakfast cereals).

Omega-3 fatty acids
Vegetarian sources of omega-3 fatty acids include flaxseeds and flaxseed oil, olive oil, walnuts, canola (rapeseed) oil, avocado, and eggs.

Vegetarian sources of omega-3 fatty acids are primarily the short chain variety and likely to have lower concentrations of the particular essential fatty acids (EFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The body can synthesize small quantities of EPA and DHA from other omega-3 fatty acids, such as alpha-linolenic acids, which are present in vegetarian sources of omega-3 fatty acids. The human body can also convert DHA into EPA. DHA supplements derived from DHA-rich microalgae are available. Whilst the human body can in theory do this conversion, in practice modern diets and lifestyles reduce the effectiveness of the conversion systems. Roughly ten times more of the short chain omega-3s must be consumed to have the same effect as the long chain form from fish oil.

While there is no scientific consensus on the role of omega-3 fatty acids, it is generally believed that they may reduce the risk of coronary heart disease, lower triglycerides, stabilize mood and help prevent depression, help prevent ADD, reduce joint pain and other rheumatoid problems and reduce the risk of dementia in older age. It must also be noted that, while Omega 3 from fish oil is beneficial, there is debate about the benefits of Omega 3 fats derived from plants.

Vitamin D
The human body can synthesize Vitamin D when skin is exposed to ultraviolet radiation from the sun. Vegans who do not eat foods or pills fortified with synthetic vitamin D and with little exposure to the sun's ultraviolet radiation, e.g. who don't expose their extremities for at least 15-30 minutes per day or those living at latitudes close to the poles, are vulnerable to Vitamin D deficiencies.

Vitamin D acts as a hormone, sending a message to the intestines to increase the absorption of calcium and phosphorus, which produces strong bones. Vitamin D also works in concert with a number of other vitamins, minerals, and hormones to promote bone mineralization. Research also suggests that vitamin D may help maintain a healthy immune system and help regulate cell growth and differentiation.

Iodine
According the British Journal of Nutrition there is a "potential danger of [Iodine] deficiency disorders due to strict forms of vegetarian nutrition, especially when fruits and vegetables grown in soils with low [Iodine] levels are ingested." Iodine, however, is usually supplied by iodized salt and other sources in first world countries.

Riboflavin
According to the American Dietetic Association, “Some studies have shown vegans to have lower intakes of riboflavin, compared with nonvegetarians; however, clinical riboflavin deficiency has not been observed.”