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.

Studies show that the health of vegetarians compares favourably with that of non-vegetarians. British vegetarians have lower death rates than non-vegetarians, although this is at least partly due to non-dietary lifestyle factors, such as a low prevalence of smoking and the generally high socioeconomic status of vegetarians, or to aspects of the diet other than the avoidance of meat and fish.

Notably, a vegetarian diet avoids the negative health effects of red meat. 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.

Vegetarians are less likely to die by choking on food since the most common food to obstruct the airway is fish which caused about 4,500 accidents a year in the UK as of 1998. Meat, poultry and bones were cited as the next three most common causes of choking, followed by sweets and non-food objects. A 2007 report from San Diego in the US confirms that the most common cause of choking was on meat products.

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. Vegetarian diets are usually relatively low in protein, which may be beneficial.

Combining proteins

Despite a widespread belief 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", this has never been substantiated by research. The protein-combining theory was brought to popular attention in Frances Moore Lappé's 1971 bestseller Diet for a Small Planet. In later editions of the book, as early as 1981, Lappé withdrew her contention that protein 'combining' is necessary.

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 or B₁₂-fortified foods 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).

nori(Seaweed) contains B₁₂ very abundantly. However, plant sources of B₁₂ (or analogues) have not yet been shown to benefit humans. There is a patent for a cultivation method of a mycelium's enriching vitamin B₁₂ of the vegetable.

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 reduce symptoms of ADD, reduce joint pain and other rheumatoid problems and reduce the risk of dementia in older age.

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., those 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. Additionally, it should be noted that any iodine found in animal products is sourced from plant life (see: Iodine: Sources).

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.”

References

See also

• Nutrition
• Vegetarian cuisine
• Vegetarianism
• Veganism
• Vegan cuisine
• The China Study

Further reading

• Mayo Clinic's synopsis
• Vegetarian Resource Group
• Protein Basics Chart
• Focus on vegetarians research from EPIC-Oxford.
• The China Study: The Most Comprehensive Study of Nutrition Ever Conducted and the Startling Implications for Diet, Weight Loss and Long-Term Health (2005) by: T. Colin Campbell ISBN 1-932100-66-0
• Becoming a 'Veggie' : The Smart Move
• Vegetarian Nutrition Resource List - USDA, NAL Food and Nutrition Information Center (PDF|72 KB)