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Vegetarianism

Other common name(s): vegan, ovo-vegetarian, lactovegetarian, lacto-ovo-vegetarian, fruitarian. (People who eat mainly plant-based foods but include small amounts of certain meats sometimes call themselves semi-vegetarian, partial vegetarian, pesci-vegetarian, pesco-vegetarian, pescetarian, flexitarian, and other names)

Scientific/medical name(s): none

Description

Vegetarianism is the practice of eating a diet consisting mainly or entirely of food that comes from plant sources such as grains, nuts, fruits, and vegetables. Vegetarian diets vary widely. Some people use no animal products at all, while others who describe themselves as vegetarian may eat dairy products, eggs, or even fish and poultry.

Overview

Some studies have linked vegetarian diets to lower risk for heart disease, diabetes, high blood pressure, obesity, and certain types of cancer, such as colon cancer. A strictly vegetarian diet must be properly planned to be sure it provides all the required nutrients.

How is it promoted for use?

Many proponents believe a vegetarian diet promotes health because it contains less saturated fat, protein, and cholesterol than diets in which both plant and animal foods are eaten. Vegetarian diets also provide more fiber, vitamins, minerals, antioxidants, and other phytochemicals (plant chemicals) than diets that contain meat (see Phytochemicals). Some vegetarians believe it is more natural for humans to eat plant-based foods. Still others choose to reduce or stop using animal products because of religious, cultural, moral, or philosophical reasons.

What does it involve?

All vegetarian diets include plant-based foods such as grains, legumes, seeds, nuts, vegetables, and fruits, but they vary based on whether and what kinds of animal products are consumed. For example, a vegan diet excludes all animal products such as meat, fowl, fish, dairy, and eggs. A lacto-ovo-vegetarian diet adds dairy products and eggs; a lacto-vegetarian diet adds only dairy products; and ovo-vegetarian diets add only eggs.

One small group of vegetarians called fruitarians eat only raw or dried fruits and fruit vegetables (like tomatoes). They believe that cooking fruit damages its nutritional properties. Fruitarians eat all types of fruits, nuts, and seeds, including non-sweet fruits such as olives, cucumbers, and avocados.

Semi-vegetarians may eat mostly plant-based foods with small amounts of fish and/or poultry. Pesci vegetarians add only fish or seafood. Pesci vegetarians also call themselves pesco vegetarians or pescetarians.

The macrobiotic diet, which is discussed in a different document, focuses on whole organic grains. It is mainly plant-based, although certain fruits and vegetables are not eaten. Some types of fish may be allowed (see Macrobiotic Diet).

What is the history behind it?

Vegetarianism has long been a part of many cultures. In the United States, the vegetarian movement began in the mid-1800s. The American Vegetarian Society was founded in 1850. Today, vegetarianism is very popular in the US and abroad because it is thought to be a healthier approach to diet and nutrition.

The American Cancer Society's most recent nutrition guidelines recommend eating a balanced diet with an emphasis on plant sources, which includes:

  • 5 or more servings of vegetables and fruit each day
  • choosing whole grains over processed and refined grains
  • limiting processed meats and red meats
  • balancing calorie intake with physical activity to get to or stay at a healthy weight
  • limiting alcohol intake

For more information, see ACS Guidelines on Nutrition and Physical Activity for Cancer Prevention, which is online at www.cancer.org. Or you can get a copy by calling our toll-free number.

The National Cancer Institute (NCI) also recommends a diet that balances food intake with exercise and includes plant foods like fruits and vegetables to decrease cancer risk.

Because vegetarianism is becoming more common, the American Dietetic Association (ADA) has put out a position paper that supports its benefits. The ADA reported that in 2006, around 2.3% of US adults surveyed -- nearly 5 million -- followed vegetarian eating plans. They also reported a 2005 survey of children that showed 3% of 8 to 18 year-olds were vegetarian.

What is the evidence?

Studies that look at people and their habits have linked vegetarian diets with a decreased risk of heart disease, diabetes, high blood pressure, obesity, and colon cancer. A review of studies looked at the effects of vegetarian diets among Seventh-Day Adventists, whose religious doctrine advises against eating animal flesh. The review found that Seventh-Day Adventists had less heart disease and fewer cases of some types of cancer than most people. For instance, vegetarians tended to have lower rates of prostate and colon cancer. On average, Seventh-Day Adventist males had serum cholesterol levels and blood pressures that were lower than average. And, their overall cancer death rate was about half that of the general population. The overall cancer death rate of females was also lower. The report cautioned that abstinence from tobacco and alcohol was very likely responsible for some of the health effects that are often credited to vegetarian diets in Seventh-Day Adventists.

A study that looked at groups of people in Germany found the death rate for colon cancer was lower among moderate and strict vegetarians compared with that of the general population. The authors of this study also noted vegetarians tend to be more health conscious than average. In Great Britain, a 17-year study followed 11,000 vegetarians and health-conscious people. They concluded that eating fresh fruit every day was linked to a significant reduction in deaths from ischemic heart disease, stroke, and all causes of death combined. Another population study found men who ate a diet rich in grains, cereals, and nuts had a lower risk of prostate cancer.

In 1991, two nutritionists studying the benefits and risks of vegetarian diets reported that vegetarians are not necessarily healthier than non-vegetarians. They found that well-planned omnivorous diets (which include meats) can provide health benefits as well. The nutritionists also pointed out that many vegetarians adopt a healthier lifestyle, including more physical exercise and not smoking. These factors would likely improve the overall health of vegetarians and account for part of the health benefit that was first thought to be due to their diet.

To look at these other health factors, a study published in 2005 compared more than 1,000 German vegetarians with nearly 700 health-conscious non-vegetarians over a 21-year period. This study found that there were no major differences between the groups in terms of death and disease, although the vegetarians had slightly less heart disease. Both groups were healthier than the general population, in part due to less smoking and more physical activity.

Most human evidence about vegetarianism consists only of studies that observe people (observational studies) and their risk for various diseases such as cancer. These studies don't test different diets; they only look at what people are already doing. Because of this, the studies often can't control for non-food differences (like exercise and other healthy habits) between vegetarians and other people.

Very few clinical studies have been reported in which people are put on different diets and studied over time. A few studies of men with prostate cancer have reported that major life changes including vegetarianism, exercise, and stress reduction can slow the rise in blood PSA levels. How much the vegetarian diet contributed to these benefits remains unproven.

Are there any possible problems or complications?

Strict vegetarians, such as vegans (who eat no animal products at all), must be careful to eat enough protein. Other nutrients that may be missing from some vegetarian diets include vitamin B12, vitamin D, calcium, zinc, and iron (see Calcium, Vitamin B, Vitamin D, and Zinc). Some health care professionals consider vegan diets potentially risky, especially for infants, toddlers, and pregnant women.

The American Dietetic Association (ADA) now holds the position that even children can be vegetarians if the diet is planned and set up properly. But the ADA also says that anyone who plans to be a vegetarian should be assessed by a registered dietitian before starting. This is because vegetarians vary greatly in what they actually eat, and some will not get all the nutrients they need. Seeing a dietitian is even more important for children and pregnant women. Vegan diets must be carefully planned to be sure that enough nutrients are consumed to ensure normal growth and development.

Vegan women who breastfeed their infants may want to take supplements containing sufficient vitamin B12. Severe B12 deficiencies in breast-fed infants of vegan mothers have caused failure to thrive, poor brain development, and other serious problems.

A person who switches to a vegetarian diet may increase the amount of dietary fiber consumed, which can cause short term problems like bloating, discomfort, and gas. Dietitians suggest a gradual rather than quick diet change.

Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

Additional resources

More information from your American Cancer Society

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

Dietary Supplements: What Is Safe?

The ACS Operational Statement on Complementary and Alternative Methods of Cancer Management

Complementary and Alternative Methods and Cancer

Placebo Effect

Learning About New Ways to Treat Cancer

Learning About New Ways to Prevent Cancer

References

Alternative Medicine: Expanding Medical Horizons. A Report to the National Institutes of Health on Alternative Medical Systems and Practices in the United States. Washington, DC: US Government Printing Office; 1994. NIH publication 94-066.

American Dietetic Association. Vegetarian Lifestyle. Accessed at www.eatright.org/Public/content.aspx?id=6372 on March 2, 2010.

American Dietetic Association. Position of the ADA: Vegetarian Diets. J Am Diet Assoc. 2009;109:1266-1282. Accessed at www.eatright.org on March 2, 2010.

Chang-Claude J, Hermann S, Eiber U, Steindorf K. Lifestyle determinants and mortality in German vegetarians and health-conscious persons: results of a 21-year follow-up. Cancer Epidemiol Biomarkers Prev.2005;14:963-968.

Dingott S, Dwyer J. Vegetarianism: healthful but unnecessary. Accessed at www.quackwatch.org/03HealthPromotion/vegetarian.html on March 3, 2010.

Fraser GE. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr. 1999;70(3 Suppl):532S-538S.

Frentzl-Beyme R, Chang-Claude J. Vegetarian diets and colon cancer: The German experience. Am J Clin Nutr.1994;59:1143S-1152S.

Hebert JR, Hurley TG, Olendzki BC, et al. Nutritional and socioeconomic factors in relation to prostate cancer mortality: a cross-national study. J Natl Cancer Inst. 1998;90:1637-1647.

Key TJ, Thorogood M, Appleby PN, Burr ML. Dietary habits and mortality in 11,000 vegetarians and health conscious people: results of a 17 year follow up. BMJ. 1996;313:775-779.

Kushi LH, Byers T, Doyle C, et al. American Cancer Society Guidelines on Nutrition and Physical Activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity. CA Cancer J Clin. 2006;56:254-281.

Ornish D, Weidner G, Fair WR, et al. Intensive lifestyle changes may affect the progression of prostate cancer. J Urol. 2005;174:1065-1069.

Saxe GA, Major JM, Nguyen JY, et al. Potential attenuation of disease progression in recurrent prostate cancer with plant-based diet and stress reduction. Integr Cancer Ther. 2006;5:206-213.

Singh PN, Fraser GE. Dietary risk factors for colon cancer in a low-risk population. Am J Epidemiol. 1998;148:761-764.

US Department of Agriculture. Vegetarian Diets. Accessed at www.mypyramid.gov/tips_resources/vegetarian_diets.html on March 2, 2010.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

Last Medical Review: 05/13/2010
Last Revised: 05/13/2010