Other common name(s): semi-vegetarian, pesci-vegetarian, lacto-ovo-vegetarian, ovo-vegetarian, lactovegetarian, vegan, fruitarian

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 fruits and vegetables. Vegetarian diets vary widely. Some people use no animal products, while others who describe themselves as vegetarian may consume dairy products, eggs, fish, and even 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 vegetarian diet should be properly planned to ensure it provides all the required nutrients.

How is it promoted for use?

Many proponents of vegetarianism believe a vegetarian diet promotes health because it contains less saturated fat, protein, and cholesterol than omnivorous diets (those 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 containing meat (see Phytochemicals). Some vegetarians believe it is more natural for humans to consume plant-based foods. Still others choose to eliminate or reduce their consumption of 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 according to whether any animal products are consumed and what kinds. For example, a vegan diet excludes all animal products including 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. A semi-vegetarian may eat mostly plant-based food with small amounts of fish and poultry; and a pesci-vegetarian adds only fish.

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

The macrobiotic diet, which is discussed in a different document, focuses on whole organic grains. It is also mainly vegetarian, although certain fruits and vegetables are excluded. 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 United States 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 that includes 5 or more servings a day of vegetables and fruit, choosing whole grains over processed and refined foods, and limiting red meats and animal fats. The National Cancer Institute (NCI) also recommends a diet low in fat and high in plant foods such as fruits and vegetables in order to decrease cancer risk.

Because vegetarianism is becoming more common, the American Dietetic Association created a food guide for the North American vegetarian in 2003. The Association estimated that, as of 2004, there were about 6 million US adults who followed vegetarian eating plans.

What is the evidence?

Population studies have linked vegetarian diets with a decreased risk of heart disease, diabetes, high blood pressure, obesity, and colon cancer. A review of research on the effects of vegetarian diets among Seventh-Day Adventists, whose religious doctrine advises against eating animal flesh, found that Seventh-Day Adventists experienced less heart disease and fewer cases of some types of cancer than the general population. On average, Seventh-Day Adventist males had lower-than-average serum cholesterol levels and blood pressure and their overall cancer death rate was about half that of the general population. The overall cancer death rate of females was also lower. A couple of studies indicated an increased risk of colon and prostate cancer with increased animal fat intake. An increase in the consumption of beans and lentils appeared to decrease the risk of colon cancer and prostate cancer. The report cautioned that abstinence from tobacco and alcohol may have contributed to some of the health effects associated with vegetarian diets in the Seventh-Day Adventist community.

A population study in Germany found the death rate for colon cancer was lower among moderate and strict vegetarians compared with that of the general population. However, the authors of the study also noted vegetarians tend to be more health conscious than average. In Great Britain, a seventeen-year population study that followed 11,000 vegetarians and health-conscious people concluded that the daily consumption of fresh fruit 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 and that well-planned omnivorous diets can provide health benefits as well. They also pointed out that many vegetarians adopt a healthier lifestyle, including more physical exercise and not smoking, which would likely improve their overall health and account for part of the health benefit that was first thought to be due to their diet.

A study published in 2005 compared more than 1,000 German vegetarians with nearly 700 health-conscious non-vegetarians over a 21-year period, and 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.

The majority of human evidence regarding vegetarianism consists of observational population studies of the risk for various diseases such as cancer. Very few clinical studies of people with cancer have been reported. A few studies of men with prostate cancer have reported that comprehensive lifestyle changes including vegetarianism, exercise, and stress reduction can slow the rate increases in blood PSA levels. The contribution of maintaining a vegetarian diet 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 consume adequate amounts of protein. Other nutrients that may be missing from a vegetarian diet 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. Vegan diets must be carefully planned to ensure adequate amounts of required nutrients are consumed.

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.

Switching to a vegetarian diet may increase the amount of dietary fiber consumed, which can cause temporary problems such as bloating, discomfort, and gas. Dietitians suggest a gradual rather than quick change in diet.

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).

• Guidelines for Using Complementary and Alternative Methods

• How to Know What Is Safe: Choosing and Using Dietary Supplements

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

• Complementary and Alternative Methods for Cancer Management

• 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. A new food guide for North American Vegetarians. Accessed at: http://www.eatright.org/cps/rde/xchg/ada/hs.xsl/governance_5105_ENU_HTML.htm on June 10, 2008.

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: http://www.quackwatch.org/03HealthPromotion/vegetarian.html on June 10, 2008.

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, Teas J, Ma Y, Hampl JS. 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 Journal for Clinicians. 2006;56:254-281.

Ornish D, Weidner G, Fair WR, Marlin R, Pettengill EB, Raisin CJ, Dunn-Emke S, Crutchfield L, Jacobs FN, Barnard RJ, Aronson WJ, McCormac P, McKnight DJ, Fein JD, Dnistrian AM, Weinstein J, Ngo TH, Mendell NR, Carroll PR. Intensive lifestyle changes may affect the progression of prostate cancer. J Urol. 2005;174:1065-1069.

Saxe GA, Major JM, Nguyen JY, Freeman KM, Downs TM, Salem CE. 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 factor for colon cancer in a low-risk population. Am J Epidemiol.1998;148:761-764.

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: 11/01/2008
Last Revised: 11/01/2008