A vegetarian is a person who does not eat meat (including fowl) or seafood, and vegetarian diets: Diets devoid ofall flesh foods, but also include egg (ovo) and/or dairy (lacto) products.

However, these very broad categories mask important variations within vegetarian diets and dietary practices

Benefits and drawbacks of a vegetarian diet

Common reasons for choosing a vegetarian diet include health considerations, concern for the environment, and animal welfare factors.Vegetarians also cite economic reasons, ethical considerations, world hunger issues, and religious beliefs as their reasons for following their chosen eating pattern.

Vegetarian diets can meet all the recommendations for nutrients. The key is to consume a variety of foods and the right amount of foods to meet calorie needs. Follow the food group recommendations for age, sex, and activity level to get the right amount of food and the variety of foods needed for nutrient adequacy.

Vegetarian diets are often associated with a number of health advantages, including lower blood cholesterol levels, lower risk of heart disease, lower blood pressure levels, and lower risk of hypertension and type 2 diabetes [Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc. 2009;109: 1266-1282].

Vegetarians tend to have a lower body mass index (BMI) and lower overall cancer rates.

Vegetarian diets tend to be lower in saturated fat and cholesterol, and have higher levels of dietary fiber, magnesium and potassium, vitamins C and E, folate, carotenoids, flavonoids, and other phytochemicals. These nutritional differences may explain some of the health advantages of those following a varied, balanced vegetarian diet.

However, vegans and some other vegetarians may have lower intakes of vitamin B-12, calcium, vitamin D, zinc, and long-chain n-3 fatty acids.

Vitamin B12, iron and unsaturated fats (omega 3): where can we find these nutrients in a vegetarian diet?

Vitamin B12

The vitamin B-12 status of some vegetarians is less than adequate due to not regularly consuming reliable sources of vitamin B-12. Lacto-ovo-vegetarians can obtain adequate vitamin B-12 from dairy foods, eggs, or other reliable vitamin B-12 sources (fortified foods and supplements), if regularly consumed.

For vegans, vitamin B-12 must be obtained from regular use of vitamin B-12-fortified foods, such as fortified soy and rice beverages, some breakfast cereals and meat analogs, or Red Star Vegetarian Support Formula nutritional yeast; otherwise a daily vitamin B-12 supplement is needed. No unfortified plant food contains any significant amount of active vitamin B-12. Fermented soy products cannot be considered a reliable source of active B-12.

Vegetarian diets are typically rich in folacin, which may mask the hematological symptoms of vitamin B-12 deficiency, so that vitamin B-12 deficiency may go undetected untilafter neurological signs and symptoms may be manifest. Vitamin B-12 status is best determined by measuring serum levels of homocysteine, methylmalonic acid, or holotranscobalamin II.

Iron

The iron in plant foods is nonheme iron, which is sensitive to both inhibitors and enhancers of iron absorption.

Inhibitors of iron absorption include phytates, calcium, and the polyphenolics in tea, coffee, herb teas, and cocoa. Fiber only slightly inhibits iron absorption. Some food preparation techniques such as soaking and sprouting beans, grains, and seeds, and the leavening of bread, can diminish phytate levels (20) and thereby enhance iron absorption.

Other fermentation processes, such as those used to make miso and tempeh, may also improve iron bioavailability. Vitamin C and other organic acids found in fruits and vegetables can substantially enhance iron absorption and reduce the inhibitory effects of phytate and thereby improve iron status.

Because of lower bioavailability of iron from a vegetarian diet, the recommended iron intakes for vegetarians are 1.8 times those of nonvegetarians. Whereas many studies of iron absorption have been short term, there is evidence that adaptation to low intakes takes place over the long term, and involves both increased absorption and decreased losses. Incidence of iron-deficiency anemia among vegetarians is similar to that of nonvegetarians.

Although vegetarian adults have lower iron stores than nonvegetarians, their serum ferritin levels are usually within the normal range.  

Omega 3

Whereas vegetarian diets are generally rich in n-6 fatty acids, they may be marginal in n-3 fatty acids.

Diets that do not include fish, eggs, or generous amounts of algae generally are low in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), fatty acids important for cardiovascular health as well as eye and brain development. The bioconversion ofalpha-linolenic acid (ALA), a plant-based n-3 fatty acid, to EPA is generally less than 10% in humans; conversion of ALA to DHA is substantially less (14).

Vegetarians, and particularly vegans, tend to have lower blood levels of EPA and DHA than nonvegetarians (15). The Dietary Reference Intakes recommend intakes of 1.6 and 1.1 g ALA per day, for men and women, respectively.

These recommendations may not be optimal for vegetarians who consume little if any DHA and EPA and thus may need additional ALA for conversion to DHA and EPA.

Conversion rates for ALA tend to improve when dietary n-6 levels are not high or excessive (14). Vegetarians should include good sources of ALA in their diet, such as flaxseed, walnuts, and soy. Green leafy vegetables, sea vegetables, and pecans also provide smaller amounts of alpha-linolenic acid.

Dr. Ph.D. Alessandro Terrinoni 

Professor of Molecular Biology at the Master of Nutrition and Cosmetics, Faculty of Science of Human Nutrition

University of Rome Tor Vergata