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Nutrition & Weight Control

2004 Edition

The Rewards of Eating Vegetarian
A plant-based diet has compelling health benefits. At the same time, it can require planning to get the optimal balance of nutrients.

The American Dietetic Association (ADA) asserts that vegetarian diets are healthful, nutritionally adequate, and provide benefits for the prevention and treatment of certain diseases. Studies show that vegetarians have reduced risks of heart disease, high blood pressure, type 2 diabetes, obesity, and some types of cancer.

How do vegetarian diets produce these health benefits? Generally lower in total fat, saturated fat, and cholesterol, they help decrease blood cholesterol levels. In addition, plant foods contain compounds that interfere with the actions of carcinogens (cancer-causing chemicals), help repair damaged cells, and alter levels of hormones involved in cancer development. They also provide ample fiber, which may lower the risk of heart disease, stroke, diabetes, and gastrointestinal cancers.

Do Vegetarians Get Enough Protein?

Proteins are composed of amino acids—substances that the body needs for growth and for the maintenance of muscles, tendons, ligaments, and other tissues. Although many amino acids are manufactured in the body, nine “essential” amino acids can only be obtained from food. A food protein that supplies all of the essential amino acids is called a complete protein (animal foods are sources of complete protein). A food protein that does not supply all the essential amino acids is called an incomplete protein.

Plant proteins (with the exception of soy protein) are incomplete. But if the sources of dietary protein are varied, plant foods alone can supply enough of the essential amino acids—especially if the diet regularly includes high-protein plant foods such as beans, lentils, nuts, nut butters, and whole-grain breads and cereals. In addition, certain combinations—for example, rice and beans, or corn and beans—form complete proteins. And while it’s not necessary to eat these food combinations at the same meal, they should be consumed over the course of a day.

Soy foods contain especially high-quality protein. In fact, soy protein (found in soybeans, edamame, tofu, tempeh, soy nuts, and soy milk) contains enough of all the essential amino acids to be considered a complete protein equal in quality to proteins of animal origin.

Nutrient Needs for Strict Vegetarians

While a vegetarian diet is healthful, strict vegetarians (vegans) may be deficient in certain nutrients—such as vitamin B12, vitamin D, calcium, iron, and zinc—that are found principally in animal products. Careful food choices and use of a multivitamin supplement can help prevent nutritional deficiencies caused by strict vegetarian diets.

Vitamin B12. Found in such animal foods as fish, dairy, eggs, meat, and poultry, vitamin B12 is required to maintain healthy nerve cells, to produce red blood cells, and to make DNA, the genetic material in all cells. As we age, our ability to absorb vitamin B12 diminishes. In fact, some experts estimate that 10% to 30% of older adults do not absorb vitamin B12 efficiently from food.

Because they eat no animal foods, strict vegetarians are at risk for developing a deficiency of this important vitamin, especially if they also eat few B12-fortified foods (such as fortified cereals). For this reason, it is a good idea for vegetarians—particularly those who are over the age of 50—to take a vitamin B12 supplement.

Vitamin D. This vitamin is vital for maintaining proper calcium balance, which is necessary for bone and muscle health and other functions. Mostly produced by the body through exposure to sunlight, vitamin D is also found in some foods, principally fatty fish and fish oils, as well as certain fortified foods, such as some brands of soy milk, cereal, cow’s milk, and orange juice.

Studies show that the diets of many vegetarians, particularly vegans, contain inadequate amounts of vitamin D. And though lacto-ovo-vegetarians probably get enough vitamin D, and vegans can get vitamin D from fortified foods, it is still a good idea for them to consult their physician or a registered dietitian about supplementation.

Calcium. This mineral is essential for numerous functions, including regulation of the heartbeat, conduction of nerve impulses, stimulation of hormone secretions and blood clotting, as well as for building and maintaining healthy bones. Because lacto-ovo-vegetarians consume dairy foods, their calcium intakes are comparable to or higher than those of nonvegetarians. However, the calcium intakes of vegans are generally lower than those of either lacto-ovo-vegetarians or omnivores.

Good plant sources of calcium include bok choy, broccoli, napa cabbage, collards, kale, okra, and turnip greens. In addition, vegans may find it easier to meet their calcium needs by including fortified foods in their diets. Foods fortified with calcium include certain brands of orange juice and apple juice, breads, cereals, soy milk, and tofu. If you are concerned about your calcium intake, consult your physician about taking calcium supplements.

Iron. Adequate iron intake is necessary to prevent anemia. Because the richest dietary sources of iron are red meat and liver, vegetarians have a greater risk of iron deficiency than nonvegetarians. Although plant foods can contain iron, it’s a type of iron (“nonheme” iron) that is not absorbed as well as the “heme” iron contained in meat. In addition, the absorption of nonheme iron can be inhibited by certain substances in plant foods such as fiber, phytates (in cereal grains), and oxalates (in green leafy vegetables).

Nonheme iron can be absorbed better if a source of vitamin C is eaten at the same time as the iron-containing food. Good nonmeat sources of iron include dried beans, peas, whole-grain breads, spinach, enriched products, nutritional yeast, and dried fruits. Plants foods that are a good source of vitamin C include citrus fruits and juices, strawberries, tomatoes, broccoli, bell peppers, cooking greens, and potatoes.

Zinc. This essential mineral supports a healthy immune system and is required for DNA synthesis. It is also needed for wound healing, as well as maintaining your sense of taste and smell. Zinc is most abundant in animal foods, and although the mineral is present in certain plant foods—such as whole grains, wheat germ, fortified cereal, nuts, and legumes—its bioavailability appears to be lower in vegetarian diets.

Vegetarians may need as much as 50% more zinc than nonvegetarians because of the lower absorption of zinc from plant foods; so it’s very important for vegetarians to consume high-quality sources of zinc on a regular basis. In addition, most multivitamins contain enough zinc to help make up for any deficiencies in a vegetarian diet.

 

Vegetarian Lexicon

While all vegetarian diets place plant-based foods on center stage, the extent to which animal products are avoided can vary. For example:

• Vegans (pronounced VEE-gans), also called strict, pure, or total vegetarians, eat only plant foods; they avoid all products derived from animals (including honey).

• Ovo-vegetarians allows eggs in addition to plant foods.

• Lacto-ovo-vegetarians allow dairy and eggs in addition to plant foods.

• Pesco-vegetarians don’t eat red meat, but do eat fish, eggs, and dairy.

• Semi-vegetarians don’t eat red meat, but do include poultry, fish, eggs, and dairy.


 


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2005
WHITE PAPERS
Nutrition & Weight Control

The Nutrition & Weight Control White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.

 

 

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