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Deriving Essential Nutrients from Vegetarian and Vegan Diets

Jan 09, 2012

Written by Pamela S. Hinton, Ph.D.

A vegetarian is someone who does not eat meat, poultry or fish, although self-described vegetarians come in many forms. Some eat fish, but not meat or poultry (semivegetarians). Some eat dairy products and eggs (lacto-ovo vegetarians). Some eat only plant-based foods (vegans).

There are many reasons people adopt a plant-based diet, such as economic reasons, religious beliefs or concerns for personal health, the environment or animal welfare. Regardless of the motivation for choosing this diet, vegetarians can be healthier than their omnivorous counterparts. However, by not eating animal foods, vegetarians eliminate prime sources of protein, n-3 fats DHA and EPA, iron, zinc, calcium and vitamins D and B12 from their diets. These potential deficits can be overcome with some careful planning and wise food choices.

Dietary protein is broken down into its essential elements, amino acids, which the body uses as building blocks to make new proteins. Animal-based proteins contain the essential amino acids needed for protein synthesis, and they are considered “complete” or “high-quality” proteins. Although legumes, grains, nuts and seeds contain protein, they do not provide the ideal mix of amino acids that the body needs, so they are said to be “incomplete.” In addition, plant sources of protein tend to be harder for the body to digest, so less of what we eat is available for use. However, eating the right combination of plant proteins can give a vegetarian the needed mix of amino acids. Plant proteins that provide the required amino acids when combined complement each other to make a complete protein source. For example, whole wheat bread and peanut butter or beans and corn are complementary proteins. Complementary proteins should be consumed within the same day, but they do not have to be eaten simultaneously.

Vegetarians who do not regularly eat fatty fish—such as salmon, tuna or cod—may be short on the essential n-3 (also called “omega-3”) fats DHA and EPA, which are important for cardiovascular, emotional and cognitive health. The n-3 fat found in plant sources—such as flax seed, walnuts, canola oil and soy—is α-linolenic acid (ALA). Unfortunately, the body converts only a small percentage of ALA into DHA and EPA, so vegans should increase their intake of ALA-containing foods. While the most common DHA/EPA supplements are derived from fish oil, there are microalgae-produced supplements available for vegetarians who want extra assurance they are meeting their DHA/EPA requirements.

The minerals iron and zinc—which are needed for oxygen transport, energy production, immunity, brain and nervous system health and muscle function—are likely to be lacking in a plant-based diet. There are compounds in plants that tie up iron and zinc so only a small fraction can be absorbed. The reduced bioavailability of iron is so significant that vegetarians need nearly twice as much iron each day as omnivores. Food-preparation techniques, such as soaking and sprouting beans and grains and leavening bread, allows more of the zinc and iron in these foods to be absorbed. Other strategies to increase the amount of iron and zinc absorbed are to consume them with a source of vitamin C and to avoid drinking coffee or tea, which naturally contain compounds that reduce mineral absorption, at meals. It is preferable to use wise food selection to meet zinc and iron requirements, rather than take dietary supplements, because ingestion of large doses of a nutrient at one time can interfere with the absorption of other nutrients.

Vegans, who do not consume milk and dairy products, are missing important sources of dietary calcium and vitamin D. Although these are especially important during childhood and adolescence when the skeleton is growing, calcium and vitamin D are also essential for skeletal health in adults, and low intakes of these nutrients might explain why vegans have a higher risk of bone fracture. Although there are plant-based foods that provide calcium, some of these (e.g., spinach) also contain compounds that tightly bind calcium, preventing it from being absorbed. Good sources of usable calcium include broccoli, kale, tofu and calcium-fortified products, such as soy and rice milk or fruit juice. Products that are fortified with calcium also are typically fortified with vitamin D, but check the label just to be sure. Foods are supplemented with either vitamin D3 or D2. Although vitamin D3 is animal-derived, vegans can opt for products or supplements containing vitamin D2, which is made from yeast.

Vegans need to either regularly consume foods fortified with vitamin B12 or take a supplement, as active vitamin B12 is present only in animal-based foods, such as dairy and eggs. The typical vegetarian diet contains enough folate to hide the early signs of a vitamin B12 deficiency, so the condition might go undetected until symptoms of nerve problems emerge.

By following the suggestions above, vegetarians and vegans can derive the health benefits of a plant-based diet and meet requirements for these key nutrients, which are needed not only for optimal health but to maximize the positive effects of exercise. Vegetarians can get enough of the right amino acids in the right combinations to build muscle mass and strength with weight training. Likewise, a well-planned, plant-based diet can provide the iron needed to improve fitness with regular aerobic exercise and the calcium and vitamin D needed to increase bone mass following weight-bearing activity. Regardless of a person’s dietary preferences, it is critical to consume a diet with essential nutrients in order to maximize health.

View the full spring 2011 issue of the ACSM Fit Society® Page supported by Liberty Mutual online.

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