vegetarian diets & exercise performance

According to the American Dietetic Association (ADA) and the Dietitians of Canada, in the year 2000, 4 percent (%) of Canadian adults and 2.5% of the U.S. adult population consumed a vegetarian diet, defined as one that did not include meat, fish or fowl (ADA 2003). Slightly fewer than 1% said they followed an even stricter vegan diet, meaning they consumed no animal products at all (ADA 2003).

As fitness professionals, you are probably seeing an increase in vegetarianism among your own clients. The purpose of this article is to focus on the key nutrients recommended for physically active vegetarians.

Taking a Stand

Studies supporting the antioxidant properties of vegetables and the benefits of soy protein have fueled an interest in vegetarianism in athletes. In a recent position paper, the ADA concluded that most physically active individuals (with the possible exception of those who eat only fruit or follow a strict macrobiotic diet) can easily meet all their nutrition requirements without adding animal foods to their vegetarian diet (ADA 2003).

In fact, the ADA has created a separate Vegetarian Food Guide Pyramid (see page 80) that presents a daily guide for people who follow a plant-based diet (ADA 1997). For a look at some specific foods recommended for vegetarians, see “Nutrient Boosters for Vegetarian Athletes” below.

Protein

The protein needs of active people vary according to the type of activity performed, the level of training and the individual’s weight. According to the ADA and the Dietitians of Canada, endurance exercisers have daily protein needs ranging from 1.2 to 1.4 grams (g) per kilogram (kg) of body weight, whereas those who perform resistance training may need as much as 1.6 to 1.7 g/kg of body weight; these amounts are higher than the 0.8 g/kg established for sedentary individuals (ADA 2003).

On average, vegetarians get 12.5% of their total energy (calories) from protein, whereas vegans get approximately 11% of their total calories from protein (Messina & Messina 1996). Most experts say that vegetarian athletes can get all the protein they need from plants.

Legumes, which include soybeans, are an excellent source of protein (and carbohydrates). Soy also contains two phytochemicals shown to prevent osteoporosis and relieve postmenopausal symptoms (ADA 2003). Moreover, research indicates that 25 g of soy protein eaten daily can help reduce total cholesterol levels and increase HDL (“good”) cholesterol levels (ADA 2003).

Research has shown that eating protein-rich, low-glycemic-index (GI) foods, such as lentils, 1 hour prior to exercise may prolong endurance activity by keeping blood glucose levels higher toward the end of the exercise bout (Thomas, Brotherhood & Miller 1994). However, many protein-rich plant foods, like beans, nuts and seeds, also contain high levels of fiber and carbohydrates, which can be hard to digest. Individual clients will react differently, but athletes may want to avoid beans and other high-fiber foods 3 to 4 hours before exercising, to prevent gastrointestinal problems.

Essential Amino Acids

Essential amino acids (EAAs) are the building blocks for proteins. If certain EAAs are missing from the diet, the proteins that rely on those EAAs cannot be manufactured. One thing vegetarians need to be aware of is that plants are generally missing one or more of the EAAs found in all animal-based foods.

Vegetarians used to be encouraged to “complement their proteins” by eating at least two plant protein sources in the same meal, to ensure that all EAAs were obtained. The theory was that any EAA missing in one protein source would be offset by the EAAs contained in the other protein source. However, recent studies indicate that eating a wide variety of protein-rich plant foods throughout the day is just as effective as combining plant protein sources in one meal (Larson 2003).

Iron is a critical mineral needed to carry oxygen to the working muscle cells. For vegetarians, iron requirements are 1.8 times higher than for nonvegetarians (ADA 2003). That’s because plant foods contain nonheme iron, a form of iron that is more difficult to absorb than the heme iron found only in meats. Nonheme iron absorption can also be inhibited by phytic acid (a chemical found in leafy green vegetables), calcium, teas (even some herbal varieties), coffee, cocoa, certain spices and fiber (ADA 2003; Wildman & Miller 2004). Substances that enhance iron absorption include vitamin C and other organic acids found in fruits and vegetables.

In most cases, vegetarian athletes can achieve proper iron status without iron supplementation (Larson 2003). In fact, iron supplements do not appear to improve athletic performance in individuals with marginal iron status (Wildman & Miller 2004). Vegetarian athletes should eat a wide range of iron-rich foods from plant sources and should pair these with foods high in vitamin C to increase iron absorption (ADA 2003).

Zinc

Zinc is a growth mineral that plays a key role in energy metabolism and recovery. Zinc derived from animal sources is better absorbed than zinc from plant sources (ADA 2003; Wildman & Miller 2004).

Athletes in training are at risk for low zinc levels due to sweat loss, blood dilution during plasma expansion, and tissue redistribution (Wildman & Miller 2004). Eating large amounts of green, leafy vegetables, like kale, collards, spinach or mustard greens, can increase that risk because phytic acid decreases zinc absorption (Wildman & Miller 2004).

The key to vegetarians getting optimal levels of zinc is to eat a balanced diet and a wide variety of foods. Zinc absorption may be enhanced by certain food preparation techniques, such as soaking and sprouting for beans, grains and seeds (ADA 2003). Although more research is needed, zinc supplements do not appear to have any effect on athletic performance (Larson 2003).

Calcium is essential for optimal bone growth and also plays a role in muscle relaxation. In fact, muscle cramping, often blamed on inadequate potassium levels, is usually due to calcium deficits.

Vegetarian athletes who eat dairy products, such as milk, cheese and yogurt, should easily be able to obtain adequate calcium from dietary sources (Larson 2003). However, vegans, people who are lactose intolerant, those who avoid dairy products, and women on severely restrictive diets may be at greater risk for calcium deficiency (Larson 2003).

Oxalic acid, a chemical occurring naturally in spinach, Swiss chard and beet greens, can decrease calcium absorption. While these foods are high in vitamin A, they are not good sources of calcium (ADA 2003).

If food sources cannot supply adequate amounts of calcium, supplements in doses of 500 mg or less are sometimes recommended (National Institutes of Health 1994). Calcium supplements should be taken between meals to ensure maximum absorption.

Found only in animal-based foods,
vitamin B₁₂ optimizes nervous system function and plays a critical role in the formation of red blood cells. Vegetarians who eat eggs, dairy products, fish or poultry typically get an ample supply of this vitamin (Larson 2003). However, studies indicate that vegans and other vegetarians do not regularly consume adequate amounts of vitamin B₁₂ (ADA 2003). Additionally, vegetarian diets tend to be high in folic acid, which can mask the symptoms of a vitamin B₁₂ deficiency (ADA 2003).

The ADA recommends that all vegetarians use a supplement, fortified food, dairy products or eggs to meet recommended vitamin B₁₂ intakes (ADA 2003). Absorption is most efficient when foods containing small amounts of this vitamin are consumed at frequent intervals throughout the day (ADA 2003).