P ART II Nutritional Concerns of Athletes in
CHAPTER 7 CHAPTER 7 Nutritional Concerns of Vegetarian Athletes
A. Protein
The quantity of protein in the diets of athletes, while important, is rarely a concern, regardless of whether they are meat eaters or non-meat eaters. Increased dietary intake can be accomplished easily by both choosing high protein foods or by supplementing with protein powders, Nevertheless,
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the quality of protein can pose a problem. Well-processed soybean protein is equal in quality to animal protein. However, other legumes do not contain a full complement of the essential amino acids required for the efficient manufacture of protein by the human body.
Previous vegetarian dietary guidelines recommended that a variety of plant protein sources (such as grains and beans) be combined simultaneously at one meal to complement each other and provide a complete protein source. Current research supports the notion that by eating a variety of legumes, as well as all other food groups throughout the day, one can obtain the full array of essential amino acids required for efficient protein metabolism.
Thus, by combining various plant proteins and making use of soybean protein, most vegetarians can easily get an adequate level of dietary protein. Vegetarian athletes, on the other hand, may find that combining complementary proteins at one meal may be beneficial.
Ensuring Adequate and High Quality Protein
The mixture of proteins from grains, legumes, seeds, nuts, and vegetables provides a comple- ment of amino acids, enabling deficits in one food to be made up by another. At present, it is felt that, for most vegetarians, not all types of plant foods need to be eaten at the same meal, since the amino acids are combined in the body’s protein pool.
In general, proteins of animal origin contain adequate amounts of the essential amino acids and hence, they are known as first-class proteins. On the other hand, many proteins of vegetable origin are relatively deficient in certain amino acids, notably lysine and the sulfur-containing amino acids.
However, soy protein has been shown to be nutritionally equivalent in protein value to proteins of animal origin and, thus, can serve as the sole source of protein intake if desired.
The essential amino acid lysine is consistently at a much lower concentration in all major plant- food protein groups than in animal foods. Since lysine is the limiting amino acid, the addition of limited amounts of lysine to cereal diets improves their protein quality. Studies in Peru and Guatemala have demonstrated that growing children benefited by this addition.11 In addition, the sulfur-containing amino acids are distinctly lower in legumes and fruits, and threonine is lower in cereals than in proteins of animal origin.
Complementary Proteins
There are important differences among and between food products of vegetable and animal origin, including the concentrations of proteins and indispensable amino acids they contain. The concentration and quality of the protein in some foods of vegetable origin may be too low to make them adequate as sole sources of proteins. In some of the poorer parts of the world, diets are based predominantly on a single plant (e.g. corn), and they frequently lead to malnutrition.
Foods of plant origin contain many amino acids, but single food items usually do not contain all the essential amino acids in adequate amounts to support good health. Vegetarian diets are planned so that the amino acid content is adequate to support good nutritional health. Amino acids are the building blocks of protein, the nutrient that is supplied in the greatest quantity by meat, fish, poultry, eggs, milk, and cheese. The mainstays of strict vegetarian diets, vegetables, whole grains, legumes, nuts, and seeds, which do not contain an optimal balance of essential amino acids when eaten separately. Therefore, the vegetarian must combine foods that comple- ment each other, thus providing the body with the right amino acid mix. Mixtures of plant proteins can serve as a complete and well-balanced source of amino acids for meeting human physiological requirements.12 However, combining the right foods is necessary to obtain the necessary levels of both the essential or indispensable and conditionally indispensable amino acids. The addition of eggs and/or dairy products with meals or snacks greatly improves the overall protein quality of the vegetarian diet.
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122 NUTRITIONAL APPLICATIONS IN EXERCISE AND SPORT
Fortunately, the amino acid deficiencies in a protein can usually be improved by combining it with another so that the mixture of the two proteins will often have a higher food value than either one alone. For example, many cereals are low in lysine, but high in methionine and cysteine. On the other hand, soybeans, lima beans, and kidney beans are high in lysine but low in methionine and cysteine. When eaten together, these types of proteins give a more favorable amino acid profile.
Rice, the staple food for more than half of the world’s population, is inadequate in its amino acid content when it is the sole protein source, but when combined with another type of plant protein such as legumes, a complete protein mixture is formed. A mixture of red beans or black- eyed peas and rice is an example of complementary protein foods, as is a peanut butter sandwich (peanuts are legumes while the wheat of the bread is a grain). Other examples are corn tortillas with refried beans, and tofu with fried rice.
Soybeans, which are low in sulfur-containing amino acids, can be combined with cottonseed, peanut and sesame flour, and cereal grains, which are deficient mainly in lysine. In general, oil- seed proteins, in particular, soy protein, can be used effectively in combination with most cereal grains to improve the overall quality of the total protein intake. A combination of soy protein, which is high in lysine, with a cereal that contains a relatively good concentration of sulfur- containing amino acids results in a nutritional complementation; the protein quality of the mixture is greater than that for either protein source alone.
Nutritional Responses to Combining Two Dietary Proteins
Various nutritional responses are observed when two dietary proteins are combined. These have been classified by Bressani et al.13into one of four types.
1. No protein complementary effect is achieved. For example, this occurs with combinations of peanuts and corn, where each of the protein sources has a common and quantitatively similar lysine deficiency and both are also deficient in other amino acids.
2. Combinations are made of two protein sources that have the same limited amino acid, but in quantitatively different amounts. Corn and cottonseed flour, for example, are both limited in lysine, but cottonseed is relatively less inadequate than is corn.
3. A true complementary combination, because there is a synergistic effect on the overall nutritive value of the protein mixture; the protein quality of the best mix exceeds that of each component alone. This type of response occurs when one of the protein sources has a considerably higher concentration of the most limiting amino acid in the other protein. An example of this response is observed when corn and soy flour are mixed so that 60% of the protein intake comes from corn and the remainder from soy protein.
4. Both protein sources have a common amino acid deficiency. The protein component giving the highest value is the one containing a higher concentration of the deficient amino acid. Combinations of some textured soy proteins and beef protein follow this type of response.
These nutritional relationships have been determined from rat bioassay studies. However, the more limited results available from human studies with soy and other legumes confirm the appli- cability of this general concept in human nutrition. This knowledge helps to understand and evaluate how nutritionally effective combinations of plant protein foods can be achieved.
Even when combinations of plant protein foods are used, there is still the concern of timing of ingestion of complementary proteins. Is there a need to ingest different plant proteins at the same time, or within the same meal, to achieve maximum benefit and nutritional value from proteins with different, but complementary, amino acid patterns? This concern may also extend to the need to ingest a significant amount of protein at each meal, or whether it is sufficient to consume protein in variable amounts at different meals and even different days, as long as the average daily intake meets or exceeds the recommended or safe protein intakes.
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According to FAO/WHO/UNU,14 estimates of protein requirements refer to metabolic needs that persist over moderate periods of time. However, the body does not store much protein outside of a scant free amino acid pool, and begins certain catabolic processes in the post-absorptive phase (after a meal) making the ingestion of regular amounts of protein critical for maximizing the anabolic effects of exercise.
There is a limited database that we can consult to make a definitive conclusion on the timing of consumption of complementary proteins or of specific amino acid supplements for proteins that are deficient in one or more amino acids. Earlier work in rapidly growing rats suggested that delaying the supplementation of a protein with its limiting amino acid reduces the value of the supplement.15,16Similarly, the frequency of feeding of diets supplemented with lysine in growing pigs affects the overall efficiency of utilization of dietary protein.17 Studies in human adults showed that overall dietary protein utilization was similar whether the daily protein intake was distributed among two or three meals.18,19
In general, especially under conditions where intakes of total protein are high, it may not be necessary to consume complementary proteins at the same time. Separation of the proteins among meals over the course of a day would still permit the nutritional benefits of complementation.
However, in athletes trying to maximize protein synthesis and muscular hypertrophy, it is necessary to have a full complement of amino acids present for every meal to maximize the anabolic effects of exercise. With the presence of the full complement of amino acids, there is a meal-related decrease in proteolysis and increase in protein synthesis.20
The decrease in whole-body proteolysis is closely associated with the rise in plasma insulin concentrations following meal ingestion. This suggests that the transition from tissue catabolism to anabolism is the result, at least in part, of decreased whole-body proteolysis. This meal-related decrease in proteolysis is independent of the dietary amino acid composition or content. In contrast, the rate of protein synthesis was sustained only when the meal complete in all amino acids was provided, indicating a predominant control of protein synthesis by amino acid availability. Therefore, it appears important for athletes to consume meals that contain an optimal mixture of amino acids.