Topic of the Month
28 October 2019
01 September 2012
The number of people who exercise, and their understanding of the role of nutrition in sports performance, is increasing: The percentage of Americans and Europeans who are physically active increased significantly over the last decade (1-3). In addition, people are tending to stay active for longer (4). The body needs carbohydrates, protein, fats (especially polyunsaturated omega-3 fatty acids), vitamins and minerals in order to function properly. Prolonged exercise performed on a regular basis may result in increased micronutrient losses from the body or in an increased rate of turnover, resulting in the need for an increased dietary intake. Today’s science of sports nutrition is sophisticated, revealing new insights about the measurable benefits of micronutrients, the amounts needed thereof, and the appropriate timing of intake.
Sports performance can require additional hydration and energy before and during physical activity, as well as a sufficient intake of the nutrients required to support recovery afterwards. Many micronutrients play key roles in energy metabolism and, during strenuous physical activity, the rate of energy turnover in skeletal muscle may increase to up to 100 times the resting rate (5). Although an adequate vitamin and mineral status is essential for normal health, marginal deficiency states may only be apparent when the metabolic rate is high. An increased food intake to meet these requirements will generally increase intake of dietary micro-nutrients. Athletes may need to pay particular attention to their intake of several micronutrients.
Exercise activates a finely orchestrated interplay of the body’s physiological systems to produce the desired skeletal muscle contractions at the right time. To do this, the human body needs:
During the first few minutes of intense exercise, energy is provided primarily by anaerobic metabolism, using up muscle glycogen and glucose that are present and readily available within the skeletal muscles. Anaerobic metabolism can energize a short burst of intense activity, such as weight lifting or sprinting, but not prolonged exercise.
After a few minutes oxygen becomes more available and aerobic metabolism takes over, using glycogen reserves from the liver and muscles, triglycerides from body fat and amino acids from several sites for continuous, extended muscle activity. Endurance sports require efficient use of oxygen to generate energy for continuous, extended muscle contractions. Body glycogen stores can support moderate to high intensity activity for 1.5 to 3 hours, depending on the nutritional status and fitness of the individual (6). These and other factors determine the relative amounts of energy derived from carbohydrates and fat. With increased training, there is a greater use of fat, a key factor in increasing endurance. As these energy sources are spent, the intensity, pace and performance of the athlete decline. The body will begin to break down muscle tissue for fuel, with potential undesirable consequences (7). Prudent intake of nutrients before, during and after exercise can help to maintain blood glucose and muscle glycogen stores, improve endurance, strength and performance, spare amino acids for protein synthesis, and optimize recovery after exercise (8). Recent research also shows that appropriate enrichment of the diet with nutrients such as amino acids, carbohy-drates, vitamins and minerals can improve athletic performance, recovery from fatigue after exercise and ward off immunodeficiency (9).
Antioxidants such as vitamin C, vitamin E and beta-carotene can protect cells against oxidative damage from exercise. Exercise increases oxidation and may require higher amounts of antioxidants to prevent free radical damage. Taking supplements of vitamin C and E may strengthen the antioxidant defense system by decreasing reactive oxygen species (10). Other research reports that taking supplements of various antioxi-dants, including vitamins C and E, may prevent oxidative damage in plasma induced by playing soccer (11). In addition, antioxidant supplementation has been found to reduce muscle soreness after exercise (12,13).
B vitamins participate in energy production and amino acid metabolism, and play many other important roles in the body. Because routine exercise increases the turnover and loss of these micronutrients, athletes’ requirements may be as much as twice the amount currently recommended for the general population (14). Intense training mainly affects thiamin (vitamin B1) concentration in the blood (15). Athletes who participate in sports that limit body weight such as gymnastics, ballet and wrestling may
be at risk of vitamin B deficiencies due to limited food intake (7).
Vitamin D acts directly on muscle to increase protein synthesis (16). Vitamin D status is positively associa-ted with muscle strength and physical performance, and vitamin D supplementation has been shown to improve muscle function and balance test scores in deficient seniors (17). A high percentage of athletes may be vitamin D deficient, especially: those in Canada, Europe and the northern US; indoor athletes; and dark-skinned athletes. Leading experts believe the current recommended intake of vitamin D is too low to compensate for the lack of formation of vitamin D from sun exposure (16). They recommend athletes control their blood levels of vitamin D and take advantage of vitamin D supplementation (18).
Coenzyme Q10 is an antioxidant produced by the body. In preliminary research, CoQ10 supplementation reduced exercise-induced muscular injury and improved endurance, performance and recovery time in trained athletes. Untrained individuals reported feeling more energized during exercise (19 22).
Lutein and zeaxanthin
Lutein and zeaxanthin form part of a special protective layer directly over the vision sensors in the eye. Good vision is essential in numerous sports, but many athletes are unaware that nutrition has an impact on this critical skill. In human studies, lutein and zeaxanthin have been shown to enhance contrast acuity, reduce glare and protect against hazardous short-wave light. Although lutein and zeaxanthin are found in the diet, normal intakes are low, and supplementation has been shown to enhance visual performance (23).
Essential fatty acids
Omega-3 fatty acids (DHA + EPA), derived principally from fish or algae, are known to have beneficial effects on heart health, the brain, fetal development, eye health, lung function and immunity. Some of these effects stem from the powerful anti-inflammatory actions of omega-3 fatty acids and are relevant to exer-cise. Studies have found that fish oil supplementation can produce the following effects: reduced heart rate and oxygen consumption during exercise; improved aerobic capacity; and relaxation of the air passages in elite athletes (24,25).
Minerals and trace elements
Levels of minerals and trace elements – primarily calcium, magnesium, iron, zinc and chromium – are likely to be low in the diets of many athletes, especially females and vegetarians (7). Inadequate calcium intake increases the risk of low bone mineral density and stress fractures. Optimal calcium nutrition for bone health is particularly important for athletes in weight-controlled sports (26). Experts may recommend they take supplements of calcium combined with vitamin D to prevent osteoporosis. Inadequate magnesium intake has been reported for weight-conscious athletes such as wrestlers, dancers and gymnasts. This mineral is particularly important because it is involved in many metabolic processes, and a deficiency may lead to muscle cramps and decreased muscle performance (27).
Iron is essential for carrying oxygen to the working muscles, and an inadequate intake, coupled with injuries and menstruation, can produce iron deficiency. Correcting iron deficiency anemia through supplementation may improve performance (26). Endurance athletes with normal hemoglobin status who want to increase their red blood cell and hemoglobin levels are thought to potentially benefit from iron supplementation. Poor zinc status may result in decreased heart and lung function, as well as reduced strength and endurance. Chromium may support the action of insulin at the cellular level and thereby stimulate glucose uptake by muscle (28).