Sports nutrition: an overview of vitamins, supplements and dietary requirements
The latest sports nutrition research
FISH OILS are big news and destined to get even bigger. Already thought to prevent heart disease and other circulatory disorders by working against the degenerative processes of atherosclerosis, it now appears that these oils, rich in Omega-3 fatty acids, may also play a role in boosting aerobic fitness.
Interestingly, there were no significant differences in blood fat profiles, despite previous evidence that fish oils can reduce blood levels of both cholesterol and triglycerides. This may have been because the subjects' blood fat levels were already quite low at the outset of the study.
But the most fascinating result was an increase in aerobic fitness parameters- V02max and ventilatory anaerobic threshold (VAT)-not only in the exercise groups but also, to a lesser degree, in the fish-only group. The researchers, from Western Washington University, suggest that the fatty acids in fish oil exert direct effects on blood cells which help to enhance aerobic metabolism and thus boost fitness. (Journal of Sports Medicine & Physical Fitness, 1990)
DANISH RESEARCHERS carried out a study to show whether switching to a vegetarian diet leads to any changes in immune function - a vital question for serious athletes, who are more than usually susceptible to infections.
Eight well-trained male endurance athletes followed two different diet regimes, each for a six-week period. Both diets were nutritionally sufficient and delivered carbohydrate, protein and fat in the same proportions, but one was a mixed meat-rich diet while the other was a vegetarian diet, including eggs and dairy products.
The athletes followed their normal training schedules throughout, and blood samples were taken for analysis of their immune status at the end of each dietary regime.
In fact, the tests showed that the concentration, composition and function of immune blood cells used for combating infection were unaffected by the dietary changes, even thought the vegetarian diet contained twice as much fibre as the meat diet and a much higher ratio of polyunsaturated to saturated fatty acids.
However, this does not mean that any athlete can switch to a vegetarian diet with impunity. As the researchers point out, the vegetarian diet used in the trial was probably atypical since it involved extensive use of bean products to ensure a sufficient protein intake. Athletes who change their diet without expert advice might find this quite difficult to achieve. (Medicine & Science in Sports & Exercise, 1991)
FOR YEARS, scientists have searched for a way to greatly reduce the risk of dehydration during summer training and competition. Now, scientists at the Veterans Administration Hospital in Albuquerque, New Mexico, have discovered a safe, natural chemical which they claim can do the job. The chemical is glycerol, a three-carbon molecule which is found in every molecule of fat in the human body. When glycerol is ingested with water prior to exercise, blood volume stays high, heart rates remain low, and hot-weather performance improves, say the researchers.
In the research, 11 competitive cyclists took glycerol and water and then tried to exercise on a bicycle for as long as possible in high temperatures. When glycerol was taken, the cyclists were able to exercise about 21 per cent longer, compared to consuming only water. Glycerol was also superior to water at preserving blood volume and preventing significant rises in body temperature or heart rate during exercise. Inside the body, glycerol creates a high osmotic gradient which 'drags' water into the blood vessels, moderating heart rates and allowing more blood to be sent to the skin for cooling. 'But more research needs to be done,' say the scientists. (A study presented at the 1992 annual meeting of the American College of Sports Medicine)
NEW RESEARCH suggests that increased blood levels of vitamin C are associated with more moderate blood pressure readings. In recent investigations at the Medical College of Georgia, researchers examined blood vitamin-C concentrations and systolic and diastolic blood pressures in 168 healthy volunteers (108 women, 60 men) ranging in age from 19 to 70. Systolic blood pressure ranged from 84 to 152 mm Hg, diastolic pressure varied from 52 to 96, and serum vitamin C-levels fell between 5.7 and 143 micromoles per litre.
The researchers found that - for non-smokers - a 100mm in blood vitamin-C concentration was linked with a 12mm drop in systolic pressure and a 10mm drop in diastolic pressure. Why did some individuals have higher-than-average C levels? Consumption of C-rich foods certainly helped, as did the ingestion of vitamin-C supplements. People who took supplements had blood-C concentrations 11 per cent above the average.
For smokers, there wasn't an inverse relationship between blood-C concentration and blood pressure. In fact, rises in vitamin C were actually associated with increases in blood pressure for nicotine addicts.
Seven other recent studies in the US, Finland and Japan have also linked vitamin C with reduced blood pressure. (American Journal of Clinical Nutrition, 1993)
MANY ENDURANCE ATHLETES wolf down dietary supplements in the hope of boosting their performances, and four of the most popular are coenzyme Q10, cytochrome C, inosine and vitamin E. However, new research suggests that these additives have a slim chance of helping anyone set a new PB. Investigations carried out at Cornell University and the University of North Carolina-Greensboro indicate that the four compounds have no measurable physiological effect during strenuous competitive efforts lasting from three to six hours.
Why did anyone believe that the four supplements might boost performance? All four chemicals are naturally present in muscles and play a role in energy production. Coenzyme Q10 and cytochrome C both participate in a process called 'electron transport' which produces most of the energy used by muscles during endurance exercise. Inosine may dilate blood vessels which bring oxygen to the muscles, and vitamin E stablises key muscle enzymes and might enhance oxygen utilization during exercise. Because of their potential, the four supplements have been bundled together into a commercial product called 'CAPS', or Coenzyme Athletic Performance System.
To determine the actual effects of CAPS, the North Carolina-Cornell scientists conducted a carefully controlled, 12-week study with 12 highly trained triathletes. The athletes had been running at least 30 miles and cycling 100 miles per week prior to the research and possessed V02max values of about 68ml/kg/min.
During a regular four-week training period, six of the athletes received a large daily dose of CAPS consisting of 1286mg of coenzyme Q 10,1286mg of inosine, 6430mg of cytochrome C, and 2572 IU of vitamin E, while six other athletes received only a placebo. None of the athletes was aware of what they were actually taking.
After the four weeks, each triathlete took part in a rugged test of endurance which consisted of 90 minutes of continuous running followed by 90 minutes of steady cycling. After this 180-minute exertion, each athlete continued cycling as long as possible at a tough intensity of 80-85% V02max. A monetary award system assured that all athletes attempted to exercise for as long as possible during the test.
Following this strenuous effort, the athletes trained normally for four weeks without CAPS or placebo, and then the individuals who had previously received CAPS ingested the placebo for four weeks, and vice-versa. Thus, all athletes had an opportunity to train and exercise to exhaustion with both CAPS and placebo.
Although the four compounds in CAPS are involved in energy production, CAPS supplementation had no effect on performance. Total endurance times, which averaged about three-and-a-half hours, were similar with CAPS and placebo, and CAPS didn't lower lactate, increase blood concentrations of glucose or free fatty acids, or make endurance exercise feel any easier.
Although many endurance athletes use CAPS, or the ingredients in CAPS, fairly frequently, there's no scientific evidence that such supplementation is beneficial. As the scientists put it: 'Ergogenic aids are never a substitute for an appropriate training programme'. (International Journal of Sport Nutrition, 1992)
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