A Critical Review of Contemporary and Popular Reports Within the ‘Lay’ Literature on the Use of Nutritional Supplements for Performance Benefits.

A critical review of contemporary and popular reports within the ‘lay’ literature on the use of nutritional supplements for performance benefits.

There is an endless list of ergogenic aids that claim to enhance sports performance that are religiously supplemented by amateur and professional athletes. Almost half of the general population have reported taking at least one form of dietary supplement, and the vast majority, if not all professional athletes use legal supplements, with a certain few resulting to using illegal methods to improve their performance (Ahrendt, 2001). Currently, the Australian Institute of Sport (AIS) provides a program list of supplements classified into four groups according to their effectiveness, safety and legal status as reviewed in scientific studies. (AIS, 2011). The supplements in; Group A are supported for use in specific situations in sport; Group B are considered for provision to AIS athletes only under a research protocol; Group C show little proof of beneficial effects and the supplements in Group D should not be used by AIS athletes. Creatine has been reported as the top-selling nutritional supplement in the world, mainly due to it being, affordable, relatively free from side-effects and because it works.
Creatine is made up of three amino acids; glycine, arginine, and methionine. The liver naturally produces about 1 gram (g) of creatine per day; the rest is mainly found in foods such as meat and fish. An average diet will also ingest about 1g of creatine per day. Creatine as a supplement can be taken in the form of a tablet or as a powder to be mixed with water. It is generally claimed (Smith, 2011) that supplementing creatine has several benefits for hard training athletes as when creatine is taken, it bonds with phosphate molecules to form creatine phosphate (CP). The phosphate molecules in creatine phosphate are then able bond with adenosine diphosphate (ADP) to form adenosine tri-phosphate (ATP), the energy currency of the cell, used in all cellular functions and muscular contraction. Therefore, it is believed that supplementing creatine will cause an increase in the body's ATP production leading to performance improvements and decreased fatigue in intense, short duration exercise such as weightlifting and sprinting (McArdle et al, 2007).
Additionally creatine is thought to benefit athletes as it improves hydration of muscle cells. (Mens Health, 2011). Creatine draws fluid from outside the muscle cell into the cell membrane. Due to the increase in water retention of the muscle cell, other ions such as nitrogen are drawn into the muscle cell leading to an increase in muscle protein synthesis allowing athletes to recover from exercise faster and increase muscle growth (Mens Health, 2011). Creatine supplementation is recommended to be specifically beneficial to athletes participating in high intensity exercise that require short, sharp bursts of energy. (McArdle et al, 2007). There is a considerable body of research studies that supports the efficacy of creatine in increasing body mass and performance in high intensity, short duration exercise. A study by Kraemer et al (1997) was undertaken to investigate the effect of creatine supplementation on muscular performance during high-intensity resistance exercise. The researchers compared the effect of 25g/day creatine supplementation for a week against that of a placebo on 10 repetition maximum bench press and squat in 14 active men. They found that there was no improvement in the placebo group, but those men supplementing creatine had significant improvements in both their maximum bench press and squat. Additionally, the participants who were supplementing creatine showed a body mass increase of upto 3kg. A similar study by Tarnopolshy and MacLennon (2000) also found that active men and women who supplemented creatine also showed an improvement in an anaerobic cycle test, 1RM leg extension and grip strength. The participants took a loading dose of 5g creatine, 4 times a day for 4 days, and followed this with a maintenance dose of 5g a day for 3 days. Dawson et al (1995) had found in a previous study that creatine supplementation can enhance both single and repeated short sprint performance when compared with a placebo group. Despite being arguably the most researched supplement, researchers have not agreed consistently on the exact dose to supplement. Most studies suggest that there should be a loading phase where typically no more than 300mg per kg of body mass should be consumed for 4-5 days, after this a maintenance phase of 30mg/kg body mass is required for the remainder of the course, most likely to be 2-3 weeks (Bird, 2003). Bird advised to not supplement creatine for longer than a month at a time as it can affect renal function, although there are very few studies that investigate the long-term effects of supplementing creatine and of these, there is no evidence to suggest short or long-term side effects of creatine supplementation. Carnitine is another very popular ergogenic aid; it was in the top 3 of reported dietary supplements taken by athletes at the 2000 Olympic games in Sydney. (Mens Health, 2011). Despite this, it is found in group B of the AIS supplements list.
Carnitine is a short chain of coboxylic acid that contains nitrogen, it is vital for normal metabolism as it is required for the transport of fatty acids from the cytosol into the mitochondria during the breakfown of lipids for the generation of metabolic energy.
A typical diet will contain 20-200mg of carnitine per day, this accounts for around 75% that is used by the body. The other 25% is synthesized in the liver and kidneys from the amino acids methionine and lysine. Similarly to creatine, the largest dietary sources of carnitine are meat, poultry, fish and dairy products meaning that vegetarians may only ingest as little as 2mg per day. It is claimed that supplementing carnitine will encourage faster post-exercise recovery from muscle fatigue and faster skeletal muscle tissue repair. (Holland and Barrett, 2011).
Carnitine is also believed to lead to an increase in endurance capacity. (Greig et al, 1987) suggest that carnitine will boost energy by stimulating the bodies burning of triglycerides as fuel, sparing the supply of glycogen stored in the liver for heavier exertion. Therefore, during exercise the body will burn fat at 75-80% of maximum exertion, thus less glycogen from carbohydrates is burned. Rebouche and Paulson (1986) claim that by carnitine supplements allow the body to access an otherwise unavailable energy source. The marketing of carnitine targets endurance athletes by stating that “metabolic stimulators” in carnitine enhance fat burning and spare glycogen. Because of this there is an appeal to body builders as an aid to reducing body fat. Studies have shown contrasting results as to whether the supplementation of carnitine can increase fat oxidation in sub-maximal exercise. Vukovic et al (1994) conducted a study analysing the effect supplementing carnitine of muscle carnitine and glycogen content during exercise in participants with purposely raised levels of triglycerides. Participants were asked to supplement 6g/day of carnitine for 7 or 14 days and compared with a placebo group. They all consumed 90g of fat 3 hours before cycling for 60 minutes at 70% of their VO2 max. Muscle biopsies were taken at 30 minute intervals and a blood sample was taken every 15 minutes. The study found that increased carnitine intake does not affect the amount of carnitine stored in muscle cells. They also found that increased levels of carnitine do not increase the rate of fat oxidation. The researchers went on to add their opinion that there is adequate muscle carnitine within the mitochondria to support lipid oxidation.
A meta-analysis by Brass (2000) also concluded that supplementation of carnitine does not increase muscle carnitine content, adding that the literature available of experimental clinical studies assessing the effect of carnitine on exercise metabolism or performance in healthy humans does not draw definitive conclusions. He further disregarded using carnitine as a supplement by suggesting that it also does not improve maximal oxygen uptake or metabolic status during exercise. However, there are some research studies that contrast this. Kraemer et al (2001) examine the influence of carnitine supplementation on muscle tissue disruption after high-intensity, high repetition exercise. They found that against a placebo, a daily carnitine supplement was effective in decreasing lower body muscle recovery time.
Although carnitine is one of the most widely used nutritional supplements, there is little conclusive proof that it is significantly effect on increasing performance and decreasing recovery time that the ‘lay’ literature suggests. In conclusion, using supplements as a professional athlete is essential because every possible extra benefit that they can attain should be utilised. Although many supplements claim to do a lot more than they actually do, there is evidence to suggest that even this placebo can give and extra benefit in the mind of an athlete.

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