The Dark Side of Supplementation: Antioxidant Dietary Strategies in Sport

Oxidative stress reflects an imbalance between production of reactive oxygen species (ROS) and the ability to detoxify reactive intermediates or to repair the resulting damage by an adequate antioxidant defense. This adverse state may lead to damage of all cellular components including proteins, lipids and carbohydrates. Oxidative stress is recognised to be involved in many physiological conditions (aging and exercise) and disease (including inflammatory conditions, cardiovascular and neurodegenerative diseases, and cancer). While regular moderate training appears beneficial for oxidative stress and health, acute and strenuous bouts of of aerobic and anaerobic exercise can induce ROS overproduction.

In recent years, the consumption of supplemental antioxidants in athletes has increased enormously despite the unclear evidence of their benefit. Of particular interest, exogenous supplemental antioxidants has received attention as a non-invasive tool useful to decrease muscle damage, improve exercise performance, prevent or reduce oxidative stress, improve lifespan and lower risks of pathological outcomes that strenuous exercise produces in athletes. Moreover, the revision of available data has indicated that exogenous antioxidant supplementation, in most cases, fails to produce a positive effect, with some studies suggesting detrimental effects of antioxidant supplementation on the health and performance of trained athletes. For example, a too low oxidative stress status may prove unfavourable and blunt related to hormesis (positive exercise adaptation for future training). Conversely,  high doses of antioxidant may negatively affect important physiological process leading to pro-oxidant effects (NB: pro-oxidants can cause oxidative damage).

Interestingly, very few studies, if any, approach this topic from a whole food/dietary perspective. An adequate intake of vitamins and minerals , and the use of natural foods rich in antioxidants (fruits and vegetables), through a varied and balanced diet rich in fruits, fibres and vegetables could represent the ideal approach to maintain the optimal antioxidant status. The Mediterannean diet could be a suitable candidate, although data in this field remains scare.

Dietary vs Supplemental Antioxidants: Same Effectiveness?

It has been previously held that antioxidant supplementation is effective against the cumulative effects of strenuous exercise-induced free radical damage to the heart and skeletal muscle. Vitamin C at various dosages, administered alone or in combination, is the most frequently used antioxidant in human and experimental studies, despite the protective role of this antioxidant proving sundry. One of the key determinants for these differences is the dose employed. For example, vitamin C intake of at least 200 mg/d can be reasonably considered 'optimal', because it is the amount of vitamin C that has been shown to achieve near-saturation of plasma and full saturation of cells, and presumably tissues. Interestingly, a diet including 5 to 9 servings of fruit and raw/steamed vegetables and 200 ml of fresh orange juice could provide the 200 mg vitamin C dosage proposed. Male athletes have a range of vitamin C intake of 95 to 520 mg/d, whereas females have intakes ranging from 55 to 230 mg/d, as compared to the recommended daily allowance of 60 mg/d. However, higher doses of vitamin C can have deleterious effects. For instance, vitamin C > 1 g/d can reduce mitochondrial biogenesis (process where new mitochondria are formed - the engine of our cells) and ROS generation, reducing beneficial training adaptations and impair performance.

What I find concerning is that the above-mentioned concerns are the same for polyphenols (quercetin (tomatoes, blueberries, cherries, onions and broccoli), curcumin, resveratrol, luteolin and catechin); alpha-lipoic acid; Ubiquinones (Co-enzyme Q10); N-3 Polyunsaturated Fatty Acids (Fish Oil) and Vitamin E. For instance, 500 mg of quercetin for 8 weeks was effective in reducing oxidative stress and inflammation in athletes, however doses of 1g/d for 8 weeks proved ineffective, and encouraged ROS generation. Athletes need to be careful in developing a quality supplement regime at the correct dosage, reflective of the latest research, and question whether supplementation is necessary.

Nonetheless, it is important to point out that antioxidant intake may be beneficial in athletes not consuming a balanced diet. However, in making this suggesting, the athlete must appreciate that athletic performance is improved and maintained by incorporating a healthy diet (Vegetables, not just fruit), with failure to do so impacting on performance.

Dietary Strategies, Oxidative Stress and Exercise:

The Mediterranean Diet, characterised by high consumption of monounsaturated fatty acids primarily from olives and oil, vegetables and fruit , whole grains and a moderate consumption of red meat has been found to improve body composition (free fat mass vs. lean muscle mass) and cardio-respiratory fitness when combined with moderate to high intensity endurance. Moreover, combination therapy has been shown to improve physiological response to submaximal effort than diet alone. NB: To gain the effect, Train Smarter, Train Hard and Eat Well!

If you have any questions regarding this post please make contact:

Mark Hinchey Naturopathy, 601 Glebe Road Adamstown, Newcastle, New South Wales, Australia.

P: (02) 40235959

M: 0432234822 (Appointments)



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