Seminar 12: Nutrition and sport

Nutrition’s contribution to performance in sport – realities and myths was the subject of the latest of C3’s International Breakfast Seminars, given by Roger Clemens, president of the Institute of Food Technologists (2011–12).

• Slides from the event are available here >>
• A full report of the event is available here >>

Professor Clemens began by explaining that optimum nutrition and optimal health are different for everyone – the 12,000-calorie-a-day diet of Michael Phelps would hardly be appropriate for most of us, and even his diet may not have been ideal. Nutrition really can help ‘to make a better athlete’ – and yet most athletes and their trainers do not know what, when or how to eat. He is very focused on obtaining and disseminating accurate data – which is often in short supply.

Basic dietary guidelines for athletes include about 50–80kcal/kg per day (compared to 25–35 for non-athletes). Also essential are protein (1.4–2g/kg per day – critical for immune function and recovery from muscle damage) and carbohydrates (around 8–10g/kg per day – to maintain muscle glycogen) – but some long-distance cyclists (for example) still think it is sensible to avoid carbs.

Triglycerides (fats) are also important – about 50 per cent of energy during exercise comes from fat, so we need it. At low-intensity levels of exercise, fat is the primary source of energy. But as intensity and length of the exercise increases, the athletes need to ensure changes in diet to maintain their glycogen levels. After about three hours of exercising, however, most of the muscle glycogen has been used for energy.

Athletes also often do not drink enough, so they need to look at the composition and adequacy of the fluids they consume: hypohydration clearly leads to slower running times, as well as greater perceived effort.

Roger also addressed many of the myths and pitfalls surrounding elite athletes and food:

• Athletes often – wrongly – think of fluids as contributing to weight, or caffeine as supplying energy.
• Coffee and tea are promoted as ergogenic aids (things that help to enhance performance) – but the data on this are tenuous.
• Iron does not cause constipation, but is helpful in tackling sports anaemia. Less than 3 per cent of the iron in broccoli and spinach is biologically available (it requires vitamin C for absorption) – instead, red meat, chicken and fish are good sources of iron.
• Creatine increases strength and enhances glycogen storage, and is readily available and is not itself an illegal substance – but should be used only with caution as there can be contraindications – e.g. tachycardia (changes calcium balance).
• Dimethylamylamine, a supplement, is legal in most of the world, but has been banned by, among others, the US military and Canadian ministry of health. Even the UK has launched efforts to ban this substance. It is a powerful stimulant, and may not be appropriate for athletes. The website for one product shown by Roger claims that two independent clinical studies have been done; Roger has looked, and cannot find them anywhere (and certainly not in a peer-reviewed journal.

There are good data on branched-chain amino acids (found in, for example, milk protein), which reduce the time to exhaustion. Also, particular β-glucan, particularly the branched form from yeast, can help to boost or prime the immune system – but a dose of 250–500mg a day has had mixed results, with marathon runners seemingly more responsive than cyclists.

A topic of international interest is currently functional foods. There are good data on isotonic drinks (hypotonic and hypertonic drinks), and interesting data on improved endurance from high carbs and citric acid. There is evidence on enhanced muscle strength from protein intake etc., and the evidence on reducing injury and fatigue is clear for high carb intake.

He concluded that there is much more to understand about nutrition and its impact on athletic performance.

The discussion included:

• how to convince people who are winning that their diet needs addressing;
• the role of microbiome’s role in gut function, and whether probiotics are important for athletes’ diet;
• the lack of serious investment in good-quality research (despite the fact that there is so much money in sport, where the difference of a second can make a huge difference); and
• given that optimal nutrition is different for each individual, whether genetics will have a big impact on nutrition in the coming decades.