Supplements fall into two distinct camps – pills and powders, and specially formulated sports drinks and foods. When it comes to pill supplements, Dr Asker Jeukendrup, professor of exercise metabolism and the director of the human performance lab at the University of Birmingham’s school of sport and exercise sciences, is dubious.

“Generally, nothing works. The whole area is dominated by marketing and not scientific evidence,” he says. However, Dr Jeukendrup points out that there are a handful of things that may help athletes out. Creatine is a naturally occurring substance that helps supply energy to muscles. Ingesting creatine may give you more energy for high intensity exercise, and some limited evidence suggests it may help build lean mass.

“When you exercise at a high intensity you break down creatine phosphate very rapidly, “ explains Dr Jeukendrup. Taking supplements replenishes supplies and may be beneficial if you are doing a series of sprints or repetitions in the gym. But for an endurance event like a triathlon, creatine supplements probably won’t help. “It could even have a disadvantage because you gain a bit of weight due to water retention – about one to three kilos,” he says.

Dr Samantha Stear, head of nutrition at the English Institute of Sport, says that creatine is one of three key supplements, the other two are caffeine and what are known as buffers, such as sodium bicarbonate, that are supported by the International Olympic Committee in its 2004 consensus statement on sport and nutrition. Caffeine ingested before exercise has been shown to enhance performance, and more recently, evidence has suggested that it can also help recovery after exercise by enhancing the speed at which muscles refuel with glycogen, their primary fuel source. Buffers reduce the build up of lactic acid in muscles – but Dr Jeukendrup points out that there are side effects. “You have to [ingest] large amounts – it tastes terrible - but can also lead to stomach problems and diarrhea.”

Dr Stear will be in Beijing with England’s elite athletes in the run up to the Olympic Games. Professional athletes often have tailored individual nutritional programmes. However, for all athletes the same basic rules apply - be well hydrated and well fuelled. If you are too nervous to eat a proper breakfast before the triathlon, Stear recommends eating a sports bar to deliver nutrition and carbohydrates. During the event, sports drinks, designed to replenish fluids, carbohydrates and sodium, can be useful. “During a triathlon you’re on a bike and you can actually eat something then, like a carbohydrate gel or bar,” she adds.

Dr Jeukendrup also focuses on carbohydrates. As well as delaying the onset of fatigue, ingesting carbohydrates during exercise of two hours or more can improve endurance and performance. Combining different forms of carbohydrates, Jeukendrup says, can improve carbohydrate delivery by as much as 75 per cent.

Research in the human performance lab over the last ten years has looked at the maximum amount of carbs a body can utilise in one hour – 60 grams. “The idea is to avoid that problem with different carbs that use different transports,” says Jeukendrup. For example, combining glucose and fructose can increase total carb absorption compared to either substance in isolation. Jeukendrup says that use of carbohydrate supplements can boost performance by about nine per cent, and claims that using combined carbohydrate supplements can boost performance by a further eight per cent.

Dr Justin Roberts, a senior lecturer in sports and exercise science (nutrition) at the University of Hertfordshire says Jeukendrup’s results broadly match those from their own lab. Only a few companies currently manufacture the combined products, but they are set to become more popular, and the university is currently working with sports drink companies. “Sports drinks are important to facilitate performance, but they’re not the be all and end all. Yes, you do perform better, but there are several factors that make up performance,” cautions Roberts. In other words, don’t expect to speed through the event fuelled by sports drinks if you haven’t trained sufficiently.

Both Dr Jeukendrup and Dr Roberts point out that the biggest difference will be made for long endurance events, such as iron man triathlons. For an Olympic distance triathlon, you don’t need to go overboard.

Dr Jeukendrup is in the process of setting up a website, www.nutrifit.co.uk, which aims to bring together nutritional information and advice for athletes in a clear, easily understandable form. If you want tailored advice, Roberts recommends going to see a professional with a recognised qualification, such as a British Association of Applied Nutritional Therapy practitioner. Even then, there are no guarantees. “At the moment there is no formal sports nutrition body,” Dr Roberts points out.