Should athletes be drinking to thirst or according to guidelines?

I attended the Sport & Exercise Nutrition Register Showcase in Birmingham a few weeks ago, where Dr Ian Rollo discussed the controversial topic of hydration and presented his opinion on whether we should be drinking to thirst or following the guidelines.

This is indeed a difficult topic with conflicting advice. On the one side, we have the likes of Prof. Tim Noakes saying that we should drink intuitively by listening to our thirst, our biological control mechanism that doesn’t require conscious adjustment. This stemmed from an increase in cases of exercise-induced hyponatraemia in the 2000s when marathoners were drinking ‘as much as tolerable’ to stay ‘ahead of thirst’ as they were being advised by the drinking guidelines at the time.

Nowadays, guidelines such as those from the American College of Sports Medicine suggest that athletes should consume a pre-determined volume of fluid that depends on the exercise intensity, individual’s sweat rate and environmental conditions.

Most research shows a decrement in both endurance and cognitive performance when fluid losses are more than two per cent of body weight. Dehydration can cause an increase in cardiovascular strain due to an increased heart rate and decreased stroke volume, which ultimately reduces cardiac output and affects aerobic performance. The increased competition for blood flow between the working muscles and skin (for heat loss) also reduces cardiac output. An increase in an athlete’s core temperature can moreover reduce their motor-neural output during exercise, making exercise harder to sustain.

However, some research supports better performance when drinking to thirst. A study conducted by Dr Rollo demonstrated that runners covered 10 miles almost a minute faster on average when allowed to drink according to their thirst, even though they were significantly more dehydrated and taking in 70 per cent less carbohydrate compared to the prescribed-drinking trial.

One reason may be the subjective ratings of greater gastrointestinal discomfort experienced in the prescribed-drinking trial. However, Dr Rollo revealed that the participants in the study were unaccustomed to drinking during the relatively short period of exercise. One participant happened to be a triathlete and regularly used sports drinks during training – he was the only one to perform better in the prescribed-drinking trial. This suggests that athletes should practice taking in fluid and carbohydrates during longer training sessions (in excess of an hour) to possibly improve their race day performance.

One point that Dr Rollo stressed is that we must be cautious when interpreting studies as we don’t know the baseline hydration status of the participants in those studies. It isn’t really taken into account. Considering that the majority of us are somewhat dehydrated most of the time, it is likely that participants already start off in a hypohydrated state and this may be skewing results.

Instead of debunking one side of the debate, we should try to embrace both and put them into context. What this means is that drinking to thirst can be a good approach for some athletes, while a more specific and individualised hydration strategy is needed for others. Factors that may determine one or the other include training status and the individual’s goal for a particular race. Elite athletes are likely to benefit more from an individualised hydration strategy compared to more recreational athletes. If an individual’s goal is to win a race, they may also benefit more from an individualised hydration plan. If the goal is just to participate and have fun, then there is no real need for a specific plan and drinking to thirst might be a suitable option. Other factors to consider are access to fluid at checkpoints during a race (unlimited vs limited), the duration of exercise (marathon vs ultra-marathon), the environment (cold vs hot), the need for carbohydrates and electrolytes, as well as the individual's sweat loss and thirst sensitivity. We moreover must not forget the individual’s personal preferences. There’s no point designing a hydration plan for an athlete who does not want to follow it and is already performing great just by listening to their own body.