How much water should athletes drink? They should drink as much as they can tolerate, right? Is there any evidence to support that claim? Is drinking excessive amounts of water unsafe? Here’s an excerpt from Jamie Hale’s book, Knowledge and Nonsense, regarding water consumption.

“In a 2006 interview conducted by Louise M. Burke, Noakes explained his findings on fluid intake during sport and exercise. Below are some excerpts from the interview:

‘Louise Burke: Over the past two decades, Professor Tim Noakes has championed the case for a change in the way we educate athletes about fluid intake during sport and exercise. In particular, readers are directed to a recent publication: Noakes TD and D.B Speedy, 2006. Case proven—exercise associated hyponatraemia is due to overdrinking. So why did it take 20 years before the original evidence was accepted (British Journal of Sports Medicine 40:567–572)? In this interview, I ask professor Noakes to further develop some of the themes that have convinced us to refine fluid intake guidelines and to explain some of his more controversial beliefs or statements.

Tim Noakes:When athletes were advised not to drink during exercise, as was the case when I began running in 1969, there were no cases of overdrinking during exercise. Whether or not this advice produced its own problems is open to debate. But the point is athletes were told that they must ignore those biological cues that normally regulate drinking behavior. So perhaps it was to be expected that the new guidelines that became popular in the early 1980s continued to advise athletes that they must still ignore their intrinsic physiological cues. So they must stay ‘ahead of thirst’ because by the time they become thirsty they are already ‘dehydrated’ and at risk of all sorts of dire medical consequences. Athletes were also encouraged to ‘drink as much as tolerable’ without being warned that over drinking could be fatal. It seems to me that the advice to ‘stay ahead of thirst’ or ‘up size’ is a symptom of the same problem—the influence of consumerism that is focused on profit, not on human health. What athletes need to be told is that they would be better advised to listen to their bodies than to the marketing spin generated by Madison Avenue.

Louise Burke: It might make sense in a marathon to tell a runner not to over drink or to only drink from the aid station if they are thirsty. In this circumstance, the runner can be pretty sure that if they make such a decision at one aid station, there will be another aid station within a reasonable distance, which will provide them with another opportunity to revise their actions.

However, in other sports, opportunities to drink and access to fluid are limited or sporadic. If a soccer player knows that they will not be able to drink during the 45-minute halves of a game in hot weather, perhaps it makes sense for them to have a drink just before the start of the game even if they aren’t thirsty. A literal reading of your fluid guidelines would say that the soccer player shouldn’t do this, even if it makes them feel better or helps them to reduce the accrued dehydration.

Tim Noakes:Ideally, soccer players all involved in team sports played in the heat should have access to fluid every 15 to 20 minutes. The problem here is not the guideline that athletes should drink only in response to thirst. Rather the problem is that fluid should be made available to soccer players whenever they are thirsty and would like to drink.

Louise Burke:Can I give you another example where your proposed fluid guidelines cater for marathon runners (and perhaps) at the expense of the greater number of other situations of sport that are practiced around the world every day? Recently I did some fluid balance monitoring of elite cricket players, and I took along a freshly prepared education sheet on ‘fluid facts for cricket,’ which I planned to hand out in conjunction with the individual results. In good faith, I wrote a statement in bold at the bottom of the sheet, which I had intended to make a generic statement on all of our fluid information for athletes: ‘You should not drink more than you sweat during exercise so that you gain weight over the session.’

I agree this can be a concern in marathon runners, especially if they have been hydrating over the days leading up to the race and are already overhydrated when they take the starting line. But when these cricket players came to their morning training session—a 2.5 hour session undertaken in hot weather—we found that nearly half of the group was dehydrated (based on the specific gravity of their urine). Many had trained hard or played in a match the previous day. There are several other reports in the literature that show that many team athletes in daily training carry dehydration from one session to the next. In my cricket situation, one player who reported with a very high urinary specific gravity did a skill-based session and was found to have quite a modest sweat rate. His fluid intake over the session was also quite modest but was slightly higher than sweat rates so that he gained about half a kilogram over the session.

Although my handout strongly criticized what had just happened, in retrospect, it was probably a sensible strategy that helped him to maintain his fluid balance from day to day. So while we need to safeguard the health of a subgroup of athlete—the slow runners at the back of a marathon—do you think we have forgotten about the needs or scenarios faced by the majority of sports people?

Tim Noakes:Human physiology is not specific exclusively to one group of athletes. Either thirst is the biological control that all creatures in the known universe evolved optimally to regulate their body water content or it is not. What we now know is drinking ‘as much as tolerable’ is the worst possible advice that can be given to anyone involved in exercise that lasts more than about 4 hours (and not just slow marathon runners). For the reality is that once the exercise lasts more than about 4 to 6 hours, the exercise intensity becomes sufficiently low that it becomes possible to drink too much.

Your completely valid question is whether athletes involved in exercise of shorter duration and higher intensity might be at a disadvantage if they drink only according to thirst. The natural assumption is that this must be so because that is exactly what the drinking guidelines of many influential organizations tell us, as do the advertisements sponsored by the sports drink industry. To answer this question, I reviewed all the published studies in which exercise performance was measured in well-controlled trials in which athletes drank either according to their thirst (‘ad libitum’) or according to a drinking schedule that insured they drank more, usually ‘to replace all the fluid lost as sweat during exercise.’ Some studies also included a trial in which athletes drank less than ‘ad libitum.’

The conclusions were absolutely clear—when athletes drank less than ‘ad libitum,’ they were likely to under perform compared to ‘ad libitum’ drinking. But there was no study in which drinking more ‘ad libitum’ improved performance more than the ‘ad libitum’ condition. Thus, if we are to be entirely evidence-based in the advice we give athletes, at this moment, we have to say that drinking ‘ad libitum’ produces the optimum performance.’

Practical implications regarding fluid consumption:

  • Hyponatremia can be fatal.
  • Fluid contained in foods should be counted toward daily totals.
  • Generally, all fluids count toward daily water totals.
  • When sweating profusely for long periods of time, drink electrolyte-based drinks.
  • Don’t become obsessed with drinking only bottled water.”