What We (Don’t) Know About Water Loading

“The research team did in fact find that Vasopressin was suppressed in the water loading group, however it did not stay suppressed during the time when water intake stopped. It not only did not stay suppressed, it rebounded much higher than the control group. Essentially the signal that says ‘hold on to the water’, shot up in the water loading group. All of a sudden, the kidneys are being told to hold on to water, yet the water loading group lost more.”

If there’s one practice within Combat Sports that has withstood the test of time without having to stand trial it is water loading.

For a practice that we know next to nothing about, so many coaches, fighters and practitioners put a lot of stock in it. I won’t call the kettle black, my athletes do it, but I would be lying if I said I could explain the ins and out of what is happening in their body while they’re doing it.

What I do know is that for some people it seems to work, for others it doesn’t, but why that is the case, I cannot tell you. In fact, anyone who tells you that they can is likely telling you porkie pies (unless they’re sitting on some research the rest of us are yet to see).

Athletes, regardless of their weight, will usually drink 8L a day, for a number of days before completely cutting the fluid for a set period of time. This, theoretically, allows their body to ‘flush’ out water while there is none coming in. That’s the theory anyway, so how does it hold up in the research?

Well, the reason I say no one knows how this process works is because as it stands there is only one peer reviewed paper that has looked at this process in combat sport athletes.

The study was conducted at the AIS by Dr. Reid Reale as part of his PhD. Dr. Reale studied 21 grappling athletes who were split into two groups that were matched for weight (each athlete had a pair, for example each group had a set of 70kg, 85kg etc athletes). One group drank 40ml/kg and the other water loading group drank 100ml/kg for 3 days and then both groups reduced to 15ml/kg on day 4.

The researchers controlled their diets to eat 125kJ/kgFFM, with typical ‘fight week’ diets so they ate 5-6g/kgFFM protein, 1-2g/kgFFM of fat and each group had 300mg/kg of sodium, so they were not eating a low sodium diet. Why did they not eat a low sodium diet? As the researchers explain, as part of the scientific process you need to control as many variables as possible. In reality, when athletes complete a fight week, they are using a number of different strategies to make weight. This could include no carbs, water loading, supplements, fasted exercise, handstands (I have actually heard of athletes doing that) etc.

By controlling as many of those factors as possible, you can get a better understanding of how much this one particular practice contributes to the overall process. Before you say ‘that’s not what happens in reality’, bite your tongue, the authors acknowledge that and this is just how the scientific process works. Anyway, the researchers had some interesting results.

What they found was that the water loading group lost twice the amount of fluid with the control group losing 0.6% body mass and the water loading group losing 1.2% body mass. This effect was noted to be statistically significant and despite not mentioning it in the actual paper, upon personal discussion with the author about this, he has noted that there seemed to be a high degree of individual response to the practice among the participants.

What is most interesting to me as a practitioner and scientist is the physiological mechanism as to why this happens. Many people will say that water loading ‘tricks’ your body to pee more. It is theorized it does this by suppressing a hormone called Vasopressin which tells your body to hold on to water. By decreasing that hormone the signals that say to hold onto water are also decreased.

It is often said that during the period of no water intake this effect will hold for a set amount of time and because these signals to hold on to water are decreased, despite not drinking any water, the body will still release it. Or so the theory goes.

The research team did in fact find that Vasopressin was suppressed in the water loading group, however it did not stay suppressed during the time when water intake stopped. It not only did not stay suppressed, it rebounded much higher than the control group. Essentially the signal that says ‘hold on to the water’, shot up in the water loading group. All of a sudden, the kidneys are being told to hold on to water, yet the water loading group lost more. What’s happening here?

Well, by using extrapolations from animal studies, the researchers theorize that this effect could be due to decreases in Vasopressin causing an up-regulation of Aquaporin II channels in the collecting ducts of the kidneys. If you’ve never heard of an Aquaporin channel, they essentially work as flood gates that let water in and out of a particular part of your kidney. The more gates that are open, the more water that goes out.

This means that the water loading group lost more weight not due to ‘tricking’ their hormones to release more fluid, but by upregulating the Aquaporin channels which allowed more fluid to be released.

What was also theorized was that this process is not a switch that happens when we drink a particular amount of water, say 8L. Rather, it is similar to a dial where each individual athlete will have a response in relation to their body weight as they drink more water. More of these Aquaporin II channels will open with the more water you consume causing this effect.

So practically, what can we take from this? A number of things;

  • We cannot make a lot of assumptions due to the limited research in this area but what this study suggests is that common thoughts of how water loading works on a mechanistic level may be incorrect.
  • There is likely a high degree of individual variance between athletes and like most things in Sports Nutrition there will be responders and non responders.
  • It is likely that it is the effect not the dose that matters. This means an arbitrary number of 8L for everyone is not necessary, and some athletes may upregulate these Aquaporins on lower dosages than others. Anecdotally I have found consumption of fluid on a regular day plays a role in the degree of response ie a labourer who drinks 6L a day will need to drink a higher amount per kg of body weight than an office worker who struggles to drink 1L.
  • Sodium may not need to be completely restricted during a fight week. The researchers found that this effect occurs despite maintaining regular sodium intake, however this should be assessed in light of individual Fight Week strategies.
  • There is no ‘golden standard’ protocol for water loading. It may be the case that a longer water load may induce higher losses, however the duration, overall amount of water, and time when to cease water intake is yet to be explored in the research. Please note that a prolonged water load carries risks of hyponatremia and should only be used as a Fight Week strategy not during fight camp as it will upset the delicate balance of electrolytes in the body.

A little confused now about what do when it comes to water loading? You’re not alone, this is a conversation I have with students and other practitioners all the time. This is my advice.

  • Practice it with the athlete. Understand their daily water intake and then increase and monitor their response. It does not need to be 100ml/kg, trial it with 20ml/kg, 50ml/kg or 75ml/kg. There is no set standard and everyone responds differently. You do not need to be forcing crazy amounts of water in, remember it is the effect ie increased regular urination not the dose that is important. Find the dose that works for your athletes body. 
  • Have a trial run with all of their Fight Week strategies, maybe water loading isn’t necessary for them to make weight.
  • If the athlete is going to complete rapid weight loss aka a water cut in the sauna or bath, then I would advise a 3-4 day water load, or to make sure they are adequately hydrated each day leading in to that process. You want to start that process from an as minimally dehydrated position as possible and never want to be losing more than 3-4% body weight during this phase. 
  • Lastly, keep an open mind, be mindful of the potential risks of this practice, understand your athletes body and be willing to accept that if they pee their pants on the highway going to training, then water loading might not be for them (that is a true story).

For the full article follow the link here and for an in depth discussion of this topic with Dr. Reid Reale follow the link to his episode on The Fight Science Podcast.


Jordan Sullivan Founder and Head Dietitian – TFD



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