Proper hydration during any sort of physical activity is an absolute necessity- there are few more self-evident statements in the entire field of sports nutrition. When the body begins to run low on water, the list of systems that become compromised is so extensive that it’s almost not worth listing- suffice it to say that anybody who has become dehydrated or severely dehydrated while engaged in any sort of physical activity is well aware how devastating it can be.The purpose of this article is to outline how to best hydrate during any sort of extended physical activity, and how to NOT approach hydration. While drinking enough water may be a simple enough goal during short runs, a much more in depth plan is needed when performance over an extended duration in the heat is the goal. Simply chugging water can lead to complications (such as hyponatremia, which is admittedly rare for most recreational athletes) or a complete loss of energy as the system begins to run low on macronutrients, while imbibing large amounts of sports drinks may lead to gastric upset and vomiting. Understanding why this occurs and what precisely to consume can improve and extend performance tremendously.Hydration isn’t just about water
Yes, this statement is technically incorrect. Hydration IS just about water, by definition, but practically speaking the athlete should not JUST be concerned with H2O- there are numerous other nutrients whose absorption and function are intimately related to the body’s overall hydration status that must be considered at the same time.
How is water absorbed by the body?
Water is one of the few substances that the stomach is capable of absorbing- the stomach is primarily a processing station, and few compounds actually make it across the stomach lining into the bloodstream. It is not, however, the primary organ for water absorption, and why this is important will become more relevant later on. The majority of water is absorbed in the small intestine, and what is most critical is the understanding that MOST water is NOT ACTIVELY TRANSPORTED across the intestinal lining. In other words, there are no cells or transporters that carry water into your bloodstream- it just sort of flows by itself. Why is this so important? Because it means water absorption is heavily dependent on osmotic gradients- if the gut is filled with large quantities of mineral ions (particularly sodium), free glucose, etc., water will remain in the gut to serve as a buffer. If you’ve ever been on an exceedingly long run and taken in a massive quantity of Gatorade, you’ll understand exactly what this feels like. It sloshes around, flows back up into your esophagus, and can inspire truly astounding looking technicolor yawns.
Most other nutrients, on the other hand, are more actively transported- there are certain receptors lining those intestinal cells (cells called enterocytes, if anybody cares) that pull salts, sugars, amino acids, etc. through the intestinal lining into the cells in exchange for other compounds (e.g. they’ll pull in a hydrogen ion at the same time as an amino acid, then exchange the new hydrogen atom for a sodium molecule later.) One interesting fact here is that many compounds are co-transported, for example sodium cannot be efficiently absorbed without some sugars (remember this), as sodium uptake is coupled with glucose uptake, and absorption of both accelerates water uptake (as it forces water into the cells to buffer the two.) Almost as importantly, amino acid uptake is ALSO coupled with sodium uptake, an interesting fact that will soon become relevant.
Now, granted, this is simplified- there are a number of ways in which the body can continue to absorb water against an osmotic gradient (look up “three compartment model” if you’re truly curious), but the end lesson still holds- if the gut is too full of solutes, water absorption is slowed. The body needs to absorb these solutes in order to optimally absorb the water, which means the more electrolytes, sugars, and other molecules in the gut, the longer this will take. It also means that, in order for optimal absorption, there needs to be good blood flow to the cells in the gut to keep “sweeping” absorbed molecules away… which in turn lets more molecules be absorbed (again, simplified but fundamentally accurate).So if keeping the gut free of sodium is the best way to facilitate passive water uptake, why not just drink plain water? Well, simply put, for short exercise duration this is indeed often the best option- plain old water is absolutely adequate to hydrate during a typical weight lifting session, short set of sprints, or short distance run in moderate temperatures.During longer duration activity, however, it becomes important to take in compounds OTHER than water that are lost, which includes the aforementioned sodium, as well as carbohydrates to fuel continued activity. If you take in nothing but water, sodium and potassium loss through sweat can eventually be exceedingly detrimental to performance, as these compounds are absolutely vital to muscle contraction and, indeed, life in general. (Note that this will not cause cramping- cramps are not caused by low sodium or potassium. The reader is encouraged to repeat this to everybody who will listen until this myth dies. Cramping is caused by under-conditioning; this will be the focus of a later article). Replacing lost carbohydrates is also critical, as glycogen losses will eventually result in the body losing its ability to perform under anaerobic conditions, which means even the most efficient runner will be reduced to a slow stagger.
Hence, the advent of sports drinks- fluids that contain electrolytes that your body needs, as well as glucose to continue fueling activity (and aid water/sodium uptake). During moderate duration exercise, these sports drinks may seem like a godsend- they taste good (your body craves the salt and sugar), they go down easily, and they taste better than lukewarm brackish bottle water. The electrolytes replace those being lost through sweat, and the glucose is both useful for extending performance and for assisting in electrolyte uptake.
There is one major issue with these drinks, however- they are almost all calibrated to be ideally absorbed by a body at rest. Once the body begins to exert itself, blood concentrations of certain electrolytes and carbohydrates can decrease, and most importantly circulation to the gut can decrease. This last point bears explaining- when you exercise, the body shunts blood away from momentarily less essential systems (like the digestive system) and towards more essential systems (heart, lungs, muscles). If less blood is getting to your digestive tract, what does this mean for nutrient absorption? Remember how water is passively diffused and relies on the bloodstream to keep those molecules flowing away from the gut? If that slows down, suddenly the body can no longer establish a strong gradient (since those molecules that were previously being actively carried into the bloodstream then swept away are now just sitting there), and water just ends up sitting in the gut as a buffer.
Well, this is all very interesting but bloody useless. Give me something I can use.
The purpose of all the background information was to drive home a point- pure water alone can be detrimental to long term performance, as athletes require other nutrients to function, while too much sugar or salt in the digestive system will slow water absorption and result in a similar performance decrease, along with severe GI distress.
So what is ideal? Sports drinks, as mentioned earlier, tend to become increasingly too high in electrolyte and (mainly) sugar concentrations as activity increases, as the uptake of these nutrients slows and they begin to accumulate in the gut. The ideal glucose concentration used in Oral Rehydration Therapy (ORT- for patients with cholera or other diseases affecting the GI system whose lives depend on absorbing water and electrolytes, but who may not have access to an IV)- about 7 grams of carbohydrates per 8 ounces of fluid. The best drink on the market with that ratio, and therefore perhaps the best hydration drink for the athlete? Pedialyte.
Many MMA fighters, ultra runners and triathletes out there are probably already aware of how effective Pedialyte is during extended exercise- indeed it is becoming increasingly more common at Ironman events. Note that Pedialyte is higher in electrolytes than most sports drinks, which would seem to fly in the face of the recommendation regarding reducing gut concentrations of electrolytes. This is actually not a bad thing, since the lower level of glucose is actually more efficiently absorbed by the gut even when the system is under stress, which results in much faster sodium uptake. There is, however, one thing that Pedialyte is missing.Remember how amino acids are also coupled to sodium uptake? Some ORT formulations use small amounts of free floating amino acids to aid in hydration, and as these use different transporters that create different gradients (amino acids use a hydrogen ion gradient), the two can work in unison under similarly stressed conditions. Therefore adding amino acids to Pedialyte would create a superior formulation for the athlete (not to mention that amino acids during exercise can aid in recovery- another reason to include them). One critical item to mention, however, is not all amino acids are absorbed with sodium- the main amino acids aiding in sodium absorption are Aspartate, Glutamine, Alanine, Cysteine, Serine, and Glycine. Leucine also has some affinity for this process, though the branched chain amino acids in general are not the strongest sodium transporters. Small peptides (more than one amino acid linked) are also absorbed with sodium, though these are less easily dissolved in drinks, and harder to digest when the stomach is under stress. (If anybody has tried Accelerade™, they may notice it is incredibly effective at hydration until the gut begins to slow down, as the peptides from the whey protein contained within are no longer effectively breaking down in the system.)So the ideal sports drink?
Pedialyte or diluted Gatorade (though the low electrolyte concentration here may become a concern) with added free amino acids, such as glutamine (2-3 grams per 8 ounces of fluid). Note that I am a big fan of Branched Chain Amino Acids for exercise in general (to aid in recovery), but they don’t assist with sodium transport (and therefore hydration). There is one exception: At Large Nutrition makes a BCAA product with added glutamine- IDEAL for addition to a sports drink. It can be found here: BCAA+ (link opens in new window)
Full disclosure- neither this author nor Complete Human Performance receives any compensation, monetarily or otherwise, from At Large Nutrition. The author just believes that At Large is one of the few supplement companies on the market that makes consistently excellent supplements and includes all ingredients at their advertised doses.Simply adding 4-5 grams of this BCAA + Glutamine formulation to 16 ounces of Pedialyte should create a drink that allows for ideal hydration. And there you have it. That may have been a lot of reading to tell you why you should add BCAA+ to Pedialyte or diluted Gatorade and drink that over anything else, but isn’t it useful to know WHY?If, at this point, you’re wondering how to get in enough carbohydrates and calories to fuel activity, given all the issues surrounding water absorption… stay tuned. That will come in a later installment.
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