Hydration. It seems like it should be so easy: drink some water, go about your day, the end. If only it was that simple. In fact, there are many (often contradictory) opinions out there about what we should be drinking, and how much, and when, especially for the athletes among us. I have written about hydration before , and kept up to date with breaking research in recent years. Now, as I am working on the completely revised, updated, and expanded edition of The Primal Blueprint (slated for release in December 2016), I’d like to share a more sophisticated and nuanced opinion on the subject. As you might recall, in the original Primal Blueprint I essentially said, “obey your thirst like Grok  did” and left it at that. So let’s dig a little deeper, especially for those of us who are active and athletic.
Hydration is a critical component of optimal health. It is important for digestion, muscle contraction, circulation, thermoregulation, and neurologic functioning, among others. My seemingly flippant “obey your thirst” message actually has good scientific support. Your body has a built in, well-regulated thirst mechanism that will tell you if you need to drink additional fluids. If you’re low, besides initiating thirst to get you to drink more, your body is able to respond by releasing an anti-diuretic hormone called vasopressin, or AVP , to retain more fluid in your body. To hydrate optimally, you simply need to tune in to your body’s  thirst sensations, tailor your fluid intake to your individual needs, and make appropriate adjustments for exogenous factors like climate (drink more if it’s hot) and exercise (replenish water lost through sweat). Obviously, these outside influences should be reflected in your thirst. There is no good evidence that we should all adhere to conventional wisdom’s  old 8×8 rule: drink at least eight eight-ounce glasses of water every day without fail. Nor is there any benefit to drinking even greater quantities of water; in fact drinking too much can bring about the dangerous condition of hyponatremia —where excess fluid compromises the all-important sodium balance in your blood. This situation can quickly become debilitating and even fatal. You may have heard the news stories in recent years of novice marathon runners losing consciousness, or radio station contestants drinking themselves into the ER or even to death.
Nothing I’ve seen in the past few years, since the last time I updated The Primal Blueprint, makes me inclined to change my advice for the average healthy person who isn’t engaged in heavy physical activity. Drinking to thirst is still the best bet. Remember, too, that we get up to 20% of our hydration needs met through food , especially watery fruits and veggies, which you should be eating plenty of if you are eating primally. If you are eating a healthy (Primal!) diet, drinking when you feel thirsty, and aren’t exhibiting signs of dehydration (headaches, dizziness, very dark urine, etc.), you should be fine.
And don’t forget about salt. Dietary sodium has been positioned in a negative light by conventional wisdom. I have argued that that is unfounded , and scientists are beginning to reconsider  the anti-salt crusade as well. Sodium, which we get from salt (NaCl—high school chemistry anyone?), helps transport water through the walls of your small intestines, where 95% of fluid absorption takes place. You need salt, and we primal peeps are probably getting less of it compared to the rest of the population since a large proportion of most Americans’ dietary sodium comes from processed foods . In fact, when transitioning from a Standard American Dietary pattern to a primal/paleo style pattern, it’s possible to become deficient in sodium and develop a need to consume supplemental sodium to get rebalanced. In general, don’t be afraid to salt your food. If you are not eating while you drink, you can even add a pinch of salt to your water to boost absorption (keep reading for a further recommendation that will really blow your mind).
Advice for Fitness Enthusiasts (and Other High Energy, High Calorie Burners)
For athletic types—anyone who goes out and works up a serious sweat—the hydration issue is considerably more complicated, and my view on how they should hydrate has become more nuanced. For us folks, especially those of you engaged in endurance sports such as long distance running or triathlons, or back-to-back events such as CrossFit competitions featuring multiple physical efforts in the same day, or those doing physical labor in warm climates, you are putting your body under considerable physical and metabolic stress. (I won’t lecture you about chronic cardio here, but you know how I feel about it ). You have greater-than-average hydration needs both because you are losing fluids through sweat and because you need to be properly hydrated in order to perform at a high level. Your body (your muscles, your digestive tract, your brain) is really counting on water, just when it is being depleted. While some amount of incidental dehydration is inevitable during intense exercise, being as well-hydrated as possible is important for performance, thermoregulation, and recovery, and it can be difficult to right the ship if your hydration starts being compromised.
So what is the responsible, hydration-conscious athlete to do? Here is where it gets tricky. Athletes need to consider a range of factors, including exercise duration and intensity, environment and temperature, training status, heat acclimatization, previous hydration level, diet, body mass, and so on. It is clear that there is no single best practice for all athletes. However, there are some guidelines that have been suggested by some of the leading researchers in hydration and athletic performance.
What to Drink
While plain water is ok, you are better off consuming a solution of water, salt, and glucose/sucrose. WAIT, STOP THE PRESSES! Did Mark Sisson really just recommend adding sugar to water?!? I did. Hear me out. For maximal water absorption, the body requires sodium and glucose/sucrose to facilitate the transport of water through channels in the small intestine. Please be clear, this sugar is not for fueling, and it’s not a lot. Your food/fuel is a totally different issue for a different post . What the experts are now talking about here is a solution of 16 oz of water, a pinch of salt, a teaspoon of maple syrup  (because it has a good composition of sucrose and glucose).
I do not advise you to rely on engineered “sports nutrition” drinks in general. They are usually carbohydrate dense because they are designed to combine hydration with fueling. Many follow the long-standing advice to consume a solution of 7% glucose, although Dr. Stacy Sims (exercise physiologist, nutrition scientist, and co-founder of Osmo Nutrition ) recommends a 2-4% osmolality solution for optimal hydration. It can be extremely difficult to know how concentrated your drink is, and you might purposefully be making it extra concentrated if you are using one of those powdered formulas you mix yourself. This is a problem because fluids that are too concentrated and too sugary , like many sports drinks on the market, can sit in your stomach (if you have experienced the dreaded sloshing belly during a marathon know about slow gastric emptying ). Then, once the sugary fluid is in your digestive tract, your body actually draws stored water into the intestine to dilute them. This has a net dehydrating rather than a rehydrating effect. Ouch! Time to change the narrator’s text in the sports drink commercials, eh? Note that anything like a lemonade or fruit juice or even coconut water can also be problematic because they too have too much glucose to provide ideal hydration.
What’s more, engineered sports drinks like the ubiquitous Gatorade often have undesirable ingredients like dyes and chemical preservatives that I don’t want in my system. (Unless they sign me to a multi-year endorsement deal; how does “Gatorade presents MarksDailyApple.com” sound?) If you do decide to use one of these products, dilute it with water unless you know it is specifically engineered to have a lower osmolality.
When and How Much to Drink
There are many respected scientists, including the inimitable Dr. Timothy Noakes (author of Waterlogged , world-renowned expert on hyponatremia, long considered one of the leading endurance exercise physiologists in the world, and recent convert to primal-style eating!) and Drs. Marty Hoffman and Kerry Hoffman (Director of Medical Research and Medical Director of the Western States 100-mile endurance run, respectively) who recommend drinking to thirst  even for extreme endurance athletes. This means no schedule, no “per hour” guidelines, all idiosyncratic and intuitive. However, there is also ample evidence that the thirst sensation can be suppressed even with systemic dehydration . Plus, in a high-stress situation like an Ironman, or during a high stress block of training or living (jet travel, etc.), there is a real concern that individuals might become too mentally and physically taxed to be attuned to their thirst. This could happen in the middle of an endurance event or ultra race, where so much focus is on pacing/competing instead of on biofeedback, or it could happen over time from the accumulation of ambitious workouts.
Brad Kearns, my Primal Endurance  co-author and Primal Blueprint Publishing  sidekick, sustained a serious medical setback this past summer (severe dehydration and emergency appendectomy—sordid details are in the book for your reflection and edification) despite his decades of experience as a seemingly optimally hydrated athlete. This happened in June during a week of 100-plus-degree heat and two high-intensity sprint/strength workouts over a four-day period. The lesson here is that as the athlete stacks up big workouts over time, it’s possible to bring a bit of dehydration to the table at successive workouts. You might not notice your condition working at your desk the day before you bang out sprints and max effort high jumps in 106 ºF heat, but entering a hard workout slightly underhydrated, then burning up more energy and generating more heat at the workout, might throw you into catch-up mode that could spiral downward over time. Yes, even if you faithfully down fluids right after the workout until your thirst is temporarily quenched.
Brad recalls, “Of course I drank like a fish after my high intensity session on Tuesday in the heat, rested carefully for a couple days, then hit it hard again Friday. I felt fine—recovered, hydrated, and explosive during the workout. But that pretty much always happens during a workout when the juices get flowing! After the Friday workout, I started to not feel so good (appendix acting up as I would learn later). As I convalesced in bed over the weekend, the health disturbance was enough to put my thirst mechanism out of order. By Sunday, I had burned up an organ and received nine IV bags in succession before and after the surgery, until I was finally declared rehydrated.”
If you are exercising primally , you are not putting sustained, intense stress on your body (by design!), so you can safely drink to thirst. Likewise if you’re only out there for an hour or two in temperate conditions. If you are exercising for more than a few hours, or in extreme conditions, I think it is wise to have a hydration plan. This does not mean a hard-and-fast rule to drink a certain amount per hour, despite what some experts recommend . This means reminding yourself to drink periodically and doing so if it feels comfortable. It also means going into races adequately trained, having tested and practiced hydration strategies, and being heat acclimatized if appropriate. But by all means, never force yourself to drink! This is a primary way people induce hyponatremia , which can be fatal.
Advice for Women
As Dr. Sims reminds us, “women are not small men .” Most of what researchers “know” about hydration comes from studies of men, whose hydration needs can be very different from women’s due to female hormone cycles. In particular, for women during the luteal phase (between ovulation and onset of period), when estrogen and progesterone are high, blood volume and total body sodium are low. At the same time, women’s homeostatic threshold for AVP release and thirst are lowered . The effect of these together is that women are physiologically closer to being hyponatremic and so have to be particularly careful not to overhydrate (this might be why women are at greater risk for exercise-associated hyponatremia). Dr. Sims also advises that women in the high hormone phase sodium preload  before exercise and hydrate using a water-sodium-glucose/sucrose solution as described above (this advice applies to all women, but is it especially important for female athletes).
The Bottom Line
- For the average person, people engaged in shorter-duration exercise, and endurance athletes not immediately preparing for or actively engaged in long workouts or races, drinking to thirst is still the best recommendation.
- Drink throughout the day. Keep water handy so it is available if you want it, but don’t be a slave to it. Remember, we can only absorb so much water. Drinking more doesn’t necessarily make us more hydrated. If you are a Nalgene addict who is in the bathroom every 30 minutes, you are just cycling water in and water out with no actual physiological benefit.
- Eat lots of high water-content fruits and vegetables.
- Don’t be afraid of salt. Salt your food to taste. Add a pinch of salt (and a teaspoon of maple syrup) to your water. Athletes, especially women in the luteal phase of their menstrual cycles, should consider sodium preloads, particularly before hot workouts.
- Athletes should consider hydration preloads before extreme events or training phases, particularly in hot weather.
- Never force yourself to drink or drink past the point of comfort.
- Most sports drinks are not your friend. Look for ones that use a combination of glucose and sucrose instead of fructose, maltodextrin, sucralose, or xylitol, and avoid ones with a lot of unnatural ingredients like dyes. In a race situation, if you are desperate you can drink whatever is available at the aid station, but dilute it with water.
- Remember, hydration needs and optimal strategies are idiosyncratic. Just as I advise you to experiment with your diet to find what works best for you, do the same with hydration. Especially if you are an athlete, you must do the tinkering in training so you know what your body needs and how it responds.
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