Hydration seems like it should be so easy: drink some water, go about your day, the end. Back in this blog’s early days, and when I first published The Primal Blueprint, my hydration advice was simple: drink when you’re thirsty.
Over the years, however, my thinking on the hydration issue has become more nuanced. When I updated and expanded the most recent edition of The Primal Blueprint in 2016, I expanded on that basic advice to include more details about what we should be drinking and how much.
For the most part, I still think that “drink to thirst” is a sound strategy for the average person. Your body has a built-in, well-regulated thirst mechanism that will keep you from becoming dehydrated in normal circumstances. However, some folks, like the endurance athletes in the crowd, would be wise to take a more intentional approach.
Benefits of Proper Hydration and How It’s Regulated
Hydration is a critical component of optimal health. Digestion, muscle contraction, circulation, thermoregulation, and neurologic functioning all rely on having appropriate fluid balance in the body.
Your brain and kidneys are constantly working to maintain optimal hydration status. When you become even slightly dehydrated, several things happen. First and foremost, your blood osmolality (concentration) increases. Dehydration can also cause a decrease in blood volume and, often, blood pressure.
The brain and kidneys sense these changes and release hormones and hormone precursors designed to restore homeostasis.1 For example, the pituitary gland releases an anti-diuretic hormone called vasopressin, or AVP, which tells the kidneys to hold on to water. Blood vessels constrict. Most importantly, a brain region known as the lamina terminalis initiates the powerful sensation we know as thirst.
Pay Attention to Your Thirst!
For most people, proper hydration is as simple as 1, 2, 3.
1) Tune in to your body’s thirst sensations and respond accordingly.
2) Tailor your fluid intake to your individual needs. Rules like “drink at least eight eight-ounce glasses of water” or “drink half your body weight in ounces” are all well and good, but they might not be right for you. There’s not a lot of scientific support for those nuggets of conventional wisdom. Some days you might need less or considerably more.
3) Make appropriate adjustments for exogenous factors like climate and exercise. When it’s very hot, or you’re sweating buckets during some long endurance event, it’s best to stay on top of hydration rather than waiting for thirst to kick in.
Don’t Become Waterlogged
You can have too much of a good thing. While I’m all about the trend of carrying stainless steel water bottles everywhere we go for environmental reasons, there’s never any call to drink literal gallons 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.
Hyponatremia can quickly become debilitating and even fatal. You may have heard the news stories of novice marathon runners losing consciousness after over-hydrating or radio station contestants drinking themselves to death in water-chugging contests.
By and large, your kidneys can deal with you drinking more water than you need within reasonable limits. You’ll just pee it out. Still, there’s no reason to force yourself to drink water beyond your natural thirst.
Salt: A Hydration Gamechanger
Maintaining proper fluid balance isn’t just about how much water you have in your body but also the concentration of key minerals, notably sodium. When you become dehydrated, you may experience not only thirst but also salt cravings.2
Salt continues to get a bad rap, though thankfully the tide of conventional wisdom seems to be turning as more people recognize that salt is not the enemy. Salt—or rather, sodium—is essential in the truest sense of the word. Without enough, and without the right balance between salt and other minerals, our bodies literally cannot function.
Sodium helps transport water through the walls of your small intestines, where 95 percent of fluid absorption takes place. We Primal folks naturally consume less sodium than the average person since a large proportion of most Americans’ dietary sodium comes from hyper-processed foods that we avoid.3 For optimal absorption, I recommend adding a pinch of salt to your water, especially if you’re craving the stuff. You can also make a jar of sole (“soh-lay”) water and add up to a teaspoon to a glass of water.
Do You Need to Add Electrolytes to Your Water?
Sodium is one of the main electrolytes, along with magnesium and potassium. Most Primal folks will get electrolytes by salting their food and consuming a diet containing nose-to-tail animal products and a diverse array of vegetables.
However, keto dieters and hard-charging athletes or other folks who sweat a lot, like those who work outside in hot climates, probably need to add electrolytes to their water to ensure proper fluid balance. Check out my guide to electrolytes on keto. I’ll talk more about considerations for athletes below.
How to Stay Hydrated Without Drinking Water
There’s no question that good ol’ fashioned water is the best, most Primal beverage. Some people tell me they don’t like the taste of water. I can’t relate, but if you’re one of those people, you can also meet your hydration needs with a combination of:
Mineral water or any of the sparkling waters on the market
Coffee, regular or decaf (no, coffee and caffeine aren’t dehydrating even during exercise45)
Hot or iced tea
Vegetable or fruit juice, though I’d caution you to limit your consumption of the latter
Still, I’d encourage you to work on embracing water. Maybe you need a water filter to make your tap water taste better. Try adding sliced citrus fruits, berries, ginger, cucumber, and fresh herbs to a pitcher of water to infuse flavor without a ton of sugar.
Remember, too, that we get up to 20 percent of our hydration needs met through food, especially fruits and vegetables. Carniflex enthusiasts, you still get some water from meat and the limited vegetables you might enjoy, but less than an omnivorous diet provides.
Hydration for Athletes
For athletic types and anyone who goes out and works up a serious sweat, the hydration issue is more complicated.
Athletes who engage in endurance sports such as long-distance running, triathlons, or events such as CrossFit competitions put their bodies under considerable physical and metabolic stress. (I won’t lecture you about chronic cardio here, but you know how I feel about it). They have greater-than-average hydration needs because they are losing fluids through sweat and because they need to be adequately hydrated to perform at a high level. Their muscles, digestive tract, and brain are really counting on water, just when it is becoming depleted.
While some incidental dehydration is inevitable during intense exercise, performance, thermoregulation, and recovery depend on being as well-hydrated as possible. Moreover, in the heat of the moment—no pun intended—it can be difficult to right the ship if fluid balance becomes compromised.
Does “Drink to Thirst” Work for Sports Hydration?
Here is where it gets tricky. Athletes need to consider factors including exercise duration and intensity, environment and temperature, training status, heat acclimatization, previous hydration level, diet, and body mass. There is no single best practice for all athletes. However, we can glean some guidelines from the available research.
Many respected scientists, including the inimitable Dr. Timothy Noakes (author of Waterlogged, world-renowned expert on hyponatremia, and low-carb eating enthusiast) and Drs. Marty Hoffman and Kerry Hoffman (Director of Medical Research and Medical Director of the Western States 100-mile endurance run, respectively) still recommend drinking to thirst.6 They don’t prescribe a hydration schedule or “ounces per hour” guidelines even for extreme endurance athletes.
However, there is also ample evidence that the thirst sensation can be suppressed during exercise, even when athletes are experiencing systemic dehydration.7 Plus, in a long, high-stress event like an Ironman, athletes cmay become too mentally and physically taxed to attend to their thirst.
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, let thirst guide you if you’re only out pounding the pavement 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. Remind yourself to drink periodically and do so if it feels comfortable. Practice your hydration strategy before race day, making an effort to train in similar weather conditions as you’ll likely encounter on the big day. But by all means, never force yourself to drink, especially not large quantities of water without also replacing lost electrolytes.
What to Drink for Optimal Sports Hydration
While plain water is ok, you are better off consuming a solution of water, salt, and glucose or sucrose.Wait, 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 or sucrose to facilitate the water transport through channels in the small intestine. This sugar is not for fueling, and it’s not a lot. Your fueling needs are a topic for a different post. I’m talking about a solution of 16 ounces of water, a pinch of salt, and a teaspoon of maple syrup (because it has a good composition of sucrose and glucose).
I do not advise relying on engineered “sports nutrition” drinks in general. They are usually more concentrated and higher in carbohydrates than you need. Those of you who have experienced the dreaded sloshing belly during a marathon know how they can sit in your stomach due to slow gastric emptying.8 Then, once the sugary fluid is in your digestive tract, your body draws stored water into the intestine to dilute it. This has a net dehydrating rather than a rehydrating effect. Ouch!
What’s more, engineered sports drinks like the ubiquitous Gatorade often have undesirable ingredients that I don’t want in my system. I prefer to make my own hydration drink for long, hot days of Ultimate Frisbee. When I know I’ll be sweating a lot, I also increase my electrolyte intake during or after exercise by salting my food more than usual or using an electrolyte product like LMNT.
Beware the Dehydration Sneak Attack
Dehydration can also sneak up on athletes who adopt an ambitious training schedule of back-to-back workouts if they aren’t careful about staying on top of their hydrating needs. Brad Kearns, my co-author on many books including Primal Endurance, sustained severe dehydration and an emergency appendectomy after attempting two high-intensity sprint and strength workouts over four days in 100-plus-degree heat.
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. Entering a hard workout slightly under-hydrated, then burning up more energy and generating more heat at the workout, might cause a dehydration spiral. Yes, even if you faithfully down fluids right after the workout until your thirst is temporarily quenched, you’ll find yourself in catch-up mode.
Hydration Accommodations for Female Athletes
As Dr. Sims, exercise physiologist, nutrition scientist, and co-founder of Osmo Nutrition reminds us, “Women are not small men.” Most of what researchers “know” about hydration comes from studies of male athletes. Female hormone cycles can profoundly affect women’s hydration needs.
In particular, 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 have lower homeostatic thresholds for AVP release and thirst.9 This means that women are physiologically closer to being hyponatremic, so they have to be particularly careful not to over-hydrate. (This might be why women are at greater risk for exercise-associated hyponatremia.10)
Dr. Sims advises that women in this phase sodium preload before exercise and hydrate using a water-sodium-sugar solution as described above.11
Designing an Optimal Primal Hydration Strategy
For most people, 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 force yourself to drink beyond thirst. If you’re constantly drinking water and in the bathroom every 30 minutes, you’re probably just cycling water in and out with no physiological benefit.
It’s not enough to drink water; you also have to absorb it. This is where salt comes in. Salt your food to taste, and add a pinch of salt to your water.
Eat high-water-content vegetables, plus some fruit if you want.
Athletes probably need a more intentional hydration strategy where they plan to check in with their thirst at regular intervals, consume a solution of water + sodium + sucrose or glucose, and replace lost electrolytes. Practice hydration strategies during training to prepare for race day.
Female athletes in the luteal phase of their menstrual cycles should consider sodium preloads, particularly before long or hot workouts.
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.
Q: What foods contain the most water?
All food contains some water. Fruits and vegetables contain the most water, so they are the most hydrating. At the top of the list are the ones you’d probably expect: watermelon, cantaloupe, and other melons; lettuce and spinach; berries; celery; and squash.
Q: Does sparkling water hydrate you?
Sparkling water, or carbonated mineral water, is just as hydrating as regular water.12 Sparkling water makes an ideal substitute for soda if you’re trying to cut back on sugar-sweetened beverages. Mix sparkling water with kombucha for a refreshing mocktail.
Q: Is coffee or decaf coffee dehydrating?
Caffeine does have a mild diuretic effect, meaning that it can increase urination. However, the preponderance of evidence confirms that coffee is not dehydrating when consumed in reasonable amounts, meaning two to four cups per day. Go ahead and count your coffee toward your hydration goal.
Q: How do I hydrate fast if I think I might be getting dehydrated?
Unless you show signs of serious dehydration, it’s enough to drink water to thirst with a pinch of salt to increase absorption. Signs of dehydration include extreme thirst, dark urine, dizziness, and confusion. See a doctor immediately if symptoms are severe.
Q: Do I need a home water filter? Is a pitcher filter, reverse osmosis system, or whole-house water filter best?
Plain water is the best way to hydrate. You may want to invest in a water filtration system if you don’t love your water. Pitcher, under-sink, and whole-house filters can all improve the taste and odor of tap water. Check out my guide: How to Choose the Best Water Filter.
Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.