<p><span style="font-weight: 400">A lot of people worry about dehydration on a keto diet. Dehydration often gets blamed for the headaches, weakness, and cramps that comprise the infamous keto flu.</span></p><p><span style="font-weight: 400">As a result, water gets advertised as a keto cure-all. Tired? Pep up by slugging water. Hungry? Curb those cravings with a cool glass of H</span><span style="font-weight: 400">2</span><span style="font-weight: 400">O. Head throbbing? Find the jug, quick!</span></p><p><span style="font-weight: 400">It seems logical. You lose more fluids on a low-carb diet, so you probably need to drink a bit more to replenish. In my experience, however, a water-only hydration strategy usually makes things worse. Keto or otherwise.</span></p><p><span style="font-weight: 400">I’m not saying that dehydration is never an issue. It can be. But overhydration is the problem that keeps me up at night, and not just because of the frequent bathroom breaks.</span></p><p><span style="font-weight: 400">The thing that concerns me is that overhydration may cause severe electrolyte imbalances. Add this to an electrolyte-depleting ketogenic diet and I’m very concerned.</span></p><p><span style="font-weight: 400">It’s crucial to manage your electrolyte levels on keto. If you don’t, electrolyte deficiencies will manifest as symptoms like headaches, low energy, or muscle cramps. And drinking more water will only make the symptoms worse.</span></p><p><span style="font-weight: 400">Nonetheless, conventional wisdom encourages overhydration. We’re supposed to drink 8 glasses of water per day. (Or more on keto!). I have a few thoughts on this.</span></p><h2><strong>The Myth of 8 Glasses of Water Per Day</strong></h2><p><span style="font-weight: 400">You’ve probably heard of the 8×8 rule. It’s a slice of pseudo-wisdom that’s been handed down for generations. It states that you should drink 8 ounces of water 8 times per day for optimal health and hydration.</span></p><p><span style="font-weight: 400">The 8×8 rule dates back to 1945, when </span><span style="font-weight: 400">the Food and Nutrition Board of the National Academy of Sciences </span><a href="https://onlinelibrary.wiley.com/doi/full/10.1111/j.1753-6405.2012.00866.x" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">recommended</span></a><span style="font-weight: 400"> adult males should consume about 2500 ml (~84 ounces) of water per day. There was no supporting science, but the recommendation stuck anyway. I mean NONE… 8 times 8 doesn’t even equal 84.</span></p><p><span style="font-weight: 400">In the 1960s, the physician Irwin Stillman </span><a href="https://onlinelibrary.wiley.com/doi/full/10.1111/j.1753-6405.2012.00866.x" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">encouraged</span></a><span style="font-weight: 400"> 8×8 hydration to support his high-protein low-carb Stillman Diet. He claimed the water was necessary for the kidneys to wash away fatty acids after breaking down fat. Again, there was no supporting science for this cockamamy theory.</span></p><p><span style="font-weight: 400">A medical professor named Heinz Valtin also thought 8×8 was cockamamy, so in 2002 he </span><a href="https://journals.physiology.org/doi/full/10.1152/ajpregu.00365.2002" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">reviewed</span></a><span style="font-weight: 400"> all the relevant literature on hydration. The punchline? “No scientific studies were found in support of 8×8”.</span></p><h2><strong>Fluid Balance and Hydration</strong></h2><p><span style="font-weight: 400">Hydration is best defined as maintaining adequate fluid balance in body tissues. It can also mean “drinking water”, but that tells us nothing about </span><i><span style="font-weight: 400">healthful </span></i><span style="font-weight: 400">hydration</span><i><span style="font-weight: 400">.</span></i></p><p><span style="font-weight: 400">Healthful hydration isn’t just about drinking water. That’s just one input in the system. The other inputs are electrolytes like sodium, chloride and potassium. These minerals maintain fluid levels inside and outside your cells so you can function at your best.</span></p><p><span style="font-weight: 400">Thanks to your kidneys, you don’t need to get these inputs exactly right. If you drink too much water, you dispose of the excess through urine. And if your fluid intake is low, you secrete antidiuretic hormone (ADH) so your kidneys retain more fluid. You pee less.</span></p><p><span style="font-weight: 400">Your kidneys also </span><a href="https://journals.physiology.org/doi/full/10.1152/ajpregu.00365.2002" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">regulate electrolyte levels</span></a><span style="font-weight: 400">. As electrolyte levels rise (called rising osmolality), you excrete more electrolytes. As osmolality falls, you retain them.</span></p><p><span style="font-weight: 400">But if you’re on a keto diet—or any diet, really—how much water should you drink?</span></p><h2><strong>Preventing Dehydration</strong></h2><p><span style="font-weight: 400">There are two common hydration strategies:</span></p><ol><li style="font-weight: 400"><span style="font-weight: 400">Drink on a set schedule (8×8, etc.)</span></li><li style="font-weight: 400"><span style="font-weight: 400">Drink to thirst</span></li></ol><p><span style="font-weight: 400">The first strategy is designed to prevent dehydration, or net water loss from the body. When total body water decreases by 2% or more, that’s called hypohydration.</span></p><p><span style="font-weight: 400">Dehydration is the process of losing water. Hypohydration is the undesirable consequence.</span></p><p><span style="font-weight: 400">Rigorous athletes often become hypohydrated due to sweat loss. It happens faster than thirst can keep up. In other words, drinking to thirst is inadequate to compensate for water losses in these people.</span></p><p><span style="font-weight: 400">For the ordinary individual though, thirst can often be a great indicator of hydration levels (of course there are exceptions where thirst becomes less accurate, even for the average Joe—high altitude training and very cold climates, to name two).</span></p><p><span style="font-weight: 400">The question is: does it matter? Is preventing dehydration such an important goal?</span></p><p><span style="font-weight: 400">Perhaps not. In a </span><a href="https://pubmed.ncbi.nlm.nih.gov/30659500/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">2019 systematic review</span></a><span style="font-weight: 400"> that looked at drinking on a set schedule vs drinking to thirst in 82 athletes, dehydration didn’t significantly impact athletic performance. Athletes drinking to thirst performed roughly the same as the set-schedule group, despite losing about double the body water.</span></p><p><span style="font-weight: 400">But isn’t dehydration dangerous? Again, perhaps not as much as it’s cracked up to be. According to a </span><a href="https://www.mdalert.com/article/brief-review-of-the-literature-on-hyponatremia-death-and-injury-in-endurance-athletes" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">review</span></a><span style="font-weight: 400"> from MDAlert, there isn’t a single sports-related death from dehydration in all the medical literature.</span></p><p><span style="font-weight: 400">In fact, the bigger danger is drinking too much.</span></p><h2><strong>The Problem With Overhydration</strong></h2><p><span style="font-weight: 400">To prevent dehydration, many athletes drink on a set schedule. But this overhydration strategy causes a more serious problem: </span><a href="https://pubmed.ncbi.nlm.nih.gov/19523574/#:~:text=Exercise%2Dassociated%20hyponatremia%20(EAH),the%20kidney%20to%20excrete%20water." target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">Hyponatremia</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">Hyponatremia is the clinical term for dangerously low sodium levels. The symptoms of hyponatremia include muscle cramps, fatigue, weakness, and confusion. In severe cases, hyponatremia can be fatal.</span></p><p><span style="font-weight: 400">Common causes of hyponatremia include heart failure, kidney failure, liver disease, cancer, diuretics, vomiting, diarrhea, and—relevant here—excess fluid intake. Excess fluids literally water down your blood. The sodium concentration plummets.</span></p><p><span style="font-weight: 400">Because the symptoms of dehydration mimic the symptoms of hyponatremia, people often get them confused. But drinking sodium-free water to treat “dehydration” only makes hyponatremia worse. Tragically, one basic army trainee </span><a href="https://pubmed.ncbi.nlm.nih.gov/10091501/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">perished</span></a><span style="font-weight: 400"> from this mix-up. He was given water when he needed sodium.</span></p><p><span style="font-weight: 400">Most people, of course, won’t die from overhydration. The electrolyte deficiencies I see among low-carb and keto dieters are more subtle. But even subtle deficiencies can cause a constellation of keto flu symptoms.</span></p><h2><strong>Hydration on Keto</strong></h2><p><span style="font-weight: 400">There are several reasons keto dieters are more prone to electrolyte deficiencies:</span></p><ol><li style="font-weight: 400"><span style="font-weight: 400">They don’t eat enough salt</span></li><li style="font-weight: 400"><span style="font-weight: 400">They lose more electrolytes through urine</span></li><li style="font-weight: 400"><span style="font-weight: 400">They drink too much sodium-free water</span></li></ol><p><span style="font-weight: 400">Let’s look at these individually.</span></p><h3><strong>#1: Not eating enough salt</strong></h3><p><span style="font-weight: 400">When people switch to a whole foods keto diet, they lose their main source of dietary sodium: Packaged foods.</span></p><p><span style="font-weight: 400">I’m all for eliminating junk food. It’s bad for you. But is it bad because of the salt? I don’t think so. </span><a href="https://drinklmnt.com/blogs/health/is-sodium-good-or-bad-for-you" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">Salt has been demonized</span></a><span style="font-weight: 400"> because unhealthy foods—packed with </span><a href="https://drinklmnt.com/blogs/health/how-sugar-is-making-us-sick" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">sugar</span></a><span style="font-weight: 400"> or vegetable oils—also tend to be high in salt. We’ve thrown the baby out with the salty bathwater.</span></p><p><span style="font-weight: 400">The result is that Paleo and keto tribes believe it’s healthy to limit sodium consumption. And then, six hours, days, or weeks into the diet, they wonder why they feel like a donkey who just crossed the Sahara.</span></p><p><span style="font-weight: 400">They’re not supplying enough sodium to meet daily needs. The </span><a href="https://pubmed.ncbi.nlm.nih.gov/22110105/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">sweet spot</span></a><span style="font-weight: 400"> for non-keto dieters seems to be about 4–6 grams sodium per day (2–3 teaspoons of salt), and low-carb acolytes probably need more.</span></p><h3><strong>#2: Increased electrolyte loss</strong></h3><p><span style="font-weight: 400">Eating a keto diet is all about drastically restricting carbohydrates and/or restricting calories. When you restrict carbs, you limit the necessity of the hormone insulin to rise above baseline levels.</span></p><p><span style="font-weight: 400">One of insulin’s </span><i><span style="font-weight: 400">many</span></i><span style="font-weight: 400"> jobs is to tell your kidneys to retain sodium. So as insulin levels fall on keto, you get the opposite effect: </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858534/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">You lose more sodium</span></a><span style="font-weight: 400">.</span></p><p><span style="font-weight: 400">You also lose more fluids on keto, which increases dehydration risk. Which leads me to my final point…</span></p><h3><strong>#3: Drinking too much water</strong></h3><p><span style="font-weight: 400">Visit any keto blog and you’ll see confused hydration advice splattered everywhere. If you’re lucky, you’ll find vague guidance about taking more electrolytes. (Which electrolytes, we often aren’t told.) Usually, you’re told to drink water like it’s the reason you were put on Earth.</span></p><p><span style="font-weight: 400">If you’re hungry, drink water. If you’re feeling dehydrated, drink water. If you’re not thirsty, thirst be damned! Drink water anyway.</span></p><p><span style="font-weight: 400">Let me steel-man this argument before disagreeing. Low-carb diets do, in fact, have a diuretic effect. This is driven by the same </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5858534/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">insulin-mediated mechanism</span></a><span style="font-weight: 400"> that makes you excrete more sodium. On keto, you probably do need a bit more water.</span></p><p><span style="font-weight: 400">But if you make water your sole focus, you risk diluting blood sodium levels. And compared to the risks of hyponatremia, the risks of dehydration are minor league.</span></p><p><span style="font-weight: 400">But you don’t need to trade one for the other. You can prevent both dehydration and overhydration.</span></p><h2><strong>How to Stay Hydrated On Keto</strong></h2><p><span style="font-weight: 400">A keto hydration strategy should:</span></p><ol><li style="font-weight: 400"><span style="font-weight: 400">Provide sufficient fluids to cover baseline needs and any extra fluid losses</span></li><li style="font-weight: 400"><span style="font-weight: 400">Provide sufficient electrolytes (especially sodium) to cover baseline needs and any extra electrolyte losses</span></li></ol><p><span style="font-weight: 400">I recommend using thirst to guide your fluid intake. It’s a </span><a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4212586/" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">tightly-regulated system</span></a><span style="font-weight: 400"> fine-tuned over millions of years of hominid evolution.</span></p><p><span style="font-weight: 400">This brings me to my fundamental rule of healthful hydration: </span><b>drink electrolyte water to thirst</b><span style="font-weight: 400">. I created </span><a href="https://drinklmnt.com/products/LMNT-Recharge-electrolyte-drink" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">LMNT</span></a><span style="font-weight: 400">, my salty electrolyte drink mix, to make this easy.</span></p><p><span style="font-weight: 400">Drinking to thirst is usually enough, but certain situations may require more aggressive hydration. These situations include:</span></p><ul><li style="font-weight: 400"><span style="font-weight: 400">Exercising in </span><a href="https://drinklmnt.com/blogs/health/why-winter-hydration-is-important" target="_blank" rel="noopener noreferrer"><span style="font-weight: 400">cold or high-altitude climates</span></a></li><li style="font-weight: 400"><span style="font-weight: 400">Sweating profusely</span></li><li style="font-weight: 400"><span style="font-weight: 400">Consuming a low-carb diet</span></li></ul><p><span style="font-weight: 400">When you drink additional fluids, it’s doubly-important to add sodium to those fluids to prevent exercise-associated hyponatremia. The water should taste a bit salty.</span></p><p><span style="font-weight: 400">So if you’re feeling “dehydrated” on keto, it probably has more to do with electrolytes than water.</span></p>