Sparkling vs. still water: What's more hydrating?

From the desk of Robb Wolf

It was a random Tuesday a few months before we released <a href="https://drinklmnt.com/products/lmnt-sparkling?variant=41058153889815" target="_blank" rel="noreferrer noopener">LMNT Sparkling</a>. I was pouring one of our drink mixes into a glass of sparkling water (and narrowly avoiding a bubbly volcano), when I started to wonder: Does carbonation affect how hydrating a drink is? And do bubbles reduce how much fluid people consume?I couldn’t help but explore the science. Turns out, carbonation doesn’t influence how you absorb and retain fluids. But there’s a little more to it — for instance, temperature and carbonation both appear to independently influence thirst.I dug into the literature and wrote this article for those who, like myself, are curious about the relationship between carbonation and hydration. Give it a read — you might learn something useful.<h2>Is Sparkling Water More or Less Hydrating?</h2>When you add bubbles to an alcoholic beverage, it increases the rate of alcohol absorption (14 of 21 people experienced this effect, according to one <a href="https://pubmed.ncbi.nlm.nih.gov/17720590/" target="_blank" rel="noreferrer noopener">study</a>). That’s a fun fact to share at happy hour, but does a similar concept apply to hydration? Does carbonation influence how you absorb and retain fluids? The answer is: probably not.Let’s review three studies explaining why.<h3>Study 1: The Beverage Hydration Index (BHI)</h3>In this <a href="https://www.sciencedirect.com/science/article/pii/S000291652206556X?via%3Dihub" target="_blank" rel="noreferrer noopener">2015 study</a>, the authors tested the hydration power of 1 liter of various beverages compared to still water. The more a beverage promoted fluid retention (basically, the less subjects peed after drinking a beverage), the higher that beverage scored on the “beverage hydration index,” or BHI. In other words, the higher the BHI, the more hydrating the beverage.Still water was the reference point with a BHI of 1, and sparkling water <a href="https://ars.els-cdn.com/content/image/1-s2.0-S000291652206556X-gr2_lrg.jpg" target="_blank" rel="noreferrer noopener">scored the same</a>. Other drinks scored over 1.5. These high-BHI beverages included full-fat milk, skim milk, orange juice, and oral rehydration solution (water plus 18 grams glucose, ~1,300 mg sodium, and ~800 mg potassium). Why did these beverages rise above the rest? Because they each contain sodium, potassium, and glucose — all of which improve fluid absorption and retention.The authors made special note that “drinks with the highest electrolyte content tended to have the highest BHI.” Carbonation, on the other hand, made no difference to fluid retention.<h3>Study 2: Water, Carbonation, Caffeine, and Calories</h3>Eighteen young men <a href="https://www.tandfonline.com/doi/abs/10.1080/07315724.2000.10718956" target="_blank" rel="noreferrer noopener">consumed</a> one of the following five beverage protocols and collected urine throughout a 24-hour period:<ol><li>Water only</li><li>Equal amounts of water and caloric soda (caffeinated & carbonated)</li><li>Equal amounts of water and non-caloric soda (caffeinated & carbonated)</li><li>Equal amounts of water, instant coffee, and both types of soda (caloric & non-caloric)</li><li>Equal amount of water and a citrus drink (half-carbonated, but not caffeinated)</li></ol>Researchers found that hydration status (assessed by changes in body weight and blood tests) was not significantly different between the various protocols.<h3>Study 3: Bubbly Beverages After Exercise</h3>Researchers had eight men <a href="https://pubmed.ncbi.nlm.nih.gov/1521940/" target="_blank" rel="noreferrer noopener">cycle</a> in a hot room until they lost about 4% of their body weight. After the cycling session, they consumed a beverage to replace the exact amount of fluid they lost. They did this four times across four separate weeks, switching up the beverage each week. Two of the times the beverage was carbonated, while two times it was not.The results? Carbonation did not affect blood volume or electrolyte concentrations compared to the other conditions. The authors concluded that “Carbonated beverages were as effectiveas non-carbonated beverages in permitting rapid fluid replacement and recovery following dehydration.”So, equal volumes of still and sparkling water appear to be equally hydrating. However, most people don’t run this experiment in a real-world setting. Instead, they drink based on how thirsty they are. Does carbonation affect thirst? Let’s find out.<h2>Does Carbonation Affect Thirst?</h2>Thirst is a brilliant mechanism honed over billions of years of evolution. When blood volume drops from dehydration, specialized <a href="https://www.ncbi.nlm.nih.gov/books/NBK557510/" target="_blank" rel="noreferrer noopener">osmoreceptors</a> in the brain tell you to drink something.Interestingly, bubbly beverages — including <a href="https://pubmed.ncbi.nlm.nih.gov/9716439/" target="_blank" rel="noreferrer noopener">beer</a> — appear to quench thirst better than flatter ones. Let’s talk about nonalcoholic drinks, though, because rehydrating with beer isn’t going to do your health any favors.One <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042416/" target="_blank" rel="noreferrer noopener">2016 study</a> did a fantastic job exploring this topic. Researchers first had subjects drink 400 mL of two types of water (sparkling or still). Then, they offered subjects a jug of plain water for 15 minutes. They drank as much as they liked, and researchers recorded the volume consumed.The sparkling group drank about <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042416/figure/pone.0162261.g001/" target="_blank" rel="noreferrer noopener">25% less</a> plain water afterward, suggesting carbonated water quenched their thirst more effectively. Other experiments in this same study found that temperature had an independent influence — colder beverages were better at reducing thirst. Furthermore, when comparing cold still water and cold carbonated water, the carbonated variant won once again.<h2>Why Do Carbonated Beverages Quench Thirst Better?</h2>So, carbonated beverages appear to quench thirst better than non-carbonated beverages. But why? Thankfully, researchers answered this question in the <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042416/" target="_blank" rel="noreferrer noopener">same study</a>.First, cold water quenches thirst <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042416/#:~:text=The%20preponderance%20of,animals%20%5B22%5D." target="_blank" rel="noreferrer noopener">better</a> than room temperature water. A common myth online makes the opposite claim — but this is based on outdated literature from the 1980s [<a href="https://www.sciencedirect.com/science/article/abs/pii/0031938484902051?via%3Dihub" target="_blank" rel="noreferrer noopener">1984</a>, <a href="https://www.sciencedirect.com/science/article/abs/pii/0031938489900851?via%3Dihub" target="_blank" rel="noreferrer noopener">1988</a>]. What does this have to do with bubbly CO2? Well, people <a href="https://academic.oup.com/chemse/article-abstract/17/4/435/333046" target="_blank" rel="noreferrer noopener">perceive</a> carbonated beverages to be cooler in temperature than they actually are. Since carbonated water feels colder, it may mimic the thirst-quenching effect of cold.Second, bubbles amplify the drinking experience by creating biting sensations in the mouth and throat. These sensations result from CO2 passing through cell membranes, a harmless process that tricks you into believing you’ve consumed more fluid than you actually have. The colder the drink, the greater this effect.Third, carbonation <a href="https://pubmed.ncbi.nlm.nih.gov/23327968/" target="_blank" rel="noreferrer noopener">fills you up</a>, giving you the illusion of having drunk around <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5042416/#:~:text=Perceived%20volume%20was%20further%20increased%20when%20the%20beverage%20was%20cold%20and%20carbonated%20(%3E%2020%25%20increase)." target="_blank" rel="noreferrer noopener">20% more</a> fluid than you actually have. But remember — the 2016 study only gave subjects 15 minutes to drink extra water after the initial sparkling beverage. It makes you wonder: Is this satiety effect short-lived, or might it last for a while?According to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0939475309000787" target="_blank" rel="noreferrer noopener">2009 review</a>, CO2 takes 80–90 minutes to be absorbed by the wall of the stomach. Of course, not all the CO2 from your beverage hangs out in the stomach — some reaches the intestines, and some is burped out. But what CO2 remains can definitely influence how full you feel, and for quite a while. This satiety effect seems to kick in when drinking 300 mL (10 ounces) or more of a carbonated beverage.<h2>Lessons and Implications</h2>There are several lessons to draw from what we learned today.Ounce for ounce, still and sparkling water are equally hydrating. Carbonation doesn’t make a beverage more or less hydrating, no matter which metrics researchers use to assess hydration status.Electrolytes make a beverage more hydrating. Electrolytes (especially sodium) increase fluid retention and absorption.Carbonated drinks are more thirst-quenching. Bubbles mimic the sensation of cold water, which quenches thirst better than room temperature water. CO2 also fills you up and tricks you into thinking you’ve consumed more water than you have.All that lovely science aside, sparkling water isn’t for everyone. I love the crisp bite of carbonation, but not everyone feels the same way. For instance, one <a href="https://pubmed.ncbi.nlm.nih.gov/9407255/" target="_blank" rel="noreferrer noopener">study</a> found that higher carbonation levels decreased perceived sweetness and increased perceived “throatburn” in adults. Some folks enjoy these effects, while others don’t.It ultimately comes down to personal preference. If you prefer the invigorating bite of CO2, go for it! Having hydration options is one of the reasons we launched <a href="https://drinklmnt.com/products/lmnt-sparkling?variant=41058153889815" target="_blank" rel="noreferrer noopener">LMNT Sparkling</a>, not to mention convenience. Many folks have been stirring <a href="https://drinklmnt.com/products/lmnt-recharge-electrolyte-drink?variant=16358367199266" target="_blank" rel="noreferrer noopener">LMNT Drink Mix</a> into sparkling water for years — if you’re one of them, you know what I’m talking about (cleanup on aisle three!).Well, that settles it. Sparkling water and still water are both suitable for hydration. And bubbles quench thirst — what a sweet piece of trivia! Now, go impress your friends with all your newfound hydration knowledge.