Electrolytes vs Sports Drinks: What Actually Rehydrates You

Jasmine Meagher, BSc Food Science and Nutrition

Founder, Ritua · 9 min read

Walk down any supplements aisle and the two products sit almost side by side. A bottle of brightly coloured sports drink, and a sachet of electrolyte powder that promises to hydrate you better than water. The packaging on both implies they are competing for the same job. They are not.

Here is the honest answer before we get into the physiology. For most people in most situations, plain water is fine. Where the two products genuinely differ is in what they are built to deliver: a traditional sports drink is built to deliver carbohydrate as fuel, and an electrolyte product is built to deliver sodium for fluid retention. Those are two different jobs, and the research on gastric emptying, osmolality and rehydration efficacy makes the distinction fairly clear.

Two Drinks, Two Different Jobs

A traditional sports drink is a carbohydrate electrolyte solution. The Australian Institute of Sport describes the category as containing 4 to 8 per cent carbohydrate, meaning 4 to 8 grams per 100 millilitres, with sodium at roughly 10 to 30 millimoles per litre. The carbohydrate is the main event. The sodium comes along for the ride, partly for taste and partly to help the carbohydrate move across the gut wall.

An electrolyte only product inverts that. There is little or no carbohydrate, and the sodium concentration is usually several times higher. It is not trying to fuel you. It is trying to change what your kidneys do with the water you drink alongside it. Once you frame them that way, the question stops being which drink is better and becomes which job you actually need done.

For Most Sessions, Water Is Genuinely Fine

This is the part the marketing tends to skip. The AIS puts sports drinks in Group A of its Supplement Framework, which means they have good evidence behind them for specific uses, and then is quite direct about what those uses are not. For brief exercise under 45 minutes, its guidance is simply that a sports drink is not needed, and it notes that sports drinks are not required at every training session and may be an unnecessary expense.

The American College of Sports Medicine position stand on exercise and fluid replacement is similarly measured. It says that during exercise, drinks containing electrolytes and carbohydrate can provide benefits over water alone under certain circumstances. The phrase doing the work in that sentence is "under certain circumstances". A 40 minute strength session in an air conditioned gym is not one of them.

What the Sugar in a Sports Drink Is Actually For

The ACSM position stand is specific about when carbohydrate earns its place. It states that carbohydrate consumption can be beneficial to sustain exercise intensity during high intensity events of about an hour or longer, as well as less intense events sustained for longer periods, and that intakes of roughly 30 to 60 grams per hour maintain blood glucose and sustain performance. The AIS uses the same 30 to 60 grams per hour figure for efforts of one to two and a half hours, rising to as much as 90 grams per hour beyond about three hours.

Run the arithmetic on a 600 millilitre bottle at 6 per cent carbohydrate and you get about 36 grams. For a three hour ride, that is roughly the low end of one hour's fuelling and entirely justified. For a 40 minute class, it is 36 grams of sugar you did not need, delivered alongside about 280 milligrams of sodium if the drink sits at 20 millimoles per litre. That is a large fuel dose attached to a fairly small electrolyte dose, which is exactly backwards if fluid retention was what you were after.

Carbohydrate, and How Fast a Drink Leaves Your Stomach

Fluid cannot be absorbed until it leaves the stomach, so gastric emptying sets the ceiling on how quickly a drink can reach you. The ACSM position stand notes that if one beverage has to meet both fluid and carbohydrate needs, the carbohydrate concentration should not exceed 8 per cent, or should be slightly less, because highly concentrated carbohydrate beverages reduce gastric emptying.

That ceiling is not arbitrary. In a classic Journal of Physiology study by Vist and Maughan, six men drank 600 millilitres of four different solutions while researchers measured emptying by gastric aspiration. A dilute 40 grams per litre glucose solution had a half emptying time of 17 minutes. An isoenergetic but concentrated 188 grams per litre glucose solution took 130 minutes. A glucose polymer at the same 188 grams per litre, which was far less osmotically active, took 64 minutes.

The authors concluded that both osmolality and carbohydrate content influence gastric emptying, but that carbohydrate content has the greater influence. In plain terms, the more concentrated the sugar, the longer the drink sits in your stomach rather than rehydrating you. That is why sports drinks cluster around 6 per cent rather than going higher, and it is also why a fizzy drink or a neat cordial is a poor rehydration choice.

Osmolality and What Happens in the Small Intestine

Osmolality is a measure of how many dissolved particles a fluid contains, and drinks are usually sorted against blood. A 2022 Sports Medicine meta-analysis by Rowlands and colleagues used the standard thresholds: hypertonic above 300 milliosmoles per kilogram, isotonic 275 to 300, hypotonic below 275, and water below 40. Pooling 28 studies and 68 drink treatment effects, it found the smallest fall in plasma volume during continuous exercise with hypotonic drinks at 6.3 per cent, compared with 7.5 per cent for water, 7.4 per cent for hypertonic drinks and 8.7 per cent for isotonic ones. Hypotonic drinks came out very likely superior to isotonic.

It is worth being honest about how large that effect is, though, because a direct absorption study suggests osmolality matters less than the marketing implies within the normal range. Gisolfi and colleagues had seven cyclists, five men and two women, ride for 85 minutes while drinking either water or one of three 6 per cent carbohydrate beverages formulated at 197, 295 or 414 milliosmoles per kilogram. Tubes placed in the duodenum and jejunum measured absorption directly.

There were no significant differences in gastric emptying or in total fluid absorption between any of the drinks. Of the volume ingested, 82 per cent was absorbed for water, and 74, 76 and 68 per cent for the hypotonic, isotonic and hypertonic drinks. The authors concluded that within the osmotic range studied, fluid absorption from a 6 per cent carbohydrate electrolyte drink is not different from water. Osmolality bites hard at the concentrated end, as Vist and Maughan showed, but across the range where ordinary sports drinks live it is not the deciding factor.

Sodium Is the Part That Keeps the Fluid in You

Absorbing fluid and keeping it are different problems. A 2017 review in the Journal of Applied Physiology by Evans, James, Shirreffs and Maughan sets out why. Drinking a large volume of plain water dilutes plasma sodium and drops plasma osmolality, which switches off the hormonal signal to conserve water, and a prompt diuresis follows. You absorb the water and then void a good share of it. Across the studies the authors reviewed, urine output fell steadily as drink sodium concentration rose, and maintaining a positive fluid balance required sodium concentrations somewhat higher than the roughly 20 to 25 millimoles per litre typical of commercial carbohydrate electrolyte sports drinks.

The most direct head to head comparison is the beverage hydration index work published in the American Journal of Clinical Nutrition in 2016. Seventy two healthy, euhydrated men each drank one litre of still water or one of 13 test beverages over 30 minutes, and urine was collected for the next four hours. The sports drink tested contained 3.9 grams of carbohydrate per 100 millilitres and 21 millimoles of sodium per litre. The oral rehydration solution contained less than half the carbohydrate and 55 millimoles of sodium per litre.

Total urine masses over 4 hours were smaller than the still water control (1337 grams) after an oral rehydration solution (1038 grams), full fat milk (1052 grams) and skimmed milk (1049 grams). Cumulative urine output at 4 hours after a sports drink was not different from the response to water ingestion.

— A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index, American Journal of Clinical Nutrition, 2016

The beverage hydration index at two hours was 1.54 for the oral rehydration solution, against a reference value of 1.00 for water. The sports drink did not separate from water at any point. Two caveats are worth stating plainly: the participants were young men, and they started euhydrated rather than sweat depleted, so this tells you about holding onto fluid rather than about recovering from a hard session. Even so, the pattern lines up with the post exercise literature. Sodium concentration, not carbohydrate, is what moved the needle.

When Each One Is the Better Choice

A sports drink is genuinely the better choice when the limiting factor is fuel rather than fluid. Efforts beyond about an hour at intensity, long rides and runs, tournament days with back to back matches, anything where the ACSM's 30 to 60 grams of carbohydrate per hour is the point. Getting some of that as a drink is convenient and the accompanying fluid is a bonus.

An electrolyte drink makes more sense when you have lost a lot of fluid and do not need the fuel. Heavy sweat losses in the heat, a short turnaround before the next session, or the familiar situation where you have been drinking water steadily and it seems to pass straight through you. The Evans review notes that effective rehydration generally requires drinking more than you lost, on the order of 1.5 litres for every litre of sweat, alongside enough sodium to hold it.

Neither is needed for a standard gym session under an hour, a walk, or a moderate run in mild weather. That is most training for most people, and water plus a normal diet covers it. There is also no rule against combining them: a long hot event can warrant carbohydrate for fuel and extra sodium on top, because the amount of sodium in a standard sports drink was never designed to do the retention job on its own.

The Bottom Line

Sports drinks and electrolyte drinks are not rival answers to one question. Carbohydrate concentration governs how fast a drink clears your stomach and how much fuel it supplies, and the evidence says keep it at or below 8 per cent if the same drink also has to hydrate you. Sodium concentration governs how much of that fluid you keep, and the amount in a typical sports drink is modest by the standards of the rehydration research. Choose on the basis of which of those two things you actually need, and for a lot of sessions the answer is neither.

If it is the fluid retention side you are interested in rather than fuel, that is the category our Hydrate electrolyte drink sits in. One 5.5 gram sachet in 500 millilitres of cold water supplies 1000 milligrams of sodium, 190 milligrams of potassium and 70 milligrams of magnesium, sweetened with stevia and monk fruit rather than sugar. That works out to roughly 87 millimoles of sodium per litre, several times the concentration of a standard sports drink, and no carbohydrate as fuel. It is a Formulated Supplementary Sports Food, not suitable for children under 15 years of age or pregnant women, and should only be used under medical or dietetic supervision. If your session is long enough to need fuelling, you still need carbohydrate from somewhere else.

This article is general information, not medical advice, and is not a substitute for guidance from your doctor, particularly if you are managing an existing health condition or taking medication.

Jasmine Meagher

BSc Food Science and Nutrition · Founder, Ritua

Jasmine founded Ritua to bring evidence-based, TGA-compliant supplements to Australian women. She writes about the research behind every ingredient Ritua sells.

FAQs

Sources

• A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. American Journal of Clinical Nutrition, 2016; 103(3):717 to 723.
• American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and Science in Sports and Exercise, 2007; 39(2):377 to 390.
• The effect of osmolality and carbohydrate content on the rate of gastric emptying of liquids in man. Journal of Physiology, 1995; 486(2):523 to 531.
• Effect of beverage osmolality on intestinal fluid absorption during exercise. Journal of Applied Physiology, 1998; 85(5):1941 to 1948.
• Optimizing the restoration and maintenance of fluid balance after exercise-induced dehydration. Journal of Applied Physiology, 2017; 122(4):945 to 951.
• The hydrating effects of hypertonic, isotonic and hypotonic sports drinks and waters on central hydration during continuous exercise: a systematic meta-analysis and perspective. Sports Medicine, 2022; 52:349 to 375.
• Sports drink. Australian Institute of Sport Supplement Framework, Group A.