Drink Mix Builder
Formulate DIY sports drinks from bulk ingredients. See real-time osmolality, glucose:fructose ratio, and carb concentration. Compare against commercial brand presets.
Brand presets
Reference values based on manufacturer nutrition labels.
Fluid volume
Consumption rate (optional)
Bottles per hour
Race duration (optional)
Unlocks total carbs and bottle count for your race
Formula Check
Carb ratio
2:1 mix supports up to 90g/hr
Osmolality
Isotonic - fast gastric emptying
Sodium
Adequate for hydration
Concentration
Drinkable range (4-9%)
Bottle macros
Carb ratio
2:1 glucose:fructose mixes enable up to 90g carbs/hr absorption vs 60g/hr for glucose alone (Jeukendrup, 2004).
Osmolality
Concentration
What is a DIY sports drink?
A DIY sports drink is a homemade electrolyte and carbohydrate solution mixed from bulk ingredients - typically maltodextrin, fructose, and sodium citrate - rather than a pre-packaged commercial product. Endurance athletes formulate their own drinks to control exact carbohydrate ratios, sodium content, sweetness, and osmolality, often at a fraction of the cost of branded products.
This builder lets you mix ingredients in real time and see the precise nutritional output: total carbohydrates, sodium, glucose-to-fructose ratio, osmolality in mOsm/kg, and carbohydrate concentration as a percentage. You can also load formulations back-calculated from nine commercial sports drinks to understand what those products actually contain.
Why formulating your drink mix matters
Most commercial sports drinks are not optimised for ultramarathon fueling. They are formulated for mass-market palatability - often too sweet, too dilute in sodium, or using carbohydrate ratios tuned for short-duration cycling rather than 20-hour mountain runs.
Carbohydrate absorption has a ceiling. The SGLT1 gut transporter can absorb roughly 60g of glucose per hour. Without adding fructose (which uses the separate GLUT5 transporter), you cannot absorb more carbohydrates no matter how much you drink. A properly formulated 2:1 glucose-fructose mix raises that ceiling to 80-90g/hr - and gut-trained athletes using a 1:0.8 ratio can push to 90-120g/hr (Podlogar et al., 2022) after 3-6 weeks of high-carb training runs. Over a 30-hour event, the difference can be 600-1500 extra calories absorbed.
Osmolality determines absorption speed. Hypertonic drinks draw water into the intestine before they can be absorbed, causing bloating and slowing hydration. The difference between a 280 mOsm/kg drink and a 400 mOsm/kg drink can be the difference between a comfortable stomach and severe GI distress at hour 14 of a mountain race.
Sodium needs are race-specific. A cool 8-hour mountain run requires far less sodium replacement than a hot Templiers or Lavaredo race where sweat rates run at 800-1000ml/hr. Dialling in your sodium per bottle to match your conditions prevents both hyponatremia (over-drinking plain water) and cramping from salt depletion.
How to use the Drink Mix Builder
Consult a sports dietitian for personalised race nutrition advice. Osmolality values are estimates based on ingredient molecular weights.
- Load a brand preset or start blank The brand chips load back-calculated formulations from commercial products. Use them as a reference starting point.
- Adjust carb sources Mix maltodextrin (glucose), fructose, table sugar (50/50 glucose + fructose), and honey. The donut chart updates live with your glucose:fructose split.
- Add sodium Sodium citrate gives milder flavour; table salt gives more sodium per gram. Target 400-700mg per bottle for most race conditions.
- Choose your fluid volume Select 500ml, 750ml, or 1000ml. Osmolality halves when you double the water - adjust to keep the needle in the green.
- Set consumption rate (optional) Select bottles per hour to reveal SGLT1 and GLUT5 transporter utilisation bars. These show whether your hourly intake exceeds absorptive capacity.
- Refine and save The URL updates automatically. Bookmark your formula to access it again without re-entering values.
The science of sports drink formulation
Osmolality is calculated from the molar concentration of dissolved particles: mOsm/L = (grams / molecular_weight) x particles x 1000 / volume_L. Maltodextrin (MW ~1000 g/mol, 1 particle per molecule) contributes very few mOsm despite carrying many carbohydrate calories. Fructose and glucose (MW 180, 1 particle) contribute moderately. NaCl (MW 58.4, 2 particles from full dissociation) has an outsized osmolality contribution relative to its mass - 1g of NaCl adds 68 mOsm/L in 500ml. Sodium citrate (MW 258, 4 particles) is even more potent osmotically per gram but delivers less sodium. The mOsm/L approximation equals mOsm/kg for dilute sports drinks.
Dual-transporter carbohydrate absorption (Jeukendrup & Moseley, 2010) is the key principle behind modern sports nutrition. Glucose uses SGLT1 (sodium-dependent glucose transporter 1), saturating at ~60g/hr. Fructose uses GLUT5, saturating at ~30g/hr. They are independent - a 2:1 mix allows simultaneous saturation of both pathways for ~90g/hr total absorption. This is why products like Maurten 160, SiS Beta Fuel, and Tailwind all contain both glucose sources and fructose.
Concentration vs osmolality. These two metrics diverge dramatically with maltodextrin. A 9% maltodextrin solution is roughly isotonic (~290 mOsm/kg) because the large MW means few particles per gram. A 9% glucose solution would be hypertonic (~1000 mOsm/kg). This is why concentration alone is insufficient to predict gut tolerance - osmolality is the mechanistically relevant measure.
Honey contains approximately 30% glucose and 38% fructose (of total honey weight), with the remainder being water, trace sugars, and non-sugar compounds - total carbohydrate around 82g per 100g (USDA FoodData Central). As a fraction of its total sugars, honey is roughly 36% glucose and 47% fructose. The builder uses these proportions, making honey a moderately fructose-dominant carbohydrate source.
Jeukendrup AE, Moseley L. (2010). Multiple transportable carbohydrates enhance gastric emptying and fluid delivery. Scand J Med Sci Sports. 20 Suppl 1:55-60. Thomas DT et al. (2016). Position of the Academy of Nutrition and Dietetics on nutrition and athletic performance. J Acad Nutr Diet. 116(3):501-528.
Common sports drink formulation mistakes
Making it too concentrated. The instinct when training hard is to maximise carbohydrate per bottle. But a 15% carbohydrate drink is severely hypertonic and will draw water into your gut rather than letting you absorb it - causing cramps and bloating. Keep total carbohydrate below 9-10% (90g per litre) for comfortable absorption.
Using only glucose sources. Pure maltodextrin or pure glucose drinks cap out at ~60g/hr absorption. Adding fructose (or table sugar, which is 50% fructose) activates the GLUT5 transporter and can raise absorption to 80-90g/hr. For races where you need maximum calorie delivery, a 2:1 or close ratio is significantly more effective.
Ignoring osmolality when adding electrolytes. Two electrolyte tabs in a 500ml bottle can add 160 mOsm/L on top of your carbohydrate contribution. This can push an otherwise isotonic drink into hypertonic territory. Check osmolality after adding each sodium source.
Not testing in training. Even a perfectly formulated drink can cause GI issues the first time you use it at race intensity. Gut tolerance for carbohydrate intake increases with training - practice your exact mix on long runs 6-8 weeks before your race.
Frequently asked questions
What is osmolality and why does it matter for sports drinks?
Osmolality measures the concentration of dissolved particles in a solution, expressed in mOsm/kg. Blood plasma sits at around 285-295 mOsm/kg. A drink in the isotonic range (270-330 mOsm/kg) is absorbed at roughly the same rate as blood, minimising fluid shifts across the gut wall. Hypertonic drinks (>330) draw water into the intestine to dilute them before absorption - slowing hydration and potentially causing bloating. Hypotonic drinks (<270) are absorbed quickly but deliver fewer carbohydrates per mouthful.
Why use maltodextrin instead of plain sugar in homemade sports drinks?
Maltodextrin is a glucose polymer (long chain of glucose units) with a very high molecular weight (~1000 g/mol). Because osmolality depends on particle count rather than mass, you can pack a large number of carbohydrate calories into a drink without raising osmolality as sharply as equivalent grams of simple sugars. 60g of maltodextrin in 500ml adds only about 120 mOsm/L, whereas 60g of glucose would add about 667 mOsm/L. This lets you reach 60g/hr carbohydrate intake while keeping the drink comfortably isotonic.
What is the ideal glucose to fructose ratio for endurance sports?
Research by Jeukendrup and colleagues established that a 2:1 glucose-to-fructose ratio maximises carbohydrate absorption. Glucose uses the SGLT1 intestinal transporter (capacity ~60g/hr); fructose uses the separate GLUT5 transporter (capacity ~30g/hr). Used together at 2:1, total absorption can reach 80-90g/hr - roughly 50% more than glucose alone. Going beyond 2:1 fructose risks exceeding GLUT5 capacity, causing osmotic GI distress. The builder shows a live donut chart of your mix ratio so you can hit or approach 2:1.
How does sodium citrate compare to table salt in sports drinks?
Both provide sodium, but with important differences. Table salt (NaCl) delivers 394mg of sodium per gram and has a sharp salty taste that becomes unpleasant in large doses. Sodium citrate (Na3C6H5O7) delivers 267mg of sodium per gram but has a milder, slightly tart flavour that blends better into sweet drinks. Sodium citrate also contributes four particles per molecule compared to two for NaCl, making it more effective per gram at raising osmolality. For a 500ml bottle targeting 400-500mg of sodium, 1.5-2g of sodium citrate is a common formulation.
Can I replicate commercial sports drinks at home?
Yes - the brand preset buttons show back-calculated formulations for nine commercial products including Tailwind, Maurten, Skratch Labs, and SiS Beta Fuel. These are derived from manufacturer nutrition labels and represent approximate ingredient compositions. The actual formulations are proprietary and may include additional flavouring, pH buffers, or minor electrolytes not captured here. Use them as reference starting points, then adjust to your taste and gut tolerance.
Is concentration the same as osmolality?
No - they measure different things and can diverge. Concentration (%) is simply carbohydrates divided by fluid volume: a 9% drink has 45g carbs in 500ml. Osmolality counts dissolved particles weighted by their molecular weight. A 9% maltodextrin drink is roughly isotonic (~290 mOsm/kg) because maltodextrin molecules are large and add few particles. A 9% glucose drink would be severely hypertonic (~1000+ mOsm/kg) because each small glucose molecule is a separate particle. The builder shows both metrics separately so you can optimise each independently.
How do electrolyte tablets affect osmolality?
Each standard electrolyte tab contributes approximately 40 mOsm/L when dissolved in solution (based on typical sodium, potassium, and chloride content of ~300mg sodium equivalent). In a 500ml bottle, one tab adds about 80 mOsm/L. Two tabs in 500ml could push a lightly-fuelled drink from hypotonic to isotonic range. The builder accounts for this in the osmolality calculation, so you can see the combined effect of electrolyte tabs alongside carbohydrate ingredients.
Want a complete race nutrition plan built into your training?
TrailMath uses these models to build periodized plans adjusted to your goals and terrain.
Get started free