Maltodextrin vs Fructose in Sports Drinks: Why You Need Both

Your gut has two separate carbohydrate absorption pathways. Most commercial sports drinks only use one. That is why athletes who try to take in more than 60 grams of carbs per hour on single-sugar products hit a GI wall.

Why 60 g/hour is the single-sugar ceiling

Glucose and maltodextrin (a glucose polymer) are absorbed through the SGLT1 transporter in the small intestine. SGLT1 saturates at approximately 60 grams of glucose equivalents per hour. No matter how much glucose you consume above that, the transporter cannot move more carbohydrate into the bloodstream. The excess stays in the gut, draws water in by osmosis, and causes bloating, sloshing, and diarrhea.

Fructose uses a completely different transporter: GLUT5. GLUT5 is independent of SGLT1 and has its own rate limit of about 30 to 36 grams per hour.

By combining maltodextrin and fructose at a 2:1 ratio, you saturate both transporters simultaneously and can absorb 90 to 120 grams of carbohydrate per hour. This is the mechanism behind Maurten's products and every high-carb racing strategy used in elite endurance sport.

The 2:1 ratio explained

Carb source	Transporter	Max absorption
Glucose / maltodextrin	SGLT1	~60 g/hour
Fructose	GLUT5	~30-36 g/hour
2:1 blend (both)	Both simultaneously	~90-120 g/hour

The ratio 2:1 is the research-validated optimum. Lower ratios (more fructose) do not fully load SGLT1. Higher ratios (less fructose) do not fully load GLUT5. A 2:1 blend of 60 g maltodextrin and 30 g fructose per hour is the practical ceiling for most trained athletes.

The 3:1 ratio (less fructose) is sometimes used for athletes with sensitive GI systems, as fructose is harder to digest for some people. It achieves ~80 g/hour at the cost of some GLUT5 saturation.

Why maltodextrin instead of plain glucose?

Maltodextrin is a glucose polymer with a much lower osmolarity than glucose at the same carbohydrate density. A 10% glucose solution has an osmolarity of roughly 555 mOsm/kg, which is hypertonic and slows gastric emptying. A 10% maltodextrin solution has an osmolarity below 100 mOsm/kg, which is hypotonic and empties rapidly.

Lower osmolarity means faster gastric emptying, which means faster carbohydrate delivery to the small intestine, which means more energy available per hour.

This is why Maurten, SIS Beta Fuel, and every serious race fuel uses maltodextrin rather than table sugar or glucose at high concentrations.

Osmolarity check for your mix

A practical target for race-day sports drinks is isotonic to slightly hypotonic: 200 to 280 mOsm/kg. The DIY calculation:

• Each gram of maltodextrin contributes roughly 1 mOsm/kg per gram per liter
• Each gram of fructose contributes roughly 5.6 mOsm/kg per gram per liter
• Sodium citrate: roughly 3 mOsm per gram

For a 500 mL bottle with 45 g maltodextrin + 22 g fructose + 0.5 g sodium citrate:

• Maltodextrin: 45/0.5 * 1 = 90 mOsm/kg
• Fructose: 22/0.5 * 5.6 = 246 mOsm/kg
• Total: ~336 mOsm/kg (slightly hypertonic)

To bring this into range, increase water volume to 600 mL. The DIY sports drink calculator handles this osmolarity check automatically and flags hypertonic mixes.

What about table sugar (sucrose)?

Sucrose is 50% glucose and 50% fructose by mass, so it delivers a 1:1 ratio. That is functional but not optimal: you are leaving SGLT1 capacity unused. For easy training rides, sucrose in water is perfectly fine. For race day above 60 g/hour carb targets, the 2:1 maltodextrin-to-fructose blend is meaningfully better.

Honey is similar to sucrose (roughly 40% fructose, 30% glucose, 17% water, remainder various sugars). It works but the 1:1-ish ratio is not optimized for maximum absorption.

Frequently asked questions

Is maltodextrin better than sugar in sports drinks?

For high-carbohydrate intake during exercise, maltodextrin has a significant advantage over table sugar: it has a much lower osmolarity at the same carbohydrate concentration, which means it empties from the stomach faster and is less likely to cause GI distress. A 10 percent maltodextrin solution has an osmolarity below 100 mOsm/kg, while a 10 percent glucose solution is over 500 mOsm/kg. For easy training or events where carb intake stays below 60g per hour, plain sugar works fine. For race-day fueling at higher carb targets, maltodextrin is meaningfully better.

Why do some athletes use fructose in their drinks?

Fructose activates the GLUT5 intestinal transporter, which is completely separate from the SGLT1 transporter that handles glucose and maltodextrin. By combining fructose with maltodextrin at a 2:1 ratio, both transporters operate simultaneously, raising the total absorption ceiling from 60g to 90g of carbohydrate per hour. Athletes targeting high carbohydrate intakes in long events use fructose specifically to access this second pathway and deliver more fuel to working muscles without overwhelming the gut.

What is the best carb ratio for a marathon?

For a marathon, a 2:1 maltodextrin-to-fructose blend is the evidence-based choice if you are targeting 60 to 90g of carbohydrate per hour, which is appropriate for competitive marathon racing at high intensities. Slower-paced marathon runners or those running under 3 hours may not need more than 60g per hour, at which point a single-sugar source or plain sucrose is sufficient. The ratio matters most when you push past the 60g per hour ceiling; below that threshold, carbohydrate source type is less critical than total intake.

Can I use table sugar instead of maltodextrin in a sports drink?

Yes, with some tradeoffs. Table sugar (sucrose) is 50 percent glucose and 50 percent fructose, so it activates both gut transporters and can support absorption up to roughly 75 to 80g per hour. The limitation is osmolarity: sucrose at high concentrations creates a more hypertonic solution than maltodextrin, which slows gastric emptying and increases the risk of GI distress above 8 percent concentration. For training use and events where 75g per hour is sufficient, sucrose dissolved in water is a practical and cheap alternative to a maltodextrin-fructose blend.