Why Dual-Carb Fueling Works: The Science Behind Maltodextrin and Fructose

To understand why dual-carb works, you first need to understand why single-carb products have a hard limit.

When you consume carbohydrates during exercise, they travel from your stomach into your small intestine, where they are absorbed through specialised protein channels called intestinal transporters. These transporters act like revolving doors. They can only move a fixed number of carbohydrate molecules per minute, regardless of how many are queued up waiting.

The transporter responsible for absorbing glucose and glucose-derived carbohydrates (including maltodextrin) is called SGLT1, or sodium-glucose cotransporter 1. Research has shown that SGLT1 becomes saturated at approximately 60g of glucose or maltodextrin per hour (Jeukendrup & Jentjens, 2000). This is the ceiling. Beyond this point, additional glucose or maltodextrin consumed during exercise simply cannot be absorbed faster. It accumulates in the gut.

The consequences of consuming more single-carb fuel than SGLT1 can handle:

• Unabsorbed carbohydrate in the gut
• Osmotic water draw into the intestine, causing bloating
• Fermentation by gut bacteria, causing GI distress, cramping, and diarrhoea
• No additional performance benefit despite the additional intake

This is why many athletes who take more gels on long efforts still bonk. It is also why so many athletes report gut distress with high-carbohydrate single-source products.

Fructose is absorbed in the small intestine via a completely separate transporter called GLUT5 (glucose transporter 5). GLUT5 is not saturable by glucose. It operates independently, with its own absorption capacity of approximately 30g of fructose per hour.

The critical insight: SGLT1 and GLUT5 operate simultaneously and independently.

By combining maltodextrin (absorbed via SGLT1) with fructose (absorbed via GLUT5), total carbohydrate absorption capacity increases from the roughly 60g per hour ceiling of single-carb products to 90 to 120g per hour (Jentjens & Jeukendrup, 2005).

This is not theoretical. It has been measured directly. Jentjens and colleagues (2005) used isotopically labelled carbohydrates to track the actual oxidation of ingested carbohydrates in exercising athletes. They found:

• Glucose alone at 1.8g per minute: peak exogenous carbohydrate oxidation roughly 1.0g per minute
• Glucose and fructose combined at 2.4g per minute total: peak exogenous carbohydrate oxidation roughly 1.26g per minute

That is a 26% increase in the rate at which ingested carbohydrates are actually burned for fuel, simply by switching from a single-carb to a dual-carb formulation.

Subsequent research has confirmed and extended this finding. Wallis et al. (2005) demonstrated that a 1.5:1 glucose-to-fructose ratio produced the highest exogenous carbohydrate oxidation rates among all combinations tested. Later work by Currell and Jeukendrup (2008), published in Medicine and Science in Sports and Exercise, showed that cyclists consuming a 2:1 maltodextrin-fructose mixture improved 100km time trial performance by 8% compared to glucose alone, while consuming the same total carbohydrate dose.

Eight percent. From the carbohydrate formulation alone.

Maltodextrin is a glucose polymer, essentially a chain of glucose molecules connected together. It offers several practical advantages over free glucose.

Lower sweetness. Free glucose and simple sugars taste very sweet at the concentrations required for performance fueling (60 to 90g per litre). At these concentrations, the sweetness becomes unpleasant, particularly over long events. Maltodextrin is essentially tasteless despite its high carbohydrate density, allowing high carbohydrate loads in a palatable solution.

Lower osmolality at equivalent carbohydrate dose. Each long maltodextrin chain contributes fewer osmoles per gram of carbohydrate than free glucose. This keeps the solution closer to isotonic at higher carbohydrate concentrations, supporting faster gastric emptying.

Rapid hydrolysis. Maltodextrin is rapidly broken down into glucose in the small intestine. From an absorption standpoint, maltodextrin and glucose behave very similarly once they reach the intestine. The practical benefit is largely palatability and osmolality management.

The 2:1 maltodextrin-to-fructose ratio is not arbitrary. It reflects the relative capacities of SGLT1 and GLUT5.

SGLT1 can absorb approximately 60g of glucose or maltodextrin per hour. GLUT5 can absorb approximately 30g of fructose per hour. A 2:1 ratio of maltodextrin to fructose delivers carbohydrates to each transporter at close to its maximum capacity without overwhelming either, achieving the highest total absorption rate with the lowest GI distress risk.

Ratios with too much fructose (approaching 1:1) increase fructose malabsorption risk. Excess fructose that cannot be absorbed via GLUT5 sits in the intestine, drawing water osmotically and being fermented by bacteria, causing bloating, discomfort, and the kind of GI distress that forces athletes to stop or slow down.

The 2:1 ratio is the sweet spot validated by the most research, and it is the ratio used in HYDRAX CORE.

HYDRAX CORE is formulated around the 2:1 maltodextrin-fructose ratio, not because it is fashionable, but because it is the most replicated finding in applied endurance nutrition research.

Every serve of HYDRAX CORE delivers:

• A dual-carb blend at the research-validated 2:1 ratio
• High-sodium electrolytes designed to replace actual sweat losses
• An isotonic formulation at recommended mixing concentration for fast gastric emptying
• A clean ingredient profile without unnecessary additives

The result: fuel that your gut can actually absorb at the rate you need it, in an electrolyte solution that replaces what you are losing.

The same dual-carb logic applies to HYDRAX PRIMER, the pre-session product in the HYDRAX system. PRIMER delivers 29g of carbohydrates from the same 2:1 maltodextrin-fructose blend, combined with 1,313mg of sodium and 5,600mg of sodium citrate, taken 25 to 40 minutes before a hard session or race start. Where CORE applies dual-carb science during the session, PRIMER applies it before. The goal is carbohydrate availability from minute one, not from minute twenty when the fuel you ate at breakfast finally shows up.