If you have ever been three hours into a long ride or run, taken on plenty of fuel, and still felt your stomach churning and your legs fading, there is a good chance the problem was not how much you ate but what kind of sugar you ate. For years the received wisdom was that your body could only absorb around 60g of carbohydrate an hour, full stop. That number turned out to be a ceiling imposed by a single transporter, not by your legs or your willpower. Understanding the glucose fructose ratio in sports nutrition is the single biggest lever most endurance athletes can pull to fuel harder without wrecking their gut.
The short version is this: glucose and fructose are absorbed through different doorways in your intestine, so combining them lets you take on far more carbohydrate per hour than glucose alone. Get the ratio right and you can comfortably push towards 90g or even 120g an hour on the biggest days. Get it wrong and you leave energy on the table or, worse, spend the back half of your event doubled over. Here is what the science actually says and how to apply it.
Two Sugars, Two Different Doorways
Your small intestine absorbs glucose using a transporter called SGLT1. That transporter has a maximum throughput: once you are taking in more than roughly 60g of glucose an hour, SGLT1 is saturated and the excess sugar sits in your gut, drawing water in with it. That undigested carbohydrate sloshing around is exactly what causes the bloating, cramping and dreaded runner's trots so many people blame on nerves or a dodgy breakfast.
Fructose is the clever workaround. It is absorbed by an entirely separate transporter called GLUT5, which sits alongside SGLT1 but works independently. Because the two doorways operate in parallel, taking glucose and fructose together lets you absorb both at once rather than queueing them through the same gate. Studies using labelled carbohydrate have shown total oxidation rates climbing from around 1g per minute with glucose alone to roughly 1.5g per minute (about 90g an hour) when fructose is added into the mix. That is a 50% increase in usable energy, from the same gut.
Why the Glucose Fructose Ratio in Sports Nutrition Is Usually 1:1 or 2:1
Early research on multiple transportable carbohydrates settled on a 2:1 ratio of glucose to fructose, and plenty of excellent products still use it. More recent work suggests that a 1:1 ratio can support even higher intakes, which is why you now see fuels marketed at both blends. So which is right?
The honest answer is that it depends on how much you are trying to take in. If you are fuelling at 60g an hour, the ratio barely matters because you are nowhere near the SGLT1 ceiling. Once you push beyond 60g an hour, fructose has to do more of the heavy lifting, and a 1:1 blend delivers more fructose per gram of total carbohydrate, which suits very high intakes of 90g and above. For most amateurs fuelling in the 60 to 90g range (see how many carbs per hour you actually need), anything between 1:1 and 2:1 works well, and the difference between them is smaller than the difference between fuelling properly and not fuelling at all. Do not agonise over decimal points. Focus on getting a mixed-sugar fuel into you consistently.
How to Put the Numbers Into Practice
Start with your hourly target. For efforts under about 90 minutes you rarely need more than water and perhaps a small top-up, because your muscle glycogen will see you through. For anything from two hours upwards, aim for 60g of carbohydrate per hour as a sensible baseline, building towards 90g an hour for racing or very long days once your gut is trained for it. Crucially, do not attempt 90g an hour for the first time on race day. The GLUT5 transporter is trainable: taking on regular fructose in the weeks before an event measurably increases how much your gut can handle, so treat high-carb fuelling as something you practise in training.
Spread your intake rather than dumping it all at once. Taking a portion every 15 to 20 minutes keeps a steady stream of sugar arriving at the transporters instead of overwhelming them in one hit. Pair every serving with a mouthful or two of water so the carbohydrate can move across the gut wall efficiently, and be wary of very concentrated drinks in hot weather, when hydration matters as much as fuel. If you are combining a drink, a gel and a chew (formats compared in Energy Chews vs Gels), add up the total carbohydrate across all of them rather than counting each in isolation, because it is remarkably easy to accidentally overshoot or undershoot.
It also helps to know where your fuel is coming from before you start. Work out the carbohydrate content of the products you plan to carry and do the sums the night before, so that on the day you are simply eating to a plan rather than guessing mid-effort. A common trap is switching to an unfamiliar fuel at a feed station or aid stop; if it is a pure-glucose product, your effective ceiling drops straight back to 60g an hour no matter how much you cram in. Sticking to a mixed-sugar fuel you have tested in training removes that risk entirely, and it means the number on your fuelling plan is the number your gut can actually deliver.
What We Use at FTP Endurance Fuel
We built our energy pastilles around exactly this science. Each pastille uses a blend of glucose and fructose rather than glucose alone, so the carbohydrate keeps flowing through both the SGLT1 and GLUT5 doorways and you can comfortably fuel at higher rates without the gut distress that pure-glucose products can cause. They are easy to chew and swallow on the move, which matters when you are breathing hard, and because they are pastilles rather than sticky gels you can take a couple at a time and pace your intake precisely to hit your hourly target.
Our Mixed Fruit Pastilles are our everyday workhorse for long rides and runs, while the Tart Cherry Pastilles add anthocyanins on top of the dual-sugar fuel, which is handy on back-to-back training days. If you have never dialled in your glucose fructose ratio before, it is worth practising with a mixed-sugar fuel in training first so your gut adapts before you ask it to perform.
The Bottom Line
The reason so many endurance athletes hit a wall despite eating plenty is not a lack of effort, it is a single saturated transporter. By understanding the glucose fructose ratio in sports nutrition and choosing a fuel that uses both sugars, you unlock a genuinely higher ceiling: 90g an hour and beyond, delivered smoothly instead of sitting heavy in your stomach. Set an hourly target, spread your intake, train your gut in advance, and count your total carbohydrate across everything you take on. If you want a mixed-sugar fuel that does the work for you, try a taster pack on your next long session and see how much stronger you finish.
