New research on Sports Drink – What should it include? (#76)

For around 10 years, researchers have concurred that sports drinks containing a variety of carbohydrates are the most effective. This is related to the rate of stomach emptying, intestinal absorption, oxidation/utilization rates, reduced risk of gut issues, and consequently, maintained or enhanced performance. While the exact combination of different carbohydrates that is most effective is still unknown, ongoing research and newly published studies on various options continue to emerge. This fresh information could enhance your performance.

In summary, findings indicate that sports drinks with multiple carbohydrate types offer higher energy uptake, improved carbohydrate utilization, and typically a lower risk of gut issues compared to a sports drink with a single carbohydrate source. At increased energy intakes, a maltodextrin to fructose ratio nearing 1:0.8 appears to provide additional benefits, although the optimal mix can vary between individuals.

Before we delve into individual monosaccharides and their absorption, here's some background knowledge.

When you consume carbohydrates, they quickly break down into their smallest components to be absorbed and used as fuel by the body. The speed at which carbohydrates break down depends on their structure — essentially, how easy or difficult they are for our enzymes to break down. This process begins in the mouth with the help of the enzyme amylase, then continues in the stomach and small intestine where they are eventually transported through the intestinal membrane with the aid of transport proteins. At this stage, carbohydrates are broken down into simple sugars such as glucose and fructose. Proteins and fats are also broken down into their building blocks to pass through the intestines, but we won't delve into that in this article (see image below).

About 15 years ago, researchers began studying how different types of carbohydrates are absorbed in the body and contribute energy during athletic activities. It was then that earlier ideas about molecular weight being significant were largely discarded. Or well — molecular weight matters only if you're comparing glucose with different molecular weights. You've probably heard the figure 60 g/hour or 1 g/minute, which was previously believed to be the maximum amount of carbohydrates we could absorb. That's true, but mainly for glucose/maltodextrin since the gut's glucose transporters become saturated at that dosage. If you're only comparing glucose against glucose, details like molecular weight can be crucial. But when we use other types of carbohydrates, like fructose, it becomes more complex yet more promising for performance and energy supply.

It's a bit like comparing the speed of two horses (glucose vs. glucose) where you fine-tune training and feed to make one faster. Place a car (glucose+fructose) next to them on the starting line, and the specifics about feed (molecular weight) suddenly seem trivial compared to the car's potential as it races ahead with “horse lengths.” ;)

Research moved past this step long ago; now it's far more exciting — we're searching for the optimal carbohydrate composition. Now we're tinkering with the octane level in car fuel instead.

Carbohydrates are broken down into monosaccharides before passing through the intestinal membrane and entering the bloodstream. The glucose transport through the intestine has a maximum rate of about 1 g/min, dictated by SGLT1, the glucose-specific transport protein, which moves glucose into the blood toward our working muscles. Excitingly, fructose has its own transporter, GLUT5, enabling us to combine carbohydrates to saturate SGLT1 with glucose while gaining more energy through the fructose carrier.

In recent years, more transporters have been discovered, such as GLUT8 and GLUT12, which work together during the simultaneous intake of maltodextrin:fructose. We also have GLUT2, a bidirectional transporter that allows glucose to move in both directions. Then there's GLUT4, another glucose transporter commonly mentioned in relation to physical activity as it facilitates glucose uptake without requiring insulin, stimulated by muscle work. The takeaway is that the body optimizes uptake as best it can. Gut researchers (that could be you) have known since the 1980s that certain carbohydrates assist others in crossing the intestinal membrane. For instance, in 1986, it was discovered that glucose can stimulate the intestine to enhance fructose uptake when both are consumed together. After three decades, we're starting to implement this to develop optimized sports nutrition.

Once fructose crosses into the bloodstream, it doesn't follow the same route as glucose. Fructose, with a low glycemic index (GI), acts as a slow-releasing carbohydrate that helps maintain energy levels, whereas glucose provides the quick burst. Together, they complement and enhance each other's effects. About 20% of fructose can be directly used by the muscles, with the remaining 80% processed by the liver into glucose, lactate (mobile fuel), and pyruvate.

As illustrated in the image below, there are numerous transporters. The challenge now is to determine the capacity of each transporter and how to maximize their use without causing negative side effects, like gut discomfort during activity. Considering the small intestine has approximately 20 m2 of surface area, there's likely more capacity than currently realized.

In 2015, a review article was published, summarizing the research area around carbohydrate compositions in sports drinks. The article examined a total of 14 studies, focusing primarily on three compositions: 2:1, meaning two parts maltodextrin and one part fructose—the most tested variant to date and the one we use in U Sport. The second composition is the 1:0.8 variant, with one part maltodextrin and 0.8 parts fructose. Finally, there's the 1:1.25 variant, with one part maltodextrin and 1.25 parts fructose.

The 1:1.25 variant has been researched, but it underperforms in most tests. It seems that the majority of the carbohydrates should be the fast-acting maltodextrin rather than fructose, which is slower. So, the competition continues between 2:1 and 1:0.8. Across the reviewed studies, intake ranged from 36–144 g/hour, distributed over 3–4 intakes per hour—a fairly wide range but with consistent dosing.

We've been monitoring the research on 2:1 versus 1:0.8 for quite some time. We began examining studies back in 2013–2014 when we at Umara developed our first sports drink (U Sport). The research was quite new then, so we were cautious about taking too many risks, especially considering factors I'll soon discuss. However, as research has progressed, it seems that at higher doses a ratio closer to 1:1 is preferred—though not quite 1:1; the optimal threshold appears to be around 1:0.8.

Up to approximately 1.5–1.7 g/min (about 100 g/hour), there's a consistent preference for a 2:1 ratio over a 1:0.8 ratio. Most research supports the 2:1 combination of maltodextrin:fructose as the winner in terms of sweetness and minimizing gut issues. However, for doses above this, starting around 90 g/hour, the consensus shifts toward a 1:0.8 ratio between maltodextrin and fructose — that is, one part maltodextrin to 0.8 parts fructose.

Back in 1985, Rowlands et al. conducted a study on the oxidation efficiency of different carbohydrate blends. Using carbon-14 labeling and analyzing carbon dioxide in exhaled air, they tracked the usage of ingested carbohydrates. With a 1:0.8 ratio, where participants consumed 0.6 g maltodextrin and 0.5 g fructose (totaling 1.1 g/min), up to 98 percent was oxidized — indicating that at most, 2 percent remained in the gut, potentially increasing gut issues. Other compositions showed oxidation rates around 80 percent.

At these doses and compositions, researchers are also identifying additional benefits beyond more carbohydrates passing through the gut membrane to the muscles.

Interestingly, liver glycogen seems to be preserved if intake levels reach 90 g/hour and up. In more extreme scenarios, researchers have managed to temporarily halt the liver's glucose production, meaning the liver's glycogen doesn't deplete at all. This is crucial as a drop in liver glycogen often signals fatigue, since the liver struggles to maintain blood sugar at sufficient levels. However, this effect is only seen with intakes around 2.7 g/min (162 g/hour) — a level that virtually no gut can sustain for long periods.

Fructose should be included in a sports drink to maximize energy intake, delay hitting the wall, and boost power output. However, compared to glucose/maltodextrin, the oxidation efficiency of fructose isn't as high. For instance, with maltodextrin, we oxidize between 65–90% of the consumed amount. For fructose, it's between 40–65%. So, fructose isn't as effective for immediate combustion — therefore, it should be part of a sports drink or gel but not the majority.

A sports drink that combines maltodextrin and fructose is gentler on the gut compared to a drink with only one type of carbohydrate, like just maltodextrin. Part of the performance improvements in studies comparing sports drinks can also be due to a calmer gut, which keeps the athlete relaxed and allows for higher energy intake. A key reason this combination is gentler is the coordinated uptake of carbohydrates along with simultaneous fluid absorption. Here's a brief description of this:

More on stomach issues in our article on this very topic.

The gut emptying process is largely dictated by signals based on the energy content present in the small intestine. Some signals originate from the stomach itself, indicating the need for gut emptying as its volume increases. Our goal is for the stomach not to retain energy but to move it quickly into the small intestine. This is where the main control is, as we want the energy to be absorbed by the body rather than remaining in the intestine. Other factors like stress and caffeine also influence gut emptying through various mechanisms.

If you consume an excess amount of carbohydrates, surpassing what the intestinal membrane's transport proteins can absorb, fluid may be pulled in the wrong direction — toward the small intestine — due to osmotic imbalance. This increases the intestinal content volume, leading to what is commonly referred to as diarrhea. Achieving the right balance involves finding a level where the intestines can effectively transport carbohydrates through the gut and eventually to the muscles. By increasing carbohydrate content in sports drinks/gels and achieving a ratio where absorption is optimized, you not only enhance fluid balance through increased fluid uptake but also reduce the risk of stomach issues as both carbohydrates and liquids are absorbed more efficiently.

Fructose itself increases the risk of gut issues in certain individuals. There's a condition known as fructose malabsorption, fructose malabsorption, which means a reduced ability to absorb and oxidize fructose. Researchers have shown that this can partly be alleviated by the simultaneous intake of glucose/maltodextrin see e.g. However, the area is relatively new, and although maltodextrin+fructose seems to be more positive than negative, there are likely individual variations—some might not tolerate a 1:0.8 sports drink as well as a 2:1. One of the reasons we didn't go all-in on the 1:0.8 composition in U Sport and U Gel from the beginning was precisely this variation in tolerance.

You can train your carbohydrate intake, something we've mentioned earlier in the article on how to get race-ready in a month. Many can handle well over 120 grams/hour with a sports drink in a 2:1 ratio, but these users are often frequent consumers of various carbohydrate supplements.

The researchers behind the review highlight three main points which also serve well as a summary:

1. Beverages with a fructose:glucose/maltodextrin ratio of 0.5–1.0:1, consumed at 1.3–2.4 g/min, likely enhance endurance performance compared to isocaloric glucose/maltodextrin alone.
2. Performance likely improves as the fructose:glucose/maltodextrin ratio approaches equality.
3. Gastrointestinal absorption, liver metabolism, and gut-comfort feedback are likely key to determining an optimal sports beverage formulation for performance outcomes.

While further research is likely, the current focus is on fine-tuning to find the ideal mix. Keep in mind, not everyone has the same number of each type of transport proteins, hence a specific sports drink composition might not suit everyone. It's probable that transport protein levels can adjust as needed—a good reason to train and compete with the same sports drink.

Also, remember that the researchers are only examining a portion of the entire digestive system at present. There's certainly more to discover.

Embrace the energy boost and a more settled stomach. Whether a 2:1 or 1:0.8 ratio suits you best, you'll have to test to determine. We have a 1:0.8 drink in development (a couple of months away), but if you want to modify a 2:1 drink, add some extra fructose and become your own lab rat. 😉