For some sports, like running or cycling, a gooey fuel like Gu's Roctane Energy Gel might be an easy option.
For some sports, like running or cycling, a gooey fuel like Gu's Roctane Energy Gel might be an easy option. (Photo: Matt Trappe/Gu)

What’s Really in Your Gu?

There are a lot of obscure ingredients in Gu gels. Here's what they actually do for you.

For some sports, like running or cycling, a gooey fuel like Gu's Roctane Energy Gel might be an easy option.
Matt Trappe/Gu(Photo)

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If you’re a dedicated athlete, you’re probably familiar with getting your nutrients in goo form. Gels like Gu’s Roctane offer a blend of carbohydrates and electrolytes that can fuel hours of hard work without tearing up your stomach. But those of us who aren’t dietitians or food chemists might be confused by the lengthy ingredient list. In its product description, Gu claims many of these components boost our performance in obscure ways, like maintaining “heart contractility” or increasing an “intramuscular buffer.” What exactly are these ingredients, and do they live up to their stated purposes? We consulted Monique Ryan, a dietitian and author of Sports Nutrition for Endurance Athletes, to help break down what all those ingredients really mean and what they can do for our bodies.

The Carbohydrates: Maltodextrin and Fructose

Maltodextrin is a carbohydrate produced from a plant source, often corn. It’s composed of chains of glucose molecules, and when you eat it, the chains readily break apart and are absorbed as glucose by the small intestine.

Fructose is a common sugar, also typically refined from corn, and an additional source of carbohydrates. Fructose is absorbed more slowly than glucose, because the liver needs to process fructose before it can be used for energy. Fruits and vegetables naturally contain both fructose and glucose.

When you’re consuming glucose alone, your body maxes out on absorption at about 60 grams per hour, Ryan says. But mixing glucose and fructose lets you double down on carbs, because they each use different pathways in the gut. A glucose-to-fructose ratio of about two to one is ideal: “The mix really allows you to go above the 60 grams per hour, and that’s really important for endurance athletes,” Ryan says.

The Electrolytes: Sodium, Calcium, and Potassium Citrates

When you sweat, you lose electrolytes, the salts crucial to electrical signaling in the body. The major electrolytes are sodium, calcium, and potassium, and they’re critical to rehydration. When you slurp down a gel, sodium and glucose enter your cells together. When this salt and sugar combo concentrates in the cell, water then flows in as well. This process depends on the presence of water in the body, so it’s important to chase a gel with a beverage. Ryan adds that water helps the body digest concentrated carbohydrates more efficiently, which helps maintain a steady flow of energy and fend off gastrointestinal distress mid-workout.

Branched-Chain Amino Acids: Leucine, Valine, and Isoleucine

These three amino acids—compounds that form proteins and perform other important roles in the body—make up one third of the essential nine amino acids that our bodies don’t produce naturally. (A “complete protein” food contains all nine). The branched-chain molecules are used in muscle metabolism, which is why performance fuels zero in on these to provide just enough nutrients to offset muscle breakdown without upsetting the stomach. But experts are still skeptical about whether ingesting these amino acids before or during exercise substantially helps muscle repair. Eating protein after exercise, it seems, is still your best bet for recovery. Still, Ryan says, she sometimes recommends some protein to Ironman athletes when they are cycling—as opposed to running or swimming, when the stomach is more easily upset—to stymie hunger.


Taurine is an amino acid that serves as a neurotransmitter and assists various bodily processes. It was first isolated from ox bile in 1827, but these days it’s synthetic. Since our livers can produce it, taurine is considered a “semi-essential” amino acid—it isn’t critical that we get it from our diets. Still, plenty of energy drinks and performance foods list it as an ingredient.

In one recent review of ten studies published in Sports Medicine, a supplement of one to six grams of taurine was correlated with improved endurance performance; this benefit is linked to many physiological processes, such as increasing energy efficiency in muscle cells. However, the doses in this research—up to six grams a day—are higher than what you’ll find in a single Gu; all the aminos combined in one packet total 1.425 grams. Mark Waldron, lead author of the review and an exercise scientist at St. Mary’s University in London, says the lower doses found in gels and sports drinks likely aren’t enough to enhance performance.


This nonessential amino acid has the potential to “directly improve sports performance,” according to the International Olympic Committee. Beta-alanine helps the body create carnosine, a compound that combats lactic acid buildup in muscle, slowing the onset of fatigue. The International Society of Sports Nutrition, in a review of multiple studies, concluded that taking four to six grams daily for two to four weeks can provide this benefit. However, Gu contains less than the amount known to be performance enhancing.

Green Tea Leaf Extract

This ingredient is a source of caffeine, which also is known to improve performance. Gu has less than you need to be concerned about, but at very high doses, such as those found in some supplements, this extract might cause liver injury.

Medium-Chain Triglycerides

These medium-chain triglycerides (MCTs) are the same as those touted by “biohacking” entrepreneur Dave Asprey, of Bulletproof coffee fame. MCTs, usually processed from coconut or palm kernel oils, are a type of fat. The body burns these shorter-chain chemicals faster for energy than their longer-chain siblings, which make up the majority of dietary fats. This had led some researchers to think that MCTs can benefit exercise performance, but the link is still unclear, and according to the International Society of Sports Nutrition, there’s “little or no evidence to support efficacy” of MCTs.

The Verdict

For long, grueling workouts, energy gels can certainly offer a boost. Ryan says she thinks of them as a “side dish.” Still, the benefits of some of the ingredients are unclear.

It’s possible to get a lot of the key nutrients in Gu from whole foods. And some ingredients, like electrolytes, might not be useful unless you’re sweating for three hours or more. But for sports that are harsher on the stomach, like running, a gooey fuel is often easier to keep down than other options. “It’s about tolerance and digestion,” Ryan says. “You have to know what works for you and have a plan that balances out properly. It depends on your sport.”

Lead Photo: Matt Trappe/Gu