photo credit: @photowilTeamCamp


Whether you run, cycle, swim, or all three, your muscles need to remain fueled for as long as you are going, and decades of focused human research has found the basics of how to fuel endurance performance. Using that research and fine-tuning with our own field research, we engineered EFS with a combination of carbohydrates – maltodextrin, sucrose, and glucose – to maximize fuel delivery to your working muscles.

The carb sources in EFS have been honed through research and real-life testing to be effective, palatable, and mutually complementary for maximizing long-term endurance exercise. EFS works – and continues working for hours – because it takes a complete, systemic approach to fueling. It’s not just a gut-destroying, crash-inducing sugar dump.

In this article, Dr. Bucci breaks down the processes by which your body breaks down all carbs into glucose and, ultimately, into the ATP that sparks your muscles into action. He also lays out the pros and cons of multiple types of carbs, explaining the research-driven rationale behind EFS’s specific blend.


Before explaining the carb choices in EFS, it may be helpful to start by explaining why we chose carbs over other fuel sources. Your body has three choices of fuel: carbohydrates, fats, and protein (amino acids).

Forget about protein as an endurance fuel – the storage forms (amino acid pools and readily metabolizable proteins) are maintained in relatively small amounts, they’re slow to convert to carbs or fats, and they release nitrogen compounds that inhibit performance. While certain amino acids (BCAAs, Glutamine) can be important signals to keep protein where it belongs, protein cannot keep you going.

Fats are a useful fuel – they are a major part of your energy supply at rest, and endurance exercise causes changes in muscles and other organs, tissues, and cells to allow you to raise that resting rate of energy consumption. But because oil and water do not mix, using fats as the main source of fuel during long-term endurance exercise is fighting the laws of physics – and a sure recipe for violently unpleasant GI issues. Fats are a secondary player; they simply cannot be ramped up enough during exercise to keep you performing at your peak for a long-time.


Consuming carbohydrates is and always will be the main energy source for endurance exercise. They are the body’s preferred fuel for doing anything over just existing (called your Basal Metabolic Rate, or BMR). Huge amounts of human research have clearly shown that Carbs Are King for endurance performance, providing way more calories than sources like fats. That said, what is the best carb for performance?

The simple answer is glucose (aka dextrose). All carbs ultimately become glucose, which feeds your cellular energy production pathways – making ATP for muscular contraction, nerve impulses, and just about everything else your body does, wherever it happens. That ATP energy leaves carbon dioxide (CO2) and water as waste. If you can breathe, then you can remove CO2. And the water (called water of oxidation or WOO!) stays in working cells and/or goes back into circulation to help you stay hydrated.

The concept here is to keep supplying glucose before, during, and after exercise – as much as you can take and tolerate. This will help you reach peak endurance performance and recover quicker.

So does that mean you should just consume as much glucose as possible during exercise? Makes sense, but the reality is different. While carbs can be burned for fuel faster than fat, doing so does have limits. Going from glucose to ATP makes demands on your GI tract to deliver glucose to your bloodstream and cell receptors to get glucose from the bloodstream into your cells. After that, glucose still needs to be shuttled into cellular glucose destruction derbies, like mitochondria.

But there is a hitch – in high amounts, all sugars can turn your cells’ interiors into pancake syrup, throwing off your osmolytic balance and slowing everything down considerably. Thus, your body has a certain rate that limits how much and how fast glucose can be handled.

The goal is getting max amounts of glucose to muscles without glucose piling up somewhere, ruining your hydration and electrolyte balance. There are multiple ways to maximize that process. You have three practical sources of getting glucose into your working cells; 1) glucose itself; 2) glucose polymers (starches, including your endogenous glycogen); and 3) other sugars.

Only a certain amount of glucose itself can realistically be ingested, and after a while, that amount is not enough to fuel long-term endurance efforts. Simply taking more and more glucose becomes unworkable eventually. If you ingest too much glucose, your gut pulls water from your bloodstream to reset the hydration : glucose balance and avoid the pancake syrup effect. That slows stomach emptying which in turn slows getting glucose into your bloodstream. So just taking more and more glucose is not the best way to maximize glucose use. You need another source of glucose that is not glucose itself.


Glucose polymers to the rescue! Glucose can string itself together like beads on a string to make polymers, which are more colloquially known as starches. These polymers (from three up to hundreds of glucoses long) deliver glucose without risking the pancake syrup issue. If they’re the right size, they can get out of the stomach quickly because they don’t throw off osmolality ratios and attract water like sugars do.

Glucose polymer starches become a supercharged way to efficiently get high amounts of glucose into the bloodstream compared to glucose itself – like a computer file that’s “zipped” so it can be shared more easily. Our bodies are very well equipped to “unzip” or pull apart the glucoses in starches during digestion using amylase, a pancreatic enzyme. Your pancreas puts out more amylase than proteases or lipases – a jargony way to say that your ability to convert starch to glucose is big

There are many possibilities for glucose polymers, but the sweet spot is a range of glucose polymer lengths from three to about 100 glucose units. Maltodextrin (aka amylose or glucose polymer) has become the go-to glucose source for supplying glucose during exercise, for a lot of good reasons. Maltodextrins can vary in length, but they’re always in that sweet spot length range (usually 3-17), and they connect each of those glucoses in a single, precise way that our bodies can easily unpack for maximum usefulness.

Other starches that are not a straight chain (called branched-chain amyloses/starches) are a bit slower to be converted into single glucose units than straight chain glucose (with a notable exception – see EFS PRO), so are seldom used during exercise. 


Non-glucose sugars are found in human diets, and we have ways to make them cooperate into becoming glucose. The two major non-glucose wannabes are fructose and galactose. There are a few other non-glucose sugars, but they are not nearly as important as those two sugars, and human studies have confirmed they are less helpful, more expensive, and come with more side effects (trehalose, for example). For the purposes of exercise performance, fructose is the one to focus on.

Fructose acts like glucose during ingestion and stomach emptying, but getting into the gut and bloodstream is where fructose is different from glucose. Fructose has its own pathways separate from glucose to get into cells. Once inside cells, fructose has a specific pathway to be converted 1:1 into… glucose! This means that fructose can be an additive, back-door way to sneak glucose into cells.

But fructose has a Dark Side. It’s an additive instead of an effective, stand-alone carb source for endurance exercise because of a step in the metabolization to glucose, which consumes an ATP.

In order to prevent your cells’ interiors from becoming like pancake syrup, your cells immediately attach an ATP to fructose to make it more soluble and able to fit into the pathways for conversion to glucose. In other words, before fructose can be converted into ATP energy it sucks up ATP. And guess where this additional ATP needs to come from? Glucose.

It has been shown that the ATP generation from fructose nets out less than from an equal amount of glucose, so more fructose in your bloodstream does mean more fructose in your cells, which in turn increases your potential overall energy production. But it also means more ATP is needed to prime fructose, which requires more glucose in your bloodstream to be available for cells to use, and the whole process is less efficient than with pure glucose or glucose polymers like maltodextrin.


Fructose can be found by itself, but mostly it is found in our diets as a disaccharide: sucrose. Sucrose (table sugar) consists of a glucose bonded to a fructose. Thus, sucrose is like fructose, but it’s a better party guest. It brings its own glucose, maintaining glucose saturation while also opening the door for the additive benefits of fructose’s alternative metabolic pathway.

If it’s got glucose and fructose, then why not just use sucrose instead of glucose? There are a few problems that prevent sucrose and fructose from completely replacing glucose and glucose polymers. Sucrose still has the digestive pancake syrup issue which slows its delivery of glucose at high intakes. Same for fructose by itself. They also require additional processing with metabolic taxes, as explained above.

Thus, adding fructose (as fructose itself or as sucrose) can boost glucose and ATP and endurance exercise performance – BUT! – only under certain conditions, such as when intake and utilization of pure glucose is already maxed out.


Balancing all these biochemical, gastrointestinal, and osmolytic (pancake syrup) properties led to the mixture of carbs in EFS. We know glucose is king, so that’s the starting point.

But we also know that glucose can cause GI issues, which maltodextrin – with its polymer starch structure – alleviates, allowing your body to get more glucose into the bloodstream without throwing off your guts osmolality and causing GI distress.

And finally, we know that glucose has limitations at the cellular uptake stage, but sucrose (glucose:fructose) opens an additive, backdoor channel that boosts ATP production limits above where they would be with glucose and maltodextrin alone. 

Consistent with the consensus of human research on endurance exercise, EFS uses a balanced ratio of maltodextrin (glucose polymer), sucrose (glucose:fructose), and plain ol’ glucose to maximize glucose delivery and metabolism through multiple mechanisms and processes. In this way, the advantages of each type of carb can be emphasized while the drawbacks (GI distress, pancake syrup slowdown, and ATP sucking) are limited.

March 28, 2023 — Luke Bucci

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