First Endurance: Carbohydrate Fuel System Explained

Long-term endurance exercise pushes the limits of human muscle physical performance. Whether you run, cycle, climb, swim, or a combination, your muscles need to remain fueled for as long as you are going. After taking care of water and electrolytes, fuel is the next hurdle to master for extending performance. Decades of focused human research has found the basics of how to fuel endurance performance. EFS was designed with this information on hand, but was also field-tested to fine-tune the mix of fuel that has worked so well.

EFS products have been specifically formulated to deliver the ideal blend of carbohydrates for energy. EFS provides a combination of carbohydrates to maximize fuel delivery to your working muscles and the rest of your body. Let’s see how!

Exercise Fuel Choices

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 a relatively small amount, slow to convert to carbs or fats, and they release nitrogen compounds that are anti-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. 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. This truism relegates fats as a secondary player to keep you going long and hard. Fats simply cannot be ramped up enough during exercise to keep you performing at your peak for a long-time. We are water-based carbon units.

Let’s put this another way – go ahead and try to take enough fats during exercise to keep you going past your limits. You will crash and burn while spewing greasy stomach contents over the landscape. OK, let’s try taking the linker metabolites between fats and their conversion to carbs – ketoesters.

Taking enough ketoesters to provide enough caloric energy for long-term exercise has some serious drawbacks that are dancing with disaster (especially heart rhythms and GI issues). Without a carb supply, ketoesters are just stopgap, short-term, emergency fuel with problems. This leaves carbohydrates (carbs or CHO) as the main energy source.

Carbohydrates – All About the Glucose

Consuming carbohydrates during prolonged exercise 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). Like fats, you can ramp up your ability to use carbs as fuel during exercise. A whole lot more calories than fats. Huge amounts of human research have clearly shown that Carbs Are King for endurance performance. That said, what is the best carb to make me perform better?

The simple answer is GLUCOSE (aka dextrose). 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. Put yourself in glucose’s shoes. You are singled out for an all-expenses-paid, red-carpet luxury trip into your cells, where you will be torn in half, and then those pieces will be ultimately ripped to small pieces, with electrons regenerating ATP (which recycles itself, mostly). We are actually molecular slaughterhouses and rendering plants. And that ATP energy leaves carbon dioxide (CO2) and water as waste. If you can breathe you can remove CO2. And the water (called water of oxidation or WOO!) stays in working cells and/or back into circulation to help you stay hydrated. Our bodies are marvels of atomic disruption!

Without becoming a Biochem textbook, 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 ultimate 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, even that process has limits. And glucose needs to be processed into ATP, which makes demands on your GI tract to deliver it to your bloodstream, and cell receptors to get glucose from the bloodstream into your cells, and the glucose shuttled into cellular glucose destruction derbies, like mitochondria.

But there is a hitch – all sugars can turn your cellular insides into pancake syrup in high amount, slowing everything down considerably. Thus, your body has a certain rate that limits how much and how fast glucose can be handled.

Glucose will always be the best fuel to take for endurance exercise. 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. Glucose itself is quickly absorbed, transported and converted to ATP, limited mostly by your GI tract’s ability to deliver glucose to your bloodstream. But simply taking more and more glucose becomes unworkable eventually. If you ingest too much glucose, it pulls water from your bloodstream into your gut to keep it from becoming pancake syrup, slowing getting out of the stomach (called stomach emptying) which slows getting 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 Supercharge Glucose Delivery

Glucose polymers to the rescue! Glucose can string itself together like beads on a string to make starches. These polymers (three glucoses long or more, up to hundreds of sugars long) are a more efficient way to deliver glucose without the pancake syrup issues. Humans are very well equipped to pull apart the glucoses in starches during digestion, using amylase enzyme from your pancreas. Your pancreas puts out more amylase than proteases or lipases, meaning your ability to convert starch to glucose is big. Glucose polymers (of the right size) can get out of the stomach quickly because they are not attracting water like sugars do. Net result is that glucose polymer starches become a supercharged way to get glucose into the bloodstream compared to glucose itself. Of course, there are many possibilities for glucose polymers, but the sweet spot is a range of glucose polymer lengths from three to about a hundred 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 have a range of length (number of glucose units) and a single, precise way the glucoses are hooked up to each other for maximum usfeulness. Net result is to saturate glucose delivery from your mouth to your bloodstream.

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.

Glycogen is Glucose Too

Your body can store glucose as a starch (glucose polymer). But because straight-chain glucose polymers take up lots of room that makes it difficult to convert to glucose units quickly, our bodies reattach glucoses into large, branched-chain glucose polymers called glycogen. Glycogen forms a spherical shape, with lots of glucose ends facing out, enabling our cells to use specific enzymes to rapidly get glucose into circulation when needed. Glycogen also holds a lot of water, that is released when glycogen is converted to glucose – another hydration bonus during serious exercise. Glycogen is used to maintain blood glucose levels during rest and exercise. Your liver is the major site of glycogen storage. Muscles also store glycogen, and endurance training increases that amount. Excess dietary glucose can become glycogen.

Because the total amount of glycogen is limited by the space inside your liver and muscle cells, there is a finite amount of glucose storage. Ingesting glucose sources during exercise will prevent early depletion of internal glycogen stores, which are only accessed when you eventually use glucose faster than you can replenish its delivery. Glycogen is your glucose backup. When you run out of glycogen, signals are sent to your brain to make you stop using glucose (exercising), so your nervous system does not shut down (not a good thing). The more glycogen you can store, the longer you can forestall complete fatigue and exhaustion.

Other Sugars

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).

Fructose can be found by itself, but mostly it is found in our diets as a disaccharide (two-sugars stuck together). Sucrose (table sugar, aka Sugar) is glucose-fructose. Thus, sucrose (Sugar) is another delivery system for glucose, but the fructose has its own benefits. 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. Thus, adding fructose (as fructose itself or as sucrose) can boost glucose and ATP and endurance exercise performance under most conditions, such as when glucose intake and utilization is maximized but you still need more glucose.

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. As sole carb sources, both are inferior to glucose and/or glucose polymers. But combined with a saturating glucose source, they can deliver more glucose via the alternate fructose pathway.

But fructose has a Dark Side. Another reason fructose is an additive, but not a good stand-alone carb source, for endurance exercise is a little-recognized step for metabolism to glucose. That comes at a metabolic cost, a cost of ATP which could have been used for performance. Your cells have specific receptors that recognize fructose and move it inside without needing insulin to activate the receptors. In other words, more fructose in the blood stream, more fructose inside cells. This sounds great for exercise until you realize that in order to prevent your cell insides 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. The more fructose in your bloodstream, the more fructose in your cells, and the more ATP that is needed to prime fructose. 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.

In fact, high levels of fructose sucking up ATP has been linked to all the long-term, deadly health problems associated with high intakes of corn syrup (which is a majority of fructose) and excessive sucrose intakes (half fructose). At least sucrose has a glucose to make the ATP sucking not as bad as fructose by itself, so it makes sense to use sucrose as a fructose source to add more ATP, but at a lesser efficiency than glucose.

Why not add fructose itself to glucose and/or glucose polymer (maltodextrin)? Not a good idea – fructose gets into cells faster than glucose, so unless there is a lot more glucose, using pure fructose can be detrimental, or not as ergogenic, as glucose. This is a reason why hydrogels with maltodextrin plus fructose are necessary – to slow the delivery of fructose and ATP sucking.

Ideal Carb Mix for Endurance

Balancing all these biochemical, gastrointestinal and osmolytic (pancake syrup) properties led to the mixture of carbs in EFS. Not to mention the brain effects from not enough or too much sweetness, another issue with sucrose and fructose. Consistent with the consensus of human research on endurance exercise, EFS uses a balanced ratio of maltodextrin, sucrose and glucose to maximize glucose delivery and metabolism. In this way, the advantages of each type of carb can be emphasized, without allowing the drawbacks of each to limit ATP production, and thus, exercise performance.

When used as directed, the low osmolality of EFS (~6-8%) provides superior fluid absorption with optimal carb uptake and utilization. Other mechanical properties are taken into account, such as the size of carb particles and degree of processing – affecting how well EFS mixes with water and maximizing the GI phases of stomach emptying, digestion, absorption, uptake and bioavailability. Also, real-life practices such as timing of ingestion, contents and timing of the previous meal, and the co-ingestion of fat, fiber, or protein affect the ability of carbs to maximize endurance performance.

To reiterate, EFS has been honed by real-life testing to be effective, palatable and convenient for maximizing long-term endurance exercise.

This article is credited to Luke Bucci PhD and First Endurance.