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Complex Carbs – Still the Quality Choice

A closer look at the science reveals the truth about this critical aspect of sports nutrition

By: Steve Born


  • Rapid energy (GI rating of 100, same as glucose). During exercise and immediately after, that is EXACTLY what you want.
  • Longer-lasting energy (no “flash and crash,” “piece of paper on fire” effect)
  • More calories can be efficiently digested from complex carbs than from simple sugar
  • Less potential for stomach distress

Athletes know that carbohydrates are king when it comes to fueling during exercise. Unfortunately, choosing a fuel with the right carbohydrate continues to be immensely frustrating and confusing for many athletes—especially now, given the abundance of “cutting edge” sports fuels on the market and the hype that surrounds them.

But if you care about the quality of your workouts and your race results, it’s imperative to choose the right carb, because it makes an enormous difference. We wrote this article to cut through the hype. We’re convinced that you’ll no longer need to guess what carbohydrate to use, once you understand how the body responds to different forms of carbs. We’ll explain why you can count on higher quality workouts and better race results if your fuel contains higher-quality, complex carbohydrates.


The contenders: complex carbohydrates and simple sugars

For more than two decades, Hammer Nutrition has consistently and emphatically maintained that endurance athletes will perform significantly better if they fuel their bodies during exercise only with complex carbohydrates, avoiding simple sugars. Not surprisingly, Hammer Nutrition fuels are comprised only of complex carbohydrates (maltodextrin), with no added simple sugars (glucose, sucrose, or fructose).    

Still, on an ever-increasing basis, companies continue to produce sports fuels composed of simple sugars, whether solo or in combination—and occasionally with maltodextrin included as well—touting them as a superior exercise fuel. These companies usually list a number of studies to back their claims.  

So what is the best carbohydrate for the endurance athlete? Does maltodextrin stand alone as the premier source of carbohydrate energy—or do simple sugars and/or a combination of simple sugars reign supreme? To answer these questions, let’s first take a look at how your body responds to different sugars. This involves a basic understanding of “osmolality.”

What is osmolality and why does it matter?

Osmolality is the concentration of a solution’s dissolved particles, or solutes, that can permeate a cell membrane and thus contribute to osmotic pressure (think: osmosis). There are three general categories of osmolality:


  • Hypotonic = less than 280 mOsm
  • Isotonic = between 280-303 mOsm
  • Hypertonic = greater than 303 mOsm


Hypotonic – “Hypo” means deficient or abnormally low; it refers to the situation when the concentration of water outside the cell is greater than inside the cell. A hypotonic solution results in a movement of water into the cell that could burst the cell.

Isotonic – “Iso” means equal, and it describes the osmotic status the human body prefers for functional performance of cells. If a solution is isotonic, the water concentration is the same on either side of the cell membrane, and there is no net movement of water.

Hypertonic – “Hyper” is excessive or too much; in a hypertonic solution the water concentration inside the cell is greater than outside the cell. This causes water to move out of the cell, eventually causing the cell to shrink.

Why should we care so much about osmolality? Because, among other things, it determines how many calories can be efficiently absorbed from the gut. The osmolality of body fluid is 280-303 mOsm, so the solution of the fuel you’re consuming must be within those isotonic parameters for the fuel to be efficiently transported to the blood stream for eventual conversion to energy. If the osmolality of your sports fuel exceeds these parameters (hypertonic), absorption will be delayed until either:

  1. you consume more fluid and electrolytes (and by then, you may be flirting with overhydration), or
  2. your body draws a sufficient supply of fluids and electrolytes from its internal stores (and away from working muscles).

Both of these actions hinder performance. And that’s precisely the issue with fuels containing one- or two-chain carbohydrates (monosaccharides or disaccharides—a.k.a. simple sugars). The shorter the carbohydrate’s chain length, the higher it raises the solution osmolality in the stomach. To match body fluid osmolality parameters and be digested efficiently (an isotonic mixture), fuels containing simple sugars such as glucose, sucrose, and fructose must be mixed in solution concentrations no higher than 6-8%.

This weak concentration presents a problem to athletes because it provides insufficient calories (perhaps only 100 calories hourly, at the most) to working muscles. To obtain enough calories from a 6-8% solution, an athlete would have to either:

  1. consume two or more bottles of fuel per hour, or
  2. make a double-strength (or greater) bottle of fuel.

Scenario A won’t work because it increases the risk of overhydration and water intoxication, which can be extremely detrimental to performance and health. Scenario B isn’t acceptable either because the mixture exceeds 6-8%, making it far too concentrated to match body fluid osmolality—leading to the performance-inhibiting issues associated with a hypertonic (too concentrated) fuel mixture. 

Conversely, maltodextrin, which is a multiple of sugars hooked together, matches body fluid osmolality at concentrations as high as 15-18%, That means that your system can digest a greater volume of calories from complex carbohydrates than it can from simple sugars. As Dr. Bill Misner states, “The gold-standard carbohydrate source originates from longer-chain carbohydrates (maltodextrin) because more caloric volume crosses the gastric lining with less distress to the competing athlete.” Or, as another nutritional scientist states, “maltodextrin allows one to swallow more energy in less volume.” 

The trouble with those “multiple carbohydrates are better” studies

Our longstanding position is that the human body can effectively convert to energy approximately 1.0 to slightly over 1.1 grams of carbohydrates (approximately 4.0 – 4.6 calories) per minute, equaling 240-276 calories per hour. Several years ago, however, research showed that a greater volume of calories could be converted to energy—upwards of 1.8 grams (7.2 calories) per minute—using various blends of carbohydrate sources, primarily simple sugars.

That’s pretty eye-opening, wouldn’t you agree? Who wouldn’t want their body to produce more energy on a per-minute/hourly basis? Instead of maxing out at around 280 calories an hour, you could conceivably crank out closer to 430 calories an hour. What an advantage that would be! That’s why it’s not surprising that many a company has jumped (and continues to jump) on the “multiple carbohydrates are better than one” bandwagon, producing fuels that reflect the carbohydrate sources and ratios used in the various studies.

But let’s take a closer look at a couple of these studies to see if what occurs in “the lab” truly can be applied to real-world exercise situations:

(1) G. A. Wallis, D.S. Rowlands, C. Shaw, R. L. Jentjens, A. E. Jeukendrup, Oxidation of combined ingestion of maltodextrins and fructose during exercise. Medicine and Science in Sports and Exercise 37 (3), 426-32 (March 2005).

In this study, eight trained cyclists performed three bouts of exercise, each lasting 2.5 hours, all at an intensity of 55% maximum power output. The cyclists consumed a maltodextrin-only drink (1.8 grams per minute), a maltodextrin/fructose drink (1.2 grams of maltodextrin + 0.6 grams of fructose per minute), or water. The results showed that carbohydrate oxidation (energy output) was greatest with the maltodextrin/fructose combination, peaking at 1.5 grams/minute (360 calories/hour).   

COMMENT: What stands out is the low intensity of exercise: 55% of maximum power output is a recovery pace at best. So does it really matter if oxidation rates were higher using a maltodextrin/fructose combination? When exercising at an intensity that low, it’s not all that difficult to believe that the athletes were able to consume a massive 432 calories an hour—whether from maltodextrin only or a combination of maltodextrin and fructose—and not suffer stomach issues (though that was never mentioned in the study).


The real question is, “What would happen if the intensity of exercise increased to even a moderate rate/pace?” Based on our experience with thousands of athletes, we’re convinced gastrointestinal issues would result because the osmolality of both of the fuels used in the study was too high in relation to body fluid osmolality.

(2) K. Currell, A. E. Jeukendrup, Superior endurance performance with ingestion of multiple transportable carbohydrates. Medicine and Science in Sports and Exercise 40 (2), 275-81 (Feb. 2008).

Eight trained cyclists consumed either water, a glucose-only drink (1.8 grams per minute), or a drink containing a 2:1 ratio of glucose and fructose (1.8 grams per minute). They performed a two-hour bout of exercise at 55% Wmax (Watts maximum rate), and then performed a time trial, lasting about one hour, to complete a set amount of work as quickly as possible. The results showed that the cyclists consuming the glucose/fructose combination completed the time trial phase of the test 8% faster than those consuming the glucose-only drink.


COMMENT: Because the study did not use complex carbohydrates (maltodextrin), we cannot make an “apples to apples” comparison of the efficacy between simple sugars and complex carbohydrates. The study shows only that a glucose/fructose combination allows for better performance than glucose alone.


Additionally, keeping in mind that simple sugar mixtures are isotonic only in concentrations of 6-8%, it’s hard to conceive of study subjects consuming such high concentrations of either glucose or a glucose/fructose combination (7.2 calories/minute, equaling 432 calories/hour) without experiencing stomach distress. The study does not seem to discuss osmolality issues; so the only plausible explanation is that the rate of intensity during the two-hour bout of exercise was extremely low. 


(3) A. E. Jeukendrup, L. Moseley L., Multiple transportable carbohydrates enhance gastric emptying and fluid delivery. Scandinavian Journal of Medicine and Science in Sports 20 (1), 112-21 (Feb. 2010).

In this study, eight males consumed either water, glucose (1.5 grams per minute), or a glucose/fructose mixture (1.5 grams per minute). They performed three two-hour bouts of cycling at 61% VO2Max. The results showed a greater rate of gastric emptying, and increased “fluid delivery” using the glucose/fructose combination versus the glucose-only combination.


COMMENT: Similar to the previous study, this one focused only on two simple sugars, glucose and fructose. Because maltodextrin wasn’t used, it’s not possible to compare its efficacy to simple sugars. Also, as in the previous study, the exercise intensity (61% VO2Max) is quite low. Because this study doesn’t appear to factor in osmolality and potential stomach issues, the best explanation for why these subjects—who weighed an average of 164 pounds—may have been able to consume 360 calories an hour is the low intensity of the exercise.



These are but a handful of the studies that suggest that a combination of carbohydrates is more effective at allowing the body to produce energy on a per-minute basis compared to a single carbohydrate source. Although we don’t discount this research—the studies are well-designed and executed—we do dispute their applicability to endurance athletes. Here’s why:


The “superiority of multiple carbohydrates” argument is based on glucose (maltodextrin as well) being absorbed by one transporter (SGLT1) and fructose by another transporter (GLUT-5). With two different transporters being used, carbohydrates were absorbed at different rates, thus higher oxidation (burn) rates were noted. But for these benefits to be achieved, it was necessary for the test subjects to ingest large amounts of glucose (or maltodextrin), so as to saturate the SGLT1 transporter. In the first two studies mentioned earlier, the participants consumed 1.8 grams of carbohydrates (7.2 calories) per minute. Over an hour’s time, that’s a massive 432 calories. In the third study, less carbohydrate was consumed, though it was still high—especially for athletes averaging 164 pounds—at 1.5 grams of carbohydrates (6 calories) per minute, equaling 360 calories hourly.


The other factor to account for is osmolality. When you combine simple sugars and complex carbohydrates together, as some of these other company’s fuels do, the mixture’s concentration and osmolality changes dramatically, to the point where neither carbohydrate source is digested efficiently. If this is the case, why then would it matter if two different transporters were used? If the mixture is too concentrated and can’t get through the gut efficiently, it simply will not matter if glucose/maltodextrin goes through one transporter and fructose through another. 


With these things in mind, take a look at these and the other studies on multiple carbohydrate sources, and take careful note of the intensity the research participants exercised at. You’ll find that the athletes exercised at a relatively easy effort—“recovery pace,” if that. Though the studies we’ve reviewed over the course of several years don’t appear to address (let alone elaborate) any gastrointestinal issues the test subjects may or may not have had, the relaxed rate of effort is the most likely explanation for the participants’ ability to consume such high amounts of calories on an hourly basis, whether from simple sugars (alone or in combination) or complex carbohydrates (maltodextrin, alone or in combination with fructose).


Put it to the test

Exercise pace makes a big difference with regard to the ease of digestion of food and fuel. At a more leisurely pace, athletes can digest just about anything and in high quantities. Boost the intensity to moderate or high, however, and things change dramatically. The price for burning more carbohydrates at a higher rate is that effort and pace must be greatly reduced.  As Dr. Bill Misner once wrote, “Raise the heart rate and core temperature even to only 70% VO2Max, and the body must divert core accumulated heat from central to peripheral. This reduces the blood volume available to absorb ingested carbohydrate or whatever the athletes have consumed.”


Over the course of more than two-and-a-half decades, we’ve repeatedly observed that when athletes consume carbohydrate solutions containing either glucose or fructose or both— combinations that supposedly increase carbohydrate oxidation rate—they usually experience gastrointestinal upset. What’s more, when the rate of intensity exceeds what was performed in the “multiple carbohydrate” studies, many athletes fail to finish a period of prolonged exercise.


If you plan on casually jogging your next marathon or soft-pedaling your next century, then you really don’t need to be concerned with what you’re eating or how much. But if you’re planning on doing any workout or race at more than just a relaxed effort, then you DO need to be cognizant of what and how much you consume. When the intensity goes above “recovery pace,” the osmolality of the fuel you’re consuming DOES matter! Remember:


  • If you consume a simple sugar fuel, your body will only permit 6-8% of it in solution into circulating serum for fuel replacement.


  • Complex carbohydrate fuels are easily and more-rapidly absorbed in a 15-18% solution. More calories are absorbed faster, and are available for energy production, from complex carbohydrates than simple sugar.


The higher the simple sugar content, the higher the solution osmolality, the less of it is absorbed immediately. The longer the chain of sugars linked together as a complex carbohydrate, the more of it is absorbed in higher solution because its osmolality is closer to that of body fluids.


This is why we remain convinced that the ideal carbohydrate source for athletes engaged in moderate-to-high intensity training and racing is complex carbohydrates (maltodextrin) only, and it’s why Hammer Nutrition fuels are formulated the way they are. For more than 25 years, thousands and thousands athletes have enjoyed better workouts and race results—without uncomfortable GI distress—using Hammer Nutrition fuels and adopting our protocols. Put our fuels to the test against anything else out there, and we guarantee that you will too. 

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