This is the third article in a series on improving your long-distance training and racing. I hope you find this information useful.
Endurance and ultraendurance athletes require all three forms of fuel the human body uses for energy: carbohydrate, protein, and fat. A major factor for optimal performance is using the right fuel, at the right time, in the right amount. Like every aspect of success in endurance events, proper nutrition requires planning, practice, and training to reap the benefits on race day. This article will give you the background information you need about fueling, and concludes with some recommendations about what and how much to use.
As most athletes know, “carbs are king” when it comes to fueling the body for any endurance exercise. That does not mean, however, that any carbohydrate at any time will keep you going. Carbohydrates can either help or hinder performance, depending on what kind you use, how much you use, and when you use them. For example, far too many misinformed athletes continue to use energy products loaded with simple sugars, or they use complex carbs, a superior choice, but at the wrong time and in the wrong amounts. These practices will actually impair, not help, your performance.
Simple sugars, maltodextrin, and osmolality
Most dietary sugars are simple molecules known as onosaccharides and disaccharides. The shorter the chain length of a carbohydrate source, the higher it will raise a chemical measure known as osmolality when dissolved. In solution, simple sugars can only attain about 6-8% concentration or they will sit undigested in your stomach, as the osmolality will be incompatible with the digestive juices. Products containing simple sugars, typically sucrose, fructose, and/or glucose (dextrose), must be extremely dilute to match body fluid osmolality (280 – 303 mOsm). This weak of a concentration presents a problem to athletes because it cannot provide sufficient calories (perhaps only 100 cal/hour) to working muscles. To obtain enough calories from a weak 6-8% solution, an athlete would have to consume two or more bottles of fuel per hour, which means excess fluids, increasing the risk of fluid intoxication. Using simple sugar-based “energy drinks” is not a wise strategy.
“Well then,” you might say, “I’ll just mix a stronger concentration.” But this approach also fails. As mentioned in the “10 Biggest Mistakes” article, making a double or triple strength mixture from a simple sugar-based carbohydrate fuel won’t work because the concentration of that mixture will exceed 6-8%, far too concentrated to match body fluid osmolality. It will remain in the stomach until sufficiently diluted, which may cause substantial stomach distress. Drinking more water to dilute your overconcentrated concoction puts you back in the original condition of increased risk of overhydration and all the problems that causes, so that’s not a good option. But if you don’t drink more, your body will draw fluids and electrolytes from other areas (like blood and muscle) that are in critical need and divert them to the digestive system to lower the osmolality of your over-concentrated simple sugar drink. This also will result in a variety of stomach distresses, not to mention increased cramping potential and other performance-trashing issues. The simple fact is that using simple sugar-based products is simply futile! Endurance athletes who try to fulfill calorie/energy requirements with sugar-based drinks, gels, and powder mixes usually end up with a variety of complaints and poor performances.
Molecules that contain many sugar units chained together are called polysaccharides, known familiarly as complex carbs and starches. One of these, maltodextrin, can make up to a 20% solution concentration and still match digestive system osmolality. This allows very efficient passage from the digestive tract to the liver, which converts some of the maltodextrin to glycogen for storage and some directly to glucose for immediate use by the muscles. With polysaccharides you get much more energy from stomach to liver, thus providing maximal amounts of energy to be produced, and in a form your body can efficiently process.
Based on caloric delivery alone, complex carbohydrates such as maltodextrin are far superior to simple carbohydrates (simple sugars). But that’s not all. Simple sugars, even in small amounts, can incite a condition known as “insulin spike.” This sudden recruitment of insulin causes a subsequent dramatic drop in blood sugar, which can take bloodsugar levels even below the fasting level! This “flash and crash” type of energy typically results in the dreaded “bonk,” something every athlete wants to avoid. However, complex carbs, which enter the bloodstream at a 15-20% solution, do not promote this wild fluctuation in blood sugar levels. Even though a maltodextrin might have a high GI (discussed later) and rapidly elevate blood sugar levels (a desirable effect), during exercise your body processes them with far less insulin fluctuation, most likely due to the steady release and breakdown of glucose from its polymeric source, and other hormonal factors. You never get the below-baseline drop in blood glucose that simple sugars cause.
Some athletic nutritionists disregard osmolality, but we do not believe its importance can be overstated. As Bill Misner, Ph.D., states, “when osmolality goes above 303 or below 280 mOsm, the gut must pull minerals and fluids… to mediate a narrow 280-303 mOsm range for immediate calorie absorption.” Both simple sugars and complex carbohydrate maltodextrins are absorbed at equal rates if the solution concentration matches body fluid osmolality (280-303 mOsm). As mentioned earlier, simple sugars meet this criterion only when they are mixed in calorically weak 6-8% concentrations; digestion slows down or ceases at higher concentrations. When athletes make a double or triple strength simple sugar based drink, trying to increase caloric input, they usually develop problems such as gastric distress, bloating, flatulence, vomiting, and muscle cramps.
On the other hand, the maltodextrins (complex carbohydrates) match body fluid osmolality even when mixed in concentrations as high as 15-20%. This presents a distinct advantage because your body is able to digest, and thus convert to energy, a greater volume of calories from complex carbohydrates than it can from simple sugars.
Simple sugars = Ineffective fuel
The bottom line is that simple sugars are a very inefficient fuel source. Using them to fuel your body is like trying to heat your house by burning newspapers in your stove. You get a fast heat, but it burns out quickly, and you have to continually feed the fire. Not good! Complex carbohydrates, on the other hand, are similar to putting a nice big log on the fire in that they burn longer and more evenly, with the declination in “heat” (energy levels) being much more gradual. They provide a more consistent and longer lasting energy supply, without putting you at risk for stomach distress. Some manufacturers formulate their sports drinks with complex carbs, but almost all of them lade their products with cheap, inefficient simple sugars. Read the label before you buy. If there’s anything that ends in “ose” in the ingredient list, put it back on the shelf. contain no added simple sugars.
People often ask about the Glycemic Index (GI) of various carbohydrates and how those figures relate to fueling for endurance exercise. Here’s the scoop: GI rates the speed at which the body breaks down a carbohydrate into glucose. The lower the GI, the slower the process, and
therefore the more stable the energy release. For food eaten at times other than exercise and recovery, GI is an important dietary factor, and we recommend eating foods with a low-to-middle GI.
However, during and immediately following exercise, a high-GI carbohydrate—one that elevates blood sugar levels rapidly—is desirable, as long as you keep caloric intake within approximately 280 cal/hour, as hormones associated with sympathetic nervous system activity will inhibit GI impact on insulin release. Negative diet/health-specific effects associated with consumption of high GI carbohydrates are not a concern during and immediately after exercise; high GI carbs actually perform better than low GI carbs at these times.
Long-chain, high-GI maltodextrins have a GI value of about 130, compared to glucose (100) or sucrose (62). This means that maltodextrins raise blood insulin more effectively than simple sugars, but without the rapid and precipitous drop that is a common (and deleterious) effect of simple sugars. Also, as mentioned earlier, maltodextrins allow you to absorb a greater volume of calories than you can from simple sugars.
Some suggest that since maltodextrin is many chains of glucose “hooked” together, it takes the body longer to break those chains down for conversion to glucose (which all carb sources eventually become in the body). However, it needs to be noted that the bonds that compose maltodextrin are very weak so they are readily broken apart. Additionally, the amylose-amylopectin content of maltodextrin is very similar in chemistry to human stored glycogen, which is the first fuel the body recruits and uses when exercise begins. Therefore, if the body’s first-used source of fuel is “complex” in nature, it can be safely assumed that the body can break it, and endogenously supplied complex carbohydrates, down with remarkable ease.
How much to consume?
Now that you know what kind of carbohydrate to use, the next question is, “How much?” With some allowances provided for very large athletes, the human body can only return (from the liver to muscle tissue) about 4.0 - 4.6 carbohydrate calories per minute, or about 240-280 cal/hr. When most athletes consume more than 280 cal/hr from carbohydrates during an event, the excess remains undigested in the stomach, or passes unused into the bowel, where, in the unmincing words of Dr. Bill Misner, “they accumulate in gastric or intestinal channels in 100-degree temperatures and putrefy in time.”
You may be burning up to 800 cal/hr, but your body cannot replace that amount during exercise. Trying to replenish calories at the same rate as depletion only causes problems. Instead of having more energy available, you’ll have a bloated stomach, and perhaps even nausea and vomiting. You’ve seen it happen, but it’s not a necessary aspect of intense competition; more likely it’s the result of improper caloric intake.
Complex carbohydrates only or a combination of carbohydrate sources: Which is better for the endurance athlete?
Findings from research conducted by the Dutch sport scientist Asker Jeukendrup has caused quite a stir. In fact a few companies now produce sports drinks that contain the carbohydrate formulations used in the studies. In general, Jeukendrup found that a blend of carbohydrates increased oxidation rates, indicating higher energy production. In one study, cyclists who ingested a 2:1 mixture of maltodextrin to fructose oxidized carbohydrate up to 1.5 grams/minute. Another study used a mixture of glucose, fructose, and sucrose and had rates that peaked at 1.7 g/min. Both those results are pretty eye opening, considering that complex carbohydrates typically oxidize at a rate of about 1.0 g/min.
However, there’s more to the results than what first meets the eye. Most of Jeukendrup’s subjects cycled at low intensity, only 50-55% maximum power output, which I think we’d all agree is very much a recovery pace, if that.
To be blunt, at a leisurely 50% VO2 Max pace, athletes can digest cheeseburgers and pizza with no gastric issues. However, if the heart rate and core temperature are raised to only 70% VO2 Max, the body must divert core accumulated heat from central to peripheral. This reduces the blood volume available to absorb ingested carbohydrates or whatever the athlete has consumed.
After two decades of experience, we have found that in the overwhelming majority of the athletes we’ve worked with—athletes engaged in typical 75-85% efforts and/or in multi-hour endurance events—the combination of simple sugars and long chain carbohydrates, and in amounts higher than approximately 1.0 – 1.1 grams per minute (roughly 4.0 – 4.6 calories per minute), have not yielded positive results. They did, however, increase performance-inhibiting, stomach-related maladies.
Lowell Greib, MSc ND, explains that gastric emptying is a key limiting step in carbohydrate metabolism: “If your stomach can’t empty the product (no matter what it is) you are going to get nothing from it except a huge gut ache and possibly lots of vomiting! Unless there is new research that I am unaware of, gastric emptying is directly proportional to the osmolality of the solution in the stomach. Long chain carbohydrate (maltodextrin) contributes less to increasing the osmolality than do disaccharides (sucrose, lactose, maltose, etc.).”
Augmenting Greib’s statements, Dr. Bill Misner writes, “Absorption rate and how fast the liver can ‘kick it out’ are limiting factors. No matter what you eat, how much or how little, the body
provides glucose to the bloodstream at a rate of about 1 gram/minute. Putting more calories in than can generate energy taxes gastric venues, electrolyte stores, and fluid levels.”
Bottom line is not whether or not Jeukendrup’s published studies are disputable, but rather if these studies apply to faster paced, longer duration bouts of exercise. We do not believe this to be the case, which is why we do not recommend the use of multiple carbohydrate sources during exercise. Stick with complex carbohydrate fuels, and we guarantee you’ll see better results.
Fatty acids for fuel
If we can’t replace all of the calories we expend, then how do we keep going our after hour? The answer is that we have an enormous supply of calories in body fat. The typical athlete can count on a reserve of up to 100,000 calories in the form of stored fatty acids—that’s enough, if you could process it all, to fuel a run from Portland, OR to Los Angeles, CA—a distance of almost 1000 miles! These fatty acids are the fuel of choice when exercise goes beyond about two hours,
providing approx 60-65% of your caloric expenditure. In other words, your body has a vast reservoir of calories availablerom body fat stores, and it will use those liberally to satisfy energy requirements during lengthy workouts and races.
However, for this process to continue without compromise or interruption, you must not consume excess calories. If you try to match energy losses with caloric replacement from your fuel, you will not only cause a variety of stomach-related ailments, you will also inhibit the efficient utilization of fats for fuel. As mentioned in “The 10 Biggest Mistakes” article, caloric donation from consumed fuels must cooperate with your internal fat-to-fuel conversion system. Do not attempt to completely replace caloric expenditure. Your best strategy is to replenish calories in amounts that support efficient energy production and do not interfere with the use of fatty acids for fuel.
Protein for fuel
When exercise goes beyond 90-120 minutes, you need to incorporate some protein into the fuel mix. After about 90 minutes, and continuing until you stop your activity, about 5-15% of your
caloric utilization comes from protein. This process, called gluconeogenesis, is unavoidable, and if you don’t supply the needed protein in your fuel, your body will literally scavenge it from your own muscle tissue. This is called catabolism (muscle breakdown), known informally, but quite accurately, as “protein cannibalization.” It can cause premature muscle fatigue (due to excess ammonia production from the protein breakdown process) as well as muscle depletion and post-exercise soreness. Protein cannibalization also compromises your immune system, leading to increased risk for colds, flu, and other diseases. For exercise and competition that extends about two hours or more, your primary fuel should incorporate protein in a ratio of about 8:1 (by weight) carbs to protein.
The benefits of soy protein during endurance exercise
As noted earlier, it’s good to have a little protein along with your complex carbs to avoid the negative effects of muscle catabolism, but you must have the right kind of protein. The preferred protein for use during prolonged exercise is soy, primarily because its metabolization does not readily produce ammonia. Whey protein, with its high glutamine content, makes an excellent post-workout protein, but is not a good choice before or during exercise. You’re already producing ammonia during exercise, so consuming glutamine-enhanced whey protein will only exacerbate that problem.
There is some confusion regarding the glutamine and ammonia buildup. Yes, glutamine does eventually scavenge ammonia. The key word, however, is eventually.” When glutamine metabolizes, it increases ammonia initially, then scavenges more than originally induced, but it takes approximately three hours or so to accomplish this. You’re already producing ammonia during endurance exercise, and since ammonia is a primary culprit in premature fatigue, it seems logical that you’d not want to increase ammonia levels even more. However, that’s exactly what you’ll do when you consume glutamine supplements or glutamine-enhanced whey protein during exercise. That’s one reason why soy protein is preferable for use during prolonged exercise.
Soy protein has a couple of other great features, too. First, it is an easily digestible protein. Second, it has an excellent amino acid profile, with a substantial proportion of branched chain amino acids, or BCAAs, which your body readily converts for energy. During exercise, nitrogen is removed from BCAAs and used in the production of another amino acid, alanine, high amounts of which also occur naturally in soy protein. The liver converts alanine into glucose, which the bloodstream transports to the muscles for energy.
BCAAs and glutamic acid, another amino acid found in significant quantities in soy protein, also aid in the replenishing of glutamine within the body, without the risk of ammonia production caused by orally ingested glutamine.
Soy’s amino acid profile has high amounts of both alanine and histidine, which are the amino acid components of the dipeptide known as carnosine, a nutrient known for its antioxidant and acid buffering benefits also has a high level of aspartic acid, which plays an important role in energy production via the Krebs cycle. Additionally, soy protein has high levels of phenylalanine, which may aid in maintaining alertness during extreme ultra distance races.
Lastly, soy produces more uric acid than whey protein. This might not sound good, but uric acid is actually an antioxidant that helps neutralize the excessive free radicals produced during exercise. High uric acid levels, from soy’s naturally occurring isoflavones, are another strong reason for preferring soy protein during endurance exercise.
Source: The Endurance Athlete's Guide To Sucess by Steve Born