By Arnie Baker M.D.
The priorities for nutrition for aerobic endurance exercise—long rides, runs, walks, or triathlons—are water, calories, and sodium. For events under an hour, no special nutrition may be needed.
For most events over an hour, concern yourself mainly with fluids and calories. For long-distance events that last most of a day or longer, sodium must also be considered.
It is typical for cyclists to use 2,500 to 3,000 calories during a century. Runners and walkers use 80 to 100 calories per mile.
Some of this energy comes from the body’s stores of carbohydrate (glycogen) and fat. Some energy needs can be met by consuming calories while exercising.
Carbohydrate is the fuel of choice for exercising athletes. Depending upon your size, your body can use up to 300 ingested calories per hour to spare glycogen stores. As a rule, try to consume this many calories for every hour you exercise.
If not racing, cyclists do well to stop periodically and eat “real food”—especially early on in a long ride. Leftover breakfast items such as French toast or pancakes, fig bars, bananas, and Pop-Tarts (perfectly packaged for jersey pockets) are favorites for short stops.
The harder you work, the less you are able to tolerate solid food. Energy bars and gels do work, but after many hours become tiresome for most athletes.
Carbohydrate solutions are a convenient way to get calories. Typical sports drinks and diluted fruit juice have 100–125 calories per 16-ounce bottle. This usually works out to about a 6% sugar solution.
Beverages do not usually have more calories than this because solutions of higher concentration are difficult to digest. More concentrated than 6% solutions are associated with cramps, diarrhea, and other gastrointestinal problems.
There is a trick to increasing caloric content without increasing concentration: maltodextrin nutrition.
You will often want to consume as many calories as you can to gain maximum benefit. However, if you add too many—if the solution you are drinking is a concentrated one—the stomach will empty more slowly, and the gut will send in water from the body to neutralize the concentration of the fluid you have drunk, causing you to temporarily dehydrate yourself further.
Your intestines may also try to eliminate this overly concentrated solution so you may get cramps or diarrhea. Studies have shown that for most people exercising at moderate levels of exertion, a 6% to 8% simple carbohydrate solution is the maximum that can be tolerated. This is represented by A in Figure 5.
Doubling the concentration of a glucose solution from 6% to 12% will double the calories, but usually cause gastrointestinal upset. This is represented by B in the figure.
You may be able to pack more calories into a given fluid volume by combining a variety of sugars. A 6% fructose and 6% glucose solution, for example, may cause less gastrointestinal upset than a 9% solution of either of these simple sugars. Further, increased water and electrolyte movement from the gut into the bloodstream may take place, as different mechanisms of transport are involved with these two simple sugars.
This is represented by C in the figure.
Improving gastrointestinal tolerance and maximizing uptake is not the same as maximizing muscle uptake. The muscles may also take up and use more carbohydrate if energy is supplied by more than one type of simple sugar.
At rest, athletes can eat or drink more calories than their muscles can process. At moderate to high intensity, muscles may be able to process more carbohydrate than most athletes can tolerably ingest.
You may be able to increase gastrointestinal tolerance and pack more calories into a given fluid volume by using maltodextrins, or glucose polymers. These glucose chains increase calories without increasing the number, or concentration, of particles. This is represented by D.
What Are Maltodextrins?
Carbohydrates in nature are generally simple sugars or starches.
Food manufacturing processes can create intermediate length carbohydrate molecules much shorter than the thousands of sugars in starches, but longer than the one or two sugars in molecules of monosaccharides and disaccharides.
These intermediate-length carbohydrate molecules are called maltodextrins or glucose polymers.
Typically, these are about 10 sugar units long.
In general, the shorter the maltodextrin, the sweeter it is. Most 10-sugar molecule maltodextrins are almost tasteless. This allows food processors to use maltodextrins in savory foods or add sweetness, if desired.
A 6% simple carbohydrate solution will have about 100 calories in 16 ounces, a standard water bottle. A 6% maltodextrin solution will have about 600 calories in 16 ounces.
Using maltodextrins allows more calories to be ingested without causing the gastrointestinal distress associated with the higher osmotic load of concentrated simple carbohydrate solutions. That is one reason why many specialty sports products (drinks, gels, and bars) that aim to provide calories during exercise use maltodextrins.
Maltodextrins are the fuel of choice for aerobic endurance athletes. They are:
- Low osmolarity (particle concentration)
- Less likely to cause GI distress
- Minimal taste—use flavoring of choice
Most commercially available high-carb sports drinks and gels contain maltodextrins mixed into proprietary formulas for taste and color. Other ingredients, for example vitamins or herbs, may be added—generally for marketing purposes.
A few specialty sports drinks that contain maltodextrins provide more than 400 calories per bottle. Examples include the proprietary product Carbo Gain, which is described as a pure maltodextrin product and comes in an 8 pound canister option.
Powdered products are generally less expensive than premixed solutions. Powdered products sometimes have problems with dissolvability, palatability (taste), caking, or sludging. Like many proprietary products, some commercial maltodextrins, especially those sold through beer-brewing stores, will cake.
Maltodextrins are available in different average simple-sugar chain lengths. Agglomerated products (processed to yield crystal clumps) are dustless and free-flowing. They are easy to handle. Agglomerated maltodextrins have excellent dispersibility and dissolution characteristics, quickly forming clear solutions when mixed with water.
Make Your Own Maltodextrin Product
Why? It is:
- Less expensive
- Better tasting
- Easier to handle
You can make you own great solution inexpensively.
You can also purchase a wide variety of pure maltodextrin products in 50-pound bags from commercial grain processors. The cost usually is less than $1.00 per pound or one-tenth that of proprietary products. The bag generally has a shelf life of two years. You can split a $100 order (100 pounds)—generally enough for four riders for a year. Although it might be easier and more convenient to just buy a smaller, pure maltodextrin product packaged for endurance athletes like Carbo Gain.
Maltodextrin is relatively tasteless; it has minimal sweetness.
Your own maltodextrin solution taste better because you control the taste.
Generally, something with a little citric acid or tartness works best.
You can add a little lemonade, fruit juice, Kool-Aid, soda, to your own made-up solution for your personal favorite taste.
Maltodextrin solutions that contain more than 100 calories per standard 16-ounce waterbottle sometimes result in a filmy back-of-the-throat aftertaste. If this is unpleasant for you, reduce the concentration.
Pure maltodextrin powder pours well. It pours easily into a waterbottle. This is valuable when filling a bottle of water from a feeder on the fly at an aid station or while racing.
The powder does not cake; the solution does not sludge. It dissolves quickly and completely.
This maltodextrin can dissolve 3 cups (24 fluid ounces) of powder into 2 cups (16 ounces) of fluid—not that I use that amount. This works out to about 1,000 calories per bottle.
If I am planning on taking in only one 16-ounce waterbottle per hour, and no snacks, I mix one cup of maltodextrin in a 16-ounce bottle. This yields about 300 calories. I do not do this often.
If I plan to eat snacks, I usually reduce the amount of maltodextrin to about half this amount. I do this commonly.
If it is hot, I will drink two or more waterbottles per hour. Again, I will mix one-half a cup of maltodextrin, or less, in a 16-ounce bottle. This works out perfectly—as it is hot I will tolerate a lower concentration than when it is cooler—but I will still be able to average 300 calories of carbohydrate per hour because I will be drinking more.