FATS, CARBOHYDRATES, AND GELS (and Powders)

Every weekend morning throughout the year, thousands of runners hit the roads and trails for long runs that are the cornerstone of training for distance races. Long runs are important for several reasons, but one purpose that many runners overlook is the “fat-for-fuel” learning process.

SOURCES OF FUEL

When you run, your body’s two primary sources of fuel are fat and carbohydrates. Carbohydrates are stored in the muscles and liver as glycogen, and in the blood as glucose.

At very low intensity, like walking or very slow running, your body uses these two fuels at rates something like this:

At moderate intensity, like long runs, it is more like this:

At high intensity (racing), it looks like this:

Why is this important?

Fat is an abundant source of energy, but is not as efficient, nor as “preferred” by your muscles, as glycogen and glucose. Unfortunately, even the most highly fit athletes can store only 1,500 to 2,000 calories of glycogen/glucose at any given time.

When you run a marathon and hit mile 20, you’ve burned 1,800 to 2,800 or more calories depending on body size, and about 65% of that is from carbohydrates, i.e., glycogen/glucose. If you’ve only got 1,500-2,000 calories of glycogen/glucose stored in your body before the race, you will burn through all those calories by mile 20, if not earlier. If you have not (1) taught your body to be efficient at using fat for fuel and (2) replenished your glycogen supplies during the race, you will “hit the wall,” or “bonk.”

The logical conclusion is that, for long-distance races, you want your body to do several things at once:

- burn fat for fuel, because there’s plenty of it in the body

- conserve glycogen

The time to teach your body to do this is during the base period of training and into the “building” period. Primarily you will do this on your long runs.

CARBOHYDRATE GELS

Carbohydrate gels come in various flavors, some with caffeine, protein, and/or electrolytes. A typical packet contains 100 calories, with 25 grams of carbohydrates. Carbs, proteins, and fats have 4, 4, and 9 calories, respectively, per gram. Thus, 25 grams of carbohydrates equals 100 calories.

In other words, a typical gel packet is 100% carbohydrates. Check the label and you will see that the primary ingredient is often “maltodextrin,” which is made of cornstarch, and which has the same glycemic index as dextrose - 100. That is extremely high on the glycemic index. We’ll come back to the glycemic index later.

All the common carbohydrate gels – Gu, Honey Stingers, Maurten, HammerGel, PowerGel, e-Gel, ClifShots, and so on - are essentially the same. The key differences are taste, consistency, inclusion of other ingredients like electrolytes or caffeine, and caloric levels.

OTHER SOURCES OF CARBOHYDRATES

Gels are not the only source of carbohydrates for endurance athletes. Chews, bars, sports drinks, and powders (mixed with water) are alternate sources of fuel. Drinking carbohydrate powders, like Maurten, Tailwind, Roctane, and others, serves two purposes: it provides carbohydrates and rehydrates simultaneously.

The drawback to using powder mixes during races is the need to replenish the fuel, as well as the requirement to carry a bottle during the race. Elite athletes are provided with water tables to stage their own bottles during many races, but the vast majority of runners are not afforded that opportunity in races: we have to carry our own bottles or gels.

Other than arranging for friends or family to meet you on the course at designated intervals to provide you with replacement bottles, the best solution is to carry the powder packets during the race (much like you would carry gels), and then refill your water bottle at the race aid stations. That does require some time to stop, fill the bottle, mix the powder into the water, and continue.

WHEN TO USE CARBOHYDRATE GELS (and other sources)

Remember that you want to train your body to do two important things:

- burn fat for fuel, because there’s plenty of it in the body

- conserve glycogen and glucose

When you consume carbohydrate gels, chews, or drinks, your blood sugar level rises. In turn, your pancreas release insulin to regulate blood sugar. Insulin stays in the blood for up to two hours, and hinders the body’s ability to use stored fats.

Consuming the carbs causes a spike in blood sugar, which releases insulin, which stops your body from doing what you are trying to “teach it” to do: burn fat for fuel.

This is not an indictment against the use of carbohydrate sources. Indeed, you need them in your marathon as a quick and efficient source of fuel. But you don’t want to rely heavily on them in your “base” and “building” periods of training. Instead, when you feel as if you are dragging your body over the last miles in the first few weekend long runs, that is because your gas tank is empty – your glycogen/glucose stores are depleted. However, your body is learning to use fat for fuel. Furthermore, the more you slow down, the more your body turns to fat as a source of fuel.

The bottom line is that long, slow runs, without using gels or other fuels, are critical to your training.

PEAKING, RACING AND GELS

By the time you hit your peak and race periods of training, you want to have already “taught” your body to use fat for fuel, and to conserve glycogen. During your pre-race taper, your body starts socking away glycogen in the muscles. By the time you hit the start line, your body is trained to use both fat and carbohydrates and incredibly efficient rates. At regular intervals in the race (every 30-45 minutes), you want to consume carbohydrates to keep the engine pumping.

THE GLYCEMIC INDEX

Ever wonder why some endurance athletes burn thousands of calories but never lose weight? Gigantic intakes of carbohydrates have something to do with it, especially when the athlete is consuming carbohydrates that are high on the glycemic index. Why? Remember that consumption of high glycemic foods causes the body to release insulin into the blood. Not only does insulin hinder the body’s ability to use stored fat for fuel, but it also converts carbohydrates into body fat, and moves fat into the blood to storage sites within the body. Thus, during your training, you definitely need carbohydrates, but you want to increase your intake of carbohydrates that are considered “moderate” and “low” on the glycemic index. For more information on this subject, consult the website at www.glycemicindex.com.