Two Important Fueling Strategies for Endurance Athletes: Breakfast and Snacks

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By: Christopher D. Jensen, PhD, MPH, RD
Nutrition & Epidemiology Researcher


As an endurance athlete, you’ve set your sights on the goal of completing a formidable endurance event — a marathon or half marathon, a triathlon, a century ride, or something equally as challenging. Your preparation for endurance events like these can be improved by having a working understanding of what your muscles use as fuel when you train and how you can best provide for those fuel needs. Eating breakfast regularly and consuming smaller meals more frequently are two important fueling strategies.

Muscle Fuel 101
Whether you’re pounding the pavement, pedaling a bike, or churning through water, your muscles are relying on a mixture of fat and carbohydrates for fuel. The slower and less intense your training pace, the more your muscles rely on fat. But as you pick up the pace or intensity of your endurance training, you rely increasingly on your reserves of carbohydrate fuel.

No one worries about fat reserves, because you basically can’t run out. Most of us have anywhere between 80,000 and 120,000 calories worth of the blubbery stuff held in reserve at any given time. Contrast that with your carbohydrate fuel reserves. Those reserves exist in the forms of glucose, circulating in the bloodstream, and bundles of glucose packaged together, called glycogen, that are stored in your liver and muscles. You have a paltry 20 to 100 calories worth of blood glucose coursing through your veins, while the liver has 300 to 400 calories of glycogen stored away; your muscles pack about another 1,200 to 1,600 calories of glycogen. Do the math — all told, we’re talking about only roughly 2,000 calories worth of carbohydrate fuel in your entire body.

Carbohydrate fuel is precious, and this fact is important to remember because intense training for sustained periods drains your limited carbohydrate stores. In fact, a single long training run, ride, or swim of 1–2 hours can put a serious dent in your glycogen reserves, and back-to-back workouts can literally leave you running, or walking, on empty.

But with an almost unlimited supply of fat stores as a backup, why be concerned?

For two reasons: First, fat can’t be metabolically processed fast enough to keep up with muscle fuel demands when you’re exercising at an intense pace. So if you run out of carb fuel reserves, you are forced to slow down or even stop altogether. Runners call this “hitting the wall,” and cyclists call it “bonking.” It occurs because you’ve run out of the fuel that allows you to perform at your fastest, so you have no choice but to drastically slow your pace. In fact, you need to slow to an intensity level where fat can be relied upon as a fuel source.

The second reason for concern about running low on carbohydrate stores is that the brain strongly prefers glucose as its fuel. This is important because your brain is the control center that enables your body to function and you to train. But if its supply of blood glucose starts to fall, it quickly picks up on the problem and sends out powerful signals for you to shut down in order to preserve your dwindling glucose supply.

With both your brain and your muscles relying on glucose during intense endurance exercise, this is how it plays out metabolically: Exercising muscles tap into their own glycogen stores, while your brain is fed from the glucose circulating in the bloodstream. But as your training reaches the 60–90-minute mark, depending on your intensity, your muscle glycogen stores can become seriously depleted. When this occurs, glucose in the bloodstream is tapped to fuel both your brain and muscles, and your liver glycogen stores are broken down into glucose in order to maintain glucose levels in the bloodstream. But once liver glycogen stores are used up, your blood glucose level starts to decline, you “hit the wall,” and that spells the end of exercise for you.

This scenario has played out countless times for endurance athletes. There are a number of strategies that athletes use to maintain and extend their precious carbohydrate fuel stores for as long as possible. Two important strategies are eating breakfast and consuming smaller, more frequent meals.

Benefits of breakfast
Understanding the interplay between blood glucose and the glycogen you have stored in your liver and muscles helps you appreciate why eating — especially breakfast — is so important and how it helps with the carbohydrate fuel pipeline. While you’re fast asleep at night, your liver glycogen stores are steadily being drained in order to maintain a normal glucose level in your bloodstream. By the time you wake up in the morning, your liver glycogen stores are running low. If you skip breakfast and head out for an intense endurance workout, you’re likely to run into trouble, and that trouble will be an earlier-than-expected onset of fatigue. The reason is that once you deplete your muscle glycogen stores, you won’t have much glycogen left in the liver with which to resupply glucose for the bloodstream. That few calories’ worth of circulating blood glucose won’t last long — as a result, that extended training session you had planned will have to be shelved.

In the final analysis, a breakfast containing carbs does three important things: It helps replenish glycogen stores that have been depleted from the liver overnight; it tops off glycogen stores in your muscles; and it physically occupies your stomach and fends off feelings of hunger that can also undermine your focus and ability to train.

Doing breakfast right
You need a breakfast strategy for both late- and early-morning workouts. If you have time, the ideal pre-training meal is 2–4 hours before you start exercise. The goal is to start your workout fully fueled, but also feeling comfortable. Choose familiar high-carbohydrate foods and beverages, and avoid slow-to-digest fatty and high-fiber foods. Typical carbohydrate-rich breakfast foods include bread, cereal, fruit, and dairy products such as flavored yogurts and milks. Experiment during training to find the right foods, amounts, and timing of intake that work best for you.

If you have an early-morning workout, a full breakfast just isn’t realistic. But that doesn’t mean you skip carbs entirely. Instead, eat a high-carb snack such as a piece of fruit, a fruit smoothie, a meal replacement drink, a PowerBar® Performance Energy bar, a PowerBar® Performance Energy Mini bar, a PowerBar® Gel, or PowerBar® Gel Blasts™ energy chews combined with water. Generally a high-carb snack 30–60 minutes before exercise is suggested, but here again, experiment to find the right snack foods and timing that work best for you.

Graze rather than gorge
As your training progresses and your workouts become longer, tougher, and maybe even more frequent, it will be critical to take in enough carbohydrates throughout the day in order to keep your glycogen stores replenished. Ironman triathletes are a useful case study. These athletes have to train for three events — swimming, biking, and running — and they will often do long and intense workouts twice a day. Consequently, they have an ongoing need for lots of carbs, yet their training is frequently interfering with meals.

What to do
The best triathletes solve the problem by grazing rather than gorging. Instead of the standard and inflexible three-meal-a-day routine, these athletes consume smaller, high-carbohydrate meals more frequently. This approach to eating has multiple benefits for endurance athletes: First, they avoid skipping meals and therefore can get the nutrients, calories, and fuel they need in order to continue to train hard. Conversely, they tend to avoid overeating, because they don’t go for long periods without eating. And finally, they’re able to train more comfortably because they aren’t carrying around large amounts of food in the digestive tract at any time.

You can apply the grazing strategy to your training as well. Get into the habit of eating smaller amounts, but more frequently. Make and pack small sandwiches to eat in transit or between workouts. Be prepared by having energy bars or energy chews in your workout bag or ice chest, and don’t forget to snack during breaks in your training or between twice-a-day workouts if you do them. With this approach to eating, you’ll likely find that your overall energy level remains higher, you’re more focused and motivated, you’re more comfortable during training, and you have better endurance during workouts. Examples of small, carbohydrate-rich meals and snacks you can eat frequently are listed as follows:

References:
1. Schoonen JC, Holbrook L. Physiology of Anaerobic and Aerobic Exercise. In: Sports Nutrition: A Practice Manual for Professionals. 4th ed. Sports, Cardiovascular, and Wellness Nutritionists Dietetic Practice Group. Dunford M, ed. American Dietetic Association. 2006: 3–13.

2. Coleman EJ. Carbohydrate and Exercise. In: Sports Nutrition: A Practice Manual for Professionals. 4th ed. Sports, Cardiovascular, and Wellness Nutritionists Dietetic Practice Group. Dunford M, ed. American Dietetic Association. 2006: 14–32.
 
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