Nutrition with Donna Marlor
Smart eating beats fatigue Endurance athletes are by nature high-energy people. Logging miles before most people have turned on the coffeepot, their weekends are spent doing sports, not watching them.
Despite an innate love of being active, the obligations of everyday living can leave even the most motivated athlete feeling overwhelmed and fatigued. Diet can make a difference.
As a sport nutritionist, I often get questions about diet
and fatigue. Typically I need to clarify what kind of fatigue is the problem and then try to match dietary interventions to resolve the situation.
Usually complaints of fatigue fall into three general categories: 1) overall low energy or motivation to do daily tasks or train; 2) inability to put in 100 percent efforts during interval training or racing; and 3) early muscular fatigue and poor recovery. Sometimes an athlete will be experiencing all three types of fatigue.
As
important as diet is to performance, underlying health problems are always a possibility. When fatigue is prolonged and severe, it is important to be evaluated by a physician familiar with endurance training.
For many athletes, nutrition is a common topic of conversation. But somehow that conversation never is translated into actual food choices. Deadlines at work, kids soccer games and running errands push food purchasing and preparation to the low end of the priority list.
Unfortunately, when hunger pangs strike – as they do every day – a quick pickup meal may be the result. Is fast food such a bad thing? Or what about the meal that is missed completely?
Random meals can result in a low-energy level for two reasons. First, missed meals lead to eating a calorie and fat "load" later in the day. Second, restaurant food tends to be high in fat.
Researchers at the University of Maryland Department of Medicine have shown that a single high-fat meal (50
g fat, 55 g carb, 30 g protein) delivers a double whammy when it comes to health. First, a "fat load" stimulates a vasoconstrictive response, reducing blood flow through an artery by as much as 10 percent for three to four hours after eating. That means less oxygen will be available to working muscles. Second, the three to four hours following a high-fat meal increases markers of oxidative damage to occur indicating damage to arteries is taking place – not a good thing for athletes who rely
on their heart and vascular system to perform maximally.
What does a 50 g fat meal look like on the table? Here are just a few artery damaging examples.
• Taco Bell Nacho Mucho Grande: 1,320 calories and 82 g fat.
• Subway Meatball sub with cheese, a bag of chips and two M&M cookies: 1,109 calories and 56 g fat.
• Home-cooked meals can be just as bad if missed meals lead to gorging. A heaping plate of spaghetti and meatballs, with garlic bread, salad and
Italian dressing can hit 1,000 calories and 50 g of fat very easily.
What is a good strategy for improving overall energy? Here are some suggestions:
• Have a plan for the day's meals.
• Have a back-up plan.
• Learn which foods from restaurants are lowest in fat, and keep fat intake per meal below 40 grams.
• Go no longer than five hours between meals.
• Select at least one-half of your carbohydrate choices from whole grains, which have a lower
glycemic index than processed grains.
Central fatigue
During exercise, central nervous system fatigue, or central fatigue, develops in the brain because of changes in the level of certain neurotransmitters. These neurotransmitters, which act as chemical messengers, control the initiation of voluntary muscle movement, muscular coordination, motivation, concentration, problem solving ability, perception of effort and level of alertness. Since the brain is the central switchboard for
all thoughts, it also controls the initiation of voluntary movement in muscle. Once central fatigue develops, every task takes more effort to initiate and physical movement is less coordinated.
In an event lasting over three hours, central fatigue can lead to errors in judgment, clumsy transitions and a decrease in mental toughness. Exactly what triggers the neurochemical changes that causes central fatigue is still a matter of debate. However, research done by the U.S. Army has
demonstrated that carbohydrate plus caffeine improves thinking ability and endurance performance. How much carbohydrate and how often to take it depends on the duration and intensity of exercise.
What is a good strategy for minimizing central fatigue during a long event? Plan on 30 to 60 grams of a high glycemic index carbohydrate (sport gel or block) every 60 minutes, taken with water. Use a sport hydration drink that includes a mixture of carbohydrate sources (maltodextrin, brown
rice syrup, glycose polymers, fructose) for maximum delivery of oxidizable energy. Caffeine at low doses (100 mg) will decrease the perception of fatigue and improve concentration and coordination. Because of a wide variance in toleration to caffeine, athletes should experiment with its use in nonrace situations.
Peripheral muscular fatigue
An important muscle that often gets overlooked is the one in your head. Many people do not realize that one of the biggest users of glucose (or
sugar) in the body is the brain. On the average, the brain burns up about 150 g of glucose per day. That's equivalent to 900 calories.
Fortunately, the brain is able to use alternative fuel sources such as the breakdown of protein and ketones. It runs most efficiently on glucose obtained from carbohydrates. Although the brain isn't doing any actual physical work during exercise, it does call the shots when it comes to initiating voluntary movement in peripheral muscles.
Peripheral fatigue is the fatigue that occurs due to metabolic changes within the muscles that are powering physical activity. When your legs, arms and back are depleted of nutrients and fuel, they can no longer function even if you have the desire. There is absolutely nothing left. You can't go on.
The fuel, or energy to draw upon for muscular work during intense exercise like running, is primarily glycogen, which is the storage form of carbohydrate within the muscles and liver. In
humans, glycogen storage is limited to about 1,500 calories – enough to power about two hours of hard exercise. Fat stores, on the other hand, are much higher. Even in lean individuals, fat can supply about 30,000 calories of fuel.
Exercises performed at low intensity – balancing on a sled or easy pedaling – do not use up glycogen stores as rapidly as during running because the body is able to burn fat as well as carbohydrate when heart rate is lower. However, even at low intensity,
after more than three hours of continuous activity, muscle glycogen stores become greatly reduced and the liver begins to break down its stores of glycogen in an effort to maintain blood glucose. Eventually liver glycogen becomes depleted also and blood sugar drops. At this point, an athlete will feel exhausted and cease exercising unless additional carbohydrate is eaten.
Consuming a diet that has 50 percent to 70 percent carbohydrate is the best way to maintain glycogen stores when
training on back-to-back days.
What foods are the best sources of carbohydrate for beating fatigue? Look for foods that provide these characteristics:
• Low glycemic load: These carbohydrates provide sustained energy. The glycemic load (GL) is a ranking system for carbohydrate content in food portions based on their glycemic index (GI) and the portion size. Example: a 100 g portion of watermelon (GI 72) has a carb content of 5 g. The GL is calculated as 5 x .72 = 3.6, which is
low. For a complete table of GL, go to www.ajcn.org/cgi/content.
• High in antioxidants: Protects the vascular system in the brain and provide carbohydrate for energy.
• Low-saturated and trans-fat-free carbo snacks. Many carbohydrates are "packaged" with unhealthy fat. Use snack foods and baked goods that are made with flaxseed oil, olive oil or polyunsaturated vegetable oils.
For every endurance athlete, maintaining energy
for physical and mental work should be a part of an overall training program. Taking the time to plan out menus, shopping lists and learning food preparation techniques can make the difference when it comes to achieving performance goals.
Donna Marlor, MA, BSN, RD, has a bachelor's of science degree in nutrition and nursing from Northern Michigan University and a master's degree in educational psychology from the University of Minnesota-Duluth. She is a former NMU cross-country ski
team member and still enjoys competing in skiing and running at the master's level. Marlor resides in Marquette, Michigan, with her husband and chocolate Lab. She can be reached via www.DonnaMarlor.com. |
