 Maridav/iStock/Thinkstock Show Ask an endurance athlete what is the most important food to eat before a race and they will likely respond, "Carbs!" Carbohydrates are the primary fuel source burned for energy during physical activity, and our bodies are able to store some of the carbohydrates we eat in our liver and muscles as glycogen. It makes sense that eating carbohydrate-rich foods to maximize our glycogen stores — a strategy known as carbohydrate loading — provides athletes with the energy necessary to sustain an increased level of physical activity for a longer duration. For example, an athlete can store 1,800 to 2,000 calories of fuel as glycogen in the muscles and liver. This energy can fuel about 90 to 120 minutes of vigorous activity. More recent evidence suggests that in events lasting longer than 90 minutes, maximized glycogen stores may improve a runner's finish time by 2 - 3%This could translate to a 5- to 7-minute improvement for a 4-hour marathoner. The concept of carbohydrate loading has been studied for decades. But, how did this theory hold up in the real world? One of the first recorded instances of a professional athlete using carbohydrate loading in competition was during the marathon event of the 1969 European Athletics Championships. British runner Ron Hill, trailing the leader for most of the race, was able to win the gold medal with a strong finish in the final six miles, the point at which many runners experience the phenomenon known as "hitting the wall" — the feeling you get when your glycogen stores are depleted and your physical performance nosedives. Word of Hill's diet spread and athletes have been attending pasta dinners the night before an event ever since — although, true carbohydrate loading is more involved. Hill followed a classic carbohydrate-loading regimen consisting of a glycogen-depleting phase — three days of intense exercise coupled with very-low carbohydrate consumption — followed by three days of tapered physical activity with high-carbohydrate intake. This strategy, however, may not be optimal for all athletes and unnecessarily increases the risk of injury while training in a depleted state. Some studies even show that trained athletes may achieve maximized glycogen stores without the need for a depletion phase in as little as 24 hours. Eating a high-carbohydrate diet may help athletes perform at their best. The amount of carbohydrates that athletes should consume daily will depend on their unique needs, the athletic event and training regimen. Eating an unusually high amount of carbohydrates before an event could actually backfire and hinder athletic performance by causing gastrointestinal distress. The foods eaten immediately prior to an event should be the same foods eaten during training. The golden rule of sports nutrition — nothing new on race day — also applies to carbohydrate loading. Athletes should consider consulting a registered dietitian nutritionist for personalized nutrition guidance.
Many physiological and nutritional demands occur within the body during exercise. As muscles contract, the demand for oxygen, hydrogen and other key nutrients increases. The human body requires a continuous supply of energy to perform its many functions. As energy demands increase with exercise, additional energy must be supplied or the exercise will end. Factors of performance Whether a recreational athlete or an elite athlete, many factors influence performance including, but not limited to, diet, hydration, fitness level, intensity and duration. There are many factors that predict what source of fuel will be used. Proteins, fats and carbohydrates are all possible sources of fuel for exercise and muscle contraction. During moderate-intensity exercise, roughly half of the energy is derived from glycogen, while the other half comes from glucose in the blood and fatty acids. Carbohydrates (glucose/glycogen) serve as the primary source of fuel as duration and intensity increase. If exercise continues for a significant period of time, fatty acids will serve as the fuel source when glycogen stores are nearly depleted. It must be noted that fat metabolism cannot occur without the presence of glucose, and thus muscle glycogen and blood glucose are the limiting factors in performance. Protein or, more specifically, amino acids, will only be used as an energy source if other calories are insufficient. Food choices A person’s diet will influence which source of fuel is used and therefore, performance level. If a person consumes a high-carbohydrate diet, more glycogen will be used for fuel. If the diet is high in fat, fat will be used as the fuel source. A high-fat diet is not recommended as even the leanest person has plenty of stored fat for long endurance exercise. A high-fat, low-carbohydrate diet can lead to poor performance due to low glycogen stores. As a guideline for endurance athletes, roughly 60–70 percent of calories should come from carbohydrates, 10–15 percent protein and 20–30 percent from fat. You should consume a well-balanced diet containing carbohydrates, protein and fat during training periods. Carbohydrate intake before, during and after exercise is crucial. A high-carbohydrate pre-exercise meal not only prevents hunger pangs during exercise, it also provides optimal blood glucose levels for endurance exercising and increases glycogen stores. Avoid high-fat foods in a pre-exercise meal as it delays stomach emptying and takes longer to digest. This meal should be three to four hours before an event. Marathon runners talk about “hitting a brick wall.” This refers to the time when fuel sources have been drained and not replaced. When glycogen and blood glucose levels are low, the body is out of fuel and cannot keep going no matter how fast an athlete wants to go. For exercise lasting longer than an hour, you should ingest carbohydrates to fuel the brain and muscles. You can maintain a sufficient supply of energy by consuming 26–30 grams of carbohydrates every 30 minutes during exercise. Most sports drinks provide 15–20 grams of carbohydrate, so consuming 8–12 ounces every 15–30 minutes is recommended. As for protein, only a few amino acids can actually be used directly as energy. Thus, protein consumption during exercise is not advantageous. Fluid intake Muscle glycogen stores must be replaced after endurance exercise. Resynthesis of muscle glycogen is promoted when carbohydrates are consumed immediately after exercise. Unfortunately, due to an elevated body temperature, appetite is usually depressed and many athletes have difficulty consuming foods immediately after exercise. Drinking carbohydrates via a sports drink or shake provides carbohydrates and promotes rehydration. Adequate fluid intake is also crucial for any athlete. You should weigh yourself before and after an endurance event, especially during hot weather. For each pound lost during exercise, drink three cups of fluid. Fluids should not be restricted before, during or after an event. Athletes should not rely on thirst as a sign of fluid loss. Consume roughly 14–22 ounces of fluid before an event, 6–12 ounces every 15–30 minutes during an event, and after the event, 16–24 ounces for every pound of body weight lost. Anne Harguth is a registered dietitian with Mayo Clinic Health System in Waseca.
How much you need to eat or drink during exercise depends on many factors including the intensity and duration of the training session or event, goals of the session and body composition objectives. In general you won’t need extra fuel (carbohydrate) during exercise sessions lasting less than ~60 minutes (and possibly up to 90 minutes if the intensity of the session is low). However, if your training session or event is longer than 60-90 minutes topping up with extra carbohydrate during the training session can help to:
Fluid needs during exercise are highly individualised and will depend on your unique sweat rate which is determined by genetics, body size, fitness levels, intensity and duration of the training session and of course the temperature and humidity that you’re exercising in. For short, low intensity exercise sessions in cool weather you may only need a small amount of fluid, if any, during the session. For longer and more intense sessions or events, particularly if it is hot and humid you may need to be more proactive with your fluid intake to avoid becoming dehydrated. An Accredited Sports Dietitian can help you determine your individual sweat rate. What can happen if I get my nutrition plan wrong during exercise?Getting your nutrition plans wrong during training or an event usually means that you don’t optimise your potential during the session. Failing to fuel or hydrate correctly during exercise can result in:
How often should I eat or drink during exercise?There’s no one size fits all plan for eating and drinking during exercise but as a general guide:
What should I eat during exercise?Everyone is different in what they like to eat (and what sits comfortably in their stomach) during exercise but in general foods should be:
There’s no one “best” option for what to eat during exercise and it will depend on what your individual preferences and requirements are but here’s a few ideas to get you started.
What is the best fluid to drink during exercise?The ideal fluid during exercise depends on your goals. If you are using fluid mainly to hydrate for the session than water or electrolyte drinks are a good option. If you also need a source of fuel then sports drinks can be helpful as they contain both carbohydrates and fluid to help hydrate and fuel your body at the same time. For more information on this or other sports nutrition topics, subscribe to our newsletter or book to see an Accredited Sports Dietitian. |
Why is it important to consume sources of carbohydrate during activities lasting more than one hour?
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