Fuel Sources 101

Nutrition is the most commonly overlooked component in an athlete’s training schedule. Most athletes only concern themselves with nutrition a week or even a few days prior to an important event, but that will not allow them to achieve peak performance. Proper nutrition throughout the year will not make an athlete stronger or faster by itself, but it will support optimum health, support training, prevent illnesses, change body composition and weight and improve performance. It is critical to preventing an overtraining syndrome.

Second only to adequate hydration is the importance of achieving fuel intake appropriate to the needs of the particular athlete for any specific sport. Fuel equates to energy, measured in kilocalories. Energy is provided to the body as the macronutrients – carbohydrate, fat and protein. We will examine the roles and requirements for each macronutrient, at first separately, and then outline food plans for pre-race, race day and recovery.

Carbohydrate: The Fuel of Choice for Endurance Athletes

For endurance exercise, carbohydrate should supply more than half of an athlete’s energy requirements, as it is the most efficient form of fuel. This means that less energy and time is spent actually digesting or processing it. Fat should supply most of the remainder, so that protein can be “spared” for its primary need, which is to build and repair muscle tissue.

Carbohydrate Stores

Carbohydrate is stored in the body in the forms of muscle glycogen (300 – 400 grams), followed by liver glycogen (75-100 grams) and lastly, blood glucose (25 grams). These amounts vary widely among individuals, depending on their dietary intake and state of training. A trained athlete may have stores that are over 60% higher than someone who is not trained. He can further increase carbohydrate stores another 50% by carbohydrate loading before an event.

In total a normal person stores between 700-900 calories as carbohydrate and an athlete about 2,000. While this may sound like a lot, in reality, it isn’t. The brain and central nervous system require up to 80% of normal stores of carbohydrate.

Glucose, carried in the bloodstream, is the only fuel the brain and vital organs can use! If glucose is insufficient, a person is unable to think rationally, and may lose consciouness, or even die.

Because glucose is so critical to life, the body has three mechanisms to obtain it. The first is via the gut, through the digestion of carbohydrate foods. When the gut is empty, the body will first tap into the liver store, reserving muscle stores for energy the muscles need right away. When the small liver reserve of 300-400 kcal is used, the body must find another source. The final source is protein, either from food or from the muscle tissue itself. Essentially, the body will ultimately begin to cannibalize your muscles if there is inadequate carbohydrate available to “spare” muscle mass. If someone were to try to fix this by taking much more protein in the diet, it doesn’t work well for endurance athletes, because the process of conversion from protein to glucose takes far too long.

The Importance of Avoiding Hypoglycemia During Endurance Exercise

The liver acts as a regulator controlling glucose output, aiming to match the increased glucose uptake, so that blood glucose levels remain relatively stable. Even the very well- stocked liver in a trained athlete consuming a high carb diet will only be able to supply adequate glucose for 170 minutes without additional supplementation with glucose. Blood glucose becomes an increasingly important source, causing the blood sugar to fall, a condition known as hypoglycemia. Symptoms of hypoglycemia or low blood glucose include fatique, hunger, blurred vision, shakiness, slurred speech, confusion, irritability and loss of consciousness.

Prolonged hypoglycemia and neurochemical changes in the brain lead to central nervous system fatigue – the progressive shutdown of the part of the brain that drives the muscles. Recent research has revealed that the most common reason that runners stop running is central fatigue. During prolonged exercise, the brain’s production of the neurotransmitter, serotonin increases steadily. Elevated levels of serotonin bring feelings of tiredness, sleepiness and lethargy. At the same time another neurotranmitter, dopamine, responsible for feelings of excitement, reward, motivation and pleasure, falls. Caffeine has been shown to prevent dopamine levels from dropping.

Daily Carbohydrate Recommendations

It is well known that the lowest total carbohydrate intake necessary for fueling the brain is 130 grams per day. This would not be adequate to fuel any athlete or even anyone hoping to perform any physical activity without tiring. A guide for carbohydrate requirements for anyone is based on body weight in grams per kilogram per day. This is then modified according to type, duration and intensity of activity, as well as whether or not the person wishes to either gain or lose weight. In order to perform any activity, a 100 kg person will require twice the amount of carbohydrate per kilogram as compared to a 50 kg person. The amount of carbohydrate needed is matched with the level of activity and the stage of preparation toward an event.

Carbohydrate Requirements for Normal Activity and Training

Activity Level	Carbohydrate Requirement Grams/kg/24 hours
Sedentary	3-4
Average person	4-5
Athlete exercising average 60 min/day	5-6	General training needs
Athlete exercising average 2 hrs/day	6-7
Endurance athletes	7-10
Athlete training 4-6 hrs/day	10-12
Ultraendurance athletes	11-15

When beginning training for a marathon, a runner who weighs 65 kg requires approximately 325 grams of carbohydrate each day. This works out to 1300 kcal. With protein (1.2-1.8 g/kg) and fat (0.8-1.0 g/kg) included, total energy requirement would be approximately 2800 kcal per day. If the athlete wished to lose weight, energy would be reduced from 200-500 kcal per day only during early training stages. Weight loss close to any endurance event must be avoided.

Quality of food is very important, so achieving recommended intakes of all food groups according to Canada’s Food Guide is encouraged. While at rest, low Glycemic Index foods should make up the majority of carbohydrate in the diet. During activity and to achieve higher total energy requirements during training, proportionally more high Glycemic Index foods need to be consumed as well. Without some more concentrated sweets, it is virtually impossible to eat enough carbohydrate. There is a place for sugar in the diet, especially for ultra-endurance athletes!

As training intensifies, carbohydrate need would double to 650 grams – or even triple for multi-day endurance events, so energy from carbohydrate would exceed 2600 kcal from carbohydrate alone, with total energy intake reaching 4200 kcal per day or higher for a female! Talk about a fuel-burning machine! If the athlete is awake-she’s eating almost non-stop!

Carbohydrates Everywhere, but which ones do I choose?

Good question! The short answer is “It all depends on you”- your needs, your sport, the period of your training, your tolerance to different carbs, and what you like!

Carbohydrates can be classified by the type (eg: simple versus complex), by the form (liquid versus solid) or by the Glycemic Index (low, moderate, high.) The first two do not indicate the effect that carbohydrate rich foods have on blood glucose levels, either directly or indirectly via the impact that various carbohydrates can have on blood insulin levels. Only by studying about Glycemic index, would this really make sense. Check out http://www.GlycemicIndex.com to learn about GI from the actual research team.

The complexity of the differences is beyond the scope of this article, but here are a few tips that might help you choose your exercise carbs wisely.

Not all sugars are “fast” and not all starches are”slow”. It is better to think about the impact of specific foods and learn to take them at appropriate times. Sugar is not evil in an appropriate amount for your needs at a given time, even for someone who has diabetes!

Low GI foods tend to empty from the gut slowly, and bring a feeling of satiety or “fullness” after a meal. These tend to be carbohydrates close to their natural form and are loaded with vitamins, minerals, phytonutrients (chemical compounds that occur naturally in certain plant foods that can prevent a variety of diseases). The gut must do a lot of processing to make them available for energy, and so, these are excellent choices for most people, most of the time. Choosing whole grains, lots of fresh and raw fruits and vegetables, starchy beans, peas and lentil can help people maintain a healthy body weight, keep blood pressure and blood fats in the normal range, and avoid the development of type 2 diabetes.

Certain low GI foods that contain a gel-forming or “soluble” type of dietary fibre, like oatmeal, pasta, and fruits containing natural pectin eaten prior to endurance events can give good “staying power” at the initial part of an endurance event.

The body tends to slow down digestion when someone is active, preferring to allow more blood flow to moving limbs, diverting it from the gut. Some low GI carbohydrate foods may contain more indigestible or “insoluble” fibre, like bran, strings, skins, and seeds. These need a lot of gut processing. Taking too much before or during an endurance event can lead to gas, cramping and diarrhea. Race day is not a time to eat lentils and beans! You will be more comfortable if you avoid them that day, and your fellow runners will thank you!

High GI foods are important to actually cause a quick rise in the blood glucose when it might fall too low. Knowing this, it makes sense that sports drinks and high GI complex carbohydrates are meant to be taken when someone is doing the sport. They are generally not good choices for sipping on a non- working day. They are meant as re-hydration solutions, and give very limited nutrition. Similarly, a diet that is predominantly made up of lots of high GI carbs, tends to be unhealthy and may predispose someone to obesity. High GI foods include glucose, dextrose, baked goods made from refined white flour and sugar, white potatoes and most cold breakfast cereals. These are great during and immediately after a workout, but need to be moderately consumed when sedentary, or prior to a workout.

Taking too much high GI foods prior to a workout can cause the body to release too much insulin before the event. Since insulin’s job is to allow glucose to enter cells, taking too much can cause the body to draw too much glucose out of the blood stream right away – leaving you drained even before the event starts!

However, during an event, this insulin reaction is blunted, and your body uses the high GI carbs for quick energy production, sending the sugars into your working muscles. More energy to the muscles equates to more sustained ATP production to drive the muscles. Less potential for a bonk!

Osmolality is a measure of the total number of particles in a solution. Our bodies try to maintain our body fluid osmolality at a constant level. If we drink solutions that are too concentrated, or take too much food that contain either monosaccharides (glucose, sucrose, dextrose) or disaccharides (maltose, fructose, lactose) along with sports drinks, the body will draw fluid from other areas and tissues that may need that fluid eg: to digest those concentrated sugars. This can lead to disturbances in fluid balance and impacts emptying of the stomach when you are active. Your gut tends to shut down a little, allowing most of your body’s energy to be diverted to your moving limbs. Have you ever experienced a “sloshing” sensation if you take full-strength fruit juice during a run? You may experience gas, cramping, dehydration and even diarrhea. Not pleasant!

Sports drinks are usually needed at about the one-hour point of starting an aerobic workout, if the athlete has prepared well prior to the start. Someone who has type 1 diabetes may need the sports drink sooner.

At the beginning of a run, sports drinks may or may not be well tolerated at full strength. This may be caused by “starting jitters” – the body mobilizes hormones that cause the body to release sugar from stores. Additional sugar in a drink may make you queasy. If that is the case- plan to transition from water or very dilute sports drink to full- strength at about 1 hour.

Sports drinks are formulated to provide appropriate osmolility of 6-8%. For most sports, this is adequate, but during endurance aerobic activities, this concentration will only provide 100 kcal per hour. Ultra-distance runners like Theresa needs 200-250 kcal per hour to maintain energy production. Q: Should she increase the concentration? A: Absolutely NOT.

How can she make up the difference? The answer is to use some products that contain maltodextrin, which is a type of high GI glucose polymer or chain, a form of complex carbohydrate or polysaccharide. These can be easily absorbed from the intestine in a more concentrated 15-20% solution. These provide up to three times the energy while clearing from the gut at the same rate as normal body fluids. Using some energy gels and other products that contain maltodextrins will reduce odds of a DNF (did not finish)!

Are there any other carbohydrates that should be avoided? A: Yes!. Steer clear of foods that contain sugar alcohols. These are a form of carbohydrate, usually used to sweeten some, but not all “No Sugar Added” products. These taste great, but are well known to cause gas, bloating and explosive diarrhea. Look for them under the Total Carbohydrate main heading on labels. They often end in –ol, for example: maltitol or sorbitol.

Research has proven that athletes should consume a variety of carbohydrate supplements and that complex carbohydrates are the fuel of choice for ultra endurance athletes. Theresa will be eating nutritious, balanced meals, as she always has – just more of the good stuff along with some special high GI products that she will be testing out prior to race day! Very special things for special circumstances – for a very special lady!

Stay turned for more to come about protein, fat and alcohol and post-workout supplements.

Expect more about race day preparation closer to June 25!

References:
Coleman, Ellen J. Carbohydrate and exercise. Sports Nutrition: A Practice Manual for Professionals, 4th edition. Am Diet Assoc 2006

Blende, S. How much sugar can we stomach? Online at http://www.ultrarunning.com

Campbell, C , Prince, D, Braun, M et al. Carbohydrate-supplement form and exercise performance. Int J Sport Nutr Exerc Metab. 2008:18:179-190