As you discovered in the physiology section, the source of energy for running is breakdown of the food you eat. Proper intake of food or good nutrition is important for you to gain the benefits of training. A look at general nutrition for the athlete will follow along with some specifics on the relationships of the nutrients to athletic performance.
Human nutrition is thought to require six general classes of nutrients. These are carbohydrates, fats, protein, vitamins, minerals and water. These nutrients are essential for human life and inadequate intake may result in disturbed body metabolism, disease or death. Not all necessary nutrients are contained in any one food and an intake of what is called "a balanced diet", is necessary to achieve adequate nutrition.
Food has three major functions. The first is to provide energy for human metabolism. Carbohydrates and fats are the prime sources of energy. Protein can also provide energy, but that is not its major function. Second, food is used to build and repair body tissues. Protein is the major building material for muscles and other soft tissues while minerals such as calcium and phosphorus are used to build and repair bony tissue. Regulation of body processes is the third use of food. Vitamins, minerals and proteins work together to perform this function. These three functions become increasingly more important to the physically active person. Metabolic activities may increase by tenfold for periods of an hour or longer. Physical performance may be hampered seriously by inadequate nutrition. However, studies on supplemental feeding beyond adequate intake have not revealed an increased capacity for physical performance. The key is to be certain that you are receiving optimal amounts of each specific nutrient recommended by current knowledge of the requirements. Proper nutrition is necessary to optimize energy sources, build and repair tissues, and regulate body processes especially during and following exercise periods.
The four food groups can be a useful guide in taking in the key nutrients. Foods are grouped by similar nutrient values into the Meat Group, the Milk group, the Bread-Cereal Group or the Fruit-Vegetable Group. Eating a wide variety of foods throughout the four food groups helps you to receive an adequate supply of nutrients through a balanced diet. The table below shows the food groups and the recommended minimum servings for adults.
|Meat Group||Milk Group||Fruit-Vegetable||Bread-Cereal|
This approach may have some problems and not be the total solution to a balanced diet. The trend of the American public towards consumption of fats, simple sugars and alcohol led to a Subcommittee of the US Senate to recommend dietary goals for the American public. They are shown on the table below.
|Goals||Typical U.S. Diet||Proposed Diet|
|Cholesterol||500-1000 mg||300 mg|
|Salt||6-18 g||3 g|
The Human Nutrition Center of the USDA makes the following simple recommendations to help you meet the dietary goals.
A good diet is not something you go on, it is simply he way you always eat. The athlete engaged in heavy training should not attempt a weight reduction diet, but may need to change dietary habits to healthy ones. For a more complete treatment at general nutrition, we recommend Jane Brody's Nutrition Book. If you are more interested in applications of nutrition to exercise and performance, choose Williams' Nutrition for Fitness and Sport or Coleman's Eating For Endurance.
Carbohydrates (CHO's) are formed when the energy of the sun is harnessed in plants. Simple CHO's are sugars while complex CHO's are many sugars bonded together, known as starches. These are mainly found in plants as is cellulose, a fiber which does not break down in the presence of human digestive enzymes. Cellulose or fiber adds bulk to the diet to prevent constipation and to prevent other problems of the large intestine.
Complex carbohydrates are found mainly in the bread-cereal group and the fruit-vegetable group. Foods such as dry beans, dry peas, milk and ice cream also contain CHO's. Complex rather then simple carbohydrates should be stressed. The US dietary goal is 55-60% for of the total intake be CHO's with simple sugars limited to 15%. The actively training runner may want to have CHO's compose from 55 to 70% of the diet. A study from the E. B. Smith Performance Lab at Texas A&M University showed that of runners who were consuming 25, 50 or 70% carbohydrate diets, only the 70% diet could bring their muscle glycogen back to their pre-exercise level. Other exercise physiologists agree that the high consumption of complex carbohydrates is important for the endurance athlete, but disagree on the exact levels. Coleman in Eating For Endurance recommends a 55% level, stating that a higher per cent carbohydrate may influence the body to learn to burn glycogen instead of the desired fat.
Complex CHO's are broken down into simple sugars (glucose and fructose) and absorbed into the blood. Glucose is blood sugar. It may be converted either to liver or muscle glycogen. Liver glycogen can later be converted to blood glucose. The greatest amount of CHO is stored in the body as muscle glycogen. Excess blood glucose may be stored as fat or may be excreted. It is possible for the body to make blood glucose by liver action from protein and fat, but this metabolism is inefficient and potentially dangerous.
Glucose is the major supplier of energy for the body especially for the brain and muscles. Muscle glycogen in the active muscles is the primary CHO source for energy. As the muscle glycogen is used, blood glucose enters the muscles to maintain muscle glycogen stores and the liver releases some of its glucose to maintain blood sugar levels.
A review of studies on CHO ingestion before and during exercise has led Williams in Nutrition for Fitness and Sport to make the following recommendations.
The most important concern is always fluid replacement. Too concentrated a solution of glucose may be detrimental because too much sugar in the stomach delays passage of water into the blood stream. Sugar taken shortly before an event may cause overreaction by the pancreas actually leading to a lowering of blood sugar called hypoglycemia. Hypoglycemia can give symptoms of weakness, anxiety and trembling and can contribute to fatigue. Williams offers the following suggestions for glucose solutions taken during exercise.
Muscle glycogen stores can be increased by the technique of carbohydrate loading. This is useful for the marathon and requires a switch from a normal balanced diet to one very high in carbohydrate content. Carbohydrate loading is covered under Race Preparation. There you will learn the best method for loading at that time. The training period however is a good time to experiment with your body's response to different carbohydrates eaten in the daily diet and before long runs.
Fats or lipids is the general term for a number of different compounds found in the body in the form of solid fat or liquid oil. Triglycerides are the primary form in which fats are eaten and stored in the human body. They are composed of fatty acids (FA) attached to a glycerol molecule. The difference between saturated and unsaturated fatty acids concerns the chemical degree of hydrogen saturation of the chemical chain of carbon and hydrogen. Practically speaking, saturated fats are usually solid and are derived from animals, while unsaturated fats are liquid and are derived from vegetables. Fat content in foods can vary from 100% in cooking oils to less than 1% in vegetables. While there is no specific requirement for fat in the diet, there is a need for certain essential FA's that are components of fat. Most are synthesized by the body, but some must be supplied by the diet from polyunsaturated vegetable oils. Sufficient amounts of fat are found in the average diet, in fact, the problem is usually to refrain from ingesting excessive amounts of fat.
Fats are needed to transport certain fat soluble vitamins into the body. Fats are a concentrated energy supply for the body providing 9 calories for every gram making them an easy way to add excess calories to the diet. Fats are used in the diet to make foods taste better by providing flavor, aroma and texture. They satisfy the appetite and delay the return of hunger because they take longer to leave the stomach and be digested. They also dilute the nutrient value of foods by increasing calories without increasing nutrients.
Cholesterol is a fat-like pearly substance called a sterol which is found in animal products. In the human body, cholesterol is manufactured from FA's and the breakdown of CHO and protein. Cholesterol is used in the formation of several hormones and is a component of several tissues. It is vital to human physiology, but since it is manufactured in the body, there is little apparent need to obtain it through food. A relationship has been found between high blood cholesterol levels and coronary heart disease (CHD). The reduction of dietary cholesterol has been advocated by a number of health related organizations for that reason.
Fats are digested mainly in the small intestine recombining into fat droplets in the bloodstream. If you are well fed, the majority of the fat is deposited in the adipose or fat tissue of the body and converted back into triglyceride. The adipose tissue is the body's major energy storage depot and acts as an insulator and shock absorber for various organs. If you are in a fasting state, fat enters the muscle cells where it is either used immediately or stored for future energy use. Your energy balance determines whether fat stores increase or decrease. Excess carbohydrates and proteins are converted by the body to fat and stored in the adipose tissue when food intake is greater than energy output.
The liver regulates the blood lipid level. The lipids in the blood do not circulate as free compounds, but are bound to a protein complex and are known as lipoproteins. These lipoproteins can be grouped into three classes:
Coronary heart disease is atherosclerosis or plaque formation in the coronary blood vessels which narrows them and reduces blood flow to the heart. A number of risk factors have been found for heart disease. These include improper diet, high serum lipids, high serum cholesterol, physical inactivity, obesity, high blood pressure, smoking, age, heredity, and sex (being male). Dietary modifications have been shown to lower serum cholesterol and triglycerides. These modifications include adjusting caloric intake to maintain ideal body weight, reducing simple sugars and alcohol in the diet and increasing complex CHO's, decreasing dietary cholesterol, and reducing the total amounts of fat in the diet especially animal fats. Diets rich in saturated fat tend to raise serum cholesterol while polyunsaturated fats tend to lower it. Exercise has been shown to increase HDL which may contribute to protection against coronary heart disease. High fat diets have also been implicated in increased risk of breast and colon cancers.
At rest about 60% of the body's energy supply is from fat. Fat is an important source of energy during mild to moderate exercise. The muscles have the oxygen needed to convert energy from the free fatty acids (FFA's) into a form that can be used by the muscles. Fatty acids for energy production can come from the blood stream or from local stores within the muscle. In prolonged mild to moderate exercise, the fat energy stores come mainly from the muscles and from the blood free fatty acids. The adipose tissue keeps supplying FFA's to the bloodstream as it is needed. Fat can supply the majority of energy as long as the exercise remains mild to moderate. As you run faster, the FFA release from adipose tissue slows and the muscle cell begins to rely more and more on CHO as the major energy source. Specific endurance training helps you to become a fat burner at faster paces which helps to spare muscle glycogen.
A physically active person does not need to increase fat intake. Even the leanest runners have adequate fat stores to use as energy and the body can also manufacture fat from carbohydrate and protein. According to the dietary goals, fats should be limited to less than 30% of your diet with saturated fats not more than 10%. Optimally for runners training heavily, fats should comprise less than 20% of the diet to allow consumption of adequate carbohydrates.
Carbon, hydrogen, oxygen and nitrogen combine to form structures called amino acids. These amino acids are then combined to form the proteins necessary for the structure and functions of the body. The body can form some of the amino acids which are termed nonessential. Those that it cannot are called essential amino acids and must be obtained from the foods in your diet.
The protein found in animal products contains all of the essential amino acids and is called therefore complete protein. These amino acids are also contained in the proper proportions necessary for synthesizing proteins within the body. Protein is found in lesser amounts in plant materials but may be lower in three essential amino acids. Vegetables can be combined to create a complete supply of essential amino acids. Legumes, such as dried beans and peas, provide almost as complete a source of protein as animal foods.
Protein is found in every cell in the body. It has many functions such as the formation of new tissues and the replacement of worn out ones. It also regulates the balance of water, the balance of acids and bases and transports nutrients in and out of cells. Protein forms antibodies, hormones and enzymes. Protein transports nutrients and oxygen in the blood and is essential for blood clotting.
The amount of protein necessary in the diet varies with different life stages with the growth phase requiring the most. The need stabilizes in early adulthood. Throughout the life cycle the protein requirement is based on the weight of the individual. The body needs a new supply of protein every day since excess protein is stored not as amino acids but as fat. Excess intake of protein can lead to increased fat stores and can strain the kidneys in an effort to rid the body of it.
Protein is not a major energy source, but excess protein may be converted to carbohydrate or fat. During periods of starvation or semistarvation when adequate amounts of fat and CHO are not available, protein can be utilized for energy. The demand for energy in the body takes precedence over tissue building. The active individual who desires to maintain lean body mass must have adequate fat and CHO calories to spare protein to be used for its more important functions. The dietary goals of 12% allow for adequate protein intake. Many of the common sources of protein are high in fat and calories. Look for animal protein with less fat such as low fat dairy products, poultry and fish, combine small amounts of animal protein with plant sources. Protein insufficiency is one of the major nutritional problems in the world, but the average American consumes about twice as much as is needed per day.
During exercise, protein usually contributes only 1-2% of the energy. Recent research has shown that protein may contribute about 4% of energy demand during prolonged exercise with normal glycogen stores. The percentage may rise to 10% if you are depleted of glycogen, as in the last part of the marathon. CHO loading may have a protein sparing effect for distance runners. The research on whether or not there is destruction of muscular protein during exercise is inconclusive. The amino acid alanine has been found to be released by exercising muscles, but the muscles are also absorbing other amino acids from the blood. Whether there is a net loss of cellular tissue has not been determined. There is little data to support the recommendations of some individuals to increase protein intake during physical training. The overall results show that prolonged low protein intake may have adverse effects on physical performance, but intakes above what is considered normal have not been shown to improve performance.
Vitamins are extremely complex organic compounds found in small amounts in food. They are essential to the optimal functioning of the physiological processes of the human body. Since these processes increase greatly during exercise, an adequate supply of vitamins must be available. Vitamins are essential in human nutrition because of their role in the formation of body enzymes. These enzymes deteriorate over time necessitating a constant fresh supply of vitamins.
Vitamins are not a source of energy and do not have caloric value. They do not contribute to body structure. They are, however, indispensable for regulating body function and for maintenance of optimal health.
Vitamins are divided into 2 classes, fat soluble and water soluble. Fat soluble vitamins include Vitamins A, D, E and K. Some essential water soluble vitamins are Vitamins B1, B2, Niacin, B6, Pantothenic Acid, Folacin, B12, Biotin, Choline, Inositol, and C. Fat soluble vitamins are stored in the body to a greater degree than water soluble vitamins. Most vitamins must be obtained from food, a few are formed within the body.
The only difference between natural and synthetic vitamins is the way they are made. Usually it is better to get vitamins from food because they are in combination with minerals and other nutrients needed by the body. Synthetic vitamins may be indicated when deficiencies are noted. Most nutritionists feel that there is no evidence that the average American on a balanced diet suffers from vitamin deficiency. Little evidence exists to support the use of vitamin supplements by well nourished athletes or other highly active persons. However, Charles A. Garfield based on his research at the Performance Sciences Institute indicates that vitamin and mineral supplements can be important in the nutrition of competitors. He concludes that athletes can benefit from 2 multivitamin tablets with minerals per day. He also suggest extra amounts of Vitamin C (2,000-5,000 mg) and B Complex are advisable during strenuous training periods. His study of marathoners given the above vitamin supplements showed a drop in resting heart rates of 9 beats per minute while no significant changes were shown in a control group. Runners taking the supplements experienced 35% fewer injuries and 81% fewer infections than the control group. If you feel that you are not receiving a balanced diet for any reason, reasonable doses of vitamin supplements will not be harmful. However, excess quantities or megadoses can have undesirable side effects and are dangerous. A registered dietitian can answer more detailed questions regarding vitamin intake.
A mineral is a solid inorganic element found in nature. Twenty five of the elements are essential in humans and have a wide variety of functions. Some are used as building blocks for body tissues while others are important components of enzymes and hormones. Others regulate the physiologic processes of the body. The six major minerals are calcium, phosphorus, sodium, potassium, chloride and magnesium. The relationship of some of these major minerals to running will be discussed.
Inadequate intake of calcium by adults can result in a loss of bone density and in muscle cramps. Many experts believe that an adequate intake of calcium is between 1000 and 1500 milligrams per day. Good sources of dietary calcium are low fat dairy products, dried beans and many vegetables, especially green leafy ones. Calcium needs Vitamin D to be absorbed which should pose no problems to those who run outdoors most days.
Iron is important for the transport of oxygen. Iron deficiency is sometimes found in women of child bearing age, vegetarians and endurance athletes who ingest little animal-based protein. Better iron absorption from the dietary sources of meat, poultry and fish is obtained when these are combined with Vitamin C rich fruit or vegetables.
Sodium and chloride combine to form common table salt. Excess salt consumption has been linked to hypertension. The average American consumes about 2-4 teaspoons of salt per day. The suggested daily allotment, far in excess of actual need, is set at between 1-2 teaspoons per day. Enough sodium is naturally present in foods to meet the daily requirements of everyone with the possible exception of those who exercise strenuously in hot weather. If you are running in the heat, you should not restrict your salt intake unless advised to do so by your physician. If you lose over three quarts of sweat, (6 pounds of body weight), you should add 1/3 to 1 teaspoon of salt to the diet for every quart of sweat lost ( 2 pounds weight). Salt tablets are not recommended because they provide too concentrated a salt form which can impair athletic performance by drawing water out of the functioning muscle cells.
Water, the most important nutrient, is a compound composed of 2 parts hydrogen and one part oxygen. Water provides no food energy or calories, but is needed by every cell to carry out essential functions.
About two thirds of the body weight is water with the majority being within the cells. Water is the main transport mechanism within the body for carrying oxygen, nutrients and hormones to the cells and removing waste products. The waste products are eliminated from the body through the water in sweat, urine and feces. Water also regulates osmotic pressure controlling the proper electrolyte balance and acid/base balance. Water lubricates and cushions. It acts as the body's main cooling system.
The requirement for water depends on the weight and age of the individual, but the average adult needs about 2 quarts of water a day to maintain water balance within the body. The balance is maintained when intake of water matches output of body fluids. The main output for water is urine, however, some is lost in the feces and some through exhaled air. Insensible perspiration, which cannot be seen, is a significant source of body water loss. Sweat losses increase greatly with exercise or hot environmental conditions.
The major source of water is fluid intake. Solid foods also contribute through their water content and through metabolism of these foods for energy. Fat, CHO and protein produce water known as metabolic water when broken down for energy.
Normal levels of body water are maintained through kidney function. Loss of body water results in conservation by the kidneys while increased consumption leads to the kidneys ridding the body of excess water. Your body usually lets you know when you need water by thirst. In normal conditions, thirst is usually a good guide to body water needs and is effective in restoring body water to normal. Thirst is not a good indicator of body needs during exercise and especially when exercising in hot weather.
Run The Planet thanks Patti & Warren Finke and Team Oregon for the permission to reprint the complete online version of the first edition of the book Marathoning Start to Finish (Hypertext Version 1.02) by Patti & Warren Finke. © 1986, 1996 wY'east Consulting, All Rights reserved.