Energy Sources

Energy is a basic need that our body is dependent on for survival; a need that is increased by being physically active.  Our body is fueled by three essential nutrients: carbohydrates, fats, and proteins.

Carbohydrates act as the primary fuel source for cells in both the nervous system and red blood cells; they are also needed in muscle cells to fuel intense physical activity.    Carbohydrates yield approximately 4kcal/g, and are categorized into two groups: sugars, and complex carbohydrates.  Sugars are further classified into monosaccharides and disaccharides.  Monosaccharides are single sugars that are commonly found in fruits, syrups, and honey.  Glucose present in the blood is also an example of a monosaccharide.  Disaccharides are combinations of two monosaccharides and are found in milk (lactose) and table sugar (sucrose).  It is suggested that we get 15% of our total caloric intake from sugars.  Complex carbohydrates (polysaccharides) are long chains comprised of glucose units but are more commonly known as starches.  During digestion, the sugars from the disaccharides and starches are broken down and converted into glucose.  The glucose that is not needed for immediate energy is stored in the liver and muscle cells as glycogen (which is exhausted in about 18 hours if no carbohydrates are consumed).  Any excess glucose left over after digestion, converts into body fat.  Fiber is an indigestible polysaccharide that forms the structural part of plants.  There are two kinds of dietary fiber: soluble and insoluble.  Soluble forms of fiber bind to cholesterol passing through the digestive tract and prevent its absorption, thus reducing blood cholesterol levels.  Food sources of soluble fibers include oatmeal, legumes, and some fruits.  Food sources of insoluble fiber include whole-grain breads and bran cereals.  Ingesting an adequate amount of fiber (25 grams/day) has many benefits.  Fiber (especially insoluble) aids in normal elimination by reducing the amount of time required for wastes to move through the digestive tract, and as a result, it reduces the risk of colon cancer.

Fats perform many beneficial functions in our system.  They play a vital role in maintaining healthy skin and hair, insulating body organs against shock, maintaining body temperature, promoting healthy cell function, carry the fat-soluble vitamins A,D,E, and K, and they also provide a concentrated form of energy in the absence of sufficient amounts of carbohydrates.   Fat yields 9kcal/kg of energy and it is recommended that we receive 30% of our energy intake from fats.  If we intake too many fats in our diets, the leftover fat is converted into triglycerides, which make up for about 95% of total body fat.  The remaining 5% of body fat is composed of cholesterol which accumulates on the inner arterial walls. High Density Lipoproteins (HDL) and Low Density Lipoproteins (LDL) are the two types of cholesterol in our circulatory system.  HDL  is the “good” cholesterol because it transports circulating cholesterol to the liver for metabolism and elimination from the body.  HDL’s can be increased from regular exercise.  LDL’s are considered the “bad” cholesterol because they facilitate the transport of cholesterol in the blood to the body’s cells.  There are 3 types of fats: Unsaturated, Saturated, and Trans-fatty acids.  Unsaturated fats are fats that have room for one more hydrogen in their chemical structure; mostly derived from plants; and are liquid at room temperature.  Monounsaturated and polyunsaturated fats are two types of unsaturated fats and their name refer to the relative number of hydrogen atoms that are missing.  Polyunsaturated fats consist of omega-3 and omega-6 fatty acids and even though these fats reduce LDL levels, they also reduce HDL levels.  These fatty acids also perform important roles in the immune system function, vision and help form cell membranes.  The most common source for Omega-3 fatty acids is fish.  Monounsaturated fats lower LDL levels as well but they increase HDL levels and thus are currently preferred.  Peanuts and olive oils are high in monounsaturated fats, whereas corn, sunflower, and safflower oils are high in polyunsaturated fats. Saturated fats are fats that are unable to hold anymore hydrogen in their chemical structure; derived mostly from animal sources and are solid at room temperature.   A reduction in the sources of saturated fats, including meats, animal fat, palm oil, coconut oil, hydrogenated shortenings, whole milk, cream, butter, ice cream, and cheese would reduce LDL cholesterol.   Trans-fatty acids are produced when polyunsaturated oils are hydrogenated to make them more solid and resistant to chemical change.  Found in many cookies, crackers, dairy products, meats, and fast foods, trans fatty acids increase the risk of heart disease by boosting levels of bad cholesterol.  Because they are not essential and have no health benefit, there is no safe level of trans fatty acids in the blood.   

Proteins are the building blocks of our body.  They are needed for the growth, maintenance and repair of all body tissues; they also are needed to make enzymes, many hormones, and antibodies to help fight infection.  Protein intake should be around 15%-20% of total caloric intake.  Even through protein provides just as much energy as carbohydrates (4kcal/g) the body does not prefer them as an energy source.  Amino Acids are the basic units that make up proteins.  Most of the amino acids can be produced as needed in the body; other cannot be made up to any significant degree and therefore must be supplied in the diet.  The proteins that can be consumed in the diet are termed as “essential amino acids.” Dietary protein that supplies all of the essential amino acids is called complete “high quality” protein and are typically found in meat, poultry, cheese and soybeans.  Incomplete proteins are proteins that are lacking in one or more of the essential amino acids. a relatively easy way for the non-meat-eater to combine plant foods effectively is to add peanut butter and whole grains to their diet.    A diet containing large amounts of protein will not support growth, repair, and maintenance of tissues if the essential amino acids are not available in the proper proportions.  Many athletes consume twice the recommended amounts of protein.  There is no advantage to consuming more protein, particularly in the form of protein supplements.  If more protein is supplied than needed, the body must convert the excess to fat.  This conversion can create a situation in which excess water is removed from cells leading to dehydration and possible damage to the kidneys or liver.  Increased physical activity increases a person’s need for energy, not necessarily protein.  The increases in muscle mass that results from conditioning and training are associated with only a small increase in protein requirements, which can easily be met with the usual diet. 

Athletes are always looking to gain a competitive edge on their opponent.  Strategies such as “carb loading” before a marathon are more effective than protein dumping post exercise.  Athletes overestimate the amount of protein our body needs to help repair muscles.  Overall, the most efficient way to optimize performance from nutrition is to consistently consume the appropriate amounts of each energy source (60% carbohydrates, 30% fats, 10% proteins) on a daily basis.


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