Food As Energy: Its Role In Human Performance

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For Oldman who seems to like my posts about nutrition, here is another long but interesting read (at least, I hope you will find it interesting ...)#%&


Food as Energy: Its Role in Human Performance

Food functions to provide the body with sufficient energy for its optimal performance of various operations. As food is metabolized, energy in the form of heat is released. This energy is measured in the form of kilocalories (kcal). One kilocalorie is the amount of heat necessary to raise the temperature of one liter of water 1 degree Celsius from 14.5 to 15.5 degrees Celsius.

Food contains macronutrients in the form of Carbohydrates, Protein and Fats. Macronutrients are chemical elements that are needed in large amounts for proper body function. It is important to understand the role Carbohydrates, Protein and Fats play in enhancing human performance. The subsections listed below will help provide a greater understanding of each macronutrient and its roll in improving your performance.


Carbohydrates
Protein
Fats
Conclusions


Carbohydrates

Carbohydrates perform a variety of functions. Primarily they are used as the preferred fuel source for the body. Other functions include protein sparing and fat metabolism priming. Carbohydrates are obtained from plants (grains, vegetables and fruits) and are the staple of most diets in this country and others because of their availability and low-cost.

Carbohydrates as Energy

Carbohydrates are the primary energy source for bodily function and maintenance. For that reason, most nutritionists recommend a diet that is composed of 50-60% carbohydrate. Carbohydrates provide 4 kcal/g. That is, every gram of carbohydrates yields 4 calories of energy.

Protein Sparing

Carbohydrate also functions to spare protein as an energy source. That is, adequate stores of glucose allow the body to fuel its cells even hours after a meal. However if those stores are not available (because of fasting, inadequate amounts of carbohydrate intake or excessive energy expenditure during training) protein is used as an energy source. As we will see in later sections, protein is neither a preferred or efficient energy source.

Carbohydrate as a Primer for Fat Metabolism

Carbohydrate must be present if fat is to be burned for energy. Carbohydrate supplies the body with an acid that is created as carbohydrate is metabolized. This acid is required for fatty acids to be utilized by a working muscle. Periods of prolonged exercise or carbohydrate restriction in the diet that create depleted glycogen stores therefore inhibit the use of fat as energy.

The Old System: "Simple" and "Complex" Carbohydrates

Carbohydrates have been traditionally classified by their chemical structure. Monosaccharides are single sugars that include glucose, fructose and galactose. Dissacharides are two linked sugars that include sucrose and lactose. These simple carbohydrates have traditionally included fruits, honey, candies or other sugary foods such as ice cream. It was believed that these foods entered the bloodstream rather quickly, causing a short term energy supply and were not a good source of fuel for activity.

Oligosaccharides are more than two sugars linked together. Maltose is an oligosaccharide found in malted beer and malted snacks. Polysaccharides are complex starch compounds, also considered to be complex carbohydrates. Foods that fall into this category traditionally included potatoes, other vegetables, rice, cereals and pasta.

However, recent research has revealed differences in physiological responses to simple and complex carbohydrates. These classifications may no longer properly describe the characteristics and uses of carbohydrates. This subject will be addressed in a later section.

Fiber

Fiber is a polysaccharide carbohydrate that is basically undigested by the time it reaches the large intestine. Humans do not possess the enzyme for fiber breakdown and therefore it has no caloric contribution.

Fiber functions to facilitate efficient elimination, which helps reduce the risk of hemorrhoids, hernia, diverticulitis, appendicitis and certain cancers. One gram of fiber is able to bind with up to 15 g of water, making passing of wastes, carcinogens and other substances faster and easier. As we will see later, fiber has other benefits related to blood glucose levels.

Good fiber sources include:


Grains Vegetables Fruit
bran and oat cereals beans, peas, lentils apples, prunes, bananas
rye and wheat bread peanuts, sunflower seeds pears, figs
sweet corn, popcorn soybeans, cabbage, beets strawberries, citrus

Fiber recommendations include eating 40-60 grams of fiber from varieties of grains, fruits and vegetables, with sufficient amounts of water. Individuals with health problems including heart disease, diabetes and obesity are often advised to increase the amount of fiber in their diet. However, nutritionists have argued that fiber's waste-eliminating features may prevent the absorption of important nutrients. Therefore a multi-vitamin supplement is advised with large intake amounts of fiber.

Carbohydrate Metabolism

Carbohydrate is initially broken down in the mouth by chewing. As digestion continues in the stomach and small intestine, carbohydrate is further broken down to glucose or fructose, the most simple sugar form. Glucose is delivered quickly to the blood stream, where fructose is absorbed at a slower rate. These sugars are used to constantly supply energy to the brain and central nervous system. The brain uses over 400 calories of glucose per day, supplied steadily, for proper function. The brain draws most of it's fuel from liver stores, which is the preferred home of fructose.

Remaining glucose is converted to glycogen and stored with water and potassium in the liver and muscle for later use. These stores are tapped when energy demands exceed what is currently available in the blood during activity, exercise or after periods without eating. If consumption of carbohydrate exceeds what is required in the blood, liver, and muscle, the excess glycogen is stored as fat. Twenty five percent of carbohydrate calories are used in this storage process, making fat conversion a metabolically expensive process - a benefit to those trying to stay lean.

Glucose is made available to cells through the release of insulin. Insulin is a hormone that is secreted by the pancreas when high glucose levels are detected in blood. As the regulator of glucose metabolism, it allows cells to take up the access glucose and store it as glycogen. Increased levels of glucose in the blood lead to increased insulin secretion and the transport of glucose into cells.

A New Look at Carbohydrates

Research in the area of physiologic responses to food have all but proven the archaic and ineffectiveness of "simple" and "complex" classifications of carbohydrates. Diabetic research leaders first made the Glycemic Index notable. Doctors and researchers began studying the physiologic response of foods in order to help control insulin levels in diabetics. What they found was contradictory in some cases to what the simple and complex model was asserting.

Glycemic Index

The Glycemic Index is a ranking of foods according to the effect they have on blood glucose levels. A fairly new and unexposed system in the United States, the Glycemic Index (GI) was developed by Dr. David Jenkins in Toronto, Canada. It is used by dietitians in the UK, Canada and Australia with great success. Its supporters believe that manipulation of the GI can allow for improvements in diabetes control, weight loss, sport performance and overall human performance in relation to the diet.

Determining Food GI

To determine the effect that a food has on blood glucose levels, it is compared to a reference food of pure glucose. (White bread is used in some cases). The GI of glucose is set at 100 because its effects are the most dramatic known on blood glucose. (Remember that glucose is taken up by the blood very rapidly and causes a rapid and sharp rise in the release of insulin). All other foods are compared to glucose and ranked on a scale from 0 to100, depending on their effect on blood glucose levels.

The rate of digestion is the key in determining effects on blood glucose. Foods and meals that are digested at a rapid rate have a higher GI. Blood sugar raises sharply as great amount of insulin is released in response to the foods sugar amount. Slower digested foods and meals most often contain more fiber, more fat and even more protein than foods digested quickly.

What is a High GI?

GI's of 70 or higher are considered 'high'. These foods are digested rapidly, and result in a very rapid and very high blood sugar response due to a surge in insulin secretion. High levels of insulin cause feelings of fatigue and hunger, results in fewer calories burned at rest and during activity, along with a greater storage of carbohydrate as fat. Studies have shown that high insulin surges cause people to eat 60-70% more calories at a given meal and approximately 200 more calories in the subsequent meal.

What is Low GI?

Foods that elicit a prolonged and low insulin response allow for sustained energy levels, feelings of satiety and fullness. As a result, fewer calories are consumed and carbohydrates and fats are easily used as energy sources and for a longer period of time.

Benefits of High and Low GI

High GI foods are a good source of carbohydrate replenishment. After activity when glycogen stores are depleted, high GI foods quickly fill the cells need for fuel.

Prior to activity low GI foods provide the body with energy for longer periods of time. Most often these foods put less stress on the gastrointestinal system because meals can be consumed hours before activity and still provide energy. These foods are most often higher in fiber and lower in sugar and calories than other foods and therefore contribute fewer calories in an overall diet. Furthermore, because they promote feelings of fullness and provide energy for longer periods of time, hunger is delayed allowing less total calories to be consumed.

Low GI foods combined with High GI foods dilute the High GI effect on blood glucose, hunger and energy levels.

High GI Foods (70+) Moderate GI Foods (55-70) Low GI Foods (-55)
Sugars: Sugars: Sugars:
Glucose Sucrose Fructose
Honey Lactose
Maltose

Breads
White(or any made with white flour) 100% Whole grains Pumpernickel
English Muffins 100% Whole stoneground Rye
Muffins Whole Wheat
Most Bagels (the above breads made with white flour are not low GI)

Cereals
Flaked Grape Nuts All Bran
Puffed Raisin Brans Fiber One
Sugared Oatmeal (slow cooked)
Instant

Starchy Vegetables
Baked Potato, Instant Rice Boiled potato All beans, Legumes, Pasta
Winter Squash Corn Sweet potato, yams
Macaroni and cheese Pastas Long grain, brown rice
Milk Products Milk Products
Fat-free or low-fat frozen yogurt All milks (skim-whole)
Sweetened yogurt Ice Cream
Tofu sweetened desserts All cottage cheese, yogurt
Vegetables Vegetables
Carrots, Winter Squash, Pumpkin Nearly All - except root veg's
Fruit Fruit Fruit
Sweetened juices Banana, Raisins, Rockmelon Most natural juices
Watermelon Kiwi, Mango, Grapes Cantaloupe, Apple
Pineapple Cherries,Orange, Pear,
Grapefruit, Apricot
Snacks Snacks Snacks
Rice cakes, Corn Chips Popcorn Peanuts
Jelly beans Chocolate
Pretzels Angel food cake
Doughnut
*This list examines the physiologic properties of food as they relate to blood glucose levels only. Responses are general and may be specific to individuals and food combinations. This list is not exhaustive. Fat, cholesterol, protein and carbohydrate along with micronutrient considerations must be included when making food choices.



Carbohydrate Requirements for Athletes and Active People

While carbohydrates are the primary source of fuel for activities of the human body, other macro-nutrients, as we will see in later sections, are essential for proper functioning as well. It's true that a physically active individual, such as an athlete or fitness enthusiast, will use more carbohydrate than a sedentary individual. However, other nutrients will be used to a greater extent as well, and keeping carbohydrate intake at 50-60% of caloric intake will be sufficient if total caloric intake is increased as needed. This ensures appropriate intake amounts and ratios of other nutrients. Furthermore, it has been suggested that the United States has a great portion of its population that is overweight. Participation in sports, recreational and fitness activities are a method of potential weight loss only if caloric expenditure is not increased and compensated for. Many people use the induction into a fitness program as a reason to increase caloric intake even if they are already over weight! Therefore, it is important to find an optimal carbohydrate balance for each individual to ensure sufficient amounts of carbohydrate for activity without large increases in carbohydrate storage.

Protein

Every cell in the body contains protein, and it is the second most abundant substance in the body behind water. Protein is a compound made up of anywhere from 10 to 100 amino acids. Amino acids are often referred to as the "building blocks of protein," and about 22 of them are considered important. Occurring in various shapes and sizes, protein has many different roles, depending on how the amino acids area arranged.

Most commonly known for it's tissue structure and maintenance function, protein is a necessary element for much more.

Proteins other functions include:
Muscle contraction and water retention
Providing protective coating for hair, skin and nails
Contraction and relaxation of vessels for blood pressure control
Nutrient construction for clotting
Helping maintain rigidity of bones and teeth
Aiding in formation of antibodies and scar tissue
Precursor for vitamin function, hormone, DNA and enzyme formation



Protein is used as a significant energy source only when the fuel available from carbohydrate and fats is insufficient to meet the body's energy requirements. Protein yields 4 kcals/g. Only about 58% of dietary protein can be used as a source of energy. Fasting or very prolonged periods of exercise are two examples of conditions that would require the use of protein as a significant source of energy.

The tissue building and other responsibilities of protein are made possible by nitrogen and amino acids. Amino acids and nitrogen are released at digestion. Nine of these amino acids are not made by the body and therefore must be consumed in the foods we eat. They are called "essential" and include valine, leucine, isoleucine, phenylalanine, metheonine, tryptophan, histadine.

Metabolism

The mouth does not contain an enzyme that allows protein to be initially broken down there. It arrives in the stomach intact, where pepsin begins the process of digestion. The protein is then absorbed into the blood stream as amino acids and taken to the liver for more processing. In the liver, protein is excreted, used as an energy source, converted to other amino acids and proteins or put back into circulation.

It is the particular combination of amino acids strung together that determine the properties and functions of any given protein. Protein emptying from the stomach takes 2-3 hours, depending on the amount of fat present.

Animal Protein

Animal products (eggs, meat, dairy, fish) contain all of the essential amino acids in the proper ratio and quantity to meet the needs of the body. They are referred to as "complete" proteins. The chicken egg has often been referred to as the "perfect protein" because it has the highest biological value (nitrogen used vs. nitrogen excreted) and is used as comparison criterion when evaluating all other sources of protein.

It is important to note, however, that many animal sources of protein also contain high amounts of fat and cholesterol. This has great implications for those individuals that are trying to achieve a desired body weight or body composition.

Vegetable Protein

All vegetables contain at least small amounts of protein. Plants are often referred to as "incomplete" proteins because they are deficient in one or more amino acid. Eaten alone, only portions of the protein can be utilized by the body. Vegetarians then, seem to be at a disadvantage in obtaining the necessary amino acids for proper body function. However, by combining vegetable protein sources it is possible to obtain complete protein and with less fat and carbohydrate than animal sources.

Requirements

It has been reported that Americans consume twice as much protein as needed. Two ounces of meat supplies one-third of a days protein requirement for a 150lb body, and yet most people consume more than 5 ounces at a time.

Protein can not be stored for later use in the body. Nitrogen is the critical component of protein structure and the difference between the amount consumed and the amount excreted determines growth, maintenance or degradation. Excess consumption of protein beyond the immediate needs of the body is excreted or stored as fat.

Recommendations for protein consumption average 30% of caloric intake or .8 g/kg body weight for an adult. Recommendations of up to 1.2 g/kg body weight have been made for children and athletes. It is important however, to consider recommendations with discretion. A man that is 37% body fat who consumes .8g of protein for his 156 kg body will be supplying protein for inactive and non-functioning parts of his body. Such a recommendation surely will provide more weight or fat gain than a recommendation of feeding only fat-free mass.

Athletes and Fitness Enthusiasts

There is disagreement among coaches, nutritionists and athletes as to the optimal protein recommendation for athletic populations. Many nutritionists believe that because protein is not, and should not be, used as a source of energy for active individuals, there is no need for large amounts of protein that extend beyond the average recommendation. However, building and repairing muscle tissue requires protein and is a process that for athletes may require higher than average amounts. Recommendations of up to 1.2 grams of protein per pound of fat-free body mass have been made for active fitness enthusiasts and athletes. It is important to find the optimal recommendation for each individual however, based on health status, lifestyle and human performance goals.

It makes sense that if an active individual is expending a great amount of energy for physical activity his or her total caloric intake will increase. When following the 30% recommendation, protein intake will increase automatically. Even when following the .8 g/kg bodyweight recommendation, protein intake will increase if fat-free mass increases.

Regardless of how protein amounts are determined, it should be consumed often and in small amounts to ensure it is used efficiently, not stored or excreted. Furthermore, protein choices must be chosen carefully to avoid over ingestion of calories, fat and cholesterol.

Fats

Fat is an essential nutrient. However, it's excess has brought attention to it's detrimental effects on human performance and health. The actual daily requirement for fat is about a teaspoon. Most Americans consume 6 to 8 times this required amount!

Functions

Fats provide the body with fuel for proper body function. During rest, about 80 to 90% of the body's energy requirement is met by fat metabolism. As an energy source, fats yield 9 kcal/g. This is much greater than carbohydrates or proteins and is the reason that fatty foods are so high in calories.

Other functions of fat include:
insulation against extreme heat and cold
facilitation of digestion and assimilation of nutrients
nerve impulse transmission
organ protection
cell metabolism
essential precursor to substances such as vitamins and hormones
maintenance of menstruation cycle
satiety (feeling of fullness)



Metabolism

Fats, or lipids, take the longest of the macro-nutrients to be digested. Their insolubility in water and complex structure are the reasons why. In the intestines, fatty acids are separated and coated with protein. Most is sent to the lymph system and the remaining is sent to the blood stream and then liver. Whatever is not needed for energy and other immediate functions is sent to storage.

Triglycerides and Fatty Acids

Fats or lipids are divided into two groups; triglycerides and fatty acids.

Triglycerides

Mostly dietary fat and the form of stored fat, triglycerides are made up of fatty acids and other substances.

Fatty Acids

Popular author and Nutritionist Jane Brody suggests thinking of fatty acids as a baseball diamond. The more full the bases, the more saturated the fat.

Saturated: The bases are full! Saturated fat has no more room for hydrogen atoms. It is hard at room temperature and includes mostly animal fats: Butter, cheese, chocolate, egg yolk, lard, meat, milk, poultry, palm oil, coconut and coconut oil, vegetable shortening are examples of foods high in saturated fat. This type of fat increases the amount of cholesterol in your blood.

Unsaturated: Mostly vegetable fats, unsaturated fats leave room for some hydrogen atoms. This type of fat decreases the amount of cholesterol in your blood.

monounsaturated fats - can accept two more hydrogen atoms. Avocado, cashews, olives, olive oil, peanuts, peanut butter contain monounsaturated fat.

polyunsaturated fats - can accept four or more hydrogen atoms. Almonds, corn oil, cottonseed oil, fish, margarine, mayonnaise, pecans, safflower oil, salad dressing, soybean oil, walnuts, sunflower oil contain polyunsaturated fat. Omega-3 fatty acid found fish is known for its cholesterol and triglyceride lowering and artery clogging prevention properties. It is most often found in salmon, cod, trout, and sardines.

Recommendations

Nutritionists recommend that 20 to 30% of the diet or less is composed of dietary fat. Choices should include more unsaturated fat than saturated to avoid increases in cholesterol.

Cholesterol

Cholesterol is found in all cell membranes. Much like the reputation of dietary fat, despite its necessity, cholesterol has a bad reputation. Cholesterol functions to regulate the fluidity of membranes, helps make certain hormones and contributes to the production of bile acids for digestion. Cholesterol is independent from fat and is not used as an energy source. It is a fatty substance, however. It is not soluble in water and it can not travel through the body independently.

Lipoprotein, found in the liver, surrounds the cholesterol and carries it. There are basically two types of lipoproteins. Low Density Lipoproteins (LDL's) are often referred to as "bad cholesterol" while High Density Lipoproteins (HDL's) are referred to as "good cholesterol."

LDL's

These lipoproteins keep cholesterol in circulation by supplying the cells with the necessary amounts of cholesterol. They make up about 70% of the body's total cholesterol and are produced when large amounts of saturated fats are consumed. Cholesterol is deposited onto LDL receptors for deposit into cells. LDL's deliver cholesterol to cells for the production of sex hormones and cell membranes. When the receptors are full and no more cholesterol is needed, the production of receptor cells stops, and so does the body's production of cholesterol. Excess is taken up by scavenger cells in the lining of arteries. It is believed that build up in artery walls is a result of the scavenger cells. High amounts of LDL in the blood have been correlated with high risk of atheriosclerosis.

HDL's

Made mostly of protein, HDL's take cholesterol from the walls of arteries to the liver for secretion. Excess cholesterol then is excreted as bile through the intestinal tract. This actually protects against arteriosclerosis and justifies the "good cholesterol" classification. Polyunsaturated fats prefer transport by HDL's and help decrease the proportion carried by LDL's. Strenuous exercise and moderate alcohol consumption are believed to increase the production of HDLs, and high HDL levels are believed to help protect against heart disease.

The American Heart Association has created the following guideline limits for determining blood cholesterol levels:
High: 250mg/100ml
Border: 200-249mg/100ml
Desirable: less than 200mg/100ml





Heath professionals realize that total cholesterol reveals only part of the blood cholesterol picture. The ratio of HDL to LDL levels may help to provide much more information. For example, athletes often have high total blood cholesterol, but the HDL levels are much greater than the LDL levels.

Keeping Cholesterol Levels in Check

Some experts believe that blood cholesterol levels are influenced greatly by genetics. However, this does not make blood cholesterol levels unmanageable. Besides drugs that lower cholesterol levels, foods high in fiber and low in saturated fat along with exercise help keep blood cholesterol within healthy levels.

Conclusions

As previously mentioned, 80 to 90% of the body's energy requirement at rest is met by the use of fat as an energy source. The rate at which fat and glycogen are utilized as an energy source increases with activity intensity and duration. As the intensity of activity increases, glucose and stored glycogen becomes the preferred energy source and at increasing amounts. Depleted glycogen stores (as a result of long duration and intense activity or insufficient glucose ingestion) cause the initiation of protein into the energy system and result in feelings of fatigue and weakness.