A paper I wrote...

[bm2k]

Its very poor compared to my usual standard of work, and the information is very basic (2000 words doesn't leave a lot of scope for fully expressing what I could've said!). However, its about the effect each nutrient has on the body's metabolism and body composition, so might be worth a read. A critique would be nice too

The effect of nutrition upon body composition in athletes


Introduction

Body composition affects an athlete’s performance through its impact on strength, agility, and appearance. Metabolic processes are primarily responsible for determining an individual’s body composition, and are influenced by nutritional factors. Consequently, nutrition is especially important for an athlete. The body requires six separate types of nutrients: carbohydrates, fats, proteins, vitamins, minerals, and water. An imbalance of these nutrients may cause undesirable adaptations, such as an excessive increase of body fat. A proper balance of nutrients will help an athlete increase lean muscle mass, limit fat storage, and improve performance.

Body composition

Body composition is the term used to describe the different components that, when taken together, make up a person’s body weight. A distinction can be made between body composition and body weight – two entirely different concepts that are not interchangeable. Specifically, body composition is defined as the proportion of lean body mass to fat body mass (Gallahue & Ozmun, 2002). The human body is composed of a variety of different tissue types. ‘Lean’ tissues, such as muscle, bone, and organs are metabolically active, while adipose, or fat tissue, is not (Burgess, 1997). There are three different categories of adipose tissue; essential fat supports life and is extremely important to normal bodily function; storage fat protects internal organs and supplies some energy requirements; non-essential fat serves no real purpose and is detrimental to health. The difference in these tissues is not readily distinguishable by measuring body weight, which simply takes the sum of all components.

Nutrients: Carbohydrates, protein, fat, vitamins, minerals and water

Carbohydrates provide the body with its basic fuel. The simplest carbohydrate is glucose. Glucose flows in the bloodstream so that it is available to every cell in the body. Cells absorb glucose and convert it into energy to drive the cell. Glucose is classified as a simple carbohydrate or ‘sugar’. Other such carbohydrates include fructose, sucrose, lactose, galactose, and maltose. Simple carbohydrates digest and enter the bloodstream quickly. Additionally, there are complex carbohydrates commonly known as ‘starches’. A complex carbohydrate is made up of chains of glucose molecules. The digestive system breaks down complex carbohydrates into its component glucose molecules so that the glucose can enter the bloodstream (Kushi, 1993).

A protein is a chain of amino acids. An amino acid is a small molecule that acts as the building block of a cell. While carbohydrates provide cells with energy, amino acids provide the building material needed to grow and maintain cell structure. The human body is constructed of 20 different amino acids that account for 20% of its weight (Encyclopaedia Britannica, 2002). There are two different types of amino acids: essential and non-essential. Non-essential amino acids are ones that your body creates from other chemicals found, while essential amino acids cannot be created and must be consumed through food. Protein in our diet comes from animal and vegetable sources. Most animal sources provide ‘complete proteins’ that contain all of the essential amino acids. Conversely, vegetable sources are missing certain essential amino acids in different combinations. The digestive system breaks all proteins down into their amino acids so that they can enter the bloodstream.

There are two kinds of fats: saturated and unsaturated. Saturated fats are normally solid at room temperature, while unsaturated fats are liquid at room temperature. Animal fat in raw meat and vegetable oils are examples of saturated and unsaturated fats, respectively. Most fats contain a mixture of both saturated and unsaturated fats. Unsaturated fats are thought to be healthier than saturated fats, and can be further distinguished into polyunsaturated and monounsaturated fats, with monounsaturated being the healthiest. Fats enter the digestive system and meet with an enzyme called lipase. Lipase breaks the fat into its parts: glycerol and fatty acids. These components are reassembled into triglycerides for transport in the bloodstream. Muscle and fat cells absorb the triglycerides either for storage or fuel (Haas, 2002).

Consuming fat is important for a number of reasons. Certain vitamins are fat-soluble and only obtained when fat is part of the diet. There are essential fatty acids, much like essential amino acids, which must be obtained from food as the body has no way to produce them. Additionally, fat is a good source of energy because it contains twice the amount of calories per gram as do carbohydrates or proteins, and can be burnt as a fuel when necessary.

Vitamins and minerals cannot be manufactured by the cells of the body and, when lacking in the diet, can cause many problems. Vitamins are organic compounds needed for normal growth and repair of tissue. They act as coenzymes playing a part in a variety of energy reactions (Arthur & Bailey, 1998). Minerals are inorganic compounds required as catalysts to start many of the body’s functions (Merriam-Webster, 2002). Food provides the body with vitamins and minerals, but if they are lacking in the diet various problems can arise.

Water makes up about 60% of a person’s total body weight and is the nutrient most important to the body’s functioning. Water is the main component of blood plasma. Without it oxygen, glucose, fatty acids, and amino acids cannot be transported to muscles and waste products cannot be eliminated from the body.

Energy balance and metabolism

Metabolism is the sum of the catabolic and anabolic cellular reactions that contribute to all the energy needs of every cell of the body (Arthur & Bailey, 1998). The catabolic reaction – catabolism – releases energy to contribute to the digestion of the food we eat, the breakdown of muscle tissue during exercise, and the subsequent production of waste matter. Anabolic reactions, or anabolism, on the other hand, utilise energy to excrete waste matter, build muscle tissue, and store energy from digested food.

A calorie is a measurement of energy normally associated with food. A calorie is the amount of energy needed to raise the temperature of a gram of water by one degree Celsius (National Library of Medicine, 2002), and the typical measure of energy in food that the body burns as fuel. Additionally, calories measure the energy expenditure of activity. Fats, proteins and carbohydrates have characteristic calorie measurements. One gram of fat contains nine calories, while one gram of carbohydrates or protein contains four calories.

The balance between calories consumed and burnt is responsible for weight control. A neutral energy balance is one where caloric intake and expenditure are roughly equal. Similarly, a positive energy balance occurs when the amount of calories consumed is greater than the amount burnt, while a negative energy balance is the opposite. A positive energy balance will result in anabolism, while a negative energy balance will cause catabolism.

Applications of nutrition on the athlete’s body composition

For athletic purposes, catabolism refers to the tearing down of muscle and the release of energy during physical activity. Anabolism refers to the building of muscle tissue and the increase of energy capacity during recovery. Living with healthy habits through proper nutrition, adequate sleep, and controlling stress levels enables the metabolic balance to be in favour of anabolism. The metabolic process is compromised if energy stores are not replenished through a well balanced diet. This is important to athletes as the body responds by growing stronger and increasing its energy capacity. If the body does not fully recover from exercise due to poor nutrition, the balance is swung in favour of a catabolic state. Practically speaking, this is the absolute opposite of what an athlete is trying to achieve.

Proper nutrition can meet the energy needs of the metabolic process. Therefore, nutrition becomes even more important for an athlete in training. Nutrition can improve body composition in order to have a positive effect on performance. Increasing lean muscle mass and limiting fat storage are the critical factors.

Being the body’s primary energy source, carbohydrates play an extremely important role in determining an athlete’s body composition. In order for this nutrient to be used by the muscles, it must be broken down into glucose and stored as glycogen. Glycogen is stored in the liver and muscle fibres and is readily available for quick energy needs. Carbohydrate storage is limited to approximately a day’s supply (Arthur & Bailey, 1998). Therefore, carbohydrate intake through the food athletes consume must be replenished daily to ensure capability of maximum performance. It is important to regulate carbohydrate intake according to levels of activity. Eating too many carbohydrates when energy demands are low may disturb an athlete’s energy balance, and a certain percentage of the excess carbohydrate will be stored as fat. When attempting to lose fat, an athlete is able to reduce their carbohydrate intake to slightly below that of current energy demands. A reduced carbohydrate intake allows a higher ratio of fat to be burned.

Various carbohydrates release glucose into the bloodstream at different rates. The relative ability of individual foods to quickly raise blood glucose to a high level is known as the glycemic index (Miller, 1998). High glycemic foods give the body a quick jolt of energy, and it responds by releasing large quantities of insulin. Insulin is a hormone that quickly lowers blood glucose levels; in fact, sometimes it lowers levels so quickly and so much that energy levels dip. The body responds by creating an appetite for more carbohydrates to raise glucose levels, and the cycle continues – more carbohydrates, more blood glucose, more insulin released, more glucose stored as fat. Insulin not only converts excess glucose into fat in the body, it shuts down fat metabolism; thus, a cycle of high and low blood glucose levels leads to the storage of more and more fat. Carbohydrate foods with a high fibre and protein content digest slowly, inducing a slow increase of blood glucose, a slow and steady insulin response, and therefore less carbohydrate stored as fat. Low glycemic index foods are better suited to controlling an athlete’s body composition and energy levels.

Protein is the building material for the development of muscle tissue. It also provides the structural framework for hormones that control metabolic processes. To adapt to high loads associated with training, an athlete may have approximately double the protein requirements of a sedentary individual. Eating large, high-protein meals requires a significant amount of energy for digestion, slowing down the anabolic process. An evenly spaced protein intake with smaller, more frequent meals will help promote less competition between the energy necessary for digestion and that needed for the recovery of muscle tissue (Arthur & Bailey, 1998). A lack of protein will cause the athlete to enter a catabolic state, where muscle breakdown increases and body composition is negatively effected.

Vitamins and minerals cannot be manufactured by the cells of the body and, when lacking in the diet, can cause metabolic deficits. Many of the natural sources of vitamins and minerals from fruits and vegetables are not available in supplemental form, and thus, natural, fresh produce is especially important to aid recovery during intense training. Preventing vitamin and mineral deficiencies is of great importance to an athlete. Vitamin C is necessary for growth and maintenance of muscle, cartilage, and bone. Without it, wounds do not heal and bones do not grow. Without vitamin A the body has a higher incidence of infections in the lungs, eyes, and kidneys. Lack of vitamin E in the diet causes the cells of the body, including muscle tissue, to deteriorate. Iron is an essential mineral for the transport of oxygen to the muscle cells. Zinc is responsible for many cellular reactions, including the digestion of proteins. Without magnesium and phosphorus, carbohydrates cannot break down to fuel muscles cells for immediate energy production. Similarly, nerve transmission for muscle contraction is not possible without calcium and potassium.

A poor balance of vitamins and minerals has a negative effect upon the athlete’s body composition, with the metabolic process being turned in favour of catabolism, promoting muscle breakdown and adipose gain.

Water loss is accelerated during exercise, which means consuming adequate quantities of water is essential for an athlete. The American College of Sports Medicine recommends drinking one litre of water for every litre lost during exercise. As little as four percent water loss can have a devastating impact on the metabolic process, and is highly catabolic (Arthur & Bailey, 1998). In addition to many of its important functions, water is necessary to clear catabolic waste products from active muscles. Consequently, poor hydration can destroy the body’s anabolic environment and be detrimental to lean muscle mass gain, adipose loss, and overall body composition.

Recent research findings: Impact of nutrition on body composition and metabolism

A recent study by Shiue, Sather, and Layman found that following a ratio of 1.4 grams of carbohydrates for every 1 gram of protein results in greater adipose loss and maintenance of lean body weight than a high carbohydrate diet. It was also found that metabolism was enhanced. Overall, the study supported a current trend suggesting higher protein diets enable the body to function optimally, and preserve lean body mass while fat is lost.

Eating causes a rise in overall metabolism known as the thermic effect of food (Johnston, Day & Swan, 2001). Scientists at Arizona State University examined the thermic effect of a high protein-low carbohydrate diet versus the standard high carbohydrate diet. The results showed the high protein diet (consisting of 30% protein) caused an increase in metabolic processes, with bodies burning an additional 90 calories per day. Similarly, a high protein, high-fat diet has been found to enhance insulin sensitivity as well as reduce body fat levels (Sharman & Volek, 2001). Participants followed a diet of 30% protein, 61% fat and 8% carbohydrate at a calorie level close to their typical daily intake, over a six-week period, throughout which body composition and insulin levels were measured. The participants experienced a 3.6% reduction in body fat, a 1.1kg gain in lean body mass, a 2.2kg weight loss, and a 32% reduction in fasting insulin levels.

Conclusions

There is a distinct relationship between nutrition and body composition. Given nutrition is largely responsible for controlling metabolism, it has a sizeable impact an individual’s lean body mass and fat body mass. To an athlete this is particularly important, as the body’s structure is responsible for their ability to succeed. By providing the body with adequate quantities of carbohydrates, protein, fat, vitamins, minerals and water, an individual can experience increases in muscle mass and decreased body fat. Metabolic processes can be used to an athlete’s advantage. Conversely, failure to pay adequate attention to the importance of nutrition has dire consequences for an athlete’s body composition. Losses in lean muscle mass and adipose gain, as a result of catabolism, will impair an athlete’s performance. Recent research indicates the need for an athlete to pay special attention to the structure of their diet, especially in terms of ensuring adequate amounts of protein are consumed to support the body’s metabolic needs.