Nutrition, Metabolism and Sports Nutrition.

Nutrition is defined as the process by which a living organism takes in and uses food for the purpose of growth and tissue replacement. A nutrient is something that nourishes, especially as found in food (Merriam Webster, Merriam Webster New Edition, Springfield, Massachusetts, 1994.) and metabolism is broadly defined as the complex of chemical and physical processes involved in the maintenance of life.

The Surgeon General’s Call To Action To Prevent and Decrease Overweight and Obesity came out in 2001 and it had five major goals. At the top of the list was to assist Americans in balancing healthful eating habits. The role of the personal trainer is to understand nutrition and be able to assist clients with making healthy eating choices as part of a weight loss plan.

The field of sports nutrition generally refers to the study of nutrition as it relates to sport performance. Because everyday life requires adequate physical fitness as it relates to doing the things that we want to do, we want to emphasize the importance of considering all individuals that are physically active in the same man¬ner as an “athlete.” Therefore sports nutrition becomes important for any individual working to maintain his or her health. Before we can get into a greater view of sports nutrition, we need to first review the six basic nutrients.

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The Food Guide Pyramid from 1992 (shown below).

Six Basic Nutrients

Food serves many purposes, from sustaining energy to providing pleasure. Probably the most important role of food is to provide the substances (nutrients) essential for maintaining optimal health and performance. The six basic nutrients provided by food include:

• Carbohydrates

• Water

• Proteins

• Vitamins

• Fats

• Minerals

These are safe and effective recommendations. But we would like to take them one step further. Our general recommendations for those in training fall in the ranges listed below:

65% from carbohydrates (of this, 10% or less from simple sugars) Athletes should target 6 to 10 grams per kilogram of body weight, depending upon activity level and goals.

15% from fats (range of 10 to 20%) Of this, 5% or less from saturated fats.

20% from proteins (current recommendations suggest 1.2 to 1.4 grams per kg body weight for endurance athletes and 1.5 to 1.8 grams per kg for strength athletes).

These recommendations are all starting points for general guidelines. How you vary them depends upon individual needs and goals. Variations from these guidelines and the reasoning behind these guidelines are discussed through the text.

General Dietary Recommendations and Reasoning Behind These Recommendations

Carbohydrate: The Body’s Primary Source of Energy

Carbohydrate is the primary fuel source utilized within the body. Carbohydrates include sugars and starches. The problem is that the body is not very efficient at storing carbohydrates. For this reason, carbohydrates are needed in relatively larger amounts than fats (the main storage form of energy) and protein. (The only ‘storage’ form of protein is your tissues, muscles and organs.) Carbohydrates break down in the blood to form glucose. Glucose is the fuel utilized by the brain, muscles and cellular reactions. Glucose is stored in the liver and muscles in the form of glycogen. Unfortunately, the body cannot store a lot of glycogen. Although fat is a more efficient energy source (that is, it will give you much more energy than glucose will when bro¬ken down), it cannot be used without carbohydrates (glucose). There¬fore, in order to generate any energy, the individual must take in ad¬equate carbohydrates. General recommendations for carbohydrate intake vary. On one end of the scale, some strength athletes suggest that high-protein, low-carbohydrate diets are better to maximize muscle building (discussed below under Proteins). This still does not satisfy the energy needs of the body, and the excess protein is converted to either carbohydrates or fat. This is an inefficient process that can easily lead to excess fat. More importantly, breaking down proteins and then using them to create carbohydrates creates toxic products that may lead to ammonia toxicity and kidney distress. Another problem of high-protein diets is that they can easily lead to dehydration. Dehydration can result from trying to dilute the excess urea (formed from the excess ammonia) and from lack of glycogen, which is stored with wa¬ter. Minerals, such as calcium, can also become depleted when at¬tempting to neutralize the extra acid by-products from amino acid (protein) breakdown. This loss of calcium may lead to an increased risk of osteoporosis.

The opposite end of the scale sees carbohydrate recommendations approaching 80% of total intake. Although some centers have had success with this recommendation, it is difficult to determine if participants actually achieved this 80% or were attempting to approach it while only maintaining a lower percentage. Additionally, athletes might have greater protein, fat and total caloric needs than such a diet can provide. Some skeptics have hinted that higher carbohydrate diets lead to an increase in insulin and, therefore, an increase in fat storage (insulin is used to store both sugars and fats). Although it is well established that sugary foods increase the body’s insulin secretion and may lead to an increase in total fat storage, it is still not well established whether or not complex carbohydrates in high quantities result in insulin secretion at levels that will increase fat storage. What this does tell us is that a combination of fatty and sugary foods should be minimized. Nutrient timing has become vitally important before, during and after exercise. The amount of research devoted to nutrient timing has exploded over the last 10 years. It is clear that after any strenuous physical activity it is important to eat a meal high in carbohydrates (1 g/kg) immediately post exercise and then again one hour after exercise. This has been shown to decrease myofibrillar protein breakdown and urinary urea excretion, resulting in a more positive body protein balance. Also, by adding carbohydrates to a protein supplement post-exercise it increases growth hormone levels which can produce a hormonal environment during recovery that may be fa-vorable to muscle growth by stimulating insulin and growth hormone elevations.

Key Points:

1. Carbohydrate is the main fuel source for the body. Although fats yield higher energy, carbohydrate’s limited store requires sufficient regular intake. Combined with the fact that fats are relatively well stored, or utilized, and protein requirements are relatively minimal compared to carbohydrates, carbohydrates should be the primary source of energy intake.

2. Fat requires carbohydrates. Even when we exercise in a manner that derives most of its energy from fats, it is the carbohydratesthat are the limiting source. Even very lean individuals can continue burning fats for extremely long periods of time. The body stores 3,500 Calories per pound of fat. The average person can only store a total of approximately 2,400 Calories

from carbohydrates.

3. High-sugar, high-fat diets may result in a very high level of fat storage (and may be dangerous to one’s health).

4. A safe recommendation for carbohydrate intake for most active individuals is approximately 65% of the total daily in¬ take. Of this, less than 10% of the total intake should be from simple sugars. The rest should be from complex carbohydrates.

Fat: A Matter of Health

Fat is a source of stored energy that is utilized during low level, long duration exercise. There is substantial evidence that high-fat diets lead to a high risk of coronary artery disease (clogged arteries), heart attack, stroke andpremature death related to heart disease. Most recommendations, even many of the so-called ‘high-fat’ diets, recommend intake of no more than 20-35% of total intake of Calories from fat. There are several recommendations on the market that do go higher than this, however, the scientific evidence cited is not well supported and often criticized as flawed in its methodology. On the opposite endof the scale, some individuals recommend nearly eliminating fat from the diet.

Most evidence suggests lower fat diets can lead to less body fat. More importantly, significantly reducing fat intake, especially saturated fats, has been shown to lead to reduced triglycerides and low density lipoproteins (LDL), the ‘bad cholesterol.’ It is also easier to maintain a lower total Caloric intake with less fat because fat contributes a significantly greater number of Calories per gram than carbo-hydrate or protein.

The primary risks associated with very low-fat diets are be¬coming ‘fat-starved’ and athletes not taking in enough Calories during heavy training. If the body senses that it is ‘fat-starved,’ it may actually attempt to store any fat that is taken in (an important survival risk is when athletes undergo heavy training. Taking in very low-fat diets (less than 10% of calories from fat) may make it difficult to take in enough calories to offset calories burned in training.

Because lower fat diets have been associated with decreased health risks, we recommend that the average person in training aim for approximately 15% of their total caloric intake be derived from fats. From this, our recommendation is less than 5% of the total intake be from saturated fat sources. These should be dietary goals. Variations above and below are safe as long as they do not approach an excess of 35% fat or less than 5% from fat. Striving for these percent¬ages makes it easy to quickly change from a higher fat diet to a safe, low-fat diet. Remember, fat is a nutrient and is needed by the body. Certain fats, such as the monounsaturated oils, are considered beneficial to health.

Key Points:

1. High-fat diets, in an excess of 35% of their calories from fat, have been shown to increase risk of heart disease.

2. Too little fat in the diet can lead to ‘fat-starvation’ and a retention of fat.

3. A safe, low-fat recommendation is to aim for approximately15% of total intake from fat, with less than 5% of the total dietary intake being from saturated fat.

Protein

Recent research suggests that the average person who exercises may require approximately 1.0 to 1.5 grams of protein per kilo¬gram of body weight or more. (ADA, CDA, 1993) Some research suggests that protein absorption for those engaging in heavy exercisemay max out around 1.8 to 2.4 grams per kilogram of body weight (g/kg BW). Currently, the most cited research recommends 1.2 to 1.4 g/kg BW for endurance athletes and 1.4 to 1.8 g/kg BW for strength athletes. (Lemon, 1991) Some experts have suggested that an excess of 2.0 to 3.0 grams of protein per kilogram of body weight may lead to ammonia toxicity and kidney stress. To date, there are no conclusive studies on long-term damage due to excessive protein. How¬ever, as there is no benefit to intakes in excess of 2.4 grams per kilo¬gram body weight, and since there is a decrease in calcium absorption with excess protein intake, it is preferable not to exceed this limit.

It is a common belief among strength athletes that increasing protein intake will increase one’s muscle mass. What actually leads to increased muscle mass is resistance exercise. The exercise stimu-lates a more efficient uptake and utilization of the protein consumed. Excess protein will either be converted to carbohydrate and burned as a fuel or converted into fat. Protein is only converted to carbohydrate when there is inadequate carbohydrate intake. Therefore, in many cases, the protein will be converted into excess fat. More importantly than this are the health consequences listed above when protein is broken down into nonprotein products. The ammonia toxicity can place stress on the kidneys, lead to dehydration, and even lead to health problems such as osteoporosis from decreased calcium absorption. Many protein recommendations range between 10 and20%. Certain ‘experts’ recommend 30% or more of the diet come from protein for reasons listed above. An additional reason, often listed, suggests that protein will stimulate a decrease in appetite as compared to consuming carbohydrate. There is some truth to this, but the excess protein is still detrimental to one’s health and energy needs. There¬fore, a safer recommendation would be to get some protein in every meal to better control hunger, but not to overemphasize the protein.

Key Points:

1. Resistance training leads to increase in muscle size—not protein.

2. Protein is important for tissue regeneration and development; however, protein utilization within the body during trainingprobably maxes out around 1.8 to 2.4 grams of protein per kilogram of body weight.

3. The RDA for protein is approximately 0.8 grams of protein per kilogram of body weight. Athletes probably need about 1.2 to 1.8 grams of protein per kilogram of body weight. Current research suggests 1.2 to 1.4 grams per kilogram of bodyweight for endurance athletes and 1.4 to 1.8 grams per kilogram of bodyweight for strength athletes.

4. A safe recommendation for daily protein intake is approximately 20% of total daily intake or between 0.8 and 2.4 grams per kilogram of body weight. Inactive individuals on the lower end; more active individuals closer to the high end.

Water: The Forgotten Nutrient

Water is involved in many of the biochemical reactions that occur in the body. Most molecules cannot be split without water being present. Carbohydrates cannot be stored without adequate water. Water is important in blood to help transport glucose and carry away metabolic by-products, in urine to eliminate metabolic waste products, and in sweat to help dissipate heat through the skin. Without adequate water intake these processes can be inhibited, decreasing performance or even jeopardizing an individual’s health. Severe dehydration in athletes can lead to medical emergencies.

Exercise under any conditions, hot or cold, leads to water loss. To minimize dehydration effects, athletes should drink water before, during and after exercise. It is very important to note that thirst and dehydration do not correspond to one another. Often one will not be¬come thirsty until after one is already dehydrated. Therefore, it is usually recommended to drink enough to satisfy your thirst and then drink some more. Probably the best indicator of hydration levels is the color and quantity of one’s urine. When urine is clear and of a reasonable volume, you are at a normal water balance. If you are taking vitamin supplements, your urine may be darker. In that case, volume is a bet¬ter indicator of hydration levels. If your urine is dark and scanty, you are probably not drinking enough water.

The usual recommendation for water is to drink a minimum of eight 8-ou nee glasses of water every day. If you exercise or it is very hot, this is probably not enough. It is best to monitor one’s urine output. One recommendation suggests about one quart for every 1,000 calories burned throughout the day. (Clark, N. 1997. Nancy Clark’s Sports Nutrition Guidebook. 2nd Ed. Champaign, IL: Human Kinetics.) An¬other recommendation suggests targeting one ounce of water for everypound of body weight.

It is possible to drink too much water. This can result in the loss of sodium, an important electrolyte in the body. Low sodium levels are referred to as hyponatremia. Typically, this does not occur until an individual exceeds 2 to 3 gallons of water per hour. Usually this is not a problem; however, the symptoms are similar to heat exhaustion and can be misconstrued under hot conditions. The best indicator that an individual is suffering from hyponatremia vs. heat exhaustion under hot conditions is when you increase water intake, it actually starts to make the individual feel worse instead of better.

Key Points:

1. Water is necessary for many critical biochemical processes – one of which being thermoregulation.

2. Urine is the best indicator of hydration levels. Urine output should be clear and of reasonable volume. Dark and scanty urine indicates inadequate water intake.

3. Eight 8-ounce glasses each day should be a minimum in¬ take level. Most individuals who exercise probably need higher amounts.

Micronutrients: Vitamins and Minerals

Vitamins and minerals are referred to as micronutrients. Micronutrients are essential nutrients that are only required in small amounts. Vitamins and minerals are not energy sources, but are catalysts that help regulate biochemical reactions within the body. Vitamins and minerals will not give an extra energy boost. Vitamins and minerals are necessary to function optimally, but will not increase performance; although enough of a deficiency can impede performance and metabolic functions.

Ideally, if you were to eat a well-balanced diet, you would obtain adequate vitamins and minerals. There is still substantial debate concerning vitamin and mineral supplementation. In reasonable amounts, vitamin and mineral supplementation is probably not harmful. If the individual is not taking in enough vitamins and minerals, this supplementation maybe helpful. Individuals at greatest risk of vitamin and mineral deficiency are individuals on a Calorie restricted diet, individuals who are undergoing heavy exercise training, and individuals whose diet consists primarily of processed foods. Present recommendations for vitamin and mineral supplementation suggest that a general multivitamin is all that is needed for supplementation. Antioxi-dants (A, C, and E vitamins along with the mineral selenium) are often recommended because of their ability to fight off free-radicals which have been implicated as a likely cause of many cancers. This becomes especially important for athletes who create additional free-radicals during exercise.

Mega-dosing (taking vitamins and minerals at a level significantly greater than the RDA) can be very dangerous. Excess levels of any vitamin or mineral, especially the fat-soluble vitamins (A, D, E, and K) can have toxic effects. Another result from mega-dosing can occur when returning to ‘normal’ levels of vitamin or mineral intake. After mega-dosing, the body may see these ‘normal’ levels as deficiencies and react as if it is deficient in these vitamins and minerals.

When it comes to taking vitamins and minerals, it is important to note that supplementation is often absorbed at a much lower level than if the vitamins and minerals are obtained through a natural food source. Most vitamins and minerals require other vitamins and minerals to be absorbed properly and when not taken in the proper ratios, vitamins and minerals may be poorly absorbed. Unfortunately, the ideal ratios are not well understood. Finally, most supplements contain significantly less vitamins and minerals than can be obtained from a well-balanced diet.

Key Points:

1. Vitamins and minerals do not give a boost of energy. They will not improve performance, but in deficient quantities, can impede performance or metabolic processes.

2. Eating a well-balanced diet is the best way to get adequate vitamins and minerals.

3. Supplementation may be of benefit if deficient. As long as you do not mega-dose, supplementation should be fairly safe.

4. Since strenuous athletic activity may increase free-radical formation, athletes should consider antioxidant supplementation.