Nutrition Note: Exercise and Eating

We are all being told to increase our physical activity to maintain our health and help prevent chronic disease. A person will receive both mental and physical benefits from physical activity as indicated in Table 11. Along with having an active lifestyle, proper eating habits are essential. The general public is exposed to many myths associated with nutrition for an active lifestyle. What are the simple facts related to exercise and what should you eat? Whether an elite athlete, a recreational sports person, or an avid walker, all active lifestyles require the correct level of balanced nutrition to fuel the body.

Table 1. Benefits from an active lifestyle¹

Shape and toning of the body Weight control or weight loss

Decrease risk: Heart disease Colon and breast cancer Hypertension Stroke Osteoporosis Back injuries Obesity Diabetes Bone and joint disease

Increased feeling of well being Stress relief Decreased anxiety and depression

Fitness can be defined as a level of muscular strength and endurance. Greater muscular strength and a higher level of endurance is a sign of a high level of fitness. Muscle strength is increased by weight bearing exercises such as pushups and lifting weights. Endurance is how long a person can sustain a physical activity. Endurance is therefore a result of both the respiratory and circulatory systems abilities to deliver large quantities of oxygen to muscles. Activities such as running, jogging, swimming, basketball, and soccer are endurance sports¹.

An active lifestyle needs to be an integral part of a person’s daily life as the benefits of training diminish within two weeks of inactivity. Within 2 to 8 months, all benefits are lost. Depending on a person’s activity the body requires energy in the form of either glucose or fat¹, which can be obtained in the diet from fats, carbohydrates and proteins. As a person’s activity level increases, so does their need for additional energy.

Activities of low to moderate intensity such as walking, swimming, aerobic dance, and long distance running require oxygen to convert glucose into a useable energy form. This process is known as aerobic metabolism¹. The glucose is obtained from carbohydrates or the carbon skeleton of proteins and fatty acids⁶.

High intensity short duration activities use glycogen as the energy source, which is stored in muscle and liver6. Glycogen is a long chain of glucose. During intense exercise, glycogen in muscle is broken down to glucose and ultimately to lactate, while releasing needed energy. However this system of energy release does not require oxygen and is called anaerobic metabolism1 2. Short high intensity activities can only continue as long as the energy supply remains1 and athletes run the risk of running out of glycogen. Carbohydrates are required to rebuild glycogen stores. Athletes who fail to consume sufficient carbohydrates will possibly have decreased endurance and performance6. Sports like football, competitive swimming, sprinting, volley ball spiking, tennis, soccer, and basketball are considered high intensity sports.

In endurance events, many athletes become fatigued, commonly known as “hitting the wall”. This is due to low muscle glycogen and blood glucose levels. To combat this, an athlete can maintain their supply of energy by consuming 25 to 30g of carbohydrate every half hour of exercise. Typically 1 cup of a sports drink normally has 15 – 20 gm carbohydrate and can be used to fulfill this need⁶.

Sports like recreational swimming, hiking, aerobic dancing, and heavy gardening use approximately 50% aerobic and 50% anaerobic metabolism to supply the required energy. As the duration of exercise lengthens, the use of fatty acids as energy source increases², however carbohydrates are still required to be present so that the fat can be used. Intense activities require more carbohydrates as the energy source.

Three to four hours prior to a major physical event, athletes need to consider a pre-game meal. This meal should be high in carbohydrates, low in fat, and easily digested (e.g. baked potatoes, spaghetti and tomato sauce, or cereal with skim milk). In general, the majority of the studies suggest that the carbohydrates should be of moderate to low glycemic index (GI) for enhanced endurance⁵. During the event, 25 – 30g of carbohydrates should be ingested every 30 minutes. Drinking 1 cup of sports drink (6 – 8% carbohydrate) every 15 to 20 minutes will fulfill this need. Tiredness is not prevented by carbohydrate feeding; it is just postponed⁶.

After exhaustive exercise, approximately 20 hours is required to restore muscle glycogen levels, provided a total of 600 g of carbohydrates are consumed. Delaying the intake of carbohydrates can decrease glycogen resynthesis by 45%. To overcome this problem, within the first 30 minutes post exercise the consumption of 100 g of carbohydrates combined with 5 to 9g of protein will increase glycogen resynthesis (e.g. bagel with peanut butter and 2/3 cup raisins, turkey sandwich with whole wheat bread and 1 cup apple sauce). The need for the protein at this time is still somewhat controversial. Foods containing carbohydrate with high GI promote greater glycogen stores with in the first 24 hours after intense exercise as compared to foods with low GI^{4 5 6} .

Consumption of extra protein to maximize strength and endurance is generally not required because today’s western diet has protein levels that typically exceed protein needs. See www.tara-source.com for a table of protein needs for people involved in different activities. Protein needs may be higher for endurance athletes and are related to energy needs4 6. Women athletes who are on low energy diets may require addition protein. High protein intake can result in an increased excretion of urine and possible dehydration. High protein diets may also prevent adequate intake of carbohydrates which can have a negative effect on physical performance. No scientific evidence supports the use of amino acid supplementation. Large intakes of these supplements can result in weight gain, dehydration, loss of calcium, and stress on the kidney and liver6.

Fat contains over twice the amount of energy in the form of calories (9kcal/g) by weight than either carbohydrates (4 kcal/g) or protein (4 kcal/g). The body does require a small portion of fat in the diet, and during light to moderate intensity exercise the preferred fuel source is fat. However this does not mean a person should increase their fat intake. Studies have indicated that when high performance rowers were given either a 20% or 40% fat diet, those that consumed the lower fat, high carbohydrates diet had greater reserves of muscle glycogen and greater power output⁶.

Normally, if a person eats a well balanced diet following the food pyramid guidelines (see www.tara-source.com archives) with servings to match activity level, then the required levels of minerals and vitamins will be consumed. As usual, correct serving size is key. Problems occur when a person relies on snacks rather than a balanced diet to obtain the needed energy level. These individuals may also have problems meeting the required amount of minerals and vitamins. Research has indicated that unless a person is deficient in a specific mineral or vitamin, extra intake of vitamin and minerals does not enhance performance. Minerals to watch for possible deficiencies are calcium, zinc, and iron. Iron is required to help transport oxygen to all cells of the body. Low iron levels result in fatigue. Calcium is involved in bone and teeth development but also is required every time you move a muscle. Vitamins that could possibly become deficient are folate, and B₁₂. This is especially true for athletes who need to keep their weight down such as jockeys, skaters, and gymnasts^{6 7}. Vitamin B₁₂ may be low in vegetarian athletes since this vitamin is only found in animal based foods. A balanced diet will solve these potential deficiency issues.

Excessive intake of Vitamin C, E, and B carotene has not shown enhanced physical performance⁶. Studies will continue to further evaluate their role in physical activity.

Many nutritional products known as ergogenic aids are on the market with the claim to help the athletes. Table 2 lists some of the more common products and their actual effect.

Table 2^{3 6}

Erogogenic Aid	Claim	Realty
B-hydroxy-B-methylbutyrate	Less stress induced muscle breakdown	Study lacks proper control therefore results are suspect.
Creatine	Normally obtained from the diet and made by the body. Role is to help make the energy compound that fuels the body.	Does increase work capability over brief intensive exertion and increases weight. Does not improve endurance activities. Excess creatine levels can not be stored in the muscles. No studies have evaluated the possible side effects.
DHEA	Precursor to testosterone and estrogen.	Does not increase testosterone levels or enhance performance. Banned by US Olympic committee, NFL and NCAA.
ANDRO	Converted to testosterone.	No scientific evidence to support improvement in athletic performance or safety. Banned by IOC.

Whether a professional athlete or an average person wanting to stay fit and enjoy life, nutritional needs depend on same parameters as an inactive person. These parameters are age, weight, height, and gender. However the nutritional needs are also related to type, frequency, intensity, and duration of physical activity. Even with today’s enhanced scientific knowledge, no special diets, pills, powders, drinks or magic potions can increase a person’s fitness. Fitness and good health are obtained by regular exercise and a balanced diet.

Reference: Exercise and Eating

1. Brown, J. E. 1999. Nutrition Now. 2^nd ed. West/Wadsworth Publishing. Ca
2. Brody, T. 1994. Nutritional Biochemistry. Academic Press. San Diego
3. Congeni, J. and Miller S. 2002. Supplements and drugs used to enhance athletic performance. Pediatric Clinics of North America. 49(2).
4. Hawley J. and Burke, L. 1998. Peak Performance: training and nutritional strategies for sport. Australian Institute of Sport. www.ais.org.au/nutrition/PPchap11.htm
5. Kirwan, J. P. Eating for health and athletic performance: the glycemic index. 2002. Fit Society. American College of Sports Medicine
6. Mahan, L.K, and Escott-Stump, S. 2000. Krause’s Food, nutrition, and diet therapy. 10th ed. Chapter 25: Nutrition for Exercise and Sports Performance. Berning, J. R., W. B Saunders, Co. Philadephia
7. Volpe, S. L., Learning more about micronutrients. 2002. Fit Society. American College of Sports Medicine

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