chapter 9 Basic Nutrition Factors in Health
Chapter Objectives Identify the protein, carbohydrate, and fat recommendations for athletes. Know when to refer an athlete to the appropriate resource, a medical doctor, or a sport dietitian. List the dietary recommendations for disease prevention and overall health List hydration and electrolyte guidelines for different age groups and scenarios and help athletes develop an individualized hydration plan
Role of Sports Nutrition Professionals Varying degrees of nutrition knowledge Athletes with complex nutrition issues should be referred to a team physician or sports dietitian A sports dietitian is a registered dietitian with specific education and experience in sports nutrition Board Certified Specialist in Sports Dietetics (CSSD) (continued)
Role of Sports Nutrition Professionals (continued) Responsibilities of the registered dietitian include the following: Translate the latest scientific evidence into practical sports nutrition recommendations Assess and analyze dietary practices, body composition, and energy balance of athletes Provide personalized meal and snack plans to promote achieving short- and long-term goals for athletic performance and good health
Key Point Experienced sports dietitians help athletes make the connection between plate and performance. They have advanced knowledge, skills, and expertise in sports nutrition.
Figure 10.1 www.mypyramid.gov Standard Nutrition Guidelines
Key Point MyPyramid is an excellent starting point from which to evaluate the adequacy of an athlete s diet. If a diet provides a variety of foods from each group (grains, vegetables, fruits, milk, meat & beans), it is likely adequate for vitamins and minerals. However, if the diet excludes an entire food group, specific nutrients may be lacking.
Table 10.1
How to Evaluate the Adequacy of the Diet Dietary Reference Intakes (DRI) The DRI for each nutrient includes the following: Estimated average requirement (EAR) average daily nutrient intake level sufficient to meet the needs of half of the healthy population within each age & sex. Recommended Dietary Allowance (RDA) average daily nutrient requirement adequate for meeting the needs of most healthy people within each age and sex. Adequate intake (AI) average daily nutrient intake level recommended when a RDA cannot be established. Tolerable upper level intake (UL) maximum average daily nutrient level not associated with any adverse health effects. Intakes above the UL increase potential risk of adverse effects.
Macronutrients A macronutrient is a nutrient that is required in significant amounts in the diet. Three important classes of macronutrients are Proteins Carbohydrates lipids
Protein Macronutrients Structure and Function of Proteins More than half of the amino acids can be synthesized by the human body and are commonly called nonessential amino acids because they do not need to be consumed in the diet. Nine of the amino acids are essential because the body cannot manufacture them and therefore they must be obtained through the diet.
Table 10.2
Protein Requirements Macronutrients Expressed as a percent of daily caloric intake, a common protein intake recommendation is 10-15% for the general adult & 15-20% for athletes. The RDA for protein for the general adult is 0.8 g/kg (0.36 g/pound) of body weight for both men and women, and 1.0-1.8 g/kg of body weight for athletes Protein intake for strength/power athletes: 1.5-1.8 g/kg (or rounded between 1.5 2.0 g/kg) Protein intake for endurance athletes (eg, events lasting greater than 1.5-2 hrs): 1.0-1.4 g/kg (or rounded between 1.0 1.5 g/kg) Proteins provide 4 kcal/1 g of protein
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Key Point Athletes require more than the RDA for protein to build and repair muscle. Depending on the sport and the training program, 1.0 to 1.8 g per kilogram body weight of protein is recommended.
Macronutrients Protein Dietary Protein high-quality (complete) protein: contains all essential amino acids in adequate quantities to support tissue growth (anabolism) and maintenance. Usually of animal origin (e.g., meat, fish, poultry, eggs, dairy products). low-quality (incomplete) protein: deficient in one or more essential amino acids (usually of plant origin, such as grains, beans, vegetables) such that tissue growth and maintenance is not supported. Consuming a variety of incomplete proteins (e.g., vegetarian diet) provide complementary proteins, which can result in a complete protein (e.g., combining beans and rice).
Key Point Recommendations to increase or decrease protein intake should be made on an individual basis after the normal diet has been analyzed and caloric intake considered. A mixed diet is the best source of high-quality protein. Strict vegetarians must plan their diet carefully to ensure an adequate intake of all essential amino acids.
Macronutrients Carbohydrates The primary role of carbohydrate in human physiology is to serve as an energy source. Structure and Sources of Carbohydrates Monosaccharides (glucose, fructose, and galactose) are single-sugar molecules. Disaccharides (sucrose, lactose, and maltose) are composed of two simple sugar units joined together. Polysaccharides, also known as complex carbohydrates, contain up to thousands of glucose units.
Macronutrients Carbohydrates Dietary Carbohydrate All types of dietary carbohydrate sugars as well as starches are effective in supplying the athlete with glucose and glycogen. Consumption of a mix of sugars and starches is desirable. Fiber The DRI for fiber is 30-38 g/day and 21-29 g/day for young men and women, respectively (an easy number to remember 30 g/day). This level of fiber may be excessive for some aerobic endurance athletes.
Carbohydrates Glycemic Index Macronutrients The GI classifies a food by how high and for how long it raises blood glucose. Foods that are digested quickly and raise blood glucose (and insulin) rapidly have a high GI. Foods that take longer to digest and thus slowly increase blood glucose (and therefore stimulate less insulin) have a low GI.
Table 10.3 Glycemic Index (GI) of Various Foods Table 10.3 The table uses white bread (GI = 100) as a standard. When variations exist in a food item, the mean is reported. Adapted, by permission, from Foster-Powell, Holt, and Brand- Miller, 2002.
Macronutrients Carbohydrates Carbohydrate Requirements The general recommendation is to consume 50-55% of total daily calories as carbohydrate (many athletes need a higher percentage, such as 60-70%, especially during high intensity training). Aerobic endurance athletes who train for long durations (90 minutes or more daily) should replenish glycogen levels by consuming maximal levels of carbohydrate, which is approximately 8 to 10 g/kg. Carbohydrates provide 4 kcal/1 g carbohydrate.
Calculation Problem A CSCS prescribes a daily carbohydrate intake of 10 g/kg for an 75 kg triathalon athlete, who is currently training for the ironman competition and has a daily caloric intake of 4500 kcal. What percent of his daily caloric intake is from carbohydrates? A) 57%; B) 60%; C) 67%; D) 70%
Macronutrients CHO during exercise Unlike preexercise CHO, does not trigger hypoglycemia Improved muscle permeability to glucose? Insulin-binding sites altered during exercise? CHO intake after exercise essential Glycogen resynthesis high <2 h after exercise Protein + CHO intake enhances glycogen stores Stimulates muscle tissue repair
Key Points Some aerobic endurance athletes have maximal carbohydrate requirements, up to 10 g/kg per day. During high intensity exercise muscle can use 2-3 g of glucose per min. Most athletes do not deplete muscle glycogen on a daily basis, and therefore have lower carbohydrate requirements (5-6 g/kg per day).
Macronutrients Lipids Structure and Function Saturated fatty acids (and trans fats), common in animal fats, dairy products, hydrogenated shortenings, and tropical oils (eg, palm & coconut oil), contain all the hydrogen they can carry. These fats increase LDL bad cholesterol, and increase the risk of heart disease and atherosclerosis, especially trans fats but also saturated fats. Unsaturated fatty acids are missing hydrogen atoms, and carbon atoms are joined together by double bonds. These fats tend to lower LDL cholesterol, decreasing the risk of heart disease. Mono-unsaturated fats, common in olive and canola oils, contain one double bond. Poly-unsaturated fats, common in sunflower, soy, and safflower oils, contain two or more double bond. Fats provide approximately 9 kcal/1 g fat.
Fat, cholesterol, and Disease Table 10.4 High levels of LDL s and cholesterol may contribute to heart disease. High levels of HDL s and decreasing the ratio between total cholesterol and HDL s protect against heart disease. HDLs can be increased by exercise, weight loss, and a diet low in fats (especially trans and saturated fats) and cholesterol.
Lipids Macronutrients Fat Requirements and Recommendations The recommendation for the general public from health organizations such as the American Heart Association is that fat should constitute 30% or less of the total calories consumed. It is recommended that 20% of the total calories (or two-thirds of the total fat intake) come from monounsaturated or polyunsaturated sources and 10% from saturated fats (one-third of total fat intake). Cholesterol should not exceed 300 mg/day.
Fat Performance Macronutrients (continued) Intramuscular and circulating fatty acids are potential energy sources during exercise. Fat stores are large and represent a vast fuel source. Consistent aerobic training increases the muscle s capacity to use fatty acids as fuel. When the intensity of exercise increases, there is a gradual shift from fat to carbohydrate as the preferred source of fuel. Cannot use fats efficiently when carbs are low ( fats burn in the flame of carbs) given carbs are needed to sustain proper function of neural tissue and RBC
Macronutrients When Should Athletes Decrease Dietary Fat? Need to increase carbohydrate intake to support training type In this case, to ensure adequate protein provision, fat is the nutrient of choice to decrease so that that caloric intake can remain similar while carbohydrate is increased. Need to reduce total kcal intake to achieve wt loss Because fat is dense in calories and is highly palatable, decreasing dietary fat, if the diet has excess fat, can help reduce caloric intake. Need to decrease elevated blood cholesterol Some young athletes are strongly predisposed to heart disease, although this is uncommon.
Micronutrients A micronutrient is a nutrient that is required in small amounts (typically measured in milligram or even smaller quantities) in the diet. Two primary types of micronutrients are vitamins and minerals. Diets deficient in vitamins and minerals may produce decrements in physical performance. Taking a multi vitamin/mineral tablet may ensure that adequate doses of vitamins and minerals are being met. There is no scientific data to support the use of mega doses of vitamins and minerals in order to enhance performance
Table 10.5 (continued)
Table 10.5 (continued)
Table 10.6 A Key Mineral for Athletes: Calcium - athletes who consume low-calcium diets may be at risk for osteopenia and osteoporosis (deterioration of bone tissue leading to increased bone fragility and risk of fracture).
Table 10.6 (continued) A Key Mineral for Athletes (especially women): Iron - a constituent of hemoglobin & myoglobin; plays an important role in oxygen transport & utilization of energy.
Water Fluid and Electrolytes Water is the largest component of the body, representing from 50-70% of a person s body weight. Total body water is determined largely by body composition; muscle tissue is approximately 75% water, whereas fat tissue is about 20% water. Fluid Balance The average fluid requirement for adults is estimated to be 2 to 2.7 quarts (1.9-2.6 L) per day. Athletes sweating profusely for several hours per day may need to consume an extra 3 to 4 gallons (11-15 L) of fluid to replace losses.
Balance Between Water Gain and Loss
Dehydration & Exercise Performance Thirst Osmoreceptors (high blood osmolality) Baroreceptors (low blood volume) Thirst not well calibrated to hydration levels 24 to 48 h to completely rehydrate Benefits of fluids during exercise Minimize dehydration and water loss Performance and cardiovascular function maintained
Fluid and Electrolytes Water Risks of Dehydration Fluid loss equal to as little as 1% of total body weight can be associated with an elevation in core temperature during exercise. Fluid loss of 2% or greater of body weight may result in cardio-vascular strain, impaired ability to dissipate heat, and possible a decrease in performance. At 7% loss, collapse may occur. Dehydration will adversely affect endurance training and performance to a greater extent than strength training and performance. Strength will likely not affected significantly until fluid loss exceeds 3-5% of body weight.
Key Points Consuming adequate fluids before, during, and after training and competition is essential for optimal performance The ultimate goal is to start exercise in a hydrated state, avoid dehydration during exercise, and rehydrate before the next training session.
Fluids Water Monitoring Hydration Status Each pound (0.45 kg) lost during practice represents 1 pint (0.5 L) of fluid loss (16 ounces). Signs of dehydration include the following: Dark yellow, strong-smelling urine Decreased frequency of urination Rapid resting heart rate Prolonged muscle soreness
Electrolytes The major electrolytes lost in sweat are sodium chloride, and to a lesser extent, potassium. Hyponatremia can develop in those who exercise and hydrate with only water, causing blood sodium levels to become diluted (<125 mmol/l). Hyponatremia can be deadly, such as slow marathon runners that drink water excessively over several hours of low intensity running/walking in a cool environment where sweating is minimal.
Key Point Athletes who exercise for hours (especially in cool environments with little sweating) and hydrate excessively with only water or a no- or low-sodium beverage may dilute their blood sodium to dangerously low levels.
Fluid and Electrolytes Fluid Replacement Guidelines Before a Training Session Encourage athletes to hydrate properly before prolonged exercise in a hot environment. Intake should be approximately 16-24 fluid ounces (0.5 L) of a cool beverage 2 hours before a workout.
Fluid and Electrolytes Fluid Replacement Guidelines During a Training Session Provide cool beverages (about 50-70 F [10-21 C]). Have fluids readily available, since the thirst mechanism does not function adequately when large volumes of water are lost. Remind athletes to drink. Athletes should drink fluid frequently for example, 4 to 8 fluid ounces (118-237 ml) every 15 minutes. For shorter duration exercise (< 1 hr), water is an adequate fluid replacement, but for longer duration exercise (> 1 hr) a carbohydrate drink is warranted (20-30 meq Na + & Cl - /L; 2-5 meq of potassium/l; and 6-8% carbohydrate)
Fluid and Electrolytes Fluid Replacement Guidelines After a Training Session Athletes should replenish fluids with at least 1 pint (0.5 L) of fluid for every pound (0.45 kg) of body weight lost. Weight should be regained before the next workout. Water is an ideal fluid replacement, although flavored beverages may be more effective at promoting drinking. The ideal fluid replacement beverage depends on the duration and intensity of exercise, environmental temperature, and the athlete.