nutrition chapter 9
Minerals and Exercise Phosphorus (P) Phosphorus has many functions in the body, but 85% combines with calcium to form crystals of calcium phosphate (hydroxyapatite) to give strength and rigidity to bones and teeth. It is essential to energy production as a component of ATP which makes an important contribution to athletic performance and plays a role in fluid balance. Phosphate loading is sometimes used in an attempt to enhance the level of CP and ATP in muscle fibers. However, research has yet to prove this to be true. It also could possibly increase the buffering capacity of skeletal muscle and the blood to delay onset of fatigue associated with extremely high levels of lactic acid production during high intensity activities. It is not actually known just how phosphorus does contribute to athletic performance so supplementation is not recommended due to its impact on calcium metabolism. High phosphorus consumption can reduce Ca2+ levels. Calcium and phosphorus need to be in a 1:1 ratio in the blood. Athletes get enough phosphorus as it is found in protein-containing foods. The main concern is over consumption. Soft drinks contain phosphate (phosphoric acid as a preservative). Whether it is the high phosphorus content or actually milk displacement is unclear at this point. Certainly someone drinking five 20 oz. cokes /day is getting a lot of phosphorus each day and not getting enough calcium to balance it out. Magnesium (Mg2+) The main function of magnesium is as a component of bones and teeth. It is also important in several metabolic processes required for exercise (it is part of more than 300 enzyme systems in the body) and also involved in muscle contraction. Magnesium interacts with the phosphate tails of ATP to improve the efficiency rate of ATP release of energy. Magnesium is excreted in urine and sweat. Hypomagnesemia refers to low blood levels of magnesium and can occur, but is not the norm in athletes. Inadequate magnesium could limit athletic performance by causing muscle weakness. Extreme deficiency could cause cramps, spasms, or tremors. Magnesium is lost in the processing of foods and through some methods of cooking. Whole grain cereals, nuts, legumes and cocoa are among the best sources.
Minerals and Exercise Sodium (Na+), Potassium (K+), and Chloride (Cl-) Sodium, potassium, and chloride serve as electrolytes. They are vital to excitable tissue muscular and neural tissue that responds electrically to stimuli. Sodium and potassium have positive charges (+) and chloride has a negative charge (-). Sodium and potassium are also necessary for fluid balance. Chloride is a component of stomach acid (HCl) and also serves as an antibacterial agent. Unlike calcium and iron whose absorption rates are controlled by the amount our bodies need, sodium, chloride, and potassium are absorbed at about a 90% efficiency rate in the digestive tract. This means that the kidneys control the level of these minerals in extracellular fluid. Chloride follows sodium through the tubules in the kidneys and reabsorption of sodium and chloride is partly controlled by the hormone aldosterone. Potassium is absorbed at a more constant rate in the tubules and is not under hormonal control. An imbalance of sodium, potassium, and chloride can occur quickly (in one day). Imbalance affects performance due to their involvement in the function of muscle and nervous tissue (see p 304 in your textbook). Losses due to heavy sweating must be replaced with sports drink or food. The sodium and potassium content of foods varies greatly. For example: Gatorade 110 mg Na+, 30 mg K+ Powerade 55 mg Na+, 30 mg K+ Soft drinks 7-9 mg Na+, 0 mg K+ It is important for athletes to know which foods are high in salt. Salt = sodium chloride (40% Na, 60% Cl). One teaspoon of table salt has 2300 mg of sodium; the UL is 2300 mg. If lost sweat is replaced by water, hyponatremia can result. Hyponatremia is the term for low concentration of sodium in the blood. Symptoms of hyponatremia are nausea, muscle cramps, disorientation, slurred speech, confusion, and inappropriate behavior. It is estimated that approximately 30% of the finishers of the Hawaii Ironman are both hyponatremic and dehydrated (www.rice.edu). For more information on the role of electrolytes in exercise, please visit The GSSI as a great starting place. sodium content Sodium should be obtained from foods for 2 reasons. First, salty foods stimulate thirst, and second, it is difficult to ingest too much salt with food. The use of salt tablets is not as common as it once was. Over consumption of salt tablets (163 mg of sodium) can lead to hypernatremia. If salt tablets are used, they need to be taken with plenty of fluid, or it can worsen dehydration. Low Na refers to any food containing less than 145 mg of Na per serving. As previously noted, potassium is involved in nerve function, muscle control and blood pressure. Athletes also may need more potassium to replace that lost from muscle during exercise and the amount lost in heavy sweating. Potassium is found in meat, milk, fruits and vegetables. The dietary guidelines recommend at least 8-10 servings of fruits and vegetables each day.
Iron (Fe) Iron is a part of hemoglobin (RBC) and myoglobin (muscle) which are necessary to provide oxygen to active tissues. Myoglobin is a storage form of iron, particularly in Type I and IIa fibers and heart muscle. Iron also assists in many enzyme systems necessary for generation of energy (cellular respiration).It is a cofactor for many enzymes in all cells and is involved in the synthesis of new cells, amino acids, hormones and neurotransmitters. The contribution of iron to athletic performance is through its involvement in O2 transport and energy metabolism, especially for aerobic energy metabolism. It is a necessary part of the electron transport chain and aerobic ATP generation. Iron is lost through sweat, but the level of iron lost can be reduced through training. Iron can also be lost through foot strike injuries such as intravascular hemolysis in runners, intestinal bleeding from overuse of ANSAIDS such as Ibuprofen, and through heavy menstrual losses in some females. Blood loss that leads to anemia can hinder performance. Iron-deficiency anemia negatively affects performance: 1. Iron-deficiency anemia impairs performance a. VO2max (aerobic capacity) declines b. Endurance capacity declines c. A decrease in iron-containing compounds decreases oxygen utilization 2. Effect of iron deficiency without anemia on performance is unclear The prevalence of iron deficiency and iron-deficiency anemia in female athletes is likely higher than in the general population 1. Unlikely in most males (<2% in males under 70 years old) 2. Infrequently seen in adolescent males or male endurance athletes (5%) 3. 12% of females 20-49 years old (CDC), ~25% of female endurance athletes in cited studies 4. Some medications induce bleeding and loss of iron 5. Greatest risk is for menstruating females 6. Athletes with low caloric intake are at greater risk 7. Sweat loss 8. Iron loss in feces and urine in times of intensive training Athletes should consume a variety of iron-containing foods 1. Adequate energy intake 2. Variety of iron-dense foods (Table 9.14 Iron-Containing Foods) 3. Heme (animal) sources are better absorbed than nonheme (plant) sources There are several sources of iron and these are classified as either heme iron which is found in animal tissues as the iron-containing part of hemoglobin and myoglobin, and non-heme iron or free iron- the only form of iron in plant tissues. Meats contain both heme and non-heme iron. *Heme iron is absorbed much more readily than non-heme iron. Animal products include red meat, poultry, fish, and shellfish, with lean beef containing the highest levels of heme iron. Plant products as a source of non-heme iron include leafy green vegetables and legumes. Iron status in the body is regulated at the point of absorption. There are factors in our diet as well as in our digestive tract that affect iron absorption. Factors known to enhance iron absorption: Heme Fe Need by the body MFP - meat, fish & poultry factor Vitamin C - keeps iron soluble HCL (acidity of the stomach) Inhibitors of Iron Absorption: Phytates Oxalates Soy (protein and fiber) Tannic Acid - tea, coffee, nuts EDTA (additive) Excessive intake of other minerals (Zn, Cu, Ca) Reduced gastric acid production Iron deficiency occurs when dietary intake is low (nutritional or primary) The DRI varies based on age so look in the DRI table. Absorption can't compensate for losses (non-nutritional or secondary). This includes blood losses such as: internal bleeding, regular blood donations, and menstrual losses. Iron deficiency anemia is the most common nutrient deficiency worldwide (15% of the population).Most vulnerable are infants, young children and pregnant women. Nutritional causes include inadequate intake (ignorance, lack of food, overuse of iron poor foods). Non-nutritional causes include blood loss due to parasitic infections of the GI tract, menstruation, and increased loss in sweat. Symptoms of iron deficiency anemia include fatigue (exercise performance decreased, also decreased in Fe depletion), weakness, apathy, pallor (pale color), poor tolerance to colds, pica (eating non-nutritional things such as laundry starch), decreased cognitive function in children. Iron deficiency anemia is the result of long-term iron deficiency and severe depletion of iron reserves. It is also called microcytic hypochromic anemia which means RBCs are small in size and pale in color. In addition, the number of RBCs is reduced due to a lack of hemoglobin. Anemia occurs in 5-6% of athletes and up to 60% in some female athletes (female runners). Iron supplementation can be used by taking ferrous sulfate (60 mg/d between meals), however, unless you are a vegetarian, it would be better to include heme sources several times a week as they are better absorbed. Please refer to this page for more details about iron supplementation. It's a informative read, but you can click directly to the link referencing 'Some facts about iron supplementation'. A form of iron toxicity called hemochromatosis which is a hereditary condition resulting in excessive iron absorption, tissue damage and vulnerability to infections occurs in some males so use of iron supplements in any male is discouraged. © Carol Bradley 2009 updated by J. Boynton 2015, Cengage Learning 2015
Minerals and Exercise Zinc (Zn) and Copper (Cu) Zinc (Zn) Zinc is the most prevalent mineral in the body and supports multiple enzymes (~200). Zinc is involved in almost every physiological function in the body, but is primarily involved in immune function and wound healing and protects the body from heavy metal poisoning. It is also important in growth and development. The contribution of zinc to athletic performance is due to its involvement in exercise performance, recovery, and adaptation. More specifically, it is necessary for protein synthesis, regulation of pH, and in antioxidant systems. Dietary sources of zinc include protein-containing foods. Many individuals, including athletes, do not consume enough zinc. A zinc deficiency can result in an impaired sense of taste and smell, increased susceptibility to infections, poor wound healing, decreased cognitive function, and poor athletic performance. Zinc intake varies among athletes from 50% of female endurance runners consuming less than the DRI to a high intake in swimmers. It is important to eat a varied diet. Toxicity is possible through supplementation and can cause an imbalance in copper. Chronic zinc supplementation interferes with copper absorption. Copper (Cu) Copper is a component of several enzymes. It is part of cytochrome C oxidase, ceruloplasmin, and dopamine ?-hydroxylase, among others; all have an effect on oxygen use in the body. Lysyl oxidase is necessary for collagen formation. Little research has been done to demonstrate the relationship of copper to exercise performance. Food sources include meats, nuts, and sunflower seeds. There is currently no evidence to support supplementation. © Carol Bradley 2009, Cengage Learning 2015
Calcium (Ca2+) is the most abundant mineral in the body. 99% of the calcium in our bodies is found in bones and teeth and accounts for 1.5% of our total weight. The other 1% of calcium is found in body fluids. Our bodies strive to maintain blood calcium levels at all costs which means that we will lose calcium from the bones to make this happen. In addition to its contribution as a major component of bone structure (and hardness), calcium is necessary for transmission of nerve impulses, muscle contraction and blood clotting. Its contribution to physical activity includes skeletal and heart muscle contraction, hormone and neurotransmitter activity for exercise and blood clotting for minor hemorrhages during training and competition. In addition adaptive processes during competition make bones stronger (any weight-bearing contractions pulling on the bone). Calcium Absorption Absorption of calcium is inhibited by high protein diets, and high sodium diets can increase urinary excretion. At the same time protein intake <RDA can decrease absorption. High phosphorus intake in the form of phytates and oxalates (as in spinach) will bind calcium and prevent absorption. Absorption of calcium is enhanced by vitamin D, lactose (one of the reasons it is better to get nutrients form foods), a healthy digestive system, and high dietary requirements ( times of need such as pregnancy, lactation, early childhood). Calcium Imbalance In the extreme, children who dont receive adequate calcium can have stunted growth and deformed bones. Of greater concern is that lack of adequate intake of calcium will limit peak bone mass reached in adulthood (the late 20s). As it continues during adulthood accelerated bone loss contributes to osteoporosis and bone fractures. Calcium May Be Taken from Bone to Maintain Calcium Homeostasis (see figure 9.3 above) 1. Hormonally controlled a. Parathyroid hormone (PTH) b. Calcitriol (form of vitamin D) 2. Calcium homeostasis a. Regulation of calcium in the blood and extracellular fluid b. Primarily controlled by PTH c. Critical for proper nerve and muscle function d. Fast calcium exchange 1. PTH activates calcium pumps in membranes surrounding bone fluid 2. Calcium is mobilized from bone fluid not mineralized bone 3. PTH stimulates calcium resorption in kidney and increased GI absorption 3. Calcium balance a. Total absorption, distribution, and excretion b. Different from calcium homeostasis but related c. Increased or decreased absorption and excretion as needed d. Bone turnover is balanced under normal conditions 4. Long-term low calcium intake a. Bone turnover is not balanced b. Slow calcium exchange 1. PTH stimulates dissolution of bone 2. Increases osteoclastic activity; decreases osteoblastic activity 3. Calcium (and phosphate) released from bone Calcium Intake The DRI for calcium is 1000-1300 mg/day. Dairy products (1 c milk = 300 mg) tend to be the most bioavailable, fortified products, beans, and green leafy vegetables. Many athletes do not consume enough calcium. If you use calcium supplements, make sure the supplement label says USP U.S. Pharmacopeias standards. Calcium citrate (Citracal & Solgar) is the best absorbed form, however calcium carbonate (Tums & Caltrate) is the most common form. Calcium supplements should be taken with meals to help absorption. Avoid taking > 500 mg elemental calcium at one time. Some natural forms may contain lead such as bone meal calcium. Nutritional factors affecting peak bone density 1) Calcium 1. Greatest amount needed for ages 9 to 18 (1,300 mg/day) 2. Substantial need throughout adulthood (1,000 to 1,200 mg/day) a. Average adult female intake is ~ 650 mg/day b. Average adult male intake is ~ 925 mg/day 2) Vitamin D 1. 5 mcg/day until age 50 2. Need increases with age a. 10 mcg ages 51 to 69; 15 mcg age 70 and above b. Conversion to active form declines c. Exposure to UV light declines Osteoporosis Osteoporosis is the term for loss in mineral density (strength) that can result in an increased susceptibility to fracture. Changes in bone occur as part of the normal aging process. Bone loss continues gradually as we age, but at a faster rate in women than men. Bone loss in the spine and legs accelerates after menopause for a period of 5-10 years. In the US, 8 million women and 2 million men are diagnosed with osteoporosis. In general, it occurs as follows: Age 20 - bone stops growing in length Age 30 - peak in bone density is reached Age 35 - bone loss begins in the spine Age 40 - bone loss starts in arms & legs Risk Factors for Osteoporosis are as follows: Beyond our control: Age All women - Caucasian, Latin American, Oriental, Northern European ancestry Family history Premature menopause Things we can control: Poor dietary intake Sedentary lifestyle or bed-confinement (car wreck- one week on bed rest results in a loss of 2 years worth of calcium) Smoking Heavy and regular use of alcohol Underweight Amenorrhea (seek medical attention) The athlete's best defense against mineral deficiencies is an adequate intake of minerals daily through the consumption of nutrient-dense foods in sufficient quantities to meet caloric needs Calcium Toxicity The UL for calcium is 2500 mg /day. Normally calcium absorption decreases as intake increases. Over time excess calcium can lead to constipation, kidney stones and dysfunction, interference with the absorption of other minerals such as Fe, and calcium deposition in soft tissues. Incidentally, we are talking about supplements - not milk or dairy calcium
Moderate to Rigorous Exercise Increases the Loss of Some Minerals: • Mineral loss in sweat and urine may be greater in athletes • Moderate losses of minerals via sweat or urine can be offset by adequate mineral intake from food • Athletes who have substantial losses may need to increase their dietary intake or supplement the diet with the lost mineral(s) Poor Food Choices Often Lead to Low Mineral Intake: • Homeostasis • Generally maintained by adjusting absorption and excretion -If storage is high, absorption decreases -If storage is low, absorption increases • Hormonal and other mechanisms are also influential As stated in the book, there is a greater chance that mineral intake will be adequate when calorie intake is adequate. However, mineral adequacy typically is a reflection of consumption of a variety of nutrient-dense foods, some of which are fortified. Level Mineral Intake (% adaquacy) Potassium: <3 Calcium: 36 Magnesium: 52 Zinc: 88 Iron: 95 Copper: 95 Phosphorus: 95 Minerals required for following functions: • Energy metabolism as cofactors • Collagen formation • Bone/teeth formation • Antioxidant activities • Cell excitability • Blood clotting The Basics: •Minerals differ from vitamins in several ways: -The chemistry, absorption, metabolism, and excretion are generally very different when compared to vitamins •Minerals are found in a wide variety of foods: -Some are added to foods -Most are sold as dietary supplements, either singly or in combination with other nutrients •Minerals are classified by: 1) Amount found in body (outlined in table 9.1) -Macrominerals: typically large amounts found in the body; 5 g in 132 pound person, needed in amounts greater than 100 mg/d in our diets -Microminerals, also known as trace minerals, needed in amounts less than 100 mg/d in our diets 2) Functionality •Proper bone formation -Calcium, phosphorus, magnesium, fluoride •Electrolytes -Sodium, potassium, chloride •Enzyme-related functions -Iron, zinc, selenium, copper A Recommended Daily Intake Has Been Established: •Dietary Reference Intakes (DRI) -How much is enough? •Tolerable Upper Intake Level (UL) -How much is too much?
