Nutrition and Athletic Performance
Part 3 of 3
Elaine Gonya, Licensed Athletic Trainer
Aurora Sports Medicine Institute
As the last article in our three-part series on Nutrition and Athletic Performance, this edition will focus hydration, nutritional considerations for men and women, dietary supplements, and ergogenic aids. Previous discussions included an overview of protein, aspects of a training diet and carbohydrate consumption. In recent years, the quest for research documenting the beneficial effects of nutrition on exercise has often led athletes on wild chases for ideas on how to move their athletic performance to the next level. When digging for the latest research, the keys are to update often and use reputable sources.
Dehydration decreases exercise performance; therefore, adequate fluid intake before, during, and after exercise is necessary for health and optimal performance. Although no one is exempt from dehydration issues, male athletes often need to monitor fluid loss more closely than their female counterparts, due to significant sweating and rises in body temperature.
Dehydration increases the risk of potentially life-threatening heat injuries, including heat stroke. To avoid problems, athletes should drink enough fluid to balance their fluid losses. Helpful hydration guidelines include:
- Two hours before exercise: 14 – 22 ounces should be consumed.
Before exercise, hydration practices should be reflective of the intended exercise duration and intensity, as well as climate considerations. For long-distance events, especially those in challenging climates, some research suggests hydration practices begin the day prior to the event to ensure proper hydration. Although the primary goal is hydration via water sources, long distance events may require some incorporation of electrolytes to replace those most likely to be lost during exercise.
- During exercise: 6 – 12 ounces every 15 to 20 minutes, depending on the athlete's tolerance.
During exercise, the primary goals for nutrient consumption are to replace fluid losses and provide carbohydrate (30 – 60 grams/hour) to maintain blood glucose levels. These guidelines are especially vital for: endurance events lasting longer than an hour; athletes who have not consumed adequate food or fluid before exercise; or training sessions in extreme environments (i.e., heat, cold, altitude). If fluid balance cannot be maintained (i.e., loss is greater than amount replenished), the maximum amounts that can be tolerated should be ingested.
- Re-hydration following exercise should include fluid replenishment to replace sweat losses during training. Sweat rates vary depending on body size, exercise intensity, ambient (air) temperature, humidity, and acclimation. An athlete should drink at least 16 – 24 ounces of fluid for every pound of body weight lost during exercise. In addition to water, sweat also contains substantial amounts of sodium, modest amounts of potassium, and small amounts of minerals such as iron and calcium.
In most cases, athletes do not consume enough fluids during exercise to balance fluid losses, often completing their workout dehydrated to some extent. Some studies suggest drinking 150% of the weight lost during exercise may be necessary to cover the fluid lost from sweat plus urine production that will increase following fluid replacement after activity. Since most commercially available sport drinks do not include sodium levels equal to those lost during distance events, a typical American diet (i.e., high in sodium) combined with water consumption may be the best electrolyte-replacing strategy.
Special conditions that warrant attention for hydration and re-hydration practices are hot and humid environments where heat may not be dissipated efficiently through sweat or increased skin temperature evaporation. Cold environments do not yield as many cases of dehydration as hot climates, but it does occur most generally due to respiratory fluid and sweat loss that may be high if insulated clothing is worn during intense exercise. In addition, if the athlete feels chilled and available fluids are cold, the incentive to drink may be reduced. Altitude training also has an effect on hydration/dehydration status; attention should be paid to proper hydration when training in high altitude conditions.
Worth noting: Electrolyte drinks, although incredibly well marketed, often contribute unnecessary calorie intake and increased sugar levels for the recreational runner/athlete. There appears to be limited physiologic need to replace electrolytes during a single exercise session of moderate duration (less than 3 – 4 hours), especially if the participant's diet contains sufficient sodium. Additionally, electrolyte-laden fluid sources are not always necessary for everyday exercise sessions, especially those shorter than 1 – 2 hours in duration.
Nutritional Considerations for Men & Women
According to past research, nutritional considerations for training do not differ drastically between male and female athletes; however, it's important to note that the vast majority of scientific studies on athletes have used males under the assumption that principles applying to men are similar to those for women. New gender-specific studies are emerging every day, but many of those that serve as hallmark studies or the basis for additional research are based on the male athlete.
The largest disparities in research relative to gender and sports nutrition have been concerning protein requirements and carbohydrate loading – some studies have suggested that women are unable to super-compensate (i.e., "carbo load") muscle glycogen like their male counterparts. Some data has indicated menstrual status of female athletes may affect glycogen storage, with greater storage occurring during the luteal, rather than follicular phase.
For athletes that participate in both endurance events and strength activities, a general range of 1.2 – 1.7 g/kg is suggested. Although no study has specifically calculated protein requirements for elite female athletes, nitrogen balance data implies that the requirements for women are about 25% lower than those for men (1.2 – 1.3 g/kg/day). Female athletes prove to be at the greatest risk for low bone mineral density (BMD) if: energy intakes are low, dairy products are eliminated from the diet, and menstrual dysfunction is present. In addition, a great number of female athletes have been diagnosed as having iron deficiencies/anemia.
Vegetarian athletes may be at risk for low energy, protein, and micronutrient intakes due to their high consumption of low-energy-dense foods, as well as the elimination of meat and dairy from their diet. This dietary lifestyle does not imply that vegetarians cannot achieve adequate nutrition for training and endurance sports. Rather, as with any other variation in diet, special attention needs to be paid to food choices that meet the energy requirements of participants' events.
Micronutrients (i.e., vitamins and minerals) do play an important role in energy production, hemoglobin synthesis, maintaining bone health, and immune function. In addition, their role in building and repairing muscle tissue following exercise is significant. Research still indicates that the current RDAs are appropriate for athletes, as well as the general population, unless advised to make modifications by a healthcare professional. Supplementation using single micronutrients is discouraged unless clear medical, nutritional, or public health reasons are present, such as the use of an iron supplement to combat iron deficiency anemia or folic acid to prevent birth defects. Many dieticians believe that the necessary vitamin and mineral intakes – even for athletes – can be achieved through diet or a daily multivitamin.
Breaking down the supplements
The B-complex vitamins (i.e., Thiamin, Riboflavin, Vitamin B-6, niacin, pantothenic acid, biotin, Vitamin B-12, and folate) perform two major functions directly related to exercise:
- Involved in energy production during exercise, and
- Required for red blood cell production, protein synthesis, and in tissue repair and maintenance.
Although there is not an overwhelming body of literature supporting a higher need for the B-complex vitamins by athletes, some data does suggest that an athlete may need twice the amount as the average person. If you are a fan of B-complex vitamins, make a point to monitor where this type of research is heading.
The primary minerals low in the diets of athletes – especially female athletes – are calcium, iron, and zinc. Low intakes can often be attributed to energy restrictions or avoidance of animal products such as meat, fish, poultry, and dairy.
- Calcium is important for:
- Building and repair of bone tissue, and
- Maintenance of blood calcium levels.
Inadequate dietary calcium increases the risk of low bone mineral density (BMD) and stress fractures.
- Vitamin D is required for:
- Absorption of calcium,
- Regulation of serum (blood) calcium levels, and
- Promotion of bone health.
Beyond sun exposure and foods fortified with Vitamin D, Vitamin D must be acquired through supplementation.
- Iron's role in exercise is:
- Hemoglobin and myoglobin formation for binding oxygen in the blood, and
- Enzymes involved in energy production.
Low iron levels have not been shown to negatively impact athletic performance, but in situations where low iron levels progressed to chronic iron deficiency anemia, exercise performance has been hampered. Specifically, chronic iron deficiency anemia does not allow for adequate oxygen delivery and often results in fatigue and/or an increase in exercise recovery time.
Poor and/or loss of iron levels can be attributed to:
- Inadequate energy intakes,
- Avoidance of meat, fish, and poultry containing iron in the readily available heme form,
- Vegetarian diets with poor bioavailability, and
- Sweat, feces, urine or menstrual blood.
Based on the majority of micronutrient research that has been conducted, a balanced diet is the best weapon against vitamin and mineral deficiencies. If a low level of a certain micronutrient is suspected, most data supports the simple incorporation of a daily multivitamin to remedy the situation.
An international, multimillion dollar business, ergogenic aids (i.e., items claiming to increase work output or performance) prey on the desires of athletes to be the best. Currently, in the United States, manufacturers of supplements are permitted to make claims regarding the effect of products on the structure/function of the body provided they do not claim to "diagnose, mitigate, treat, cure, or prevent" a specific disease. As long as the special supplement label indicates the active ingredients and includes the entire ingredient list, claims for enhanced performance – whether valid of not – can be made.
Evaluating nutrition-related ergogenic aids requires significant research by the consumer – know there is a difference in placebo-controlled scientific studies versus mainstream media ads, sales associate at a local supplement store, and/or TV testimonials. A number of sporting associations (i.e., NCAA, US Olympic Committee, etc.) have discouraged or banned the use of many supplements or ergogenic aids that appear questionable or potentially dangerous to the health of athletes. Some health care professionals discourage the use of all ergogenic aids, though others suggest they be used with caution and only after careful examination of the product for safety, efficacy, potency, and legality. Athletes considering using a specific supplement or ergogenic aid should discuss the use of the product with a qualified nutrition or health professional, especially if the athlete currently uses any medication or other supplements.
The fundamental differences between an athlete's diet and that of the general population are the additional fluid requirements needed to cover sweat losses and energy for fueling physical activity. Incorporation of carbohydrates to improve muscle glycogen storage, along with protein balance to ensure tissue repair and recovery are important considerations. Before committing to the financial investment of expensive supplements or ergogenic aids, speak with your doctor or a registered dietician to find the appropriate nutritional combination for you.
Want help wading through the volumes of material available on nutritional topics for athletes? A registered dietician who specializes in sports nutrition can help athletes to create, and then maintain a healthful diet during training and competition.
For more information about nutrition and athletic performance or other sports medicine topics, call the Aurora Sports Medicine Hotline™ at (414) 219-7776 or (800) 219-7776.