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Nutrition and Athletic Performance

Chalk talk

Part 2 of 3

Elaine Gonya, Licensed Athletic Trainer
Aurora Sports Medicine Institute

The first installment of this three part series on nutrition and athletic performance included a review of literature relative to the roles, types and sources of protein specific to training and recovery. In this edition, energy requirements for athletes, training diets, and a brief introduction to carbohydrate consumption will be addressed. Part 3 will examine hydration, dietary supplements, ergogenic aids, and nutritional considerations for male and female athletes.

Energy requirements during training

Meeting energy needs is of utmost importance for athletes during training and competition. Achieving energy balance is necessary for the maintenance of lean body mass, immune and reproductive function, and optimal athletic performance. Energy balance is defined as a state when energy intake (the sum of energy from food, fluids, and supplemental products) equals energy expenditure (the sum of energy expended as basal metabolism, the thermic effect of food, and any voluntary physical activity). Inadequate energy intake compromises both performance and the benefits associated with training.

Energy expenditure is influenced by age, heredity, sex, body size, lean-body mass and the intensity, frequency and duration of exercise. Although some research has supported energy intake values for male endurance athletes ranging from 3000-5000 kcal/day, a precise equation still remains to be identified. As a rule, an athlete needs to consume enough energy to maintain appropriate weight and body composition while training. Despite the energy demands present in highly trained female athletes – amounts that can mirror the caloric needs of their male counterparts with similar body composition – some women consume less energy than they expend. This low-energy intake can lead to weight loss, disruption of reproductive function, and impaired athletic performance. Training diets exhibiting these symptoms are often noted with caloric intakes of 1800-2000 kcal/day.

Training diets and the introduction to carbohydrate incorporation

During times of high physical activity, energy and macronutrient needs (i.e., carbohydrates, protein, and fat) must be met in order to maintain body weight, replenish glycogen stores, and provide adequate protein for the building and repair of tissue. Fat intake should be sufficient to provide essential fatty acids and fat-soluble vitamins. In addition, diets should supply moderate amounts of energy from fat (i.e., 20-25 percent). Interestingly, there appears to be no health or performance benefits from consuming a diet that yields less than 15 percent of its energy from fat as many magazines in the grocery stands may suggest.

Consuming adequate food and fluid before, during, and after exercise can help maintain blood glucose during exercise, maximize exercise performance, and improve recovery time. Before exercise, a meal or snack should:

  1. Provide sufficient fluid to maintain hydration,
  2. Be low in fat and fiber to help with allowing the stomach to digest food and empty efficiently,
  3. Include a substantial carbohydrate source for maintaining blood glucose levels during training, and
  4. Contain moderate protein content.

Always an important rule for runners, choose foods that are familiar and well tolerated before and during training.

The fundamental differences between an athlete's diet and that of the general person are the additional fluids and energy sources needed for covering sweat losses and fueling training activities. Pre-exercise meals have been shown to improve performance much more so than fasting before exercising. The size of the meal or snack and the timing of intake are two important factors to consider. Since most athletes do not like to train or compete on a full stomach, incorporating smaller meals closer to event time can allow for digestion and stomach emptying. Larger meals should be consumed three to four hours before training sessions with carbohydrate composition being 200-300 grams of the meal. Just as runners are particular about clothing or preferred running shoes, pre-event and event "meals" should be tailored to each athlete's needs to include substances that digest easily, as well as food sources that do not cause gastric distress.

Most data does not support food or carbohydrate consumption as being beneficial during events lasting less than one continuous hour. For longer events, hydration is advisable, usually in fifteen-to-twenty minute intervals. Many studies suggest consuming water during the initial phases of a long workout/event, introducing carbohydrate supplementation forty-five minutes to one hour into the training/event, and then continuing carbohydrate and fluid supplementation for the duration of the exercise. For longer endurance events, consuming 0.7 grams of carbohydrate/kg of body weight per hour (30-60 grams) has been shown to extend performance endurance. Additional information on carbohydrate loading (glycogen super compensation) can be accessed on the Aurora Sports Medicine Institute's website under the "Chalk Talks" listing.

The timing and composition of the post-event meal/snack depends on the length and intensity of the training session – specifically, the occurrence of glycogen depletion – and the determination of when the next high-intensity training session will take place. Consumption of carbohydrates beginning immediately after exercise is still standard practice for athletes (1.5 grams of carbohydrate/kg of body weight at two hour intervals), especially if another training session is scheduled within twenty-four hours. Recovery following a longer event without a future high-intensity scheduled workout is usually achievable when consuming a normal diet in the first 24 hours. The type of carbohydrate selected after an event can also affect post-event glycogen synthesis. Simple sugars – glucose and sucrose – appear to be equally effective after exercise, while fructose is less efficient at improving blood glucose levels. A number of studies advocate post-event refueling that includes a balance of carbohydrate, protein, and fluid replenishment to assist in muscle protein repair, rehydration, and glycogen restoration.

Summary

Training diets should be individually planned and based on the athlete's tolerance to food sources, specific training goals, and nutritional needs. Compared to athletes who train/compete in events lasting longer than one hour, participants in shorter distance/duration training and events should not be concerned with carbohydrate loading.

Training diets should allow athletes to maintain a functional and consistent weight with adjustments made if excessive weight loss/gain occurs. More important than isolating specific food groups, the athlete's diet should be well balanced and tailored to the event for which the person is training. For resistance training, a mild increase in protein is advisable, whereas runners may find greater nutritional benefits from hydration and consistent carbohydrate consumption. Any changes or experimentation with diet should be done during training, and not before or during an event. Before you lace up your training shoes and hit the road, take time to stock up on some healthy "running" foods – your body will thank you.

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.