Nutrition and Athletic Performance
Part 1 of 3
Elaine Gonya, Licensed Athletic Trainer
Aurora Sports Medicine Institute
If you are like the majority of runners on the road today, you've probably been overwhelmed by the never-ending siege of nutrition-related articles published. What information has actually been clinically proven? How do you know what to believe when so many articles seem to conflict with one another?
The first step is to understand that the science of nutrition is ever evolving, and new research occasionally emerges to add to the confusion that already exists. The next three issues of the Badgerland Striders' Newsletter will present a review of some of the most recent nutrition studies conducted. These articles will examine current studies on the role of protein in training and recovery; a brief assessment of the contributions of a training diet including carbohydrate consumption, hydration, nutritional considerations for men and women; along with dietary supplements and ergogenic aids.
It is the position of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine (2009) "...that physical activity, athletic performance, and recovery from exercise are enhanced by optimal nutrition". These organizations recommend appropriate selection of food and fluids; timing of intake; and supplement choices for optimal health and exercise performance.
Protein has become one of the most publicized nutrients because of its ability to stimulate muscle protein synthesis, thereby increasing muscle development. Beyond muscle growth, protein has several other functions critical to sports performance: cell regulation, muscle repair, immune function, neurological function, nutrient transport, and structural support. However, a notable limitation exists relative to the vast majority of nutrition studies completed to date on protein consumption – namely, studies have primarily focused on resistance-trained or power sport athletes and not distance runners.
Protein requirements during training
Protein metabolism during and after exercise is affected by age, sex, intensity, duration and type of exercise, energy intake, and carbohydrate availability. The high volumes of training along with the training intensities realized by elite athletes result in estimated protein requirements that are nearly twice those of sedentary individuals. The Recommended Dietary Allowance (RDA) of protein for the average American is 0.8 g/kg. of body weight; guidelines for endurance athletes suggest 1.2-1.4 g/kg to improve aerobic capacity through mitochondria synthesis, as well as build muscle mass and strength. For athletes that participate in both endurance events and strength activities, a general range of 1.2-1.7 g/kg is suggested.
A quick conversion of body weight in pounds to body weight in kilograms (kg): Divide your weight (lbs) by 2.2. Using this formula, a 160 lb. runner would have a mass of 73 kg. If that same runner chose to consume 1.2 g/kg, his/her protein consumption would be approximately 88 g/day (73kg X 1.2 g).
Protein requirements have been estimated from results of nitrogen balance studies. Muscle protein synthesis occurs when a positive nitrogen balance is maintained. Although no study has specifically calculated protein requirements for elite female athletes, nitrogen balance data imply that the requirements for athletic women are about 25% lower than those for men (1.2-1.3 g/kg/day). It has been well supported from studies that most athletes will achieve these protein intake levels from an everyday diet that derives 10-15% of energy from protein.
Timing of protein intake is key
The timing of protein intake appears to be the most important factor in achieving positive training adaptations, specifically for improving recovery from intense endurance training sessions. Protein consumed after exercise will provide amino acids for building and repair of muscle tissue. Goals of post-training/event nutrition for the distance athlete should be centered on refueling, rehydration, repair and adaptation, and preserving the immune system.
During both resistance training and intense exercise bouts, muscle damage almost always occurs. This damage can be one of three types: muscle soreness that occurs 24-48 hours after activity (also termed delayed onset muscle soreness [DOMS]); acute damage from a minor or major tear in muscle fibers; or muscle soreness or cramp that happens during or immediately after exercise. The amount of muscle tissue damage may not be severe, but it does occur during and after exercise, so recovery is a very important part of training. The majority of research on protein intake timing is focused on the post-exercise period – often defined as the hour immediately following exercise. Protein consumption after exercise has been found to minimize protein breakdown, stimulate muscle protein synthesis, and therefore aid in building muscle tissue.
Types of protein
Once a topic solely for muscle magazines and power sports athletes, protein and supplementation have recently found a place in magazines that runners and multi-sport athletes pick up at local bookstores. Although many products on the market claim to be the best protein sources for athletes, research still supports dietary sources as fully sufficient to meet the needs of athletes. Some common protein sources used by athletes to enhance muscle tissue development and assist with repair after workouts are: proteins from milk, whey, soy, egg, and amino acids.
Consists of both "fast" and "slow" absorbing proteins with 80% casein and 20% whey protein. The dairy industry has long promoted the health benefits of milk but has focused mainly on the micronutrients of calcium, vitamin D, and potassium. Studies have indicated that consumption of milk protein for extended time periods after exercise appears to support lean mass building more than other types of protein. For runners and other athletes, some research does suggest post-workout consumption of milk products, specifically chocolate milk, as a means to replace vital nutrients and electrolytes (protein, carbohydrates, sodium, potassium, calcium) lost during exercise. Although inexpensive, milk sources do contain lactose, which is difficult for some athletes to break down if they have a lactose-intolerance. Additionally, some athletes report having "cotton mouth" after consumption.
Whey protein is one of the most popular (and advertised) protein supplements for athletes. Studies conducted to examine the effect of this protein during the post-exercise period of resistance-trained athletes have found an increase in muscle protein synthesis with whey protein supplements when compared to receiving a carbohydrate supplement after exercise. It's important to note that the vast majority of studies completed with whey protein have been conducted using untrained subjects, and clearly would show an increase in muscle protein synthesis.
"Fast" absorbing, whey protein leads to increases in amino acids in the blood and stimulation of protein synthesis. There is a body of research that suggests whey protein may: improve immune function; decrease cardiovascular risk; function as an antioxidant; and decrease the risk of high blood pressure. Worth noting, many whey protein supplements contain lactose and are expensive.
Soy protein is a high-quality protein that provides all of the essential amino acids needed for protein synthesis. It is available from a number of plant-derived food sources, as well as in powder form as a muscle-building supplement. Comparable to animal-based protein, soy protein is considered a "fast" absorbing protein; some literature suggests it may also reduce the risk of prostate cancer. Although soy protein may not build muscle tissue as rapidly as whey and casein, it may be a good choice for runners who are not concerned with muscle mass as much as post-exercise muscle repair and acquiring all essential amino acids.
Often considered the "perfect" food because of their essential amino acid profile and ease of digestibility, eggs contain 13 other essential nutrients. Although egg whites are fat-free and cholesterol-free, the yolk is high in cholesterol with half of the protein found in eggs contained within the yolk. Egg protein is a high-quality source of protein, but it takes four to five eggs to get the 10g of essential amino acids that appear to be needed for stimulating protein synthesis.
There is a lack of research supporting ingestion of amino acids for enhanced performance, but amino acids theoretically could provide specific substrate for needed physiological functions. Arginine produces nitric oxide needed for blood vessel dilation; Glutamine assists with immune function; and branched-chain amino acids (BCAA's) are often cited as a fuel source for endurance athletes. Leucine, which also is a large component of whey protein, has been found to stimulate signaling pathways that increase muscle protein synthesis. The largest disadvantage to consumption of amino acid supplements – beyond the lack of scientific research to support their use – is the high cost.
The effect of protein consumption on hydration
Often overlooked within the discussion of high intake of dietary protein is the effect protein consumption has on hydration and it's potential to displace carbohydrates. When an increased amount of dietary protein is consumed, athletes must spend adequate effort to rehydrate after exercise sessions. Endurance athletes that consume higher levels of protein must realize their rehydration needs are driven by both the negative effect of protein consumption, as well as fluid and electrolyte loss. All athletes should balance protein intake with sufficient carbohydrate intake and adequate fluids for peak performance.
There is still a great deal to be learned about protein and its role in sports performance. For now, there is a substantial body of literature that supports its use as a recovery aid for runners, if consumed in moderate amounts and shortly after long or intense exercise bouts. Although a great deal of money can be spent on products that may or may not work, it might just be equally wise to continue packing a peanut butter and jelly sandwich and a bottle of water in your race bag.
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.