Proper nutrition helps an athlete produce and utilize energy more efficiently. Furthermore, a sound nutrition program will help prevent nagging injuries that can interfere with training.

Recently, I completed full nutritional analyses on a group of 25 competitive athletes, including elite-level distance runners (12 males, 13 females), to see what nutritional deficiencies existed. The purpose of this research project was to determine the overall metabolic efficiency and adequacy of a runner's diet in relation to the high demands of the sport and the recommendations specified by National Research Council.

The following three surprising discoveries were made:

1. The runners weren't eating enough.

Runners, especially those training for the marathon and beyond, expend extraordinary amounts of energy -- in some cases over 4,500 calories a day. In fact, the energy needs per pound of body weight are amongst the highest of any endurance sport; it's estimated that runners require 16-30 calories per pound of body weight, an amount dependent on time spent running per day.

The calculated needs for the runners in this study were 21 calories per pound of body weight based on the mean calculated daily energy expenditure of 3,105 calories (see below). In contrast, the average energy intake of these runners was only 2,392 calories, over 700 calories short!

Energy intake vs. energy expenditure in runners Gender Calorie intake Calorie expenditure Female 2,007 2,794 Male 2,810 3,441

While a 700-calorie imbalance is suggestive of a 1- to 1.5-pound loss per week, very few of the runners were actually losing weight. Why? The human body has an ability to adapt to a lower level of energy intake, allowing for preservation of weight despite a calorie shortage. Unfortunately, this means the body is less efficient at using the calories and nutrients consumed during training. A lack of calories also depresses immune function, making the athlete more vulnerable to illness and injury during intensive training.

So, it's feasible to conclude that these runners would perform at higher levels if they consumed an additional 700 calories. For those runners who want to lose weight during training, a calorie deficit of 250-500 calories a day is more appropriate.

Solution: Based on approximately an hour of running a day, runners should consume 21 calories per pound of body weight each day.

2. The runners weren't consuming enough carbohydrates

There's a plethora of sound research showing the profound performance benefits associated with high carbohydrate intake, including optimal mental functioning, muscle glycogen saturation, enhanced fat burning, protection against protein/muscle breakdown and improved immune function, so it was surprising to find these runners were only consuming 69 percent of their daily carbohydrate needs (see below).

Mean carbohydrate intake vs. mean carbohydrate goal in runners Gender Carb intake Carb goal* Female 250 grams 419 grams Male 396 grams 512 grams *Carbs goal intake was based on 60% of total goal calorie amount as determined by physical activity diary

A significant carbohydrate deficiency like this can negatively affect performance because the athlete is more vulnerable to liver and muscle glycogen depletion, increasing risk for the mental "bonk" and performance-declining "wall."

For optimal performance, athletes should try to consume 3 to 5 grams of carbohydrate per pound of body weight; the runners in this study had a calculated carbohydrate need of 3.2 grams per pound body weight.

At meals, try to fill three-quarters of every plate with carbohydrate-rich foods like fruits, starchy vegetables and whole grains; fill the remaining quarter with protein-rich foods like meat, poultry, fish, nuts and dairy products.

Solution: Based on approximately an hour of running a day, runners should consume 3.2 grams of carbohydrate per pound of body weight.

3. The runners were following erratic eating patterns

A consistent, balanced intake of nutrients throughout the day will improve metabolic efficiency necessary for peak performance. Breakfast is the most important meal of the day because it kick starts your metabolism, allowing the body to utilize fuel more efficiently. Eating every two to four hours after breakfast keeps the engine running at high levels throughout the day.

Sixteen percent (four) of the runners in this study skipped breakfast, with only 20 percent (five) actually eating in two- to four-hour increments. Furthermore, the majority of runners weren't balancing out their plate properly, ultimately leading to waning energy levels during the day.

So which foods should you choose for meals and snacks? There's a term in the field of sports nutrition that all runners should become familiar with: glycemic index. Glycemic index refers to how quickly foods enter and leave the bloodstream. High-glycemic foods enter the bloodstream rapidly, giving a quick energy boost, but they also leave the bloodstream rapidly, causing reduced energy levels and increased cravings.

In order to prevent the quick drop in energy levels, consume high-glycemic foods with protein. For example, have rice -- a high glycemic food -- with beans -- a protein-rich food with a low-glycemic value. Another example: Mix a banana into yogurt.

Moderate-to-low glycemic index foods should be consumed on a more consistent basis due to their ability to sustain energy levels and overall metabolic efficiency for longer periods of times. See below for a listing of glycemic indices for common foods, or visit http://www.glycemicindex.com/ for more information.