Most susceptible are competitive runners, who maintain a high training workload but maintain the mindset of the sedentary. These athletes are too stringent in their portion control and consequently live in a chronic state of mild undernourishment. This hinders their performance, if not their health.
Several clinical sports nutritionists I know tell me they help their endurance athlete clients perform better by increasing their food intake, more often than by reducing it. This is especially true, they say, with their female clients.
More: How to Fuel Your Runs
A Case Study
My friend Paul Goldberg, the strength and conditioning coach and team dietitian for the Colorado Avalanche—who also works with individual clients at a facility in Evergreen, Colorado—describes one such case:
Stephanie was a 24-year-old recreational triathlete when I started working with her. She was already fit and healthy, with solid dietary habits and a low, 16 percent body fat measurement.
Her one complaint was that she experienced a lack of energy that afflicted her training. I looked into the timing of her meals and quickly saw that she wasn't getting enough calories before and during her workouts to fuel performance, nor after workouts to speed her body's recovery from training. So we moved roughly 300 total calories from her lunch and dinner and added them back during and after her training sessions.
After two weeks on this regimen, Stephanie came back to me and reported that she felt better during training and had even lost two pounds and one percent body fat. However, she now felt especially fatigued in the evening.
After giving this information some thought, I came to the conclusion that Stephanie's body probably adapted to the poor nutrient timing of her past regimen by slowing her metabolism during and after workouts (by capping her muscles' rate of energy use), which is probably why she felt lethargic in training.
When we started fueling her workouts and recovery processes better, her body started burning all of the extra energy during her training (enabling her to perform better) as well as during the post-workout recovery period. But this left her in a state of energy deficit during the rest of the day, which is why she lost weight and felt fatigued late in the day.
So, we added the 300 calories back to her lunch and dinner without removing them from the workout period. And what happened? She felt great during her training and all day in fact, but she lost another two pounds in the next two weeks, as well as another one percent body fat.
My final conclusion was that Stephanie wasn't able to work to her full metabolic capacity due to poor nutrient timing and a slight but significant energy deficit. Two years later, she still feels great and remains at 16 percent body fat.