Ellie was a 23-year-old professional triathlete who was preparing for the Ironman 70.3 World Championships in 2016. Like many athletes, Ellie believed she could improve her race performance by refining her body composition and pre-race fuel strategy. Both of these goals meant she’d need to change her diet. Ellie was unsure of how to do this without hurting her training or her taper for the big day.
Ellie posed this challenge to Ryan Kohler, manager of sports performance at the University of Colorado Sports Medicine and Performance Center. Kohler had already worked with Ellie for 1.5 years and knew she possessed disciplined eating habits.
How does an elite athlete refine her diet without impacting performance?
The two needed to devise a hyper-focused diet that maximized glycogen stores leading up to her race, without negatively impacting body composition or weight. The pair also needed to determine the appropriate timing and amount of carbohydrates to include in her diet, while allowing for her caloric needs and adjusting for her taper.
“It was just a matter of including additional objectives to focus her nutrition around specific times of the season,” Kohler says.
Kohler and his team initially performed a skinfold body-composition measurement and gathered body weight and food-log information. Then, they used MuscleSound software to accurately and non-invasively determine Ellie’s stored carbohydrate. MuscleSound was co-developed by Dr. Iñigo San Millan, the director of the Performance Center and a prominent physiologist with decades of experience working with professional cyclists.
It works in conjunction with a portable ultrasound device to calculate relative glycogen concentration, tissue thickness, body fat percentage, and lean mass. It does this by automatically detecting fat-muscle boundaries. If you imagine your muscles as fuel tanks, the ultrasound allows you to see how much gas is in the tank.
The rectus femoris muscle was used as the measurement site. Studies in endurance athletes have shown this muscle provides a good assessment of lower-body storage, and can reflect small to large changes due to nutrition, training, or recovery interventions.
The MuscleSound test revealed Ellie was approximately 70 percent “full,” meaning she was adequately storing carbohydrates for her daily training needs, and she had additional room to super-compensate — in this case for the priority event.
Kohler prescribed a carb-rich diet, slightly above what Ellie was accustomed to eating. She tried the new meal plan for one week, and combined specific food suggestions. For example, she ate things such as oats, yogurt, and egg whites for breakfast; lunch might include a deli sandwich and salad; and dinner could be fish, sweet potatoes, and broccoli.
Then, Ellie spent a week eating whatever she wanted, so long as it supported her training, was low in fat, and allowed for maximal carbohydrate storage. She ate 2,600 kilocalories per day, broken down into six grams per kilogram of carbohydrates and 1.7-1.9 grams per kilogram of protein.
Ellie maintained her total caloric intake (while reducing fat intake) by consuming additional calories from (1) carbohydrates, to support training and provide additional substrate for glycogen re-synthesis; and from (2) protein to support recovery and increase satiety in the absence of additional fat. Kohler focused the timing of Ellie’s carbohydrate doses to provide the additional energy when necessary.
Ellie followed the experimental diet for one week. Then her glycogen stores were retested under the same conditions. The ultrasound revealed that her proverbial fuel tank was at 90 percent of its glycogen capacity (which Kohler considered to be near the maximum attainable), and she reported having increased energy levels. Over the one-week trial, Ellie also experienced a one percent decline in body weight and five percent decline in body composition.
Because the test was conducted five weeks prior to worlds, Kohler returned Ellie to her usual training diet to allow carbohydrate levels to return to normal.
The week before her big race, Ellie went back on the carb-rich diet. She finished 11th at the world championships.