Last year, both Jill Castle and I wrote about athletes adopting ketogenic diets by severely restricting carbohydrates and protein and eating a very high fat diet for performance:

High-Fat/Ketogenic Diet: Love It or Lose It?

Top Reasons Swimmers Should Forego a Ketogenic Diet

Since that time, the ketogenic diet is still gaining traction with some coaches, trainers and athletes. And, a major sports nutrition company promotes a “ketogenic” diet with a meal replacement line for those athletes who have hopped on the ketogenic bandwagon.

In October, I attended the Academy of Nutrition and Dietetics Food & Nutrition Conference & Expo in Boston. One of the sessions featured John Hawley speaking on promoting endurance training adaptation in skeletal muscle by nutritional manipulation. Dr. Hawley is head of exercise and nutrition research at Australian Catholic University in Melbourne, and is one of the leading sports nutrition researchers in the world. I was interested to hear what he had to say about ketogenic diets as a nutritional strategy for athletic performance. 

First, Dr. Hawley laid out how training and the timing of feeding affect muscle adaptation. Using sophisticated laboratory techniques, researchers are gaining a better understanding of how periodized nutrition signals muscle to get bigger, stronger, and use carbohydrate and fat as fuels to power endurance exercise. Here are some the highlights of his presentation:

• One size doesn’t fit all when it comes to nutrition; athletes don’t need a high carbohydrate diet all of the time. An athlete’s daily training load (intensity + duration) should determine how much carbohydrate should be consumed. Stay tuned for my January column where I will lay out a generic meal plan for swimmers, showing how much carbohydrate is needed on heavy training days and when to eat carbs.
• Training without carbohydrates over a period of time can hurt the muscle’s ability to use glycogen (stored carbohydrate.). So instead of being “glycogen sparing,” (as proponents of ketogenic diets insist) it is in fact “glycogen impairing.”
• Based on research in his lab, athletes who follow ketogenic diets have reduced power output and report an increased rate of perceived exertion. In other words, their muscles produce less power and it feels harder to exercise.
• When muscles are needed to produce quick powerful movement (think a kick to the finish or sprint swimming) they need carbohydrate.
• High fat, low carbohydrate diets reduce the economy of movement and impair performance.

Swimmers should focus on eating a variety of healthful foods that have been proven to be part of a performance-enhancing diet. Timing meals and snacks around training sessions can help the muscle adapt to make you a better athlete.

Chris Rosenbloom is a registered dietitian, certified specialist in sports nutrition, and professor emerita of nutrition at Georgia State University. She welcomes questions from swimmers, parents and coaches. Email her at chrisrosenbloom@gmail.com.