Ask a Cycling Coach Podcast - Presented by TrainerRoad · TrainerRoad

KETO AND LOW CARB FOR CYCLISTS | Dr. Kyle Pfaffenbach | Ask a Cycling Coach 535

·1 hr 14 min·7 clips

Dr. Kyle Pfaffenbach reveals why your body will always choose carbs over fat for high-intensity efforts, no matter how fat-adapted you are.

This episode features Coach Jonathan Lee and Dr. Kyle Pfaffenbach, a professor and elite running coach, examining low-carb and ketogenic diets for cycling performance. They address a listener's question about combining low-carb eating with high-intensity training, noting the common focus on carbs for performance versus low-carb for health. The hosts clarify the discussion will center on athletic performance, not general longevity. Coach Jonathan Lee shares his personal experience trying keto and low-carb diets for extended periods before returning to a higher-carb approach. He references studies from researchers like Louise Burke and older work from Phinney, finding no consistent performance benefit in systematic reviews. The core finding is that while low-carb diets increase fat oxidation, this does not reliably translate to improved endurance performance. Dr. Pfaffenbach explains the biochemical hierarchy where the body preferentially uses carbohydrates when available, even in fat-adapted individuals. He details the metabolic pathways, comparing fat's slow, oxygen-dependent process to carbohydrate's faster, more pliable energy system. A key insight is that glycogen's branched structure allows rapid energy release, unlike fatty acid chains which are broken down two carbons at a time. The discussion notes that fat metabolism cannot support anaerobic efforts, limiting high-intensity surges. Dr. Pfaffenbach uses an analogy comparing fat fuel to an efficient Honda Civic and carbohydrate fuel to a high-power Bugatti. He emphasizes the body adapts to specific stresses, but not always in the assumed or desired way for performance. The hosts discuss how individual responses vary, with some people adapting to fat burning quickly, but this adaptation has a ceiling for power output. For practical application, Dr. Pfaffenbach advises against using calorie percentages for macros, instead recommending fixed protein and fat intakes based on body weight. With his athletes, he adopts an "offensive" carbohydrate strategy, focusing intake before and during key workouts. The tone is deeply educational and conversational, with Dr. Pfaffenbach offering a detailed, "magic school bus" style walkthrough of cellular biochemistry. The style is explanatory, using analogies to make complex metabolic concepts accessible to athletes. Cyclists and endurance athletes interested in the science of fueling and performance nutrition would find this episode highly valuable. Listeners seeking a simple endorsement of low-carb diets for athletic gains or those uncomfortable with detailed biochemical explanations might choose to skip it.

As heard by us

A steady look at low carb and hard training, with a focus on how the body adapts.

The episode frames a familiar cycling nutrition question in practical terms: where low carb fits, where it does not, and what changes when training intensity goes up. Dr.

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