#130 - "Contextualising Fat Oxidation During Exercise" with Ed Maunder PhD(c)
Feb 19, 2020
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In this episode, Ed Maunder PhD(c) discusses contextualising fat oxidation during exercise. Topics include defining and differentiating fat oxidation and fat burning, substrate oxidation during endurance exercise, testing methods for maximal fat oxidation, relevance to exercise performance and a case study on Ironman triathlon. The chapter descriptions highlight the importance of fuel utilization, customizing exercise protocols, and optimizing substrate utilization in triathlon training.
Exercise intensity affects the body's utilization of fat and carbohydrates as fuel sources.
Maximal fat oxidation may not be the most important metric to focus on for endurance athletes.
Preserving carbohydrate stores and enhancing fat metabolism are crucial for optimal performance in Ironman triathlons.
Deep dives
Overview of the podcast episode
This podcast episode features an interview with guest Ed Monda, a researcher in heat stress and endurance athletes. The conversation explores the topic of fuel utilization and substrate metabolism in endurance sports. The host and guest discuss the relationship between exercise intensity and fat oxidation, highlighting that fat oxidation increases at low intensities and decreases at higher intensities, while carbohydrate metabolism shows a linear increase with exercise intensity. They also touch on the differences between intramuscular and peripheral fat stores, emphasizing that longer duration exercise leads to a shift in fat and carbohydrate utilization. The discussion further delves into the challenges of accurately determining an individual's fat-burning zone and the importance of considering overall energy balance for weight and fat loss.
Maximal fat oxidation and its relevance
The concept of maximal fat oxidation is explored in the context of endurance training and performance. The guest suggests that in most individuals, it is not the most important metric to focus on, as it can be influenced by training and fitness level. The emphasis is placed on structured endurance training to improve overall fat oxidation and create an energy deficit for weight and body fat loss. It is noted that serial testing over time can provide useful information on an athlete's metabolic characteristics and adaptations.
Substrate metabolism in Ironman triathlons
The podcast delves into the specific context of Ironman triathlons and the differences in substrate metabolism among athletes of varying performance levels. The conversation challenges the polarized debates around low-carb high-fat diets versus carbohydrate-based diets for Ironman events. The guest and host propose that the metabolic demands of winning an Ironman versus completing it without stopping can vary significantly. They suggest that estimating energy expenditure based on swim time, cycling power, and running time can help characterize the metabolic requirements of different performance standards in Ironman triathlons.
Understanding Fuel Utilization in Endurance Exercise
During endurance exercise, the body utilizes both fat and carbohydrates as fuel sources. The combustion of these fuels depends on various factors such as exercise intensity and training status. At lower exercise intensities, the body predominantly uses fat for energy, while at higher intensities, carbohydrate oxidation becomes more dominant. Training can increase the body's ability to utilize fats as an energy source, but even well-trained athletes still rely on carbohydrates during intense exercise. In events like Ironman triathlons, preserving carbohydrate stores is crucial for optimal performance, and carbohydrate ingestion during the event is often necessary, even for athletes with high rates of fat oxidation.
Fat Oxidation Testing and Strategies
Fat oxidation can be assessed using tests like the Fatmax test, which measures the rate at which an individual can burn fat during exercise. However, it is important to note that the specific numbers obtained from these tests should not be overinterpreted. Instead, they provide a useful tool for understanding an athlete's physiology and informing interventions that may enhance performance. Strategies to manipulate fat metabolism may vary depending on the performance level and the demands of the sport. For longer endurance events, like Ironman triathlons, fat oxidation plays a significant role, and interventions to enhance fat metabolism, along with the preservation of carbohydrate stores, are recommended. However, the precise periodization of carbohydrate intake and the interaction between fat and carbohydrate metabolism are still emerging areas of research, requiring cautious interpretation and individualized approaches.
Episode 130 of the Institute of Performance Nutrition's "We Do Science" podcast! In this episode, I (Laurent Bannock) discuss "Contextualising Fat Oxidation During Exercise" with Ed Maunder PhD(c) (Sports Performance Research Institute New Zealand, Auckland University of Technology, Auckland, New Zealand).
Discussion Topics Include:
Defining and differentiating "fat oxidation" and "fat burning"
Fat as a "fuel" for exercise: storage and metabolism
Substrate oxidation (fuel use) during endurance and ultra-endurance exercise
Substrate availability and performance: a case for optimising maximal fat oxidation?
Testing methods to determine maximal fat oxidation (FatMax) and its value to inform performance nutrition strategies
Maximal fat oxidation: what we know, don't know, and what's relevant to elite and recreational endurance athletes
Relevance to exercise performance: substrate utilisation during Ironman triathlon case study discussion
Episode 130 of the 
