#32 - Carbohydrate metabolism during exercise with Dr Mark Hargreaves
Jan 29, 2023
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Dr Mark Hargreaves, leader in exercise metabolism/physiology, discusses the effects of muscle glycogen availability and carbohydrate ingestion on exercise metabolism and performance. Topics include high fat/ketogenic diets, personalized management, continuous glucose monitors, heat and glycogen metabolism, fatigue when consuming carbohydrate during exercise, and the impact of excess carbohydrate and fat.
Carbohydrate availability and intake can impact glucose uptake, glycogen utilization, and exercise performance.
Excess intake of carbohydrates or fats can have negative consequences and may affect insulin sensitivity differently.
Balancing fluid intake with electrolyte needs is crucial, considering individual factors such as sweat rate, intensity, and duration of exercise.
Deep dives
The importance of carbohydrate metabolism and exercise
Carbohydrate metabolism is crucial for exercise performance. Muscle glycogen is the primary fuel source during exercise, while blood glucose plays a role in muscle function and brain metabolism. As exercise intensity increases, the reliance on carbohydrate fuels also increases, leading to a reduction in fat utilization. However, there is a limit to how high exercise intensity can rely on fat oxidation. Studies have shown that manipulating carbohydrate availability and intake can impact glucose uptake, glycogen utilization, and exercise performance. While there may be adaptations in metabolism that allow for increased fat burning at lower intensities, there are challenges to maintaining carbohydrate oxidation on high-fat diets during higher intensities. It is important to consider individual responses and context when determining the optimal carbohydrate and fat intake for exercise.
The complexity of nutrient interactions during exercise
The effects of carbohydrate and fat intake during exercise go beyond energy substrate utilization. The type and source of nutrients, as well as individual responses, play a role in overall health and performance. Excess intake of carbohydrates or fats can have negative consequences and may affect insulin sensitivity differently. Additionally, the quality and processing of foods contribute to their impact on metabolism. Balancing nutrient intake, considering whole foods, and personalizing nutrition approaches are essential. While studies have explored the interactions of nutrients, the complexity of individual responses and long-term health outcomes necessitates ongoing research.
Considerations for fluid and electrolyte intake during exercise
Fluid and electrolyte intake during exercise is important for hydration and performance. While electrolytes play a crucial role in fluid balance, their optimal levels depend on the individual and activity. Studies have shown that excessive fluid intake without the need for rapid rehydration may lead to hyponatremia. Balancing fluid intake with electrolyte needs is crucial, and individual factors such as sweat rate, intensity, and duration of exercise should be considered. Additionally, understanding the limitations of laboratory studies and the physiological differences between ingesting single nutrients versus whole foods is key in interpreting research findings and optimizing fluid and electrolyte intake during exercise.
Carbohydrate availability and glycogen depletion influence exercise performance
Carbohydrate availability, particularly muscle glycogen, is crucial for intense exercise. This applies not only to elite athletes but also to individuals engaging in high-intensity workouts. However, individual factors such as exercise intensity, duration, and recovery time should be considered when applying general recommendations. Changes in carbohydrate metabolism can be achieved through dietary modifications, and an excess of carbohydrates or fats may have both benefits and downsides. It is important to strike a balance and be aware of the body's response to nutrient excess. Additionally, the complexity of human performance and fatigue suggests that significant changes in metabolism do not always translate into meaningful performance improvements. The scientific process takes time, and while social media platforms like Twitter demand quick answers, scientific understanding evolves gradually.
The role of glute for expression and the influence of exercise
Understanding the regulation of glute for expression has been a focal point of research in recent years. Studies have explored how a single bout of exercise and training impact glute for expression in muscle tissue. The complexity of glute for regulation extends beyond muscle tissue, with potential implications for adipose tissue as well. Evidence suggests that individuals with type 2 diabetes may have lower glute for expression in adipose tissue. However, the relationship between glute for and insulin resistance is not straightforward, and more research is needed. Acute exercise has been found to increase glute for expression in muscle tissue, but the same response is not consistently observed in adipose tissue. The mechanisms underlying exercise-induced changes in glute for expression are actively studied, with ongoing research focusing on histone modifications and the role of specific proteins. Overall, glute for plays an important role in glucose uptake and signaling, but its regulation is multifaceted and still not fully understood.
Dr Glenn McConell chats with Professor Mark Hargreaves from the University of Melbourne in Australia. He is a leader in exercise metabolism/physiology and was Glenn’s PhD supervisor. The discussion centred around the effects of muscle glycogen availability and carbohydrate (CHO) ingestion on exercise metabolism and also performance/fatigue. There was also discussion of high fat/ketogenic diets, GLUT-4, the central nervous system and the effect of the volume of fluid ingested with and without addition of electrolytes.
0:00. Introduction and Mark’s beginnings in exercise research
9:10. Effect of exercise intensity on the fuel mix used
12:27. High fat/keto diets and exercise metabolism/performance
16:10. Hazards of too much fat or too much carbohydrate
Also, what type of dietary fat and what type of dietary carbohydrate matters.
18:40. Need personalized management of people
21:05. Hard to keep muscle glycogen low
24:32. Continuous glucose monitors
25:30. Why use more glycogen during ex than need if start high?
27:00. Heat and glycogen metabolism
28:26. Why fatigue when consuming carbohydrate during ex?
31:50. Carbohydrate ingestion and liver glucose output
33:30. High doses of carbohydrate ingestion during exercise
38:00. Need increased CHO availability if ex less than an hour?
41:25. Repeated sprints and glycogen etc
43:05. Resynthesis of glycogen during low intensity exercise?
47:12. Both excess CHO and excess fat can cause problems
52:35. Caffeine vs coffee and metabolism
53:40. Rehydration with meals vs special solutions
54:25. Fluid ingestion and electrolytes
59:10. Glycogen and AMP-activated protein kinase (AMPK)
1:00:50. Mark’s current senior academic position
1:02:47. Mark’s “photographic memory” and the literature
1:04:39. Exercise and GLUT-4 expression
1:09:00. Muscle GLUT-4 normal in muscle in T2D
1:10:23. Takeaway messages
1:14:34. Outro (9 secs)
Inside Exercise brings to you the who's who of research in exercise metabolism, exercise physiology and exercise’s effects on health. With scientific rigor, these researchers discuss popular exercise topics while providing practical strategies for all.
The interviewer, Emeritus Professor Glenn McConell, has an international research profile following 30 years of Exercise Metabolism research experience while at The University of Melbourne, Ball State University, Monash University, the University of Copenhagen and Victoria University.
