Table of Contents

• Is Lionel Sanders right to worry about his above n …

• Gerard and Jordy Donnelly, the father-son duo behi …

• Episode takeaways:

  • References used for the MMB

Is Lionel Sanders right to worry about his above normal HgbA1C and are we as triathletes at risk for developing diabetes later in life?

The Medical Mailbag dives in to the science on carbohydrate intake, athletic performance and the risk of developing diabetes. The long and the short of it? No need to worry!

• Type 2 diabetes mellitus (T2DM) is characterized by high blood glucose (hyperglycemia) due to insulin resistance and/or β-cell dysfunction (1). 

• T2DM begins with excess blood sugar stimulating insulin production to prevent hyperglycemia, but chronic hyperinsulinemia leads to decreased insulin sensitivity and/or β-cell dysfunction leads to insulin deficiency. (1)

• Through a variety of acute and chronic mechanisms, physical activity (2, 4, 8) reduces DM risk.

• Despite this, there are anecdotes (Lionel Sanders, Peter Attia, etc.) of endurance athletes developing insulin resistance, ‘pre-diabetes’, having high A1C, etc. There is a (small n) study where this occurs even in athletes that are not consuming more than the recommended amount of carbohydrates, which is what LS attributes his prediabetes to in his video (3).

• “Indeed, it is well recognized that endurance athletes have increased lipid storage in the musculature, which is often described as a paradox as this is commonly observed in insulin-resistant subjects“ (7)

• However, long-term studies have shown that athletes have a lesser disease prevalence of T2DM and impaired glucose tolerance than controls (n=599, 392 athletes, in 5).

•  A study in 1992 found that “Trained subjects have, compared with untrained subjects, the same overall insulin secretion and average plasma glucose concentration despite a higher food intake.” The authors attribute this to adaptations in the pancreas/pancreatic β-cells and/or adaptation in insulin-sensitive tissues that allow for carb-loading without the resulting issues mentioned in bullet point 2 (6)

• Carbohydrate availability is important in athletics, and while hyperglycemia can be detrimental to health, hypoglycemia can also be detrimental to both health and performance. The authors of (7) argue that the most convincing piece of evidence from continuous glucose monitoring studies is that individuals have vastly different responses to carbohydrates and exercise (they have “highly individual glucose profiles and often spend a significant amount of time with hypo- and hyperglycemia”) (7)

Gerard and Jordy Donnelly, the father-son duo behind TriVelo and the Train Smarter, Race Faster podcast

About the Donnelly’s according to the Donnelly’s: Father/Son Duo Gerard and Jordy Donnelly run a a Triathlon Coaching podcast and program dedicated to help improve you as an athlete. If you're a triathlete competing in Ironman, Ironman 70.3 or Olympic triathlon this is for you. Gerard Donnelly is a Former Australian Ironman Champion himself and together with his son they help beginner age groupers all the way through to pro athletes perform at their best.

Gerard and Jordy Donnelly, who run Trivelo Coaching, share their wealth of knowledge about the struggles that beginner athletes face when trying to maintain consistent power output in the unpredictable outdoor conditions. They use humor to illustrate the absurdity of how challenging it can be to pedal efficiently while contending with varying terrain and elements. Their banter emphasizes that if anyone thinks this is an easy feat, they clearly haven’t experienced the trials of cycling in a triathlon. The conversation transitions smoothly into a discussion about the importance of developing a solid coaching philosophy, which centers around two core principles: improvement and enjoyment. The Donnellys stress that while striving for progress is essential, it should never come at the cost of enjoyment, and they encourage athletes to celebrate even the smallest victories along their journey.

In addition to the practical advice on cycling power, the episode touches on the broader themes of community and the coach-athlete relationship. Gerard and Jordy emphasize that building trust and accountability is crucial for athletes to thrive in the sport. They discuss the importance of communication and feedback in fostering an environment where athletes feel supported and encouraged. This dynamic is particularly evident as they recount personal experiences with their coaching clients, showcasing how recognizing progress can transform an athlete's mindset and performance.

Episode takeaways:

• Diabetes is a risk for those who are sedentary and overweight and who eat a lot of high sugar foods

• Being active and athletic is highly protective against type II diabetes

• ‘Pre-diabetes’ is not a true clinical state and merely a construct based on lab values

• There is no established link between high carbohydrate intake as an endurance athlete and the development of diabetes

• The challenge of maintaining consistent power output while cycling is notably complex, especially for beginners.

• Understanding how environmental factors such as wind and terrain influence power is crucial for effective training and racing.

• Coaching should focus on both improvement and enjoyment to prevent burnout and promote longevity in triathlon athletes.

• Establishing trust between coach and athlete is essential, emphasizing the importance of communication and shared goals in training.

• Athletes must recognize that racing strategies should align with their current fitness levels, rather than aspirations based on past performances.

• Monitoring metrics like power output can greatly enhance training effectiveness, but should not overshadow the need for adaptability during races.

References used for the MMB

1. Banday, M. Z., Sameer, A. S., & Nissar, S. (2020). Pathophysiology of diabetes: An overview. Avicenna journal of medicine, 10(4), 174–188. https://doi.org/10.4103/ajm.ajm_53_20

2. Colberg, S. R., Sigal, R. J., Fernhall, B., Regensteiner, J. G., Blissmer, B. J., Rubin, R. R., Chasan-Taber, L., Albright, A. L., Braun, B., American College of Sports Medicine, & American Diabetes Association (2010). Exercise and type 2 diabetes: the American College of Sports Medicine and the American Diabetes Association: joint position statement. Diabetes care, 33(12), e147–e167. https://doi.org/10.2337/dc10-9990

3. Thomas, F., Pretty, C. G., Desaive, T., & Chase, J. G. (2016). Blood Glucose Levels of Subelite Athletes During 6 Days of Free Living. Journal of diabetes science and technology, 10(6), 1335–1343. https://doi.org/10.1177/1932296816648344

4. Borghouts LB, Keizer HA. Exercise and insulin sensitivity: a review. Int J Sports Med. 2000 Jan;21(1):1-12. doi: 10.1055/s-2000-8847. PMID: 10683091.

5. Laine MK, Eriksson JG, Kujala UM, Wasenius NS, Kaprio J, Bäckmand HM, Peltonen M, Mertsalmi TH, Sarna S. A former career as a male elite athlete--does it protect against type 2 diabetes in later life? Diabetologia. 2014 Feb;57(2):270-4. doi: 10.1007/s00125-013-3105-8. Epub 2013 Nov 21. PMID: 24257894.

6. Dela F, Mikines KJ, von Linstow M, Galbo H. Does training spare insulin secretion and diminish glucose levels in real life? Diabetes Care. 1992 Nov;15(11):1712-5. doi: 10.2337/diacare.15.11.1712. PMID: 1468305.

7. Flockhart, M., & Larsen, F. J. (2024). Continuous Glucose Monitoring in Endurance Athletes: Interpretation and Relevance of Measurements for Improving Performance and Health. Sports medicine (Auckland, N.Z.), 54(2), 247–255. https://doi.org/10.1007/s40279-023-01910-4

8. Slentz, C. A., Tanner, C. J., Bateman, L. A., Durheim, M. T., Huffman, K. M., Houmard, J. A., & Kraus, W. E. (2009). Effects of exercise training intensity on pancreatic beta-cell function. Diabetes care, 32(10), 1807–1811. https://doi.org/10.2337/dc09-0032Not a subscriber to the podcast? Click here!

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