Nobody knows the answer to this question yet. Lots of smart minds and deep pockets are trying to figure it out. Many marketing departments will tell you they know the answer. There are SO many good questions yet to even be asked.
The answer for optimizing performance is almost certainly above 100 for most folks. I'd bet it's also a relatively steady value but that a range is reasonably optimal. Yes, avoiding massive troughs is probably valuable for performance. I doubt peaks are harmful so long as there's no trough that follows. It won't surprise me at all if we find in 10+ years that a positive rate of change of blood sugar is associated with peak performance, rather than some stable high value. There is a similar finding in the literature on stimulants and cognitive performance IIRC. As in, maybe 120 is optimal throughout the race but that if you can ramp blood sugar towards the finish, especially where higher cognitive demand is needed (sprinting) then maybe there's increased performance with a blood sugar ramp over 20 minutes.
Whether the optimal value is 105, 120, or 160... is probably highly individual and we're at least 5 years from figuring it out with a high level of certainty. Maybe 10-15 years when you consider that the mechanism of elevating the blood glucose itself can be so confounding to performance outcomes (causative of gut distress). This may be an area where some tech startup (possibly ours) figures it out faster than the research community, because of the growing ease of access to huge amounts of athlete data. I'll let you know what we find, when we find it. We're in a SAFE note funding round at the moment so development & partnerships stand to accelerate.
PS. [soapbox warning] The primary harm risk to the pancreas appears to be regular rapid insulin production, and that doesn't happen during exercise. Therefore, you and everyone are correct not to worry about increasing blood sugar during exercise, as far as the evidence and mechanistic understanding of T2D risk stands today.
The epidemiological evidence strongly confirms. As in, folks that only spike blood sugar during exercise have a near zero incidence of type 2 diabetes.
There are lots of well-funded marketing departments that intend to convince folks otherwise. "Learn what foods spike your insulin today!" implying or outright stating that all incidences of high blood sugar are bad. Thankfully, that's false. :)
My recommendation: Don't purchase CGMs unless your personal MD tells you it's medically advisable. If you do use them, just use it with the understanding that you're mostly contributing to some company's research on blood sugar's actual relationship to performance and disease, and not to make well-informed decisions yourself, as much as their app might help you feel like you are, because we know very very little about what is actually optimal for performance or health. :)
Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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