Yup, i guess puberty and pregnancy are the two times in life where insulin resistance is an actual normal physiologic adaptation (as opposed to pathological like diabetes) where both blood glucose is high and insulin is high. When your body cannot keep up with additional insulin output to offset the higher blood sugar levels, that’s where it can become a problem. Luckily once the darn placenta comes out, most people are in the clear although at greater risk of developing diabetes in the future. I am actually being induced on Monday so obviously far along and when I was being screened for gestational diabetes, I failed by a close margin the first glucose challenge test. That made me have to do the elongated 3 hr glucose tolerance test and i passed that one with flying colors, in fact was hypoglycemic at the end. What a journey pregnancy is…
“This is the first study to demonstrate that post-exercise feeding to replace the carbohydrate expended during exercise can attenuate glucose tolerance and insulin sensitivity the following morning. The mechanism through which exercise improves insulin sensitivity is therefore (at least in part) dependent on carbohydrate availability and so the day-to-day metabolic health benefits of exercise might be best attained by maintaining a carbohydrate deficit overnight.”
The post-exercise paradox of reduced glucose tolerance and insulin sensitivity
“To conclude, the post-exercise paradox of reduced glucose tolerance and insulin sensitivity should be considered as a potential consequence of a pronounced metabolic adaptation to regularly performed endurance exercise. It is a transient phenomenon which demonstrates the complexity of the coordination of insulin-dependent and insulin-independent glucose and fatty metabolism in skeletal muscle and serves more investigation to fully understand the underlying mechanisms and potential consequences.”
The reduced glucose tolerance was seen most drastically in the group that did a 3 hour endurance ride. These are acute effects though, and I assume over time the training will improve sensitivity.
Thanks for sharing that linkThese 3 or so hour endurance rides (with efforts) are my bread & butter with my friends A couple of times a week as well as solo longish rides. Always got some protein and carbs in after the rides. Result - Diagnosed with Pre-diabetes at the end of last year. I’ve continued with the protein but stopped the carbs after the ride and together with one or two other nterventions it would appear that so long as I carry on as i am doing my glucose is back more or less where it should be. So much for the Golden Hour after excercise. The recent podcast guest Dr. Kyle Pfaffenbach’s advice seems to be right “I could care less about carbing up after a session, but make sure you get the protein in”
I’m reading that study as an argument against dieting on the bike. But it would be interesting to see how it fits with the larger body of literature on this topic
I still eat on the bike but as my ftp is a somewhat below elite levels, its no where close to even 90g/hr. It’s after the ride I’ve stopped putting in carbs unless it happens to be one of my normal meals.
100 watt ave power will be about 360 calories or 90g of carbs. I guess you aren’t burning 100% carbs (probably) but still…for your 150 watt per hour ride you literally can’t take in as many calories as you are burning while exercising.
I do wonder about the post ride carbs though…we all need continuous glucose monitors to understand what the heck is going on.
Joe
I don’t know what you base your numbers on, but 100w should be, for most on this forum at least, be mostly fat. If you fuel that with 90g of carbs/hour you are definitely messing up something with regards to you glucose.
90g carb/hour starts, for me, at sustained (multiple hours) of 200+ watts.
I agree. I wasn’t clear . I fuel with nothing like 90 g / HR . 30-50g/HR depending on intensity. I was being sarcastic saying I was somewhat below elite. I’m a long long way from that.
It’s never over 50% fat…or is it?
It’d put your 90g/hr starting at 200 watts just right, even if 50% is from fat.
Joe
Worth listening to this Inside Exercise podcast if you want a greater understanding what is going on: Spotify
Just got some results back… 5.8 A1C. Kind of at a loss. Guess ima be cutting carbs
https://www.sciencedirect.com/science/article/pii/S1550413121001029
Just confusing myself more. Here is one nugget:
" We also assessed continuous blood glucose profiles in world-class endurance athletes and found that they had impaired glucose control compared with a matched control group."
That’s fun. Their discussion has important points for interpreting this paper if you are a lay person:
we do not see a high risk that people wishing to improve their health through exercise enter the state of mitochondrial impairment and glucose intolerance due to ET volumes
The negative metabolic effects of excessive exercise found in this study are likely reduced as soon as the training load decreases. Indeed, we found a substantial improvement in metabolic parameters after only 1 week of reduced training in the RE compared with the ET phase.
From a health perspective, we do not advise against intensive exercise training as former elite athletes have lower mortality rates and seem to live longer compared with the general population
My additional (non-methodological-focused) personal comments would be:
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This study is focused on the metabolic situation that’s happening during overreaching/overtraining. I would have assumed that there would be altered glucose utilization during this based on what else we know about that syndrome, so these results don’t surprise me. It does make me wonder whether you could use CGM to help identify when an athlete was starting to enter non-functional overreaching territory, so that could be an interesting application.
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The “significant” difference in glucose control they saw in elite athletes is statistically significant. When you look at the actual degree of difference and what their glucose values actually were, it is extremely unlikely that this is clinically significant from a health perspective.
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Diabetes is a disease of insulin deficiency, not a disease of high glucose. We just use glucose values as a surrogate marker of the insulin situation because they’re easier to measure. It’s not clear to me that the normally assumed relationship between glucose and insulin that allows us to use it as a surrogate marker, is still present in well-trained endurance athletes. Ie: high glucose in overtrained endurance athletes is not the same thing as high glucose in an insulin deficient diabetic.
Maybe it just causes a different disease, called cnidosism, that makes you argumentative on the internet.
As a scientist, instead of relying on statistics I often rely on what the data actually looks like. I don’t feel the difference is very impressive in practical terms:
I’m not concerned.
extremely unlikely that this is clinically significant
We can go further: it is not clinically significant.
Thanks guys lol
I’d suggest getting a CGM if you are worried about it. 5.8 A1C converts to an eAG of around 120, which may not even be worth worrying about if you are doing a higher volume of training. When you go ride, even without any carbs on the bike, your blood glucose levels rise to support the workload, which in and of itself can raise eAG and consequently A1C. Most sane people typically don’t do aerobic work for more than 20-30 mins a day, and that population won’t see it, but if you do 12-20 hours a week, you may. This can be exacerbated with on-the-bike fueling, which supports consistently elevated blood glucose levels and in turn long duration performance without bonking.
Imagine a guy that rides 6 hours, and keeps his blood glucose at an average 140. A sedentary person during that time period might only have 100-110. The sedentary person would likely have a lower eAG that day than the guy who rode 6 hours, even though the guy that rode 6 hours is actually more metabolically fit. For you a 5.8 may not mean what it does to a sedentary population.
Further, carb restriction can actually cause glucose intolerance, not improve it. While it can lower A1C and eAG, it may have negative metabolic effects. I can cite studies if needed.
FWIW, I did a 5 hour day on Saturday and my average 24 hour average blood glucose was 118. Sunday I took the day off and my 24 hour blood glucose was only 102. I had as many carbs on Sunday as I did on Saturday, and yet average blood glucose was lower. That doesn’t mean exercising had a negative effect, actually the opposite. Context is important here…
What @lee82 said, but I’ll add to it. I’m type 2 and on 1000mg Metformin with an a1c ~5.6%.
When using the Supersapiens CGM, I’d always see an S-like curve at the start of any effort before I’d stabilize more or less around 140mg/dL. Post effort, I’d see a sharp spike that would come down generally by the time I had showered.
After very big days on the bike (4+ hours, endurance or tempo pace), I’ll have slightly higher fasting blood sugars for a few days. But higher is like from ~95mg/DL to 101mg/dL. And, during these days, Whoop usually has me in yellow recoveries.
I do eat strategically - more carb-y foods before & during rides.
I just ordered a CGM to play around with it, really appreciate these experiences, thanks both.
I was told I was pre-diabetic last November. Looking at the Hb1ac number I’d tipped over the line by 1 point (42mmol.mol - UK). To say I was shocked considering the amount of cycling I do was an understatement. On reflection I rationalised it by thniking I’d fallen into the trap of thinking I could eat anything as I was very active…
I made the following changes to my life (very easy as I’m retired).
- Cut out almost all gratuitous carbs - cakes , sweets , chocolate, ice cream outside of meals
- Reduced considerably the amount of bread I ate and switched to sourdough for what I did eat. I also freeze it before eating it.
- Tried wherever possible to walk for 30 minutes after every meal that had carbs in it.
One result after having had a stable weight for years is I lost 6 kg in 3 months. Admittedly it was there to lose.
In May I got a CGM and wore it fo 14 days and according to the data I appeared to have improved my blood sugar, I had to relate something called a Glucose Management Index to the HB1ac number and all seemed good.
Later I read about the paradox of some people who exercise a lot are seemingly prone to pre diabetes so I got another CGM and am currently wearing it.
On the last couple of days when I have ridden a 7 hour and a 4 hour ride (consuming about 40-50g per hr of carbs on the bike my average blood sugar has been 5.2 mmol and 5.4mmol. However when I adjust for the elevated readings whilst on the bike which I understand is completely normal the numbers come out at 5.0 mmol and 4.7 mmol for the time not on the bike which appears to be perfectly normal
I’ve decided to carry on with the changes I’ve made to my life, keep riding and walking, and stop worrying about it.
Interesting. What did this accomplish?