Today I started a 10 day session with a Dexcom G7 continuous blood glucose monitor. Arguably one of the most reliable monitors on the market.
I’m a 37 year old male in pretty good overall metabolic health. My typical weeks are around 9-12 hrs on the bike w/ 1.5-2 hrs weight lifting. I’m not diabetic so am looking forward to seeing the impact of the typical on bike nutrition during training rides. I did a similar test with the same monitor some time back (a year or more?) but my fitness and on-bike nutrition have increased significantly since then.
My biggest takeaways from last time:
the difference in blood sugar impact between instant oatmeal and steel cut oatmeal is huge. Instant was a spike and crash while steel cut was a rise and much more moderate drop. Since then, I eat steel cut oatmeal for breakfast about 95% of the time.
Even with the standard 100ish grams of carbs per hr during endurance rides, the blood sugar remained relatively steady aside from a massive spike after the ride. I didn’t have enough experimentation time to dive into this more.
A 20-30 minute walk after meals or desserts makes a HUGE positive impact on blood sugar. I could eat a huge bowl of ice cream and do a 20 minute walk immediately after and my blood sugar levels would look better than eating a healthy meal with complex carbs and doing nothing. Unfortunately, the habit of walking post dinner hasn’t stuck (living on the gulf coast doesn’t help).
If anyone has any questions or suggestions for experiments I try, feel free to reply below and I can see if I can fit them into the plan. I am leaving for a 2 week camping trip to Colorado next Tuesday, so I won’t have as many rides or days of my ‘normal’ routine as I would prefer. I do have another monitor that I will go for a round 2 of experimentation at a later date.
My general training rides are 60-100g carbs depending on intensity and duration. A 1 hr endurance ride may only have 60g carbs, while anything longer than 2 hrs (and especially over 3 hrs) always has a 100g/hr target.
I’m becoming more and more vigilant in consuming low glycemic carbs off the bike. I’ve always used steel cut oats in the am, but frequently have white rice for lunch and dinner, but aim to start tackling that. Could you do a comparison between brown and white rice? Oh, I always go for a walk after dinner with my dog, so good to know how powerful that is bringing BG down.
What do you eat the rice with? I should be able to do a comparison between the two. If I made chicken stir fry with identical ingredients and one meal with white and one with brown, would that be reasonable?
My current questions/interests are about when I finish my ride what happens to BG, i.e., people say there’s a window to consume carbs still using the GLUT4 receptors (no insulin spike), but how long does that last post-ride, and then you eat a post ride protein/carb shake (or a piece of pizza) and then what happens (as in, your muscles are absorbing the glucose in your blood and then is there some point that suddenly your body starts pushing insulin again? Like you said, you get a spike after riding, and I’ve used finger pricks a few times, that resulted in a really low BG reading the first time (which is why I checked it, because I got home and felt awful), and then the next time I rode from home I overcompensated with the carbs and was in a big (for me) BG spike when I got home, and then tried one or 2 more times with a little less fueling and not eating a gel 15 minutes before I got home, and BG seemed fine.
For lunch, I eat the rice with raw salmon chunks and avocado. For dinner, some sort of animal protein but mostly chicken, and paired with various veggies.
Yes, I think that would be a reasonable test, and carry over well to what I normally consume with my rice.
@MikeMunson - that’s a very important topic on my end as well based as what I experienced during my last long ride and spike/crash while using the CGM. I’m planning a 4 hr ride Saturday that will be pretty structured for my carb intake. I’ll likely stop consuming carbs 30 minutes prior to finishing the ride and seeing what happens. I would hope that stopping slightly earlier would have less of a chance for a spike.
@ddetch - that is great! Please feel free to use this thread as an update with your findings as well!
As a general observation from 8-10 years ago, I was having issues with what seemed like low blood sugar symptoms. I bought a regular blood sugar tester and found I was having occasional hypoglycemia issues. I ultimately tied it to having a whey protein shake (protein and articifical sweeteners), on a very empty stomach. What I think was happening is that the artificial sweeteners were sending a ‘glucose’ type signal and causing my body to release insulin, crashing my blood sugar. Because there were no actual carbs to counteract this, it was sending my blood sugar down.
Regardless of what science says, I do think that artificial sweeteners and caffeine can have some impacts on blood sugar.
Glut4 seems to stay active for about 2 hours on the cell membrane. “In the initial hours after exercise (0-2 hours post exercise), the insulin sensitizing effects of acute exercise on the myocyte are likely explained by increased GLUT4 content on the plasma membrane, with subsequent exposure to insulin slowing the rate of GLUT4 internalization. However, in the absence of insulin, plasma membrane GLUT4 content levels return to baseline within ~2 hours of recovery.” ( Post-translational Modifications: The Signals at the Intersection of Exercise, Glucose Uptake, and Insulin Sensitivity). LInk.
I couldn’t find anything about how long it takes for exercise-induced insulin suppression to end. My n=1 is that it is pretty quick because if I eat sugary stuff on a coffee stop - my blood sugar tanks when I get back on the bike. I’ve always assumed it was because I released insulin while sitting there enjoying the treat and then got back on the bike and started muscle contraction glucose uptake again and blood glucose took a nose dive.
Thanks. Sounds like it tapers, so both systems (GLUT4 and insulin) are operating at varying levels at the same time, and how long it takes varies based on something.
I probably spend too much time worrying about these things. I say that because my bloodwork doesn’t indicate issues with fasting blood glucose (and my informal testing is that BG doesn’t spike a crazy amount and it recovers very normally), but I have family history, I’m overweight (and working on losing weight), tend to binge on carbs (whether associated with exercise or sitting on the couch), and my age is over the hill. And, my SOP is to get home from my ride, eat, clean up and then take a nap (my nighttime sleep could be better).
I used to feel really bad after most rides, but I’ve finally gotten consistent with my sodium intake and embraced carbs during the ride. So, at least that intense desire to nap doesn’t feel as crashy as it did when I was egregiously under-fueling (granted I pretty much stick to around 60g/hr now). I guess I could order some more BG sticks and focus some testing on that post-ride timeframe.
Worth mentioning - but I seem to remember that CGM’s aren’t accurate or reliable enough for measuring levels intra-exercise. Has to do with the fact they aren’t actually measuring blood glucose at all, they are measuring interstitial glucose which lags, and may not represent actual blood glucose intra-exercise. Not the expert on this, but that’s my recollection so YMMV…
I am personally curious and may use one at some point to learn more about glucose (and resulting insulin) spikes outside of exercise for me.
This is interesting, and I could see it making sense in a way. I think the best way to determine this would be to spot check it with some finger pricks on a standard glucose monitor to compare.
And.. With that in mind.. I woke up this morning and my blood glucose was 113, which is concerning and in the pre-diabetic range. Never in my life have I been over 100? Maybe 101-103 a couple times, but it’s always been in the 80-95 range.
I checked the Dexcom box, and it looks like they have a short shelf life and my monitor is expired by about 8 months. A friend gave it to me around 15ish months ago, and I didn’t get around to using it right away. Between the 113 reading and expired date, I obviously became very concerned (and suspect). I pulled out my old regular blood glucose monitor, and checked it and it showed 77.. That would be great, except, those test strips were also significantly expired
SO! I just went to Walgreens and bought a new standard monitor and standard test strips. Just did a test and according to the finger prick, my blood glucose is 85 vs 121 on the Dexcom.
I am hoping (based on this mornings reading) that the expired Dexcom is no longer accurate. I will check the reading upon waking tomorrow morning vs a finger prick, and if it’s indeed off, I’m going to remove the Dexcom. Honestly, I hope it’s off vs having a fasting glucose at 113. I haven’t done an experiment like this since heavily implementing 100g carb of sugars into my training and had concerns it may have been throwing things off as a whole.
The good news is that I have another Dexcom G7 (that’s not expired) and once I get back from vacation I’ll restart this testing protocol.
I’m a certified quality auditor and the classroom work hounds on calibration/expirations an absurdly high amount. Obviously very important, but did seem like a little bit overkill in the training. I may be seeing first hand the importance of expiration/calibration. On an electronic assembly with an internal battery/monitor, I can see it’s importance more so than say.. a bottle of Tylenol.
@Trix8806 Add a nut butter or a whole nut like walnuts to your oatmeal and you should see no spike. I wore the Supersapiens sensor as part of a beta for a month a few years ago before they went out of business and that worked for me.
First there is a reason that Supersapiens folded - the device is just a lot of noise for non-diabetic athletes and doesn’t help with performance at all. These are devices for diabetics.
Second, don’t get into the mindset that a blood glucose spikes are bad. It can lead to disordered view on eating. That is the way our bodies are designed to work. Eat ice cream, blood glucose spikes, insulin ramps up to manage it. It’s only a problem when one is diabetic and the blood glucose spike goes off the chart.
If you fall down the trap that a BG spike is bad then you’ll end up in a low carb or keto diet. A couple of years ago CGMs for healthy people were the rage and low carb influencers were selling these ideas.
White rice vs brown rice - the latest studies on glycemic index have showed that white rice is not inherently bad. When you consume white rice or any starch with protein and fat, the glycemic index of the whole meal goes much lower such that the difference between having eaten brown or white or potatoes is negligible. Brown rice does have more fiber so that is a good thing if you like brown.
Now, if you are only eating rice as a snack then brown is probably a better choice. If you’re eating it for recovery right after a workout, then white might be the better choice.
Have fun with the experiment. My wife had gestational diabetes and wore a CGM. We learned all the tricks like taking walks after dinner. Her spikes were in the 500 range though so she needed to limit rice to 1/2 cup per meal, eat lots of veggies, and take walks after dinner.
Can you explain this to me a little better, because this always happens to me! After a longish coffee stop and consuming high sugar food, I feel awful getting back on the bike after riding for 5 minutes or so, and experience low blood sugar. So what is the strategy to avoid this? Other than don’t eat baked goods lol.
This is probably just the “Long-ish Coffee Stop” - your body basically starts going into recovery mode thinking that the work is over. Best way to avoid it is make your stops shorter. Less than 15-20 minutes.
I’ve noticed this when I try to do intervals indoors and then jump on the bike for a long endurance ride. If I take too much time between to swap kit, etc. - I feel like crap, and it’s not related to eating.
If you do trigger a big insulin response, then yes, that’ll make you feel like crap too. That’s personally why I don’t like to eat much in the 2 hours before a ride - I like 2.5 to 3 hours out, or right as I’m going out the door.
Sure. This is not “real” science. It is how I’m explaining my own observation in myself.
You have two ways to get Glut4 (glucose transporter) to the surface of the cell - contraction mediated and insulin-dependent. Exercise suppresses insulin secretion (I don’t know the mechanism of this). Therefore, during exercise the primary way that glucose is entering the cells is via the GLUT4 that came to the cell surface (from inside the cell) signaled by muscle contraction. When one stops for a pastry he/she is at rest. And therefore I, assume, based on my own experience, that insulin is released enough in response to that rise in blood sugar from eating that I one now has have circulating insulin. When you start exercising again those GLUT4s are still there PLUS you now has an insulin response. At least that is my theory. Could be totally wrong. Maybe it has more to do with glucagon suppression or something, I have no idea But my work around is that I don’t have my sugar bomb (or I just skip it) until I’m back on the bike. This solves the problem for me. My insurance company somehow agreed to let me buy CGMs for $15 each so I wore one for months… and my BG would go into the 70s if I ate mid-ride while at rest.
One is also more insulin sensitive after exercise. So if you find that post-ride a high carb meal causes your glucose to drop I’d do more of a mixed meal to see if that helps. This happens to me too. I eat a “normal” meal after a hard ride and I’m hypoglycemic pretty quick. I don’t know if it is related to not actually eating enough carbs to replenish or that I’m so insulin sensitive all the carbs come out of my bloodstream really quickly.
Do you experience this even when you consume 100g carbs/hr during the ride?
I used to have major blood sugar crashes when I didn’t fuel properly, but now when I have 100g/hr I usually have to force myself to eat as part of recovery.
(maybe even shorter if you can… 10-15 minutes).
But my work around is that I don’t have my sugar bomb (or I just skip it) until I’m back on the bike. This solves the problem for me. My insurance company somehow agreed to let me buy CGMs for $15 each so I wore one for months… and my BG would go into the 70s if I ate mid-ride while at rest.