Post-fasting high glucose

I did a 25 hour fast from Saturday 8pm until Sunday 9pm. Complete fast, no food or drink.

I have the 670 system from Medtronic and it worked perfectly, kept my sugar between 90-130 for almost the entire time, with a short period at around 140.

After the fast I had a high carb meal. Bolused well before the meal. About an hour after the meal my sugar was around 180. I got on the treadmill to exercise and my sugar started to spike like crazy. Corrected and corrected to no avail. Sugar hit almost 400, a number I have not seen in many months. Only after about 3 hours did it start to come down, first slowly, then rapidly.

As of this morning, sugars are still not behaving as they normally do. Still getting spikes, still taking longer to bring down the spikes, exercise still not helping bring down the spikes.

Any ideas what might be causing this? Could fasting cause unusual production of glucose by the liver? Ketones?

Hi Sal @Zale, from this distance I can not detect that you are producing ketones; I don’t get aroma over the internet. From what you described, I guess that you are NOT creating ketones. Why? Because ketones are produced when the body is using stored fat / tissues for food - you ate high carbs and you said you took insulin during that period. The insulin should have allowed your body to use some of the consumed glucose for fuel. If your treadmill activity ventured into anaerobic, that could have contributed to high body glucose [BGL] levels.

I think your body reacted properly to your “high carb” meal following a period of starvation. My opinion, I’m not a physiologist.

Thanks Dennis. The thing is that anaerobic exercise always makes my sugar drop like crazy. Why would my body react differently to anaerobic exercise suddenly and have the exact opposite effect that it normally has? It seemed as though my body was either resisting the insulin or my liver was just dumping a tremendous amount of glucose. I have not experienced such high numbers for such an extended period of time in almost a year, and the last time this happened was also after fasting sometime during last September.

Zale, sounds like Dawn Phenomenon, this is when your liver thinks you are starving and will deposit sugar in your blood stream, usually happens in the early AM because most people haven’t eaten in about 6 hours. The only way to stop this is to eat, don’t take high doses of insulin and not eat, eat first then wait for your liver to stop flooding your system with sugar. You exercised scaring your liver by burning up the sugar you just had, liver says OH! no not again. Fasting like that is too dangerous, do you not realize that the only fuel your brain uses is sugar, nothing else, you starve the brain and your in for trouble with a big T. Exercise won’t help if your body because it thought I was starving is going to do all it can to survive your brain without fuel can and will shut down the functions of your limbs and anything else it feels is stealing it’s fuel. That fast way far too dangerous, and it proved that your body and brain didn’t like it, was it worth feeling miserable for a few days, don’t think so. Ps: I think you know better. Bye Jan. I haven’t been a type 1 for 64 years and not learn something. Take care.

@Zale Sal,

Boy, you just hammered multiple systems! You were burning fats during the fast, and the byproducts of that are potentially toxic to multiple systems, including your kidneys.

I don’t have time right now to delve into the metabolics of fasting, but, by all means, drink fluids if you are fasting.


Hi @Zale,
My guess would be ketones, but I’m no doctor. Just try to drink more fluids and keep dosing to try and get those blood sugars down. For me, if I have ketones and then add in exercise, my blood sugar and ketones get worse, so the exercise may be making things worse.