The Cori Cycle – Not a new kind of bicycle (from Aug 2017)

I had an interesting response to intense exercise the other day. I was many days fasted and went to an introductory CrossFit class. I measured my blood sugar after I got home from the class and my blood sugar was around 80 points higher. Did some digging to try and find out why.

My first assumption was that the liver was dumping glycogen and that’s partly true. Turns out that the muscles store around 80% of our glycogen stores and the liver contains the rest. The muscles use the glycogen locally and they don’t dump glucose into the blood stream. All of the glucose does come from the liver which takes it out of stored glycogen. That would account for some of the rise. I usually see a ten point pop with some exercise like bike riding but not like that time. The CrossFit exercise was very hard compared to normal exercise.

Here’s where the the Cori Cycle comes into play. I was fasted during the exercise for more than 20 days. From the Wikipedia article:

The Cori cycle is a much more important source of substrate for gluconeogenesis than food. The contribution of Cori cycle lactate to overall glucose production increases with fasting duration. Specifically, after 12, 20, and 40 hours of fasting by human volunteers, the contribution of Cori cycle lactate to gluconeogenesis is 41%, 71%, and 92%, respectively.

This was a piece of data which I didn’t have before. This makes sense of the experience that I had with intense exercise. The muscles released a lot of lactate which at the end of the exercise gets converted in the liver through gluconeogenesis into glucose. Hence, the large pop in blood sugars.

[2018-06-29 – I think this is a pretty good explanation of the problem. I wish I knew more at the time about VO2max and Heart Rate Training. I could have picked the right mode of exercise (top of aerobic range) rather than the HIIT mode of Crossfit.]

Here is a great discussion of exercise and the Type 2 Diabetic with Dr Finney  (Shelley. Low-Carb preserves Glycogen better than High Carb. Me and My Diabetes. April 14, 2011).


Thoughts on Exercise from Aug 2017

I’ve edited the following since I’ve learned a lot about exercise since I originally wrote the post (August 2017).

My Original Goal

At the start of this experience my goal was to Hack My Type Two Diabetes. Per my MD, I am no longer a diabetic and am just at the bottom end of the Pre-Diabetes range. So mission accomplished???

[2018-06-29 update – My last HbA1C was 5.2 which is no longer even pre-diabetic but right in the middle of the “normal blood sugar range.]

Are We There Yet?

My initial theory was that Diabetes is just a symptom of the underlying condition which is Insulin Resistance. Eating Low Carb. Moderate Protein and High Healthy Fats reduces the need for the body to produce Insulin but does it cure Insulin Resistance itself?

[2018-06-29 update -There is a need to differentiate between insulin resistance due to diabetes and peripheral insulin resistance due to a low carb diet. An Oral Glucose Tolerance Test (OGTT) may or may not be able to distinguish the two. Some people say it takes a time of reintroducing carbs before taking an OGTT.]

What is Insulin Resistance?

Insulin Resistance is the inability of the body’s cells to take in glucose in the presence of Insulin. From Skeletal Muscle Insulin Resistance Is the Primary Defect in Type 2 Diabetes.

Under euglycemic hyperinsulinemic conditions, ∼80% of glucose uptake occurs in skeletal muscle

If your muscles are not able to efficiently take up glucose then you have Insulin Resistance. It may be that exercise is the only way to improve glucose uptake in the muscles.

[2018-06-29 update -I believe that still to be the case but with the added thought that a low carbohydrate diet causes peripheral insulin resistance. Your muscles resist the action of glucose in a state where Insulin is low so that the glucose can be conserved (some say spared) for the essential parts of the body (brain, etc) that require glucose).]

Types of Exercise

When it comes to improving Insulin Resistance, I think there may be a difference between the sorts of exercise, ie, aerobic and anaerobic exercise. Repeatedly dumping all of the glucose out of the cells is part of what is needed to increase insulin sensitivity. That seems like where High Intensity exercise comes into play. Things like rapid reps of high weights vs walking on a treadmill.
[2018-06-29 update -Change this from “may be a difference” to “is a difference”. A year of CrossFit showed me the difference. I will write a post on it – or a hundred posts on it.]

My Experience with Exercise

This would bear out with my own experience of the quick dump of glucose that I experienced in the high intensity workout. My glucose went up at least 80 points which I now think is due to Insulin Resistance.

[2018-06-29 update -It was almost certainly peripheral insulin resistance plus workouts at high intensities mobilize a whole lot of carbohdyrates – perhaps as much as 60g/hr. That’s a whole lot of sugar dumped into the blood stream. And my body doesn’t do all that well with that much sugar. Although I will say it got better with time. Until I quite Crossfit that is.]

Not only is the liver dumping in that case but the muscles are dumping too. And that’s a good thing.

[2018-06-29 update -Turned out that the muscles don’t dump into the bloodstream. Only the liver does that. Learning more every day about this.]

So perhaps if I got this right it’s more about the type of exercise when attempting to improve the underlying Insulin Resistance than it is about the exercise itself. Is it true to say the reason my blood sugar rises so high with high intensity exercise is that my muscle cells are still Insulin Resistant and that with more exercise they will get better at responding to the Insulin they are given and then I will not see high blood sugar spikes during and immediately after exercise?

[2018-06-29 update -See comments earlier about peripheral insulin resistance.]

If I have this right I should easy be able to measure and observe progress by checking my blood sugars after exercise to exhaustion and the levels should drop.

I wish I had done those measurements more often and recorded the data.

Here’s a pretty good 2014 article on the subject. [2018-06-29 update – The article did not deal with the blood sugar of diabetics. I wish I had bothered to think more about this but was happy enough with my HbA1C numbers that I didn’t care.]

So why LCHF and Fasting?

Using LCHF + Fasting has helped me get to a weight where my pulse rate is lower, the stress on my joints is lower, my BP is lower and I am now at the point where I can safely exercise. Surely my Insulin Resistance is somewhat better but the only real way to attack it that is left is with high intensity exercise.
[2018-06-29 update – That’s when I took up Crossfit which I did for almost a year.]

Exercise Studies

This will be an accumulated list of exercise related studies.

Athletic performance on Low Carb

Exercise and Diabetes

Exercise Physiology (Mechanisms)

Exercise Supplementation


Splitting Low Carb Studies BLOG into Two Sites

The Low Carb Studies BLOG is being split into two sites. The original Low Carb Studies BLOG will concentrate on the Low Carb/Ketogenic diet. This site will focus on Athletics on the Ketogenic Diet.

It will take a while to move the content over but allow more focus on each subject individually.