Here’s another study (J Clin Invest. 1980;66(5):1152–1161. Capacity for Moderate Exercise in Obese Subjects after Adaptation to a Hypocaloric, Ketogenic Diet. Stephen D. Phinney, Edward S. Horton, Ethan A. H. Sims, John S. Hanson, Elliot Danforth Jr., and Betty M. Lagrange.) on exercise while in ketosis.
To study the capacity for moderate endurance exercise and change in metabolic fuel utilization during adaptation to a ketogenic diet, six moderately obese, untrained subjects were fed a eucaloric, balanced diet (base line) for 2 wk, followed by 6 wk of a protein-supplemented fast (PSF), which provided 1.2 g of protein/kg ideal body wt, supplemented with minerals and vitamins. The mean weight loss was 10.6 kg.
The duration of treadmill exercise to subjective exhaustion was 80% of base line after 1 wk of the PSF, but increased to 155% after 6 wk. Despite adjusting up to base line, with a backpack, the subjects’ exercise weight after 6 wk of dieting, the final exercise test was performed at a mean of 60% of maximum aerobic capacity, whereas the base-line level was 76%. Resting vastus lateralis glycogen content fell to 57% of base line after 1 wk of the PSF, but rose to 69% after 6 wk, at which time no decrement in muscle glycogen was measured after >4 h of uphill walking. The respiratory quotient (RQ) during steady-state exercise was 0.76 during base line, and fell progressively to 0.66 after 6 wk of the PSF. Blood glucose was well maintained during exercise in ketosis. The sum of acetoacetate and beta hydroxybutyrate rose from 3.28 to 5.03 mM during exercise after 6 wk of the PSF, explaining in part the low exercise RQ.
The low RQ and the fact that blood glucose and muscle glycogen were maintained during exhausting exercise after 6 wk of a PSF suggest that prolonged ketosis results in an adaptation, after which lipid becomes the major metabolic fuel, and net carbohydrate utilization is markedly reduced during moderate but ultimately exhausting exercise.
Stephen Phinney et.al. did an interesting study which put elite bicycle races on a ketogenic diet (Metabolism. 1983 Aug;32(8):769-76. The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Phinney SD, Bistrian BR, Evans WJ, Gervino E, Blackburn GL).
The study measured the amount of muscle glycogen in the subjects before they went on the ketogenic diet and after then they had been in the diet for 4 weeks and before/after exercise in both diets. Here’s the mean values.
|Keto Wk 4
|Keto Wk 4
After the four weeks the subjects had approximately half the muscle glycogen in the ketogenic state. The fact that the post exercise numbers were similar pre and post keto appears to show the glycogen sparing effects of the diet. The study states that the reason that the muscle glycogen doesn’t go to zero is that there is muscle glycogen stored in fast and slow twitch muscles. The slow twitch muscles were used during this exercise and depleted by this test. Hence, glycogen use was 90 pre-keto and only 20 post keto.
RER Shift from Carbs to Fat
The difference between the two diets is also seen in the shift down of the RQ (RER) of the subjects during exercise from a mean of 0.83 to 0.72. This represents a significant shift towards fat oxidation in place of carbohydrate oxidation.
My Own Numbers on Low Carb Diet
Adding in my VO2max numbers to the chart from a previous post:
For me, 65% of my VO2max corresponds to a heart rate of about 129 or fat as about 79% of calories. My RER was about 0.75 at that rate which is not as good as the elite bicyclists in this study who were at an RER or 0.72 at that level of activity. Hopefully with additional cardio training my RER will be reduced further during exercise.
The study showed that the athletes used about 950 kcals/hr. Before keto 28% of that came from carbs and the rest from fat. After keto, the carb oxidation rate dropped to 9%.
The energy from fat when in keto was 864 kcal/hr which is 1.6 g/min. This is a high level of fat oxidation and is more than my own fat oxidation rate (of around 1.2 g/min).
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).