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Exercise and ketosis
Tomato05 posted:
Do you think a ketogenic diet is compatible with exercise?

How do you fuel a workout (say aerobic exercise for quite an extended period) when there is not enough glucose/will your muscles function satisfactorily with fat metabolism?
heretk responded:
I personally experienced an increased physical stamina and physical performance in many other ways, when I switched to a HF LC diet. I do not understand why some people would experience a decline? Perhaps their bodies are so used to glucose that they have difficulties in switching over, or perhaps they didn't give it enough time.

As far as I know, most (but not all) body tissues such as most muscles can use ketone bodies, fats or glucose as fuels, alternatively and at will. If one is in short supply they switch over to use the other two. I know of the following exceptions:

1) heart muscle can use ketone bodies primarily, glucose only in emergency and avoids using fatty acids except under pathological circumstances.

2) Brain and neural tissues uses ketone bodies and glucose (glucose - without insulin!) alternatively. It cannot or does not use free fatty acids.

3) Erythrocytes (red blood cells) - use exclusively glucose anaerobically. They cannot use any other fuel. That's the ONLY reason why we (and other mammals) must maintain at least 60mg/dl of blood glucose concentration at all time!

4) Eye cornea tissue - can only use glucose because (like erythrocytes) does not contain mitochondria.

5) Neural tissue in the spinal cord. This is still not well researched so what I will put here is somewhat speculative. Spinal cord appears to be using either only ketone bodies exclusively or some other yet unidentified energy carrier from the liver.

Interestingly, the 3 main body fuel types can be classified as:

a) hydrogen carriers, reductors - ketone bodies,

b) hydrogen and carbon carrying reductors - fats,

c) dual role "redox" fuels, that is carbon carriers (reductors) or oxygen carriers (oxidant) - which for example is glucose

Out of those the first type is the cleanest and the last is the most polluting in terms of metabolic residuals and free-radical stress.

Tomato05 replied to heretk's response:
Thanks, Heretic - that is very interesting information.

To me is is as if my exercise performance suffers when my carb intake goes very low. Strangely, I feel it more during weightlifting than during jogging (I do long runs, 8 or 9 miles).

Maybe it is because for anaerobic exercise one needs the energy fast - for short and intense periods. I wonder if fat metabolism takes longer than glucose metabolism, so that one cannot have the energy available as quickly.
heretk replied to Tomato05's response:
Yes, fat metabolism does require effective oxygenation. If your circulatory and pulmonary system is inefficient then your muscles will indeed produce more output utilizing extra glucose but not fat. That is due to a pathology, not a typical situation. Glucose metabolism, especially in hypoxia is very "dirty"! It does produce a lot of metabolic residuals! That's one of the issue diabetics have when switching to reduced carb diet or to a low carb diet: their metabolic yield decreases. That is normal. In such situation, the rate of metabolism cannot and should not be artificially boosted! If exercizing requires higher metabolic throughput then exercizing must be curtailed, otherwise it is akin of nitro-boosting an already dying or damaged car engine! (Sorry for an engineering comparison).
In case of arteriosclerotic cardiovascular disease, the body tends to switch over to an oxygen-sparing metabolic mode, out of necessity due to chronic hypoxia of tissues and organs, caused by impaired circulation. That is not good because the abundant production of metabolic residuals under oxygen-sparing glucose cycle, increases the inflammation and contributes to arterial disease. In addition, such oxygen-sparing metabolic modes involving utilization of part of glucose as oxidants, use up a lot of calcium, which aggravates calcification of the soft tissues and deplete bones. (yes absolutely - that's the glucose that depletes bones ultimately, not animal proteins! Dr. T.C. Campbell and his vegan friends are completely wrong on that!)


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