Tuesday, August 09, 2016
Glucose from fatty acids: RQ of 0.454
This is a section from Table V of Heinbecker's 1928 paper:
Studies on the Metabolism of Eskimos
This tells us certain very, very interesting things. The subject is a young Eskimo woman. Column 6 gives her RQ and, by day 3.5 of fasting, it is 0.454. Which is clearly impossible. Maybe. It took me a few minutes to realise that the result is probably correct, certainly within the limits of measuring RQ in 1928 in a tent in the Arctic. Let's assume it's ballpark correct.
I've been through this too many times. An RQ below 0.69 suggests the generation of oxygen rich molecules from fatty acids. An RQ of 0.454 suggests a huge amount of (probable) gluconeogenesis from fat is going on.
The other thing which becomes obvious from simple logic is that any oxygen rich molecule generated from fat must NOT be oxidised for it to drop the RQ. If you oxidise stearic acid to CO2 and water you will get the same amount of CO2 per unit O2 consumed whether that process goes via acetyl-CoA (as it usually does) or via ketones, oxaloacetate or glucose.
The girl, Martha, was breast feeding a baby throughout the study:
"Subject II. Nursing female".
She has eaten nothing for 3.5 days, she is excreting both glucose and galactose in her milk. She has used up her glycogen stores. Where is the glucose/galactose for the milk coming from?
The RQ is 0.454, the milk sugars are coming from fat.
How much gluconeogenesis is possible from fatty acids?
How much is a lot? It's not really practical to put a number to this, but enough to drop the RQ to 0.454 or, equally, enough to make a continuous supply of human breast milk. Both seem to be reasonable answers.
Unless you have an agenda.