Resistance to ketosis in obese subjects

(Richard Morris) #1

Interesting study done in the era before George Cahill was able to show that fasting brains run mostly on Ketones. This study observed that Obese (hyperinsulinaemic) people don’t make many ketones and make ketones slower than lean people.

kekwick1959.pdf (386.0 KB)

They showed that the lower levels weren’t from obese people somehow utilizing or excreting more than lean people. That lean people see a drop in glucose when they make ketones that obese people do not. The other interesting (but incorrect) observation is that Obese people apparently make glucose from fat.

What they observed was that lean people who fast use more protein than obese people as evidenced by their nitrogen excretion.

I believe what they are observing is that Obese people have sufficient body fat to deliver more of the bodies energy requirements, defraying the need to use protein for energy.

Also that 10% of that fat drawdown becomes freely circulating glycerin which can be turned into new glucose defraying the need to use protein to make glucose for the brain.

Finally they were still under the impression the brain needed 144g of glucose, but the reality is with the liver making ketones from fat, the liver only needs to make 44g of glucose - which requires only 440g of fat to be burned (about a pound/day). And as long as someone has enough body fat to deliver that rate of energy their protein loss would be limited to protein required for maintenance.

(Barbara Greenwood) #2

Ted Naiman recently put an info graphic up on Twitter which showed that the glycerol part of fat is only 5% of the energy. If that’s correct then it would only take 220g fat per day to produce the essential 44g of glucose. That’s quite close to the half a pound per day which Jason Fung cites as the typical nett loss during fasting ( after the inevitable rebound)

Interesting that BG does not always fall in obese people when in ketosis. Matches my experience, anyhow. I get annoyed by articles saying that a high BG prevents ketosis, if you want to be in ketosis your BG has to be less than 5 (say). My meter says different!

(bugellen) #3

I think the mechanism here has more to do with insulin resistance. The lean subjects’ insulin levels were likely much lower than the obese (extrapolated from the lower blood sugars), which allowed for a greater release of stored fat over the study time frame. Higher insulin levels would also explain the nitrogen equilibrium differences.

I sure wish they had given information on the gender of the subjects and what type of fat they were given during the 1000 kcal phase.