Blood "energy" content

"One-liner" post. This is exciting (picked up on twitter from Mike Eades):

Effects of dietary carbohydrate content on circulating metabolic fuel availability in the postprandial state

It's Ludwig's group. I've skim read but not looked at the detail. I like what I see.

Over the last year or so I've ventured in to the morass of older papers about the CNS response to infusion of various metabolic substrates where you get bogged down in the various neural groups which respond in various ways to high vs low glucose etc. It's messy and it's rare for people to have asked the questions in quite the way I might have phrased them.

Eventually I simply started adding up the energy content of "blood" in various states, especially under extended fasting when hunger becomes blunted. Being me I tended to add them up in terms of how much NADH and FADH2 might be available. I kept getting pushed towards the idea that hunger might be a simple matter of the energy content of the blood supplying the hypothalamus. Clearly that is one core thing that the CNS monitors (using ROS of course).

Could hunger be this simple?

Okay, there is also clearly a neural input (think hepatic FFA infusion via the portal vein suppressing food intake) but ultimately if the brain is being perfused with too few calories, it is going to do anything it can to make you eat. The classic is reactive hypoglycaemia or insulin induced hunger where I suspect the problem is (in myself in pre low carb days) not absolute hypoglycaemia (I could get this at BG around 4.5mmol/l) but the accompanying low FFA availability giving low brain stem energy availability. But of course measuring FFAs is not as simple as measuring glucose...

Anyway, it's fantastic to see some serious researchers looking at the concept of blood energy content. They will have to add the Protons concept eventually, to explain why things happen as they do, but they're on an exciting trajectory.

Peter