More fun with biochemistry

Tobias brings up a good point in the comments of today's linkee-poo about drinking "throw-back" pops (which use cane sugar) versus their high fructose cousins. To explain why he's seeing the effect he is, I basically explain the other part of how your body responds differently to fructose. So I thought I'd bring my comment up to the top level.

Hey Tobias, that (feeling sated faster with sugar based pops than with corn syrup based pops) is because of how you digest the different sugars (liver process), and how your hypothalamus monitors the bloodstream and the resulting reactions. First up, you have to know that the preferred form of sugar for your body is glucose. It's what insulin is geared to help facilitate. So when your liver has a choice of either processing glucose (or glycogen, which is the polysaccharid of glucose) and fructose or galactose, it will process the glucose first (it has to process the other two, which requires more energy, so it "decides"1 to hold off on the other two to prefer the form of sugar your body can use right away). You liver will actually store fructose in glycogen before processing it through to your blood stream (leading to fatty liver).

So, when you drink that "throw-back" pop, more glucose gets into your blood faster. (Just a note here, processed sugar contains both glucose and fructose with a little galactose). Whereas when you drink the high fructose corn syrup you liver first processes the fructose to glycogen, stores it as fat, and then cuts up the glycogen to release the new formed glucose.

Now, why that makes you feel sated faster has to do with your hypothalamus which rides shotgun over (many functions including) your levels of suspended glucose in your blood. More glucose sets off a cascade of events including increased insulin release (as well as other hormones and proteins). Part of that cascade includes "telling" you (through chemical markers) that "too much glucose = you're full." Again, satiation is a whole cascade of events.

Your hypothalamus doesn't check for fructose. So even the bits that spill over the first past of the liver won't trigger your brain to say, "Whoa, I'm full." It's only after your liver 1) runs out of glucose to process that it will 2) look to your glycogen stores to make and send out glucose.

That explains the delay to feel sated. It also explains why if you drink fast enough, after you feel sated and stop ingesting pop, you will then feel as if you over ate (because your glucose levels are spiking before your insulin can crash your blood glucose levels, which is the "sugar crash")

1 If this is through competitive inhibition or other functions like blocking RNA transcription, I don't know.