I like to think I've learned a fair bit amount human metabolism, and yet there's something I don't quite understand.
How, exactly, does a "sugar crash" or low blood sugar work in people eating the SAD?
Here's my thinking:
Let's assume these people are full-up on glycogen. (Normally eating lots of carbs and not doing a whole lot of exercise.) If they eat something very sugary/heavy carb, insulin is secreted to get the sugar out of the blood and into into the cells. Sometimes insulin overcompensates and removes too much glucose from the blood, which is when people start to get light-headed, shaky, have cravings, etc., and we usually attribute that to "low blood sugar."
So my question is: if these people are full-up on glycogen, why do they have the crash? Does glycogenolysis not kick in immediately? Is this why? Why would the body perceive this "lack of glucose" when there's actually plenty of it stored up in the liver and muscles? It seems like the breakdown of glycogen should be a lot "easier" than, say, gluconeogenesis from amino acids or glycerol, since glycogen is already glucose, just tons of it all strung together.
I feel like lower-carb people can get fatigued and generally feel crappy after intense workouts b/c they don't have a lot of glycogen reserves.
I hope this isn't a stupid question. Maybe there's something insanely obvious that I'm missing because it's right in front of my face...
asked byAmy_B_ (8014)
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on July 10, 2012
at 04:38 PM
Well, as you said there's too much insulin. Insulin works to drive the equilibrium towards storage and away from burning of sugar. So even if you have all the sugar you could use, the presence of insulin virtually locks it away so it can't be used. That's why insulin resistance is so insideous, you have chronically high insulin and can't use your own fuel.
Also, gluconeogenisis is expensive and slow, it's just used as a last resort. It's not just some magic that turns protein in to sugar, it's a fairly complicated set of reactions that your liver has to do, and if your liver is busy metabolizing fructose it might not get to it.
on July 10, 2012
at 04:29 PM
An over release of insulin (more than is required to bring glucose back to normal) will happen in some people. One of the functions of insulin is to suppress the release of glucose from the liver. Until the insulin clears the blood stream, it will have this effect. if the blood sugar drops too low, cortisol and epinephrine are released to force the liver to release sugar, overriding the insulin signal. The amount of glycogen in the liver doesn't really matter. There is always enough glycogen in the liver - or the brain dies.
on July 10, 2012
at 04:27 PM
There is a mistake in your assumption that, "these people are full-up on glycogen. (Normally eating lots of carbs and not doing a whole lot of exercise)."
They are not full-up on glycogen. They're muscle cells are insulin resistant, so they do not take up sugar efficiently. They're probably perpetually glycogen depleted, and thus on a carb binge 24/7, exacerbating the problem.
People who are insulin sensitive are more efficient at using glucose, so lets say 30g of glucose taken post workout in an insulin sensitive individual, and 29g will go to muscle glycogen replenishment. For an insulin resistant person, maybe only 5g will, and the rest will just wreak havoc in the blood stream until it is burned off. Then once it's gone, they eat more sugar because none of it actually got into the muscle cells. That is a sugar burner. Not whatever the heck Mark Sisson says it is.
If you are insulin sensitive ingested glucose goes towards refilling glycogen stores (and 400g is a lot of room for glucose), while free fatty acids go to fueling your resting activities.