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Comment by oasisbob | Hacker News Reader

Lipogenesis is legitimate, but it's not the primary pathway for carb metabolism if you have a healthy diet. Glycogen is the primary way that blood sugar levels are regulated, and your body greatly prefers glycogenesis to lipogenesis.

If you're exercising, your body doesn't build glycogen; rather, it shuts down the metabolic pathways for glycogenesis because burning glycogen while building it is very inefficient. (It's a form of hysteresis.)

... painting with broad strokes because my background is in biochemistry, not nutrition.

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I think the difference here is that glucose can be converted to glycogen, but fructose can't. Both high-fructose corn syrup and sucrose are a combination of approx. 50/50 fructose/glucose (the most common HFC in use is a 55/45 split; sucrose has a chemical bond between the two sugars, but HFC doesn't). My understanding is that when most people refer to sugar, they are talking about sucrose, and not glucose in isolation; therefore, ~50% of 'sugar' can't be converted to glycogen.

Fructose can be metabolized to glycogen via DHAP and glyceraldehyde. IIRC, it's a limited pathway though.

By exercising, I meant exercising regularly. In my understanding, you don't make new glycogen unless your glycogen stores are down. And the body can only store about 3 pounds of glycogen from what I've read.

So what I'm saying is if you're mostly sedentary, eating a high-carb diet, your blood sugar levels will rise to the point that insulin is secreted. And then some of that blood sugar will be converted to fat, and its energy will be 'lost' - it won't be used unless blood sugar levels go down again and glucagon is released. But many people eat way too much and too often for this to happen, and they just keep on packing on the pounds. Thus, carbs causing weight gain while fat gets the blame.

I mean, think about it. All the sugar that comes into your bloodstream from, say, two bowls of cereal in the morning. You have about 3 cups of milk, 3 cups of grains. This is a pretty big amount of carbs that gets digested very quickly. Then you drive to work and sit on your bum for 4 hours. Don't you think some of that carbohydrate energy could be converted to fat before your next meal?

Insulin is secreted every time you eat. It's not a bad thing, it's a very fundamental part of regulating your blood sugar. (Ask someone with type I diabetes -- it's a royal pain to control blood sugar manually.) It's released whether you're active, sedimentary, eating a healthy diet, or junk food.

When you eat breakfast in the morning, you're most certainly replenishing glycogen. While you sleep, it's the primary source of blood glucose. Your body will prefer to replenish the glycogen before beginning lipogenesis.

So... there's no such thing as too much insulin?

There is, if a person's diet is consistently high in sugary foods. They can build up insulin resistance as a result of a constantly high insulin level, and ultimately develop type 2 diabetes.

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