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Comment by dmritard96 | Hacker News Reader

I am most likely wrong or oversimplifying, but my understanding was that ultimately whatever macromolecules you are consuming, lipids, proteins, or carbohydrates all only get absorbed into the blood stream as glucose (putting on hold random nutrients like iron, vitamin XYZ etc etc).

If that's the case, doesn't it not matter what the originating molecules are as long as you avoid fast highs and lows in blood glucose levels since that is the main danger presented by sugars (fastest to be broken down)?

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The main dangers with sugar (table sugar, high fructose corn syrup) is how your body absorbs it, and the amount of fructose in it. Fats and proteins are broken down to glucose, yes, however this process is done over time, and it is almost ALL glucose, which is what your body uses as fuel. However when you drink sugary beverages like soda or orange juice (yes even orange juice is bad for you), you get an extreamely high dose of fruit sugar, very quickly (fruit sugar is different than sugar because it has a higher concentration of fructose in it which is bad).

Also, the reason fruits are healthy while fruit juice is not is that fruits have sugar in them, but between all the sugars, there is fiber, cell walls, and other parts of the fruit that slow down the absorption of the sugar. Another reason is that there is simply less sugar in 1 apple than there is in 1 glass of apple juice (there is around 8 apple squeezed into 8 ounces of juice).

Here is an amazing lecture which goes into amazing detail of the chemistry of sugars, and how they affect your body (also this is where I got most of my information): "Sugar the Bitter Truth" https://www.youtube.com/watch?v=dBnniua6-oM

Here is a short clip from a show called "Adam Ruins Everything" where he talks about how unnatural "natural orange juice" is: https://www.youtube.com/watch?v=ZuYPdTvqitg

I'm sorry for being the one breaking it to you, but I think you may, unfortunately, be wrong. :)

care to elaborate? open to being wrong, but also want to see who says so and why

> my understanding was that ultimately whatever macromolecules you are consuming, lipids, proteins, or carbohydrates all only get absorbed into the blood stream as glucose

Amino acids, glucose and fatty acids are all ancient molecular structures known to all cellular life and thus can and do circulate in our blood at all times. If everything got converted into glucose during digestion, that would mean we could live entirely off candy fortified with vitamins and minerals, and produce all essential fatty acids and all essential amino acids from the glucose. Not so.

PROTEINS provide amino acids, basic building blocks for near everything organic about our body (or all cellular life-forms really), not just muscles but hormones neurons etc etc. The body may convert protein into glucose but this laborious process occurs to any significant degree mostly under a prolonged lo-fat-lo-carb-hi-protein regimen or plain starvation conditions (ie post-fasting, not just normal fasting with plenty of fat reserves left, which is simply ketosis, hence protein-sparing and fat+ketone-burning). If so, this doesn't occur in the digestive tract, since glucose production (or provision from glycogen) is the job of the liver.

LIPIDS aren't and cannot be converted to glucose in the digestive tract, or we wouldn't store body fat to begin with and also have essential fatty acids circulating at all times now, would we? BUT 2 triglycerides CAN donate their glycerol backbones for the production of 1 glucose molecule, and I believe this is constantly happening in ketosis when glycogen is depleted. Again, glucose production/provisioning is a liver job, not a digestive tract job.

CARBohydrates of most any kind ARE converted to glucose in the digestive tract. Exceptions: fiber travels on to the colon for excretion or to be fermented by bacterial action (into I believe short-chain fatty acids and B/K vitamins) and fructose is "metabolized" into triglycerides by the liver. Since the blood needs a certain glucose level at all times (around 5g-ish), circulating glucose in excess is immediately shuttled into first: any cells that are receptive to the concurrent insulin signaling, second: glycogen storage (liver and muscles), third as a last resort converted into body fat.

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