Sugar in human body

[vinitharya]

This probably goes waaaay into the territory of "stupid question", but in a bit of dialogue I'm writing, an extremely pedantic character needs to make mention of how much sugar is in the (average) human body, preferably in terms of grams (or milligrams or whatever) per kilogram of body mass

Comments

[whswhs]

It somewhat depends what you mean by "sugar." The sugars we count in foods are monosaccharides like glucose or fructose or lactose, or disaccharides like sucrose, all of which taste somewhat sweet. But those molecules can be connected together to form longer chains. For example, cellulose is made up of long strings of sugars bonded together. Even your DNA contains sugars: a deoxyribose connected to a phosphate connected to a deoxyribose connected to a phosphate.

A lot of sugar in the body is stored in the liver in the form of long chains, of a type called glycogen, based on glucose. When your body needs energy, that gets broken down into glucose and dumped into the bloodstream. But the blood glucose level doesn't go up a lot; the extra glucose gets broken down to form carbon dioxide and water. The long-term glucose bank isn't "sugar" as we normally understand it; if you eat liver it's not going to taste sweet.

So do you want the amount of free sugar, or the total amount of sugar molecules, including those bound up in longer chains?

[whswhs]

Agreed. Except for the "the extra glucose gets broken down" part. Glycogen gets turned into blood glucose as needed, with the chains 'unraveling' only partially, not all at once. Of course the released glucose gets turned into water and carbon dioxide eventually, but as part of being used to do work and keep cells alive. Just wasting blood sugar would be both highly inefficient for the body, and set your blood to boil. (It's a reaction that releases a lot of energy - that's the whole point.) The muscles also contain some glycogen, though not as much as the liver. And by the way, (pork/poultry) liver does taste slightly sweet in my personal experience, though I expect that's more because of the high content of blood and therefore blood sugar, not because of the glycogen. On the other hand, I wouldn't be surprised if we humans had enzymes in our saliva to crack glycogen molecules partially in the mouth already, the way we do with starch, as part of an evolutionary adaptation to prefer and seek out high-carb foods. (That's the reason why

[whswhs]

Argh, that should be "breast-feeding", not "pregnant", sorry.

[whswhs]

The other "organ" that requires glucose as a metabolite is actually only part of an organ. It's the kidney nephron (i.e. the microscopic structure in the kidney that filters the blood to make urine).

[sashatwen]

whswhs already asked the all-important question. What we call "blood sugar" pertains to glucose, a molecule that the sugars (such as lactose or fructose) as well as all carbs we eat break down into. Carbs are essentially a form of sugar

[vysila]

I don't have the scientific background the other posters have, but my doctor told me that a non-diabetic person will typically have about 4 grams of glucose circulating in the bloodstream at any time. That's the equivalent of about one teaspoon. Diabetics, particularly insulin-resistant Type 2s, will have much higher circulating levels because cells cannot absorb glucose out of the bloodstream. It ends up getting deposited as fat.

Also, as a diabetic, I will tell you that the "normal" reading of blood glucose will vary according to the time of day. Someone who has a fasting level of 100 mg/dL (5.55 mmol/l) probably has a metabolic issue and is likely on their way to diabetes. If that same level is one hour after eating, then that is a good level.