How Sweet Are You?

I was inspired by Scully’s post that showed a unit of insulin in relation to a bunch of different things, like a nickel, a staple, and a LEGO man. (It’s pretty cool. You should be sure to go look at it.) Seeing those drops of insulin made me think of the blood sugar that it controls. What would the equivalent of all that blood sugar look like outside of the body?

Let’s see . . . the average adult body has 5 liters of blood, and a typical nondiabetic blood sugar reading might be 100 mg/dL (5.5 mmol/L). That means that there’s about

5 L x 10 (dL/L) x 100 (mg/dL) = 5,000 mg

5 grams of sugar in the blood.

A typical sugar packet contains 2-3g of sugar. So we’re talking about trying to control about two packets (or one teaspoon) worth of sugar with those tiny drops of insulin.

But blood glucose isn’t the only “sugar” in the body. There’s also glycogen stored in muscles, ready to be used whenever we start any kind of aerobic activity. Typically, about 40% of a healthy body is muscle, and 1% of the weight of that muscle (according to Wikipedia) is glycogen. So, if I weigh 150 pounds (or 70kg), the amount of muscle glycogen is 70 x 0.4 x 0.01 = 0.28 kg. That’s 280 grams (about 10 ounces, or 107 packets . . . some of which I “liberated” from the office).

The average person also has 120g of glycogen stored in the liver. Those 120g are about the same as 46 packets of sugar. This glycogen is released from the liver by glucagon and other “fright or flight” hormones. Dropping insulin levels during exercise also release it. This is the stuff you want to be able to tap into when you’re exercising.

Adding all of that blood glucose and glycogen together, you get about 400 grams of sugar (280 + 120 + 5). That’s about 9/10 of a pound of sugar, which looks a little like this:

But all of this carbohydrate pales in comparison to the amount of energy stored as fat in even the leanest body. It’s not only more plentiful; it’s also more energy dense, containing more than twice as many calories. The four hundred grams of sugar in an athletic 150 pound body stores only about 1,600 calories, which only lasts a couple of hours in an event like a marathon. (That’s why it’s necessary to take on extra carbohydrates during exercise.) That same athlete might have 15% body fat. So that healthy person’s body has 70 kg x 0.15 x 1000 = 10,500 g (or 23 pounds) of fat. There’s an almost infinite amount of energy stored in body fat. And by infinite, I mean about 94,500 calories. That’s a lot of energy. About 60 times more than carbohydrates.

So let’s recap: