In praise of sugar

1.5 liter bottle of Pepsi Cola, 3/4 full

This acidic solution of sugar passes quickly through an empty stomach and is absorbed by the body in a matter of minutes. It also tastes quite good. I would not recommend downing a large bottle of the stuff in one sitting, though! One glass at a time is enough.

I notice lately that popular science and health sites brand ordinary table sugar as “toxic” and “white poison”. I hope to convince you, noble reader, that sugar is actually the power of this planet’s yellow sun, stored in crystals that can be readily used even by ordinary humans.

Let me say a few words about myself. I am a (physically) ordinary man in my fifties, with an office job but also an outdoors hobby: The Augmented Reality game “Ingress”, where players have to visit “portals” scattered around town. Because of this, it is normal for me to walk 10 kilometers in a day, some days 20 kilometers or above. (10 miles is about 16 km, for those on that side of the sea.)

When a man my age has walked 10 km, it is normal to feel a bit tired in the legs. I am not actually an athlete, after all, but an office worker. This is when I sit down, drink half a small bottle of Pepsi Cola, and wait for the effects to kick in.

Pepsi contains a small amount of caffeine, which probably helps with feeling a bit more energetic. But it also contains 10% sugar, your supposed “white poison”. Let us take a closer look at this substance, and what happens when it is ingested by the human body.

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Sucrose or table sugar is at the same time one substance and two: Each molecule of sucrose contains one molecule of glucose and one molecule of fructose, held together by a single atomic bond. The combined molecule is stable when stored, but breaks readily into its two parts early in the digestion. What is absorbed from the small intestine is therefore actually molecules of glucose and fructose. These are treated differently by the body.

The glucose passes directly into the bloodstream and is brought to every cell in the body. Muscles will absorb glucose if they have been used, as they seek to replenish their energy and glucose is the easiest form of energy carrier to be shared through the blood. It can also be used by all other cells, and is the preferred fuel of the brain. (The brain can switch to an alternate fuel source in emergencies such as hunger, but will use glucose if this is found.)

Meanwhile the fructose is held back in the liver, the gatekeeper of the inner body, as all blood from the intestines passes through there. The reason it is held back is that the cells of the body cannot burn fructose directly. But the liver can convert it into any of two other substances. The preferred substance is glycogen, which is the body’s medium-length energy storage. The liver contains enough glycogen to power the body for about 24 hours of normal activity. The more active you are, the more glycogen is stored. If this reserve is not full, the liver will mainly convert fructose to glycogen and put it away. When the body has burned through the glucose from the first sugar rush, and the blood sugar starts to fall below ideal values, glycogen is converted to glucose again and released in the blood. In this way, fructose become glucose by an indirect process, one that only releases the sugar into the blood when needed.

If the glycogen storage is full, the liver will instead seek to convert fructose into triglycerides, the building blocks of fat. These are then released in the bloodstream, and will hopefully find a hungry muscle eventually. If not, they may be put away in fat cells for further use, or if worst comes to worst, they may settle on the walls of arteries. This is widely agreed to be a bad thing, causing angina and heart infarct, blood clots and stroke.

So what happens to the sugar from my half bottle (about one and a half table glass) of Pepsi? Well, I have just walked 10 kilometers and burned about 500 calories. (That corresponds to more than a deciliter — half a glass — of pure white sugar, if you wondered.) It is a safe bet that the fructose will go straight in the liver’s storage this time. Your liver may vary, depending on your activity level.

When the first surge of glucose raises the blood sugar above normal levels, the pancreas releases insulin. This hormone basically declares hunting season on glucose: The muscles open up their membranes and draw in as much glucose as they can handle, burning it instead of fat while supplies last. They can also rebuild their own little storage of glycogen, if they have the time. This storage is local to each muscle cell and is not released in the blood like the liver does.

In addition to muscle cells, fat cells also are invited to the glucose rush. But they are slower and less efficient, and they are not going to get that time: The feedback from the muscles and the brain itself inform me that the sugar rush has begun. My body is now burning with the atomic power from the core of the sun, captured by unsuspecting sugar cane which made the ultimate sacrifice to bring me their precious sugar crystals. It is time to get to my feet again and enlighten the city for another hour or two!

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And this, noble reader, is why I want to tell overly eager science journalists: It is not sugar which is toxic; it is the passive lifestyle that is toxic. If you don’t make a serious dip in your energy storage, then indeed sugar will do bad things to your body. Your muscles won’t absorb more sugar than they need, your fat cells will grow as fast as they can but the sugar may still linger in the blood for quite a while. The blood pressure will increase, the arterial walls will harden and attract fat made from fructose in the liver. So remember: Friends don’t let friends eat sugar and drive. Let’s go hack some Ingress portals instead … or play in the hay or whatever tide lifts all your boats. ^_^

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