Sunday 2 July 2006

Pic of the day: Possible side effects of drinking too much soda? OK, not literally. But still, there is a connection...

Sugar and heat

In the heat of summer, we grow thirsty more often. We could fix this by drinking water, but pure water tastes rather bland. And in our modern society, it is rarely far to go for a can of soda or (for the slightly more health conscious) juice or sweetened milk drink. It tastes great, but unfortunately it has another side effect besides rotting your teeth: It makes you hotter.

I have mentioned before how humans have a "weakness" compared to most other mammals: We suck at making fat from sugar. You may ask: How come we gain weight so easily, then? Actually we don't, compared to your friendly barnyard animal. Ask any animal farmer about the speed that their animals grow, and you'll realize that we lag far behind. But even at that, we add fat by hiding it away and burning sugar instead as long as we have plenty of that. We are actually quite good at this. As well we should be, as a species with no secure fat supply neither in our food nor by our own production.

So we use sugar for all our energy needs if there is plenty of it in the blood. Which there is if you sip sweet drinks all day. But at some point we simply don't need more sugar, and what then? First, the body checks if there is room in our storage of quick energy, the glycogen in muscle and liver. Glycogen is a complex starch that is made up of simpler sugar (glucose mainly). We convert sugar into glycogen and back at great speed and efficiency. But the quantity is limited, usually enough for a day or two of our average energy needs. If you return from a long swim, you have probably emptied some of this reserve and your next can of soda goes there. But if you just laze around in the sun, your storage runs full pretty fast. And this is where the fun begins.

It would be a shame to waste all the sugar (as diabetes patients do through the urine). So instead the body makes a valiant attempt to convert it to fat, by splicing it into existing fat molecules. As I said, we suck at this, but given enough time and sugar it is possible to slowly extend our fat reserves. Only a small amount of the chemical energy bound in the sugar ends up as fat, though. The rest is lost. And in living organisms, "lost" energy means heat. Any inefficient process in a living cell causes loss of energy through random heat. This is not a big problem in the winter, where it simply means shivering less. But in summer, it is definitely a bad idea. Because to lead away the heat, we sweat. And in sweating, we lose water. And then we grow thirsty again... and grab another soda.

This is not to say that a sugar-free diet will keep you cool on a hot day. It cannot block the incoming heat, after all! And even basic maintenance of the body generates quite a bit of heat, even when you are not exerting yourself in any way. You still breathe, your heart still beats, and even the brain keeps running (though you may sometimes doubt it, in some people). But if you take in more sugar than needed for this daily survival, the rest will for the very most part end up as heat. Think of that, ye thirsty, and despair.