Wednesday 8 February 2006

Pic of the day: Mental states can also influence our body temperature, but I'll leave that part out of it for now. I'm afraid there aren't many "hot" things going on here in my new Fortress of Solitude! But at least I brought my brain...

Fat, sugar and cold

I'm cold almost constantly in the new home. I am simply not used to a house without triple insulated windows and electric floor heating. It's a different generation of house, not to mention that it is a house rather than the apartment I had before. So many rooms to keep warm ... or not. I have eventually decided to concentrate on the home office when it is this cold. I have taken my electric space heater in here, and leave the other rooms to be uncomfortably cold. It is hard enough to keep it warm even in here, with two computers running, a candle and me. Yes, I heat about as much as a candle, probably more now. Like other humans, I produce more heat when the room is cold, all other things being equal.

So how and why do humans produce heat anyway? Like most mammals, we have a constant body temperature. This makes it possible for our enzymes to work at peak efficiency, as the whole mix is optimized for just that temperature. But it does take some energy to maintain this temperature. When it is cold, such as now, the normal leftover heat is not enough. By "leftover heat" I mean: There is always some heat "leaking" from the various processes at work in our body. Heat is a very low-order form of energy, and is created as a by-product from many chemical processes as well as friction during movement.

In each cell, there are many mitochondria, small organelles (cell organs) that burns the components of food – hydrogen and carbon – to produce ATP, the energy carrier of the cells. This process causes a lot of energy to leak out in the form of heat. Not a bad thing in the middle of winter. The muscles obviously use a lot of energy when we move fast or carry heavy stuff, and so the mitochondria work furiously to produce enough ATP. The resulting heat makes us sweat even in mid- winter if we run fast enough and far enough. But even if we don't use the muscles much, we still produce some heat. The brain is always active (though you may wonder with some people) and easily spends 20% or more of the body's energy on a quiet day. And the digestion itself is not a simple sieve letting nourishment filter through. It is working hard, and then the liver has to sift through the resulting molecules, destroying some and converting some. The kidneys are also quite active, the heart is always beating, and so on.

But what you may not know is that sugar makes you hot. It is not entirely safe for all people, but here's what I have found out so far.

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I happened to read in a more than 10 year old issue of Scientific American (before I threw it away) that surplus carbohydrates are quickly burned up, while eating extra fat does not increase the short-term metabolism. In another popular science magazine around the same time I read a small notice that fructose (a slightly more complex form of sugar) seems to increase the speed at which we create fat from carbohydrates. I have a box of fructose powder in my kitchen, it is supposed to be healthier than ordinary sugar in two ways: It is sweeter so you can use less of it, and it gives a slower rise in blood sugar instead of the sharp spikes from ordinary white sugar and glucose. The final part is the point which I have made from time to time in similar entries to this one, that humans suck at making fat. We are good at conserving it by burning other stuff instead, sugar especially, but constructing fat from sugar is horribly wasteful.

Only recently during one of these cold days did I connect the dots here. Let's say you eat sugar to excess. If you don't suffer from diabetes, this isn't dangerous in the short run (though many scientists believe that the sugar spikes damage the body in some way, I'm not sure exactly how). The first thing that happens is that the liver converts sugar to glycogen, or "animal starch". (Muscles, gut and kidneys also do this, but above all the liver.) This nifty storage facility lets you go without food for a day or so and still operate at peak efficiency. (Some people have longer or shorter durations.) When the glycogen reserves are full, the body will attempt to convert sugar to fat for permanent storage, if it just keeps coming. It also uses sugar to power pretty much all your energy needs, where it could have used fat if you didn't have syrup in your veins. But it is the conversion of sugar to fat that caught my interest.

Remember, this is not a very efficient process in humans, unlike some lab animals. So what happens with inefficient processes in the body? Right, they leak a lot of heat. Your organelles flail and struggle trying to make fat, and the work heats you up. Thus, sugar makes you hot. Fructose is somehow going through a different pathway, as seen by its different effect on the blood sugar. Because the body has more time on its hands working with fructose, less is lost to heat. Well, that's my conclusion. But the sugar = heat is pretty certain. It follows directly from the known facts about how the body juggles the different energy sources.

I am a kind of test subject here, I guess. Due to the mysterious illness that hits me when I eat more than a few grams of fat each meal, I subsist on a diet largely of carbohydrates. A complicating factor here is that I've lost quite a bit of my fat reserves over the last 9 months, again because the human body sucks at making fat from carbs. Not that I'm a walking skeleton or anything, but most people my age in the rich world are fatter than I now. Like, more than 80% of them. And more to the point, I wasn't born to be skinny. So my body has duly noticed there's a moderate starvation in my little corner of the world (which there isn't, but tell that to my genes) and has turned down the heat to save energy. Now I move into a cold house and gorge on carbs. Well, actually I cannot physically eat as much as I'd want. But more than I need most days. Which means my body will do its best to rebuild my fat depots. So, let's see what happens. Will I keep feeling cold, or will the body crank up the heat? Who will give in first? And what should I do about my box of fructose sugar?

(The fructose may come in handy if I make my own jam, my own juice and my own yogurt. But if I don't do that now while I'm off the Web, there's not much chance that I'll take it up later unless I learn something really scary.)