Wednesday 18 August 2004

Stomachs are not combustion engines.

G comments on my last post thusly:

I think there's a danger that in much the same way that people erroneously believe low-fat stuff is by definition good for them (something that isn't helped by misleading packaging), they'll believe that low-carb stuff is low in calories (when in many cases, it's anything but).

To which I reply, "Ah, the calorie falacy."

Firstly, I think G's plain wrong about people being misled: no-one who buys this food thinks that low-carb stuff is low in calories, because people who are into low-carb diets tend to believe that their weight loss and weight gain don't depend on their calory intake. Secondly, these people are right.

By now, the Atkins Diet is sufficiently popular that most of us know at least one person who has lost loads of weight while living on a diet of steak, fried eggs, dripping, bacon grease, and lard. Regardless of how well we may understand the biochemistry behind it, it should be clear to everyone by now that it's not the calorificity of a food that determines how fattening it is. Yet everyone still clings on to this belief that the way you lose weight is by cutting your calory intake; people still talk about taking in less energy than you expend. Trouble with this is, your body is not a simple mechanical input/output device.

A food's calory count (for those of you that don't know) is a measure of the amount of energy you get out of that food by burning it. And that's not "burning" it as in going for a run; it's actually burning it, by setting it alight. As you may have noticed, this rarely occurs in your stomach, for sound evolutionary reasons.

Simple example: wood. Wood is dead high in calories. That's what makes it such a great fuel. So, if I eat nothing but sawdust for a week, I'll put on loads of weight, right? This is obviously bollocks. (Well, I might put on weight if I get constipated, but I wouldn't put on fat.) Humans don't eat wood. It'd pass right through me, mostly undigested. Because, as we all know if we stop to think about it, our digestive systems treat different foods in different ways. This is because we convert fuel into energy not by burning it, but through chemical reactions, and different foods are made of different chemicals. Furthermore, our biochemisty adapts to changes in our diet, which is why cutting out carbohydrate completely has such an extreme effect, as Dr Atkins discovered.

The calory-intake model works very well for steam engines: you can chuck any old shit on the fire, so long as it burns. With animals, more sophistication is required.


Gary said...

Hey, it was a comment in a blog post, not a proper article.
I agree with you up to a point, but of course I'm still right. Heh.

Any single measure is flawed, but calories are still the best ready reckoner; of course, carbs are processed in a different way but ultimately the reason why a lot of people go for these kinds of diets is because they're not willing to accept that if they eat a little less and exercise a little more, they'll lose weight. Through strict scientific study I've discovered that if I eat a low-carb diet in huge quantities and then sit on my fat arse all the time, I put on weight; if I eat a balanced diet with slightly smaller portions and actually go outside from time to time, I lose it. Amazing!

Squander Two said...

Hey, I can post about comments on my own blog if I want.

Anyway, you're wrong: calories are certainly not the best ready reckoner. Again, when you see a diabetic in action, you realise just how flawed this idea is. What makes you put on weight the quickest is insulin, which converts sugar to fat pretty much instantly. You produce insulin in response to sugar in your bloodstream, and the quickest way to get sugar into your blood is by eating sugar. Actually, no, the quickest way is by drinking beer: amazingly enough, the sugar in beer is actually absorbed into your blood even more efficiently than pure glucose. But you see the point.

By far the best ready reckoner is the amount of refined sugar you eat. I'd also say that refined fat is about a zillion times worse than the natural fat you get on meat and in milk. If you were right that calories are a good measure, the world wouldn't be so full of people who go on multiple ultra-low-calorie diets yet fail to lose weight -- sometimes even putting weight on.