This is the way that _I_ understand it, which is doubtless not only smplistic, but very wrong. But what the heck ...

In the BOD (Bad Old Days) when we ate high levels of both fat and carbs, our bodies used the carbs (& stored what it didn't use as fat) and stored or otherwise disposed of the fat in lovely little niches like our arteries. In the BOD our bodies were using the nasty ol' carb burning fuel system, so it stored the fats rather than used them.

But then we all got wise, and dropped out those carbs, and our metabolisms (after a day or two of whining about it) started to get into the fat-burning thing, and now the fats are used up as they were in our caveman days (which in my case aren't that far behind me). We have very few carbs to burn, so the fat gets burned instead.

I've just had my first blood test since being on Aitkins, and my cholesterol is within normal limits for the first time in years and years of low fat eating.

Of course, someone probably has a far better explanation than me, but that's the way I understand it, and it keeps me happy, and so I stick with it.