Some cholesterol matters ... 'cos cholesterol matters.I said to Adrian the other day that I was keen to make sure my cholesterol levels weren't too bad - I realised I didn't actually know what cholesterol was, or why some of it could be 'good' and some of it 'bad'. And that the labels showing the nutritional content of food rarely mentions cholesterol. He pointed me at a little book that would answer both my questions.I've now read a lot of the material on it that deals with cholesterol, plus some related subjects around cardio-vascular disease, such as blood pressure. As much to check I've understood it, I've tried to do a short summary ...Cholesterol is one of many fats in our bodies, and we can't do without it, as it helps form cell membranes, some important hormones, and helps absorption of fat-soluble vitamins. The problem comes if we have too much of it floating around. Despite what I'd assumed, most of our cholesterol doesn't come from what we eat, but is naturally produced in our livers. LDLs carry cholesterol from the liver to the cells - but have the rather Royal Mail-like tendency to lose of its fatty payload in the arteries along the way, leading to the build-up of deposits which produces angina, blood clots and heart attacks. HDLs on the other hand carry spare cholesterol from cells back to the liver to turn them into bile acid which helps break down ingested fats. So what's the fuss?Well, the amount of fat-laden foods we eat does determine what goes on in the liver and then the blood. Eat more fats and more LDL is produced. In this, saturated fats are worse than polyunsaturated ones, which are worse than monounsaturated ones - and trans-fats are possibly the worst of all.It suggests blood levels of LDL + HDL need to be less than 5, and ideally less than 4. Back in 2002 mine was 4.8. It all suggests that more importantly that the TotalChol:HDL ratio be well below 4.5. Mine was 5.3. So, some work to do. Hence the recent exercise. There's lots of sensible-sounding advice on diet in the book, which I can summarise for me as being to eat more oily fish and nuts - particularly instead of some red meat and processed grains. Egg yolks - despite having more cholesterol than most foods - are also good for raising HDLs and lowering LDLs.The book also mentions Body Mass Index as being another useful indicator - it should be between 18 and 25. In 2002 I was 21.9, and I reckon I'm now 22.7.