It's very easy to think that as a vegetarian you have a healthy diet. However, most vegetarians eat a lot of dairy products (most of which are high in saturated fats, which increase blood cholesterol levels) and eggs (which are high in cholesterol). This can lead to high blood cholesterol even if you are not overweight. High cholesterol levels have been linked to increased risk of heart disease and strokes (though the health issues around cholesterol are complicates, as I'll talk about later in this post).
So, if you need to control your cholesterol levels, what can you do within a vegetarian diet?
You can cut down on eggs, but for some people eating eggs doesn't raise their blood cholesterol level even though eggs are themselves high in cholesterol (its complicated).
Dairy products (specially cheese) are always a problem though because they contain lots of saturated fats, which increase blood cholesterol levels. So you may want to replace them with something else. The obvious choice as any vegan would tell you is to use soya products - most people have heard of tofu and soya milk but there are also soya cheeses and soya yoghurts. I've been trying soya cheeses and struggled at first, because quite frankly some of them are pretty disgusting (no matter the cheery slogan on the packaging that says: "A Delicious alternative to cheese!") though I have now found one that's palatable. Soya products can actively reduce cholesterol and can also reduce the risk factors for certain types of cancer. However, there are some health concerns about soya products, you can read about some of them on the EnviroSeeker blog and some people suffer from soy allergy. There are also concerns about the amount of processing required to make soya beans palatable, though many cheeses and yoghurts are highly processed anyway.
Other foods that can help to reduce cholesterol include foods that contain soluble fibre (such as oats and pulses), some nuts (particularly almonds) and dark chocolate (with cocoa content over 70% - you can see a video of the many health benefits of dark chocolate here).
Other foods that are high in saturated fats (which increases blood cholesterol) include coconuts and palm oil (and you should avoid palm oil anyway because of its connection with the loss of rainforest in Indonesia and across the world). Palm oil crops up everywhere, even in health food snacks and mueslis that are otherwise full of oats and almonds, so you have to keep your eyes open! It's generally a good idea to cut down on processed foods.
Of course, I'm not a qualified dietician, and can't guarantee this post is entirely free of contradictions (though I have tried to make it as accurate as possible). If you're really interested in finding out more, there's a good, detailed article about cholesterol and dietary fat here. And it really is complicated because cholesterol is thought to be necessary for brain health, so you don't want to cut it out of your diet altogether. There's a very good article about the benefits of cholesterol here (thanks Diana Moll for that link).
As ever, text in red contains hyperlinks which take you to other webpages where you can find out more.