Fat: the good, the bad and the ugly

It can feel like we're constantly bombarded with claims and counter-claims about the harms of cholesterol and fat. Now, according to recent headlines, there's controversy over whether traditionally 'bad' saturated fats, like butter, really are 'bad' for our hearts. So how do we know what to believe? And what should we eat to keep our hearts healthy? To get to the 'heart' of the issue, Kat Arney spoke to Peter Weissberg, medical director at the British Heart Foundation...

Peter - When it comes to these sorts of study, you can't rely on any one study. So, headlines based on a new study that says a particular dietary constituent is either good or bad for you is probably not worth taking a lot of notice of. What really matters is the cumulative evidence of many, many studies over many, many years. This is true of all forms – medicine and also all forms of research. You should never really take the word of one particular study. And in those circumstances, when you look at the totality of the evidence that’s available, and the weight of the evidence that’s available, that evidence suggests that a diet that’s very high in saturated fats is probably bad for your heart. A diet which is low in saturated fats but higher in polyunsaturated fats is probably good for your heart. The problem with that is that it’s much harder to do carefully controlled, randomised control trials of different dietary approaches to determine which is the best way to achieve firstly the lowering of the bad cholesterol, but secondly, ensuring that the rest of the diet is sufficiently good for you, that you're not substituting something good. In other words, taking out the saturated fat from your diet with something which may be very harmful, putting loads and loads of calories for instance which will put you at risk for other reasons. So, I think the focus perhaps over the last few years on particular nutrients whether it be saturated fat or whether it be salt or whether it be sugar is not that helpful. What we really need is a reasonably balanced diet.

Kat - We’ve seen some headlines recently saying things like, “Margarine will kill you but butter is absolutely fine.” In terms of the argument about good fats, bad fats, trans fats, unsaturated fats, is there something that we can take away and think about from this?

Peter - Well, I think with the trans fats, where they're concerned, I think the evidence is pretty strong. They're not good for you. Actually in the UK, most of the trans fats have been taken out of the margarines and the softer spreads. So, from our perspective in the UK, it’s not really a big issue any longer. Whether you eat butter or whether you eat the lower cholesterol spreads, I think it’s entirely up to you. The important message is that if you do eat butter, don’t eat loads of it. If everything you eat is layered with butter and if you cook in butter all the time that you're taking in a very large amount of butter then that may be bad for you. And that really applies to all the other nutrients. If you overdo it, you're probably not going to do yourself any favours. If you cut it out completely, you're probably going to do yourself no favours. When it comes to dietary constituents, we’re never going to have categorical (Carl Stein) black and white evidence. It’s always going to be a balance of best evidence available and that’s liable to change. There is only one (Carl Stein) certainty about diet and health and that is, if you don’t eat, you die. So, you have to eat something.