Should people be eating more fat?

Earlier this year, for example, a systematic review, funded by the British Heart Foundation and with the rather dry title "Association of dietary, circulating and supplement fatty acids with coronary risk" caused a stir, BBC News reports. Scientists from Oxford, Cambridge and Harvard, amongst others, examined the links between eating saturated fat and heart disease. Despite looking at the results of nearly 80 studies involving more than a half million people they were unable to find convincing evidence that eating saturated fats leads to greater risk of heart disease. In fact, when they looked at blood results, they found that higher levels of some saturated fats, in particular a type of saturated fat you get in milk and dairy products called margaric acid, were associated with a lower risk of heart disease. You can watch Trust Me, I'm a Doctor, with Michael Mosley and others, on Wednesday 15 October at 20:00 BST on BBC Two or catch up on iPlayer Although there were critics, NHS Choices described this as "an impressively detailed and extensive piece of research, which is likely to prompt further study". Some academics queried the paper, others worried that this sort of research would confuse people and the message they would get would not be "it's OK to eat more of some forms of fat" but that "it's OK to eat lots more saturated fat, even if it is in pies". We know that current levels of obesity have been fuelled, at least in part, by snacks like muffins, crisps and cakes, all high in fat, sugar and calories. When I talked to one of the researchers behind this paper, Prof Kay-Tee Khaw of the Department of Public Health at Cambridge University, she was quite clear that her research was not a licence to fill up on junk food but she also accepted that new research made the dietary picture more complicated.

Khaw told me that there is good evidence that eating a handful of oily nuts a few times a week will reduce your risk of heart disease, despite the fact they are contain saturated and unsaturated fats. She said the evidence for full-fat dairy is less strong, but she is quite happy to eat butter and drink milk. She is also happy to eat red meat, although she is concerned about where it comes from. "It's very clear that cattle that are fed on pasture have very, very different fatty acid patterns from cattle that are corn-fed. So I think how the animal has been reared probably has a big impact in its nutrient profile and, presumably, on health outcomes, which may be why there's such conflicting evidence, because it depends on where the source of your food comes from." In the US, where most cattle are corn-fed, there is good evidence that higher rates of red meat consumption are associated with higher rates of heart disease. In Europe, where cattle are more commonly raised on grass, the association seems much less clear. Although eating some types of fat may not be as damaging as we once thought, surely fat is bad for you because it makes you fat? Not necessarily. A recent study, this time published in the Scandinavian Journal of Primary Health Care, "High dairy fat intake related to less central obesity", certainly questioned the link.