Serum cholesterol: mounting evidence against?
The British Medical Journal (BMJ) has just published a study the findings of which suggest that replacing saturated fats with vegetable oils rich in linoleic acid does not reduce the risk of coronary heart disease (CHD)1.
Using data from the Minnesota Coronary Experiment (MCE) which was a double-blind randomised trial conducted in the late 1960s/early 1970s, researchers found that linoleic-rich vegetable oil effectively reduced cholesterol levels but without any corresponding reduction in CHD or all-cause mortality. In fact, participants who had a greater reduction in blood cholesterol had a higher, rather than lower, risk of death: there was a 22% higher risk of death for each 0.78 mmol/l (30 mg/dl) reduction in serum cholesterol. The research group also reviewed five similar randomised controlled trials, none of which showed any evidence that cholesterol-lowering interventions conferred any mortality benefit.
The authors of the BMJ article conclude that their findings “add to the growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.” Thanks to experiments in the 1950s and 1960s that demonstrated that saturated fat increased and polyunsaturates decreased serum cholesterol which was positively correlated with heart disease risk, it followed that saturated fat was ‘bad for the heart’ and polyunsaturated fat was ‘good’. That received wisdom is now increasingly being challenged. Indeed, in 2015 US dietary guidelines removed dietary cholesterol and total fat as risk factors worth worrying about.
How excited should we be about all this? The MCE findings are derived from a relatively small cohort (2,355 lives, resident in mental hospitals) followed for up to 56 months. Nevertheless, they do rather chime with some of SelectX’s own lipid research undertaken recently, based on multiple journal articles, that suggests that serum cholesterol is of relatively little significance unless concentrations are very low or very high. (However, it should be pointed out that a) lipid-lowering via vegetable oil having no beneficial effect and b) serum cholesterol not being a significant risk factor are not quite the same.)
But concerns that some of the theory behind classic dietary advice is flawed are undoubtedly growing. The ‘diet-heart hypothesis’ that we have been exhorted to believe in over the past few decades is looking increasingly fragile. As the accompanying editorial2 in the BMJ says, while we await clarification we should consume more fish, fruit, vegetables and whole grains; and avoid salt, sugar, trans-fats and over-eating. Sounds like good advice.
- Brit Med J 2016;353:i1246
- Brit Med J 2016;353:i1512