Fear of fat – A paradigm best forgotten?

Frying BaconBy Jennifer Burr PhD

The demonization of dietary fat as the harbinger of bad health, including heart disease and type II diabetes, has been largely accepted as common sense. This idea guides the advice that governments give on what constitute a healthy diet and is based upon the hypothesis that fat contributes to what has been labeled the ‘chronic diseases of lifestyle’. But what if this hypothesis is wrong and fat may be good for us? The implications are enormous, calling for a shift in the paradigm of nutritional education, and an acceptance of a contrary hypothesis in our understanding about dietary fat in the causation of heart disease. But if this idea is wrong, then how has it become so enshrined?

Fear of saturated fat began in the 1950s when Ancel Keys suggested that saturated fat raised cholesterol, which in turn caused heart disease. The evidence which purported to link saturated fat with heart disease came from Keys’s ‘Seven Countries Study’. The study is now recognized to have had substantive weaknesses; among them that the countries he chose were not randomly selected, but deliberately targeted to support his hypothesis. The sample did not include countries with a high fat diet and which still had a low rate of heart disease (for example France and Sweden). The nutritional data was predicated upon a sample of less than 500 men, hardly statistically significant, and did not control for smoking.

However, after adoption of dietary guidelines, Keys’s hypothesis, that fat causes heart disease, had become the paradigm of dietary advice in which we are expected to reduce fat intake. In place of fat it is recommended a healthy diet should be made up of carbohydrate. For example, UK authorities recommend that two-thirds of calories should come from carbohydrates.

Yet increasingly it is argued that there is no solid evidence that fat is the main culprit for heart disease. For example, a 2002 pooled analysis of 11 American and European cohort studies (n = 344,696 persons) found no association between decreased risk of heart disease and replacement of saturated fat with carbohydrates. What is more, the approach was associated with a slightly increased risk of heart disease[1]. More recently, a 2010 study[2] found that the composition of fat intake can have a beneficial effect on heart disease.

So does this lead us to think there is a problem with the Keys paradigm? After all, excessive intake of refined sugars has been demonstrated to be particularly insulinogenic resulting in increased fat deposition, leading to excess weight, obesity, type II diabetes and heart disease. A reanalysis of Keys’s data has found that sugar intake correlated with heart disease more than fat. Dietary advice has followed this model for over 50 years but as Professor Tim Noakes, author of The Real Meal Revolution, points out, if dietary advice was effective: ‘cardiology and cholesterol-lowering drugs should be going the way of the dinosaur. Instead both are major growth industries’. The protection of a multi billion pound cholesterol lowering industry goes some way to ensure that a competing hypothesis cannot readily be taught. The question remains how much longer will it take to accept the evidence that fat is no longer the problem and might be part of the solution.

References

[1] Hu, F.,Willett, W. (2002) Optimal diets for the prevention of coronary heart disease. In JAMA. 288(20) 2569-2578

[2] Mozaffarian, D. Micha, R., Walace, S. (2010) Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Med. 7:e1000525.

Image by Sam Breach under a Creative Commons License

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