Nutrition: Fat Chance

Those who micromanage their diets instead of following Michael Pollan's sensible rule of thumb--eat food, not too much, mostly plants--may be thrown into confusion by a paper just published in the Annals of Internal Medicine.

It describes a meta-analysis (a technique which uses entire studies as single data points in an overarching statistical analysis) of 72 pieces of research involving more than 600,000 people.

Some of these were of what those people ate, or said they ate. Some were of the levels of various fats circulating in their bloodstreams. Some were of both. All had looked for relations between these facts and a person's subsequent cardiac health. And the meta-analysis comes to what will, to many, be counterintuitive conclusions.

Rajiv Chowdhury of Cambridge University and his colleagues found that one bugbear, trans-fats, are indeed associated with heart disease--though they caution that only five of the studies they looked at had pertinent data on these. Other common beliefs, however, were not supported.

They found no evidence that eating saturated fats or having high levels of circulating saturated fatty acids (the digested products of such fats) had any effect on cardiac disease. Nor did they find that omega-3 fatty acids, the current poster-boys of healthy eating, protect against heart disease.

Omega-3 fats are widely sold in capsule form as food supplements. This makes them easier than other fats to incorporate into experiments of the sort that administer something to one group while denying it to another. In their case, therefore, Dr Chowdhury's meta-analysis was based on such experiments. Indeed two big, new trials of omega-3 supplements are going on at the moment. But such trials are hard to do on other sorts of fat, since these are simply part of people's diets.

Many people do not mind being asked either to pop a capsule regularly, or to refrain from doing so. It is understandably harder to persuade them to let someone else decide their entire food consumption for the several years needed to conduct trials like these.

This sort of unwillingness is, indeed, one reason heart disease is a problem. Most people do not have the willpower to stick to a diet, any diet, prescribed by someone else--even the simple one offered by Mr Pollan, who is the author of "Food Rules: An Eater's Manual".

But eating a reasonably Spartan, mixed-ingredient diet, along with a regimen of moderate exercise, still seems the best route to a long and healthy life. Dr Chowdhury and his colleagues are not suggesting that the amount of fat you eat has no bearing on your risk of having a heart attack. What their research does suggest is that, trans-fats aside, the type of fat may not matter.

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