Monday, October 22, 2007

Low fat food does not protect against cancer

bread and butter
This truth, told by one of the largest diet trials ever, is not necessarily inconvenient for those who care about healthy food. The main reason is this one: If low fat food does not prevent cancer, then high fat food will not cause cancer. Whenever science is able to kill food-related fears, this must be good news.

Let's turn to the details of the big intervention study about low-fat diet and cancer incidence: About twenty thousand elderly women have switched to a diet that provided twenty percent less energy from fat. About thirty thousand women, randomly assigned, stayed with their usual food. All women have been followed up for an average of eight years and their cancers have been assessed.

All cancers taken together, no difference has been found between the low-fat and the food-as-usual control group. Only in ovarian cancer, a very small difference has been found. In the first four years of comparison, more cancers have been found in the low-fat group (0.52 cases per thousand person-years) than in the control group (only 0.45 cases). In the next four years, things seemed to turn in favour of the low-fat diet, with only 0.38 cases compared to 0.64 cases in the control group. In other words, in the first four years of low-fat diet intervention we see a somewhat higher risk of the dieters and in the next four years a somewhat lower risk. The figures, all in all, are very low, indicating that these differences are just a result of chance.

Very low figures indeed. If we assume a real effect (which is not proven by this study), then a low-fat diet may reduce the incidence of ovarian cancers (only those) after the fourth year of dieting (not before) from 0.64 to 0.38 cases per thousand years. In other words: Four thousand years of dieting may at best prevent one single case of ovarian cancer eight years later. This is such a tiny effect that we quickly should forget about it.

Fat is not all and cancers are not all

Of course, there are many more aspects of healthy eating than just fat. There are also vitamins, minerals, fibers and all this healthy stuff. And there are many more diseases than cancer, such as heart attacks, strokes, diabetes and what else may occur.

Thus, this study is not a refutation of healthy eating as such. But it casts some healthy doubts and skepticism on all claims that try to make us believe that we should diet to stay healthy. In this sense: Enjoy your bread and butter!

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