Thursday, February 09, 2006

Dominoes: fat, salt

Until yesterday, everyone "knew" that low-fat diets were the cornerstone of a healthy diet. Publication in the Journal of the American Medical Association of results of an 8-year, $415 million study of nearly 50,000 American women found that what everyone "knew" was dead wrong. There was no health benefit among the almost 20,000 women on low-fat diets. They had the same incidence of breast cancer, colorectal cancer, heart disease and stroke as the 29,000 women who ate regular diets. Experts on every side of the issue agree the study is conclusive due to its size and quality ... and $400+ million pricetag. Expensive study? You bet. Worthwhile investment? Priceless. Not only have we spent billions of dollars researching low-fat diets, but food manufacturers have invested additional billions re-engineering the foods we eat. Americans have not only paid premium prices for specially-concocted low-fat foods and kept low-fat cookbook publishers in business for the past quarter-century, but consumers anguished over their inability to strip even more fat out of their daily diets. No more. This was a front-page, above-the-fold story in every newspaper in the country (e.g. The Washington Post - "Low-fat diet's benefits rejected" - and NY Times - "Low-fat diet does not cut health risks, study finds"). The New York Times editorialized: "The results clearly surprised the investigators and may sound the death knell for the belief that reducing the percentage of total fat in the diet is important for health." While this is clearly the diet-related news story of our new millennium, most discussions have omitted mention of three additional key lessons we should be learning:
  • First, medical science is evolutionary. What we "know" today is subject to further investigation and revision as we learn more. It is a process of creative destruction. We need to be prepared to "move on" when the evidence demonstrates the error of our ways.
  • Second, we can save time, expense, anguish -- and people's health -- if we are a bit more patient and humble about the confidence we place in the results of medical studies. All studies are not of the same quality. This was a high quality randomized controlled trial -- the "gold standard." A well-done randomized trial of health outcomes should be required before our officials begin the drumbeat -- and trigger billions of dollars of expenditures -- for a massive dietary change. To re-state an earlier post on this blog: this is why we should insist on true evidence-based public health decision-making. Evidence-based decisions follow a rigorous process defined by the world-renowned Cochrane Collaboration.
  • Third, we should require the same kind of controlled trial of the health outcomes of advice to restrict dietary salt as we now have to restrict dietary fat. There are only ten observational studies of the health outcomes of reducing salt in a U.S.-like population. We need to ask the outcomes question: does eating less salt reduce heart attacks or extend life? We need a controlled trial of this question even though it may cost $100 million or more. As in the case of low-fat diet advocacy, the government is spending multi-fold that amount and compliant food manufacturers are investing huge amounts trying to reduce salt intakes when, in truth, we have no evidence that it will make a difference. In fact, the observational studies show that in populations with salt intakes like the U.S., there is no health benefit and may even be a risk in low-salt diets (see our website discussion).

It is hard to exaggerate the importance of this JAMA study. And it's impossible to ignore the validity of the Salt Institute's observation that pursuing a policy of universal sodium reduction without a randomized health outcomes study is sheer folly.

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