Odgovor Če apr 20, 2017 02:44

Raw data from a 40-year-old study raises new questions about

Records Found in Dusty Basement Undermine Decades of Dietary Advice

Raw data from a 40-year-old study raises new questions about fats

If biology has an Indiana Jones, it is Christopher Ramsden: he specializes in excavating lost studies, particularly those with the potential to challenge mainstream, government-sanctioned health advice.

His latest excavation—made possible by the pack-rat habits of a deceased scientist, the help of the scientist’s sons, and computer technicians who turned punch cards and magnetic tape into formats readable by today’s computers—undercuts a pillar of nutrition science.

Ramsden, of the National Institutes of Health, unearthed raw data from a 40-year-old study, which challenges the dogma that eating vegetable fats instead of animal fats is good for the heart. The study, the largest gold-standard experiment testing that idea, found the opposite, Ramsden and his colleagues reported on Tuesday in BMJ (formerly the British Medical Journal).

Although the study is more than just another entry in the long-running nutrition wars—it is more rigorous than the vast majority of research on the topic—Ramsden makes no claims that it settles the question. Instead, he said, his discovery and analysis of long-lost data underline how the failure to publish the results of clinical trials can undermine truth.

Absent a time machine, it’s impossible to know how publication of the study, conducted in Minnesota from 1968 to 1973, might have influenced dietary advice. But in an accompanying editorial, Lennert Veerman of Australia’s University of Queensland concluded that “the benefits of choosing polyunsaturated fat over saturated fat seem a little less certain than we thought.”

The Nixon-era experiment had produced only a single journal paper, in 1989, which concluded that replacing saturated fats found in meat and dairy products with vegetable oils did not reduce the risk of coronary heart disease or death. But it had few quantitative data and little statistical analysis, and was silent on many of the questions the researchers told NIH, which funded it, they intended to answer.

Ramsden wondered if there was more data from the study somewhere.

In 2011, he sought out the sons of the experiment’s principal scientist, Dr. Ivan Frantz of the University of Minnesota, who died in 2009.

“I told him I recalled lots and lots of records, whole chests full of records—IBM [computer] tapes—back in Minnesota,” said Dr. Ivan Frantz III, a neonatologist at Beth Israel Deaconess Medical Center in Boston.

Dr. Robert Frantz, a physician at the Mayo Clinic, drove 90 minutes to his childhood home, to search file cabinets. On his third trip he spied moldering, unlabeled boxes in the far corner of the basement. Inside were ancient magnetic computer tapes and reams of yellowed documents. The subject line in his email to Ramsden was “Eureka.”

After getting the tapes translated into formats that modern computers can read, Ramsden and his colleagues discovered what had been hidden for nearly half a century: records on 9,423 study participants, ages 20 to 97, all living in state mental hospitals or a nursing home. It was the largest experiment of its kind.

It was also one of the most rigorous. Participants were randomly assigned either to the group eating the then-standard diet, which was high in animal fats and margarines, or to a group in which vegetable oil and corn oil margarine replaced about half of those saturated fats. Such a randomized controlled trial is considered less likely to produce misleading results than observational studies, in which volunteers eat whatever they choose. Observational studies are weaker than randomized ones because people who eat one way, rather than another, might have characteristics that benefit their heart health.

And because the Minnesota participants were in institutions that prepared all their meals and kept records, the scientists knew exactly what they ate for up to 56 months. Many nutrition studies have foundered because people misremember, or lie about, what they ate.

https://www.scientificamerican.com/arti ... _HLTH_NEWS
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