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Op dinsdag 22 april 2014 12:07 schreef DarkAccountant het volgende:Midas zat die Belg ook al vanaf minuut één onderuit te halen en als charlatan te bestempelen, terwijl hij eigenlijk wilde aangeven dat wat hij had geschreven wel degelijk op wetenschappelijk onderzoek gebaseerd was. Van "Harvard", gaat onze grote bioloog Midas Dekkers vervolgens even al het onderzoek van Harvard University onderuit halen door te zeggen dat er helemaal niks van klopt.
Dat zei hij niet echt. De belangrijke kritiek die door Maarten 't Hart ook expliciet werd aangehaald is dat er op basis van cohort studies allerhande conclusies werden getrokken en adviezen worden gegeven. Studies met een dergelijke opzet dienen in principe als hoofddoel het genereren van hypotheses die je vervolgens d.m.v. RCT's en dergelijke test. Het is vrij gangbare kritiek op het werk van Willett en consorten. Zie bijvoorbeeld
dit artikel:
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But as Willett’s influence has grown, so has criticism of the very nature of his research. That’s because large cohort, or “observational,” studies can show associations and correlations, but never causation. The nurses’ study can suggest that people who took folic acid had a lower risk of colon cancer, but that doesn’t prove folic acid — and not something else — actually reduced the risk.
Taubes, who recently cofounded the nonprofit Nutrition Science Initiative for research, stresses that observational studies are equipped only to generate hypotheses. To prove them, scientists have to turn to a randomized controlled trial. In these, participants are randomly assigned into either an intervention group, which gets the treatment or special diet, or a control group, which gets a placebo or a standard diet.
Willett’s team falters when it jumps directly from hypothesis to dietary edict, Taubes says. “I would have no problem with Professor Willett making the statements he does if he attached caveats. If he said, ‘I think this is true, but we don’t know for sure.’ ”
Taubes points to a 2013 review of nearly 300 scientific papers. In more than half of them, the authors gave some kind of medical advice based on their observational studies. Yet only 14 percent of those papers called for randomized trials to validate the recommendations. That, Taubes argues, is a function of the blinders you don’t even realize you’re wearing when you’re so convinced that your study can give you the right answers.
The most dramatic example, he says, is hormone replacement therapy. The recommendation that post-menopausal women take HRT to guard against heart attacks, which was based on findings from the nurses’ study, was scrapped when trials concluded that the therapy actually increased the risk of heart disease, stroke, and breast cancer for some women.
[..]
Manson works both sides of the research fence, as an investigator on the nurses’ study and as someone also heavily involved in randomized trials. In between sips of her soup, she rattles off a half-dozen cases in which scientists reported promising findings based on observational studies (not necessarily Willett’s), but then the randomized trials found no benefit and even some elevated risks. Beta carotene was once thought to lower the risk of cancer and cardiovascular disease, but beta carotene supplements increased the risk of lung cancer in smokers in the trials. Vitamin E, a supplement many in the medical field were themselves taking 20 years ago, was linked to increased risk of hemorrhagic stroke in one trial and increased risk of prostate cancer in another.
Glancing down at my legal pad, where my notes of all her examples have formed sort of a wall of shame, I ask, “Are there any examples where the results of the randomized trials supported the initial hype?”
She pauses and then nods. “Yes, multivitamins.” The results of a trial published in 2012 showed a reduction in cancer. “But that was tested in men only,” she says. “We’re trying to do a follow-up study in women.” (She later adds several more apparent success stories to the list, including heart-healthy omega-3.)
Manson calls Willett “critically important — a pioneer in the field.” She says the fact that some of the trials she has been involved in have cast doubt on some of the findings from Willett’s studies doesn’t diminish the value of his contributions. “Our appreciation of the role of diet has really increased because of the research Walter has done,” she says.
For his part, Willet insists many of the findings from his studies have been supported in trials, such as the reduced risk of colorectal cancer with aspirin use and the lower risk of cardiovascular disease and Type 2 diabetes with — wait for it — nut consumption.
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Afterward, I grab Gardner as he is heading for his vegan lunch. He explains that what we know about nutrition so far comes from big studies like Willett’s and small targeted trials like his. Willett watches thousands of people, year after year, to see who dies and who lives. But Willett can’t prove that it was, say, the whole grains in their diet that protected them — so Gardner runs randomized trials to isolate one element and try to determine cause and effect. Here’s what he finds instead: “One little thing at a time never makes a difference.”
Mensen die op basis van cohort studies conclusies over causale verbanden trekken en er vervolgens adviezen aan verbinden zijn in wetenschappelijke zin prima te classificeren als charlatans.