HEALTHWATCH: How Much Proof Do We Need to Eat Healthier?

By Michael Greger M.D. FACLM

Randomized placebo-controlled trials are considered the gold standard of scientific evidence. In such studies, half of the subjects may get the active treatment, and the other half unknowingly get a sugar pill instead.

This works great for evaluating new drugs, but a concern is that evidence-based medicine has made a leap from considering randomized controlled trials to be a high standard to considering them to be the only standard.

This may not be prudent in all circumstances. Consider a review of dietary interventions for multiple sclerosis produced by the esteemed Cochrane Collaboration. In that review, they basically concluded there’s not much diet can do. But what about the success of Dr. Swank in treating MS with a low saturated fat diet, the most effective treatment ever reported, published in some of the world’s most prestigious journals?

Of course, they knew about Swank’s work, but his study design didn’t fit the inclusion criteria considered for their review, because it was not a controlled trial.

Demanding randomized trials makes sense for drugs, since drugs are expensive and risky, and their adverse side effects kill more than a hundred thousand Americans every year. But a healthy diet has no downsides—only good side-effects. So, we shouldn’t have to wait on randomized controlled trials to start potentially saving people’s lives.

Consider smoking. “[I]t took more than 7,000 studies and the death of countless habitual smokers before a consensus was reached in the medical community regarding the causal link between smoking and lung cancer.”

You’d think that after the first 6,000 studies they could have given people a heads up or something? Even then, they didn’t have a single randomized controlled trial. “One has to wonder, how many people are currently suffering needlessly while they wait for a [randomized controlled trial] to confirm the results found” by other kinds of strong studies?

A famous statistician, R.A. Fisher, railed against what he called “propaganda” created to convince the public that cigarette smoking was dangerous. No definitive fact of the matter could be established, he argued, since evidence could not be produced by randomized controlled trials. If we could conduct an experiment involving, say, a thousand kids banned from smoking and another thousand who were forced to smoke at least a pack and a half a day, there would be no difficulty. But, of course, this we cannot do.

Maybe, Fisher pointed out, instead of smoking causing lung cancer, lung cancer causes smoking! In its early stages, lung cancer may cause inflammation. So, anyone suffering from chronic inflammation is going to want to smoke a cigarette to make themselves feel better, and it’s that “kind of comfort that might be a real solace to anyone in the fifteen years of approaching lung cancer. And to take the poor chap’s cigarettes away from him would be rather like taking away his white stick from a blind man. It would make an already unhappy person a little more unhappy than he need be.”

Fisher made invaluable contributions to the field of statistics, but his analysis of lung cancer and smoking was “flawed by an unwillingness to examine the entire body of data available.” His smokescreen may have been because he was a paid consultant to the tobacco industry, but also because he was himself a smoker. “Part of his resistance to seeing the association may have been rooted in his own fondness for smoking,” which makes me wonder about some of the foods many modern-day nutrition researchers may be fond of as well.

A famous paper in the British Medical Journal titled, “Parachute use to prevent death and major trauma related to gravitational challenge: a systematic review of randomized controlled trials,” lampooned this insistence on randomized controlled trials as the only legitimate evidence.

Not surprisingly, they didn’t find any such trials relevant to the role of parachutes in the prevention of death and trauma. Sure, parachutes appear to reduce the risk of injury after “gravitational challenge.” We can observe that people who fall out of planes without them do tend to die a bit more than those with parachutes, but their effectiveness has not been proven with randomized controlled trials.

“Advocates of evidence-based medicine have criticized the adoption of interventions evaluated by using only observational data. We think that everyone might benefit if the most radical protagonists of evidence-based medicine organized and participated in a double blind, randomized, placebo controlled, crossover trial of the parachute.” In other words, individuals who insist that all interventions need to be validated by a randomised controlled trial need to come down to earth with a bump.”