Most of our devout beliefs about nutrition have not been subjected to a robust, experimental, controlled clinical trial, the type of study that shows cause and effect, which may be why Americans are pummeled with contradictory and confounding nutritional advice. Nutritional bad guys that have fallen from grace in the national consciousness—white potatoes, eggs, nuts, iceberg lettuce—have been redeemed years later. Onetime good guys, like margarine and pasta, have been recast as villains. Cholesterol is back in the probably-won’t-kill-you column after being shunned for 40 years, as of the latest nutritional advice from the Dietary Guidelines Advisory Committee in February. (That advice was still too timid, according to Cleveland Clinic cardiologist Steve Nissen, who also wants the nutritional guidelines to admit our best evidence suggests fat isn’t bad for you either). And then there’s salt—don’t eat too little, says the newest research. You could die…
…Many nutritional studies are observational studies, including massive ones like the Nurses’ Health Study. Researchers like Willett try to suss out how changes in diet affect health by looking at associations between what people report they eat and how long they live. When many observational studies reach the same conclusions, Willett says, there is enough evidence to support dietary recommendations. Even though they only show correlation, not cause and effect, observational studies direct what we eat.
Apart from their inability to determine cause and effect, there’s another problem with observational studies: The data they’re based on—surveys where people report what they ate the day (or week) before—are notoriously unreliable. Researchers have long known that people (even nurses) misreport, intentionally and unintentionally, what they eat. Scientists politely call this “recall bias”.
The coupling of observational studies and self-reported data leads some observers to the conclusion that we know neither how Americans do eat nor how they should eat. A recent PLOS One article even suggests that several national studies use data that is so wildly off base that the self-reported caloric intake is “incompatible with survival”. If people had eaten as little as they reported, in other words, they would be starving.
Peter Attia, a medical researcher and doctor, started questioning the basis of dietary guidelines when he saw that following them didn’t work for his patients. They didn’t lose weight, even when they virtuously stuck with their diets. When he took a look at the research supporting the advice he was giving to his patients, he saw shoddy science. Attia estimates that 16,000 nutritional studies are published each year, but the majority of them are deeply flawed: either poorly controlled clinical trials, observational studies, or animal studies. “Those studies wouldn’t pass muster in another field”, he told me.
It is little wonder that quackery, ignorance, and deceit are increasingly taking hold of people’s health decisions. Not only does all this contradictory or ambiguous evidence make room for all sorts of unverified or dangerous claims, but they erode public trust in science and medicine — even if specialists finally get something right with certainty, they will likely be met with incredulity or apathy.
It is not unlike how the inefficiencies of the U.S. health care system, combined with the predations of big pharmaceutical companies, taints evidence-backed medicine as a whole and sends people into the arms of frauds and scammers. With distrust of institutions and authoritative bodies — political, academic, and religious — at an all time high, it seems health and lifestyle choice will be increasingly determined by individual fiat, errors in reasoning, anecdote, or other unreliable bases.
Of course, this is not to condemn all scientific bodies or the scientific approach as a whole. The article makes clear that while a lot of the misconceptions around nutrition and health are attributed to “shoddy” research, various psychological biases, as well as the sheer complexity of measuring all the variables involved with health, make the endeavor a difficult one to pursue in itself.
Ultimately, nutrition science is still a new and burgeoning field of study, and I trust that it will be self-correcting in time, especially now that both the public and establishment are scrutinizing these problems. But while we try to work out better and more reliable ways to learn about what is good for our bodies, there are going to be a lot of mistakes — and outright fakery — made.
Moreover, let us not overstate the problem: while the minutiae and other details are an open questions, there are still general rules that seem to hold true: smoking cigarettes is broadly unhealthy, a plant-centered diet is generally the healthiest, regular physical activity is beneficial, and so on. Of course, we will have to see what more can be said about such conventional health wisdom.