Dietary guidelines need some drastic changes, as does the way we evaluate diet.
Despite several years of research, we still don’t know much about what to eat, because we lack the right tools. Lately, as scientists fail to produce consistent results, all of science is looking more closely at errors and biases that may have made their way into research findings.
Leading the way we do science is John Ioannidis, professor of health research and policy at Stanford University, in the US state of California. In 2005, he published “Why Most Research Findings Are False” in the journal Plos Medicine. In another article titled “Implausible results in human nutrition research”, which was published in the British Medical Journal in 2013, he strongly criticised findings on nutrition, noting that, “Almost every single nutrient imaginable has peer reviewed publications associating it with almost any outcome.”
Ioannidis said the research techniques we use often fail to find accurate connections between diet and health, particularly observational research, in which we collect data on what people eat, and track what happens to them.
The trouble begins with the collection of data. Research participants run the risk of forgetting what they ate, not to mention the fact that people tend to eat differently when their diets are being tracked. You would be starting with inaccurate data, and other variables such as a person’s age or socioeconomic status might be affecting your data.
“With this type of data,” says Ioannidis, “you can get any result you want. You can align it to your beliefs.”
Frank Hu who chairs the department of nutrition at the T. H. Chan School of Public Health at Harvard University, respects Ioannidis’ criticism, but says nutrition researchers have brought much to our understanding of a healthful diet and can address the problems.
He pointed out that data collection is improving, with new tools to better assess diet and reality checks with measurable biomarkers (testing the urine of respondents in a salt study for sodium, for example). And he doesn’t believe biases undermine the credibility of the field. Often, they are insignificant, he says, and the most official recommendations, such as the dietary guidelines (he was on the 2015 committee), are agreed with by of large groups of researchers and is based on scientific evidence.
Still, he acknowledges there’s work to be done.
When it comes to actual dietary recommendations, the disagreement is stark. “Ioannidis and others say we have no clue, the science is so bad that we don’t know anything,” Hu said. “I think that’s completely bogus. We know a lot about the basic elements of a healthy diet.” He lists plant-based foods – fruit, vegetables, whole grains, legumes – but acknowledges that we don’t understand enough to prescribe specific combinations or numbers of servings. He is afraid that Ioannidis’ dismissal of the entire field undermines nutritional advice.
But if nutritional advice is unsupported, a little undermining is in order. Ioannidis is in favour of fruits, vegetables and whole grains, but said the evidence behind them is not strong. Older observational studies showed big reductions in cancer risk but newer studies show small benefits, if any.
Big differences in what people eat track with other differences. Heavy plant-eaters are different from, say, heavy meat-eaters in all kinds of ways (income, education, physical activity, BMI). Red meat consumption correlates with increased risk of dying in an accident as much as dying from heart disease. It’s hard to tell how much faith we can put in observational studies. The more we learn from studies, the more difficult it is to form opinions that everyone shares. Apart from the belief that trans fats are bad, there is very little that people agree on.
And then there are eggs. We used to think they were bad, because their cholesterol content contributed to heart disease. Then we said eggs are okay! And just last week, a new study came out saying not so fast, they might be bad after all. Let the eye-rolling begin.