A set of studies released this week upended the nutrition world, suggesting that there is no need to reduce your consumption of red meat — something that’s long been recommended by a slew of public health organizations, including in Canada’s Food Guide.
The recommendations, published in the journal Annals of Internal Medicine, said that the evidence supporting reducing your intake of red and processed meat was weak.
“Based on the research, we cannot say with any certainty that eating red or processed meat causes cancer, diabetes or heart disease,” said Bradley Johnston, an associate professor at Dalhousie University, who co-led the review.
Others disagreed, saying that the studies left out important elements, and even that the authors were irresponsible to make these recommendations.
But competing headlines and claims about the nutritional benefits and harms of a given food can be confusing to follow, experts say. Nutrition research isn’t always clear.
“Any time you see a study that goes against the grain, the media loves it,” said Rosie Schwartz, a consulting dietitian who runs the website Enlightened Eater.
She believes that these studies on processed and red meat left out important groups, like vegetarians, and as such their recommendations are flawed.
Tanis Fenton, a dietitian and professor of epidemiology at the University of Calgary, believes, though, that many of the existing public health recommendations to eat less meat relied on weak evidence — a problem a lot of nutritional research shares, she said.
“As much as I’ve devoted my life to nutrition, our evidence about nutrition is kind of weak.”
Most nutrition evidence comes from observational studies, she said.
“People are familiar with the Framingham or the Nurses’ Health Studies. They’re very huge studies where they ask the people participating in the studies many times over the years to tell the researchers what they eat,” she said. “And then they’re followed up to see all kinds of health outcomes, whether it’s cardiovascular, cancer, osteoporosis, mental health.”
These studies provide valuable evidence, Fenton said, but what researchers see might be accounted for by whatever they’re looking at, like vitamin E pills, or it could be something else that the researchers haven’t thought of.
“People who have healthier diets tend to have higher income, they tend to have better lifestyles. They don’t tend to smoke. They tend to get more physical activity.” While researchers can and do account for these variables, she says, it can still be difficult to disentangle them from a study’s results.
It’s more difficult to conduct randomized clinical trials, with a control group, for nutrition research, Fenton said. If it’s just a pill — like whether someone should take daily vitamin E or not — it’s doable, but for a big dietary intervention like eating meat, it’s trickier, she said.
We keep learning more about nutrition too, Schwartz said. “Nutrition is a changing science. It’s evolving. We don’t know everything and there’s so many different factors.”
Fenton agrees. “There’s a whole process in science where studies are done and other studies done and improvements are made and more studies are done,” she said. “I think one of the unfortunate things is that messages go to the public before we’ve got enough studies done in different ways to know the full picture.”
“It looks like we’re changing our mind. And as a nutritional scientist, we’re not changing our mind, rather we’ve done another study.”
A new study might not even be better than the old one, she said. It’s just another piece of evidence.
This is why Schwartz thinks it’s important to pay attention to the consensus opinion. “Listen to what the consensus is, what the recommendations are.
“If something sounds too good to be true, it probably is.”
Groundbreaking studies do happen, she said. “When there’s one group that comes out with something, if there’s any validity to it, more studies are going to come out. So wait and see.”
Nutritional guidelines evolve over time, she said, and they change as evidence accumulates in favour of a given position.
Nutrition research has come to a few strong conclusions, Fenton said: “Variety and moderation. And eat your vegetables, just like your grandmother said.”
Basic nutritional principles haven’t changed, Schwartz said. “Fill half your plate with fruits and vegetables, a quarter with whole grains, and a quarter with your protein. Make some of them meatless, enjoy some meat, have some fish.”
“It’s not sexy but it’s based on science.”
-With a file from Reuters
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