In 2015, the World Health Organization made a declaration that eating processed meats increases the risk of developing colon cancer. The American Heart Association and the U.S. Dietary Guidelines also recommend avoiding red and processed meats.
This fall, a group of nutrition researchers called into question these ubiquitous recommendations to avoid meat with five systematic reviews published in the Annals of Internal Medicine. In the end, a panel of 14 health researchers published a new clinical guideline that recommends: reducing the amount of red and processed meats you eat does not improve your health, so it’s okay to continue your current consumption.
If this change has you stomping your feet, you’re not alone. It’s frustrating to make dietary changes that you believe are improving your health only to find out they don’t really matter anyway. Let’s take a careful look at these recommendations to find out what has actually changed.
First, it’s important to consider how nutrition studies have traditionally been conducted. Much of nutrition research uses retrospective studies that look back in time to try to understand how participants’ choices have influenced their health. If a study were looking at heart disease, researchers would recruit people with heart disease and also try to find a match participant, a person of similar age who does not have heart disease. Then researchers would conduct extensive interviews to try to determine how the eating habits of the participants differ. They would also use statistical methods to try to eliminate other factors, such as exercise and stress.
As you can probably guess, it’s difficult to come up with solid conclusions using these research methods.
In the systematic reviews published this fall, the researchers picked out only the most robust of these studies and combined that data with randomized controlled trials – the gold-standard of research studies – to draw their conclusions. They used a research rating system called GRADE to decide which studies to include in their analyses. GRADE is used across medical research, but is not typically used for nutrition research.
Four of the new systematic reviews each looked at different health outcomes – mortality, deaths due to cancer and heart disease, risk of developing cancer and risk of developing stroke and heart attack. In all four of these reviews, the researchers found either no evidence or low-quality evidence that cutting back on red or processed meat improved health or reduced participants’ chance of dying.
The fifth review examined study participants’ values about meat consumption. It found that that people who eat meat tend to be unwilling to change their behavior, and lack the skills to prepare meals they would enjoy without using meat. In other words, meat consumption is important to their quality of life.
Even using these more stringent rules, the new studies have flaws. Researchers believe that the evidence they used – even with the more rigorous guidelines about choosing studies – is considered “low certainty” and their recommendations are “weak.” This means that researchers don’t really know how eating red and processed meats affect our health; essentially, there is not high-enough quality evidence to be able to tell if it’s harmful or not.
The authors also point out that they did not take into account the impact of meat consumption on climate change, water quality and pollution.
There are plenty of other researchers who have criticized the new reviews for leaving out evidence about the harms of eating red and processed meats. And there are reports that one of the lead authors on the new studies may have been influenced by previous ties to a food industry group.
As someone who has to make dinner tonight, what does this mean for you? The take-home message: nutrition research is complicated and solid conclusions are hard to come by. But the evidence is pretty clear that fruits and vegetables, lean proteins and whole grains are healthy choices, and that it’s best to eat foods that may be unhealthy – such as red or processed meats – in moderation.
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If you follow news about nutrition, you’ve likely heard the recommendations to avoid eating red and processed meats including beef, sausages and deli meats.