A study published by the Annals of Internal Medicine on October 1 titled “Unprocessed Red Meat and Processed Meat Consumption: Dietary Guideline Recommendations from the NutriRECS Consortium” has unleashed a firestorm of controversy. This publication and the reaction to it reveal so much about medical studies and recommendations that I was tempted to write a book about it, but will try to be briefer.
The conclusion of the paper was that adults continue their current consumption of both red meat and processed meat, noting that the recommendation was a weak one based on low-quality evidence. The reaction from such groups as the Harvard School of Public Health, the American Cancer Society and the American College of Cardiology was vehement opposition to this statement, implying that the authors were irresponsible and would contribute to more heart attacks and cancer.
Why the controversy? First, we must note that the ideal way medical recommendations are reached is through randomized controlled clinical trials: a group of people are given treatment A or Treatment B, selected randomly, and neither the subjects nor the researchers know which they get. The groups are followed for an appropriate time and at the end, the researchers look for a difference in the outcome between those given A and those given B. If there is a substantial difference between the groups, and if the people given A and those given B are shown to be pretty much the same except for the treatment, it is assumed that the difference in outcome was due to the treatment. I must note that small differences in outcome may be “statistically significant” if the groups are large enough even though the magnitude of the effect may be so small that it is not “clinically significant.”
While randomized trials work well when comparing two medicines, they are impossible to do when studying diet. Most of us can tell the difference between a steak and a roasted cauliflower. Dietary studies are thus mostly done by looking at what people do, generally based on self-reporting, and comparing the outcomes between those who claim to eat one way or another. These observational studies are fraught with difficulty. We learned long ago that when you compare people who do one thing differently, it is highly likely they do other things differently. Studies comparing vegetarians with omnivores cannot assume that their diets are the only thing different between them. Vegetarians may smoke less, may drink less (or more), may exercise more, may be leaner – all factors that impact health.
The NutriRECS group took this into account when they looked at all the published studies on diet and health. They concluded that the evidence base for recommending people cut down on their consumption of red and processed meat was weak. They also noted that the absolute benefit, in terms of number of heart attacks or cancers prevented, was relatively small. One example was an estimated 7 fewer cancers per 1000 people over their lifetime, a risk that omnivores might be willing to take when weighed against quality of life.
So, who is right? Both sides! If you are a vegetarian, you can be satisfied that you are slightly reducing your risk of cancer and heart attack (though slightly increasing your risk of stroke per another recent study in the British Medical Journal!) If you like to eat meat, you can be content that the absolute risk of your preference is relatively small and you do not need to make yourself miserable – and you can always balance your love of steak by walking more and dropping a few pounds.
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