- Kenny Lin, MD, MPH
There is a widespread consensus among nutrition and environmental scientists that reducing dietary meat intake, particularly red and processed meats, is not only beneficial for personal health, but also benefits the planet by reducing deforestation, freshwater consumption, and greenhouse gas emissions associated with cattle farming. Dr. Caroline Wellbery wrote in a 2016 AFP editorial: "According to the 2015–2020 [U.S.] dietary guidelines, moderate to strong evidence demonstrates that healthy dietary patterns that are higher in fruits, whole grains, legumes, nuts, and seeds, and lower in animal-based foods are associated with more favorable environmental outcomes."
Although the effects of individual dietary counseling in patients without cardiovascular risk factors are limited, the Dietary Guidelines for Americans, which are updated every 5 years, have been influential in changing eating patterns. A recent analysis of cross-sectional data from the National Health and Nutrition Examination Survey found small but significant decreases in consumption of refined grains and added sugar and increased consumption of plant proteins, nuts, and polyunsaturated fats from 1999 to 2016. Bigger changes could be on the horizon, if the efforts of entrepreneurs profiled in a recent article in The New Yorker to bioengineer and distribute plant-based hamburger patties and other products that are indistinguishable from real meat prove to be successful.
The next iteration of the Dietary Guidelines will need to consider new evidence that beneficial health effects of eating less meat may not be as large or as certain as previously thought. In a clinical guideline published this week in the Annals of Internal Medicine, an international panel from the Nutritional Recommendations and Accessible Evidence Summaries Based on Systematic Reviews (NutriRECS) consortium made the somewhat shocking suggestion that adults can continue their current (over)consumption of red and processed meats without major health consequences. Four linked systematic reviews found low-quality evidence of small to no benefits on cardiometabolic and cancer outcomes from consuming less red and processed meat in cohort studies and in randomized trials, and a review of health-related values and preferences suggested that "omnivores are attached to [eating] meat and are unwilling to change this behavior when faced with potentially undesirable health effects." Importantly, none of the guideline authors or systematic reviewers received any financial support from the meat industry.
Critical responses from the medical and public health community have been swift and plentiful. Some experts challenged the guideline panel's assessment of the magnitude of beneficial health effects of eating less meat as "very small." For example, meta-analyses estimated that after about 11 years, dietary patterns with 3 fewer servings of red meat per week are associated with absolute risk differences of 6 fewer cardiovascular-related deaths (number needed to treat = 167) and 14 fewer persons developing diabetes (NNT = 71) out of every 1000 persons. To an individual, these differences seem small, but they compare favorably with the NNTs of established clinical preventive services such as colorectal cancer screenings and therapy for osteoporosis. Others faulted the guideline for excluding benefits to animal welfare and the environment from lower population-wide meat consumption. Goals and guidelines for what constitutes a healthy diet will continue to evolve, but this one has provided much food for thought.