Preventive medicine expert advocates a plant-based diet
In a letter to JAMA, the preventive-medicine expert addresses the failure of the newest USDA Dietary Guidelines to articulate the health and climate benefits of a low-meat diet.
Eating meat is bad for our health and bad for our planet, according to Randall Stafford, MD, PhD, professor of medicine at the Stanford Prevention Research Center.
Studies show that vegetarians and vegans have lower rates of heart disease and cancer, and that nearly 15 percent of all planet-warming greenhouse gases comes from raising cattle, pigs, poultry and other animals. The upshot is that the estimated greenhouse gas emissions of a vegetarian diet are half those of a meat-based diet. To improve public health and combat climate change, China recently released national dietary guidelines whose goal is to cut national meat consumption in half by 2030.
Yet, here in the United States, where we eat 80 percent more meat than do people in China, guidelines recently released by the federal Department of Agriculture don't recommend that we eat less meat. For good sources of protein, the new guidelines list meat, eggs and dairy first, with no suggestion that nuts, seeds and legumes could be a better choice.
Disappointed by this aspect of the USDA Dietary Guidelines for Americans 2015-2020, Stafford wrote a letter to the editor of JAMA that was published July 12. "The health benefits of specific components of plants have been documented, as have the harms associated with constituents largely unique to meat," he wrote. "Vegetarian diets have been associated with a reduction in cardiovascular disease mortality by as much as 29 percent and cancer incidence by 18 percent."
In a recent interview, writer Jennie Dusheck discussed the letter with Stafford, director of the SPRC's Program on Prevention Outcomes and Practices.
Q: What initially prompted you to write your letter?
Stafford: These guidelines have been long-awaited and there are many aspects that are improvements, but I was very disappointed by the way the guidelines dealt with recommendations about the consumption of meat.
People who consume meat generally have worse health outcomes, particularly in terms of heart disease, stroke and cancer. On the flip side, clinical trials show that people who eat mostly plants have better health outcomes. And the evidence goes further than just suggesting an association—it shows that plant-based diets directly cause better health.
The USDA guidelines clearly state that saturated fats should be reduced. We know most of the saturated fat in our diets comes from animal sources, and yet the guidelines don't take that next logical step and tell consumers to eat less meat. I am bothered by the lack of an explicit message around meat.
Q: What would you say to people who think that eating meat is essential to health and a more natural part of a "paleo" diet?
Stafford: The first way to answer that is to think about protein requirements. The average amount of protein people consume in the United States is far more than we need. A plant-based diet can provide all the protein anyone needs—40 or 50 grams. Two cups of lentils, two cups of yogurt or a single 4-ounce steak would cover a whole day's protein requirement. People are generally misinformed about the amount of protein they need, some believing they need four or five times as much protein as they actually do.
Second, the only real deficit in a vegetarian or a vegan diet is a lack of vitamin B12. That's something that all people who are eating a predominantly plant-based diet should be aware of. The recommended daily requirement for B12 is 2.4 micrograms and even that tiny amount is higher than most people need because it accounts for those people who absorb B12 poorly. On a vegan diet, you could get that much B12 from a vitamin supplement or a tablespoon of nutritional yeast or a serving of fortified tofu. Even if you eat meat, you would need only about 1.5 ounces of beef per day or two forkfuls of fish.
The idea of eating unprocessed or minimally processed foods has value—which the paleo diet emphasizes—particularly when it comes to plants. But some anthropologists think the actual meat consumption of our ancestors was quite low, which would undermine the story that justifies lots of meat in the paleo diet. But regardless of what our ancestors ate, we now live in a very different food environment and we need to be very careful about how we interact with that environment.
Q: From a global environmental perspective, would it be better if people ate mostly plants?
Stafford: Yes, for a couple of reasons. One is that the process of producing meat generates more greenhouse gases per calorie than does growing plants of the same nutritional value. In essence, we can eat the corn and soy we grow or we can feed these plants to livestock and then eat the livestock. For a lot of reasons, it's energetically much more efficient to eat the plants ourselves.
Food production also relies on other scarce environmental resources. Water is the big one, as is arable land. Both the water and land required for a calorie from meat is far greater than the amount required for plant-based foods.
Q: Do you think there's support for your point of view generally?
Stafford: I think there is general agreement among scientists interested in nutrition that a plant-based diet provides better outcomes and that this evidence should be more explicitly reflected in the guidelines. What's so striking about the new guidelines is that they are based on that same information, the same data. Clearly, the recommendation that we reduce our intake of saturated fat comes from that same pool of evidence. But the guidelines don't say which foods contribute to our consumption of saturated fats. Instead, they leave it up to the consumer to figure out that saturated fats mostly come from animals. Essentially, they're only telling part of the story, and leaving out the most practical advice.
Q: What do you think it would take for the USDA to change their guidelines?
Stafford: I think it requires a reframing of how we think about dietary guidelines. Dietary guidelines are often focused on the idea that we break foods down into particular components—micronutrients and macronutrients—and that we can define a healthy diet in terms of the proportions of these different categories of nutrients.
But the fact is people eat food; they don't eat protein or saturated fats or carbohydrates alone. So in some sense, the very process of creating guidelines that are based on these categories of nutrients misses the fact that people eat foods, not these categories.
It's not enough to just tell people what nutrients they should be consuming. I think it really has to come down to telling people what types of foods they should eat less of and what types of food they should be eating more of.
I think the guidelines have moved in the right direction. For instance, the guidelines have moved away from a recommendation to reduce total fat intake and are now focused solely on saturated fat, for which there's more evidence of harm. And the guidelines' emphasis on fibrous vegetables and whole grains are more forthright.
But the whole regulatory and guideline process really needs to become more practical and actionable by consumers. It would be much more direct to simply tell consumers to eat less meat. And that would be the most effective way to reduce the consumption of saturated fats.
Despite the tendency of consumers to be attracted to fad diets, I think Americans are more ready than ever to hear a simple recommendation to eat less meat. The dietary evidence is stronger today than it's ever been. And I think consumers are also uncomfortable with both the environmental impact of their diets and the issues surrounding the ethical treatment of animals. The time is right for the USDA to be more direct in their recommendations, even if it means making a recommendation that is contrary to the interests of some entrenched food manufacturers.
I certainly think more pressure from scientists to have the USDA state the obvious consequences of the data would help. I also think it's important that consumers complain to the USDA that the guidance is not nearly as clear as it could have been.
More information: Randall S. Stafford. US Dietary Recommendations, JAMA (2016). DOI: 10.1001/jama.2016.5625