Should you cut out meat for your health?

More than half of Americans who make New Year’s resolutions resolve to “eat healthier.” If you’re one, you might be confused about the role meat should play in your health.

It’s no wonder you’re confused. One group of scientists says that reducing red and processed meat is a top priority for your health and the planet’s. Another says these foods pose no problems for health. Some of your friends may say that it depends and that grass-fed beef and “nitrite-free” processed meats are fine. At the same time, plant-based meat alternatives are surging in popularity, but with uncertain health effects.

As a cardiologist and professor of nutrition, I’d like to clear up some of the confusion with five myths and five facts about meat.

Long-term observational studies of heart disease, cancers, or death and controlled trials of risk factors like blood cholesterol, glucose, and inflammation suggest that modest intake of unprocessed red meat is relatively neutral for health. But, no major studies suggest that eating it provides benefits.

So while an occasional serving of steak, lamb, or pork may not worsen your health, it also won’t improve it. And too much heme iron, which gives red meat its color, may explain why red meat increases the risk of type 2 diabetes. Eating red meat often, and eating processed meat even occasionally, is also strongly linked to colorectal cancer.

For decades, dietary guidance has focused on lean meats because of their lower fat, saturated fat, and cholesterol contents. But these nutrients don’t have strong associations with heart attacks, cancers, or other major health outcomes.

Other factors appear more important. Processed meats, such as bacon, sausage, salami, and cold cuts, contain high levels of preservatives. Sodium, for example, raises blood pressure and stroke risk, while the body converts nitrites to cancer-causing nitrosamines. Lean or not, these products aren’t healthy.

“Plant-based” has quickly, but somewhat misleadingly, become a shorthand for “healthy.” First, not all animal-based foods are bad. Poultry and eggs appear relatively neutral. Dairy may have metabolic benefits, especially for reducing body fat and type 2 diabetes. And seafood is linked to several health benefits.

Conversely, many of the worst foods are plant-based. Consider white rice, white bread, fries, refined breakfast cereals, cookies, and so on. These foods are high in refined starch and sugar, representing 42% of all calories in the United States, compared with about 5% of U.S. calories from unprocessed red meats and 3% from processed meats.

Either a “plant-based” or omnivore diet is not healthy by default. It depends on what you choose to eat.

Conventional livestock eat a combination of forage (grass, other greens, legumes) plus hay with added corn, soy, barley, or grain. “Grass-fed,” or “pasture-raised,” livestock eat primarily, but not exclusively, forage. “Grass-finished” livestock should, in theory, eat only forage. But no agency regulates the industry’s use of these terms. And “free-range” describes where an animal lives, not what it eats.

“Grass-fed” may sound better but no studies have compared the health effects of eating grass-fed vs. conventional beef. Nutrient analyses show very modest differences between grass-fed and conventionally raised livestock. You might eat grass-fed beef for personal, environmental, or philosophical reasons. But don’t expect health benefits.

Products like Impossible Burger and Beyond Meat are clearly better for the environment than conventionally raised beef, but their health effects remain uncertain. Most nutrients in plant-based alternatives are, by design, similar to meat. Using genetically engineered yeast, Impossible even adds heme iron. These products also pack a lot of salt. And like many other ultra-processed foods, they may lead to higher calorie intake and weight gain.

Processed meats contain problematic preservatives. Even those labeled “no nitrates or nitrites added” contain nitrite-rich fermented celery powder. A current petition by the Center for Science in the Public Interest asks the Food and Drug Administration to ban the misleading labeling.

Besides the sodium, nitrites, and heme, processed meats can contain other carcinogens, produced by charring, smoking, or high-temperature frying or grilling. These compounds may not only harm the person who eats these products; they can also cross the placenta and harm a fetus.

Most diet-related diseases are caused by too few health-promoting foods, like fruits, nuts, seeds, beans, vegetables, whole grains, plant oils, seafood, and yogurt. Additional health problems come from too much soda and ultra-processed foods high in salt, refined starch, or added sugar. Compared with these major factors, avoiding or occasionally eating unprocessed red meat, by itself, has modest health implications.

In terms of land use, water use, water pollution, and greenhouse gases, unprocessed red-meat production causes about five times the environmental impact of fish, dairy, or poultry. This impact is about 20 times higher than that of eggs, nuts, or legumes, and 45 to 75 times higher than the impact of fruits, vegetables, or whole grains. A 2013 U.N. report concluded that livestock production creates about 15% of all global greenhouse gas emissions, with nearly half coming from beef alone.

Production of plant-based meat alternatives, compared with conventional beef, uses half the energy, one-tenth of the land and water, and produces 90% less greenhouse gas. But no studies have yet compared plant-based meat alternatives with more natural, less processed options, such as mushrooms or tofu.

Which preservatives or other additives in processed meat cause the most harm? Can we eliminate them? In unprocessed red meats, what exactly increases the risk of type 2 diabetes? What innovations, like feeding cows special strains of seaweed or using regenerative grazing, can reduce the large environmental impacts of meat, even grass-fed beef? What are the health implications of grass-fed beef and plant-based meat alternatives?

Like much in science, the truth about meat is nuanced. Current evidence suggests that people shouldn’t eat unprocessed red meat more than once or twice a week. Grass-fed beef may be modestly better for the environment than traditional production but environmental harms are still large. Data don’t support major health differences between grass-fed and conventional beef.

Similarly, plant-based meat alternatives are better for the planet but not necessarily for our health. Fruits, nuts, beans, vegetables, plant oils, and whole grains are still the best bet for both human and planetary health.

Dariush Mozaffarian is the dean of nutrition science and policy at Tufts University. This article first appeared on The Conversation.