A recommendation to eat more calories from fruits and vegetables resulted in a suggestion to eat less meat. Some researchers suggest eating no meat at all. (Gene J. Puskar/AP)

A modest suggestion that American diets should be lower in meat has galvanized the debate about carnivorousness. In February, the federal Dietary Guidelines Advisory Committee issued its recommendations on improving the government’s official nutritional advice. Although the report is 571 pages, the executive summary distills it to one pithy sentence: A “healthy dietary pattern is higher in vegetables, fruits, whole grains, low- or non-fat dairy, seafood, legumes, and nuts; moderate in alcohol (among adults); lower in red and processed meat, and low in sugar-sweetened foods and drinks and refined grains.” A footnote about meat says, “Lean meats can be part of a healthy dietary pattern.”

It wasn’t a hard line against meat, but it was enough to make the industry come out swinging. The North American Meat Institute launched a Change.org petition, Hands Off My Hot Dog, that called the recommendations “extreme and ill-considered” and rallied supporters to stand with the industry in asking the Department of Agriculture to reject them. At last count, the petition had 2,472 signers.

(In other parts of the report, the committee discussed the important issue of meat’s environmental impact, but the “less meat” recommendation was based solely on nutrition considerations, and that’s what I’ll tackle here.)

Beyond the idea that a dietary recommendation to eat less meat is an assault on liberty is the position, expressed to me by Meat Institute chief executive Barry Carpenter both on Twitter and in a Washington Post Live forum I moderated , that a pro-meat stand is evidence-based: Meat is a nutrient-dense, healthful food, and we reduce intake at our peril. The institute has science on its side.

But wait! The Physician’s Committee for Responsible Medicine, advocate of a plant-based diet, recommends reducing our meat intake all the way to none. “Multitudes of studies have demonstrated the remarkable health benefits of a vegetarian diet,” the committee says. Science “is on the side of vegetarianism.”

Science, she’s a fickle mistress.

A recommendation to eat less meat was met with an immediate campaign by the meat industry. (J. Scott Applewhite/AP)

You don’t have to spend much time on PubMed, the repository of journal articles, to figure out that, when it comes to the question of meat-eating and health, there’s something for everyone. If you’re looking for evidence that meat eaters die earlier, you can find that. If you’re looking for evidence that they don’t, you can find that, too. Just to make it harder, the debate on meat incorporates two other nutrition debates: those surrounding sodium (high in processed meats) and saturated fat (high in fatty meats).

So, is meat good or bad? Nutrient-rich essential or dietary enemy? It’s neither, and that’s why the “less meat” recommendation makes sense.

Dariush Mozaffarian, dean of Tufts University’s Friedman School of Nutrition Science and Policy, points out that, although different studies of meat show different results, the range of those results is actually quite narrow. “If you look at every possible study with every population around the world, you see that meat-eating is neutral or is associated with slight harm,” he says. “I’ve never seen a benefit.”

Mozaffarian says that two of the main arguments — one for, one against — are flawed because we shouldn’t be talking about individual nutrients, whether they’re theorized to be healthful (like the minerals in meat) or dangerous (like the saturated fat). We should be talking about food.

“What the meat industry is doing is a major mistake,” he says. Basing dietary guidelines on nutrients is completely invalid, and we’ve learned that again and again.” As for saturated fats, “the sources of saturated fat are so diverse, and the health effects are so diverse, that it doesn’t make sense to combine them. Butter, cheese, milk, meat, nuts — they all have different health effects.”

Mozaffarian says he supports the dietary guidelines because they talk about food rather than nutrients, but he would have preferred the committee to have tackled meat differently. The meat to reduce, he says, is processed meat: bacon, sausage, deli meats. A review of the evidence that Mozaffarian co-authored in 2012 links processed meat to higher risk of heart disease and diabetes (the primary — although not the only — culprit appears to be sodium), and other studies have also found a stronger link between mortality and processed meats than between mortality and unprocessed ones.

Processed meats, such as bacon, have the strongest link to heart disease and mortality. (Sarah A. Miller/AP)

Not everyone agrees with that assessment. Walter Willett, chairman of the nutrition department at the Harvard School of Public Health, isn’t ready to exonerate saturated fat and says that one serving of red meat a week is low-risk, but none or almost none is even lower. He also makes the case that what’s important is what you replace the meat with. Replace it with sugar or refined grains, and it’s a health loser. Replace it with polyunsaturated fat, and it’s a win.

Which goes back to the idea that it’s your diet in total that matters, and parsing it food by food isn’t terribly helpful.

Alice H. Lichtenstein, vice chairwoman of the Dietary Guidelines Advisory Committee and professor of Nutrition Science and Policy at Tufts University, says she is frustrated by the debate over the meat recommendation. “People are making more of this than they should,” she says. “When we talk about individual foods within a dietary pattern, we frequently cause problems. We forget what else happens to the diet. If you increase or decrease meat intake, something else is going to change.”

There’s no magic number of optimal servings. And looking for very specific recommendations on diet is likely to be the wrong approach, because there’s a great deal about nutrition that we don’t know, and there are limits on how effectively we can find it out. Trying to tease out links between diet and disease from population data is tough, because people who eat meat (or almost anything else) are likely to be different from people who don’t in all kinds of ways. And controlled trials, where we feed some people Diet X and some other people Diet Y, can go on for only so long. We can’t hold subjects hostage until they begin to die (or not) of heart disease. Nor can we kill them and autopsy their livers.

Which means that all the research on meat, or on just about any other aspect of human nutrition, is necessarily limited. What are public health professionals supposed to do in the face of imperfect information? “The best we can,” says Lichtenstein. “You have an entire panel of scientists with no vested interest trying to look at all the evidence.”

And so the answer to the question “how much meat should I eat?” is maddeningly elusive. Mozaffarian says two servings a week. Willett says one, or maybe none. The dietary guidelines committee recommends an overall pattern that includes 3.3 ounces per day of meat and poultry. But there is no optimal level. “And it’s not just meat,” says Lichtenstein. “We can’t know optimal levels of anything.”

Customers shop for produce at a Whole Foods market in San Francisco. (Justin Sullivan/Getty Images)

We need to reconcile ourselves to the idea that we simply can’t expect dietary recommendations that are both science-based and very specific. Although the committee looked at all the evidence and concluded that we would be better off if we ate less meat, Lichtenstein emphasizes that that isn’t the top dietary priority (as does Mozaffarian). Two things we do know, from decades of research all pointing in the same direction, is that if you really want to improve your diet, keep your calories in balance and eat lots of fruits and vegetables.

Beyond that, cut your sugar intake. Substitute whole grains for refined. Get some exercise.

The evidence on meat isn’t iron-clad, but “less meat” seems reasonable given that people need to eat more vegetables and fruits, and less overall. The calories need to come from somewhere, and we’re pretty sure meat — especially processed and fatty meat — isn’t doing us any good, so it makes sense to cut back.

That’s the upshot. The reason the dietary guideline committee’s “less meat” recommendation makes sense is not that meat’s so very bad for you. It probably isn’t. But you need to make room in your diet for the things that are actively good for you, and something’s gotta give.

Haspel, a freelance writer, farms oysters on Cape Cod and writes about food and science. On Twitter: @TamarHaspel. She’ll join Wednesday’s Free Range chat at noon: live.washingtonpost.com.