Why don’t more people go vegan? It could be the label.

A recent experiment explored why people reject foods that are better for your health and the planet—and found answers rooted in psychology.

When food items are specifically labeled as vegan—indicating they are prepared with no animal products, including eggs or butter—people are less likely to select them, even though it is better for the planet and for their health, according to a recent experiment.

Growing and transporting food accounts for a quarter of all global greenhouse gas emissions, which are accelerating the climate crisis. Of these, the vast majority come from processes linked to meat and dairy production, which is why experts are advising societies to shift toward more plant-based eating.

“We have to make big changes to how we produce and consume food if we want to reach climate goals” and feed Earth’s ever-growing population, says Richard Waite, an expert on food climate policy at the nonprofit World Resources Institute.

But the study at the Massachusetts Institute of Technology indicates this may prove challenging.

Researchers asked some 150 people attending several university events to pre-order their lunch and choose between two options, one of them vegan. Choices included vegetable versus cheese ravioli and a vegetable hummus wrap versus a Greek salad with feta. A similar study of meal preferences was also conducted online. Half the respondents in both studies randomly received an order form in which the vegan item was labeled, with the word in parentheses.

When this vegan terminology was used, people were less likely to order the entrée than when it was not. For the in-person attendees, some two-thirds more avoided the dish.

After the research was published, some people told the study’s lead author, Alex Berke, a doctoral student at MIT’s Media Lab, the results were unexpected. But she anticipated the outcome.

Berke herself began eating vegetarian (a plant-based diet that includes dairy and eggs) at age 10 and adopted a vegan diet three years ago to help the climate. “Anyone who has been eating vegan or vegetarian for a while would not be surprised,” says Berke. “They see the bias against these foods.”

There are many reasons why people resist eating lower on the food chain—and why some shun vegan food when it is categorized that way. Some people’s identities involve seeing themselves as carnivores, especially if their family or culture is meat focused, says Susan Clayton, an expert in the psychology of climate change at Ohio’s College of Wooster.

Others don’t feel a strong motivation to change because they believe climate change is not yet having an impact. Yale University researchers say fewer than half of Americans think anyone in the country is currently being harmed, although that’s up from a third in 2015.

The term vegan may also signal deprivation, based on eating vegan foods before tasty animal-product substitutes became available. “I often have this deprivation response myself,” Clayton says. “When a coffee shop has vegan muffins I think, I want one with eggs and butter. Even though some have tasted very good, there’s still a connotation that we’re settling for second-best ingredients.”

Anti-vegan reactions can also emerge from what psychologists call reactance. First proposed in the 1960s and studied extensively since, the concept describes the mental and emotional pushback that can result when someone feels their choices are constrained.

“If your freedom is restricted, a motivational drive emerges,” says Jason Siegel, a professor of psychology who studies reactance at Claremont Graduate University in California. Some people are more prone than others, he says, but once reactance is triggered the responses that follow may not be logical or helpful. This can include pushing against the restriction or denigrating the source or the truthfulness of the information making the person feel confined. Reactance might explain why, when a rumor arose that the government was planning to banish hamburgers some people suddenly ate more of them.

To avoid activating reactance, change is best framed as a choice rather than a command, Siegel says. “If I say, Please consider this, it’s up to you, that’s often better than: You must do this or you’re a terrible person.”

Beef production is the largest agricultural contributor to climate change. A key reason is that cattle are inefficient at converting what they eat into the steaks or chopped meat we consume. Every 100 calories the animals eat result in just one calorie of edible protein.

Cattle also require a lot of grazing land. “Land use change, including clearing forests for agriculture, is responsible for a quarter to a third of the total carbon dioxide we’ve ever emitted,” right behind burning fossil fuels, Waite says. Some four times more carbon-trapping forest land has been destroyed in recent years to create grazing pastures for cattle than for the next largest agricultural use: palm oil plantations. Plus, cows burp out large quantities of methane, which is 25 times more potent than carbon dioxide at trapping heat in the atmosphere.

For these reasons, greenhouse gas emissions from food production for people who eat a vegan diet are 75 percent lower compared with those who eat the highest quantities of meat.

Chickens and pigs also consume more food than they produce, although they are more efficient than cows. If people directly ate the soy products that are grown to feed the animals that give us buffalo wings and pork chops, a lot less forest land would be cleared, Waite says. “It’s not people’s tofu that’s deforesting the Amazon,” he says.

Shifting to plants is especially important in the United States., where per capita meat consumption is among the highest in the world, more than double the global average. “By eating less meat and more plant-based foods, we can significantly reduce the climate impacts of our diet,” Waite says. Of course, this way of eating also improves health.

Consumption of animal products has declined somewhat, with two-thirds of respondents in one survey confirming in recent years they’ve eaten less, especially red meat. But the most common reasons cited are cost and health, not the environment. And quantities are not falling quickly enough. To reach 2050 climate targets, high-consuming nations like the U.S. must scale back much faster.

Environmentalists are clear they are not urging everyone to become vegetarians or vegans, but, if possible, to include more plant-based meals. “If you shift a third of your beef consumption to beans and soy, you reduce the climate impact of your diet by about 15 percent,” Waite says.

Home cooks and restaurants too often treat vegetarian options as an afterthought, Berke says. “People think about just removing the meat—taking chopped meat out of a pasta dish, for example—rather than creating a delicious option that everyone will enjoy, including people who eat meat,” she says.

That’s the approach being taken by the World Resources Institute, which is consulting with dozens of food service providers—in restaurants, universities, hospitals, company cafeterias, and the like—to create plant-based menu items that are tasty, affordable, and convenient enough that anyone might select them.

Moving items to the top of the menu also prompts more people to order them. And as the MIT researchers discovered, not plastering menus with the term “vegan” also has an impact. In Berke’s ideal world, the vegetarian or vegan foods would be the primary options and meat products could bear a label. Indeed, the odds of people selecting plant-based meals was found to be higher in a hypothetical restaurant when that was the default on the menu.

When trying to convince friends or relatives to reduce meat consumption, emphasizing the health benefits rather than the environmental impact or animal welfare issues led to greater willingness, according to a study published this month in the medical journal Appetite. Addressing people’s concerns that they can easily prepare meat-free meals or handily buy meat substitutes also made an impact.

When cooking at home, dialing down meat might involve making vegetables the star of the dish, as they are in stir fries, hearty salads, and many casseroles. Or it might mean adding vegetables to meat-based entrees. Waite suggests blending 25 percent of mushrooms into a beef patty, for example, which adds a rich, umami taste.

Habit is a strong predictor of what people eat, which is why creating a concrete plan—along the lines of, “If I eat at the office cafeteria tomorrow, I will head to the salad section first”—makes a difference, researchers have found.

Berke commonly eats oatmeal for breakfast, snacks on nuts during the day, and stuffs her burritos with beans rather than beef or cheese. “People think it’s going to be harder than it is,” she says.

But helping the environment doesn’t require everyone to eat the way Berke does. “The research is not trying to tell anyone they need to strictly transition into these diets in order to make an impact,” she says. “This is about people eating more sustainably, more often, and what can we do to guide people towards those practices.”