Are Nudges Toward Plant-Based Foods a Cheap Shortcut to Dietary Change?

Change is hard — but does it have to be? An increasingly popular school of thought over the past few decades argues that it doesn’t, and that with the right approach, people can easily and painlessly enact behavioral changes that are good for them and good for the environment. This approach is called a nudge, and on the surface, it’s very appealing. But are nudges all they’re cracked up to be?

Nudge theory, a term popularized by Richard H. Thaler and Cass R. Sunstein in their 2008 book Nudge, is the idea that small changes in design and presentation can lead to significant behavioral changes without limiting choice. Placing a product at eye level in a grocery store is an example of a nudge: nobody is pressuring you to buy it, but you might be more likely to do so if it’s in your line of vision.

Meat is bad for the environment, bad for animals and in some cases not great for the human body. The production of meat is destroying forests, creating greenhouse gases, polluting water and air and killing billions of animals every year. It’s led to the rise of dangerous antibiotic-resistant bacteria, and red meat consumption in particular has been linked to a number of adverse health outcomes. Can we nudge our way into better diets?

When you zoom out from individual research studies and take a wider view of what we know about nudges, this turns out to be a complicated question. Nudges might be useful in different, and perhaps more limited, ways than most media coverage would have you believe.

The Promise of Nudges: Cheap and Effective

The idea of using nudges to bring about dietary change, and specifically to reduce people’s consumption of animal protein, is in part a result of the fact that other methods haven’t succeeded. Meat consumption has doubled over the last 60 years, and vegetarian and vegan rates have stayed in the single digits for years.

Meanwhile, sales of plant-based meat replacements are down and many consumers still have a reflexively negative reaction to the words “vegan” and “plant-based,” even if they like the foods themselves.

In theory, nudges are a way to circumvent all of these problems. By altering the design of menus at cafeterias or changing the default offerings at hospitals, the theory goes, we can bring about a significant reduction in meat and dairy consumption without actually having to convince people of anything or restrict their ability to eat meat if they choose.

There’s at least some evidence that this can work. In 2023, New York City hospitals began offering plant-based meals to patients by default instead of meat. Before implementing this nudge, 99% of hospital meals included meat; after the nudge, less than half of them did.

This mirrored the results of a 2019 study in the UK: At three conferences, 94% of participants chose to eat meat when it was the default, but when offered vegetarian meals by default, only 13% chose meat. More recently, a UK study at university cafeterias found that when menus included pictures of animals next to the relevant meals — an image of a pig next to a bacon dish, for instance — the share of people choosing vegetarian meals increased by 22%.

All of these are examples of plant-based nudges. Nobody’s choice was restricted, and nobody was given a lecture on the downsides of eating meat. They were simply “nudged” into eating more plants, and many of them did.

This all sounds very promising, and has been held up by some as a cheap, effective, and easy way of bringing down meat consumption. But Seth Ariel Green, research scientist at Stanford University’s Humane and Sustainable Food Lab, isn’t quite convinced.

Does Scaling up Work?

The truth about nudge-based interventions is more complicated, Green tells Sentient. The findings of these studies have some important limitations, and implementing nudge interventions on a larger scale could prove far more difficult than nudge proponents imply.

“Plant-based nudges are a really big, diverse category, so it’s a little hard to figure out how to assess their efficacy overall,” Green says. “We’re talking about many different things in many different contexts.”

Green isn’t anti-nudge, and believes they can potentially play a valuable role in normalizing plant-based diets. But broadly speaking, he’s unconvinced that nudges of any kind are a silver bullet to bringing about large-scale behavioral change.

The power and efficacy of nudges has been proven time and again in academic studies, nudge proponents claim — but is this actually true? A more comprehensive look at the data suggests that it might not be.

Green points to a 2022 meta-analysis of nudge intervention studies: 126 randomized controlled trials in total, including 23 million people. Crucially, this meta-analysis included randomized trials run by governments that weren’t published in academic journals, and compared the results to published studies.

On average, 1.4% of the participants changed their behavior with the nudge. That’s a much more modest finding than the results of published academic studies, in which an average of 8.7% participants changed their behavior with a nudge.

Green calls this “pretty convincing evidence that when nudges are scaled up — like, taken out of the hands of academic researchers and put into the hands of governments — the effect sizes go down.”

That is, the nudges are quite a lot less effective. The question is: Why?

Green points to a number of reasons why nudges may not be as effective at a large scale as they appear to be in individual studies. One is the cost and effort of implementing them. Nudges are often not as cheap and low-effort as they seem at first glance.

What a Good Nudge Really Takes

Yes, printing menus with pigs on them is relatively inexpensive. But transitioning an entire cafeteria to serve plant-based dishes by default takes significant planning and training. The cafeteria might have to modify its food-purchasing agreements, train its chefs to prepare plant-based foods, or alter its kitchen layouts to accommodate the new system. Identifying which plant-based foods are actually appealing to customers is another challenge, as is ensuring those foods are actually tasty.

“Large institutions, like university dining halls and hospitals, have established ways of doing things, and getting them to change things is inherently laborious,” Green says. If such changes aren’t closely supervised, they might not be implemented as well or as fully as desired, he says.

All of this costs money — and that’s just for a single cafeteria. When scaled beyond that, those costs multiply, and can undercut one of the main appeals of nudges: that they’re inexpensive.

New York City hospitals were able to implement plant-based nudges effectively. But that required “a huge amount of hand-holding,” Green says, and “when you scale that up, that hand-holding goes away, because there’s just not that many people to hold your hand.”

Experiments like the two that took place in the UK might look promising on the face, but they too have their limits.

The 2019 study, for instance, took place over the course of one day. While it did show a significant increase in the adoption of plant-based meals on that day, it didn’t look at the participants’ eating habits after the conference. Might the people who switched to the plant-based meals have doubled their meat intake over the next few days to make up for their lack of animal protein?

It’s certainly plausible, Green says, and if that did happen, it would make the study’s conclusions much less compelling. But we’ll never know, because the researchers didn’t look beyond the dining choices on that one day.

There’s also the problem of bias, which can take a number of forms.

Studies on plant-based nudges might succumb to what Hunt Allcott calls “site selection bias.” In order to test a plant-based nudge, researchers first need to find an institution willing to implement it, because not all are. But the very fact that the institution is willing to try out nudges is itself a factor that might skew the results.

“You’ve surveyed 10 places to ask, ‘can you do my thing?,’” Green says as a hypothetical example. “One of them says yes. That one is not like the other nine, because they said yes. The fact that they’re into it is a meaningful distinction between them and the world at large.”

Green also points to a phenomenon called the “file drawer problem.” This is when a researcher’s study doesn’t arrive at the conclusion they wanted it to, and so it’s simply thrown into the proverbial file drawer and remains unpublished. The file drawer problem is “a well-understood way in which the research findings you see in social science are not a random draw of all possible findings,” Green says.

In other words, there may be a number of studies sitting unpublished in file drawers around the world, showing that nudges aren’t as effective as believed. This isn’t just a reason to doubt the reliability of studies on nudges. It’s a reason to doubt the reliability of any published study — a somewhat frightening revelation that Green encourages us all to think about.

A Normalizing Force

Despite all of these concerns, Green still thinks nudges can play a valuable role in bringing down meat consumption, just in different ways than “nudgelords,” as they’ve been called, like to claim. When institutions start offering plant-based meals as the default, it can create “an aura of normality” surrounding non-meat proteins, Green says.

“It stops being the thing for the vegans, and it starts being the thing that all of us can eat,” he says. “I think this is really important.”

Normalizing has proven a powerful tool in other situations. For example, in 1990, the Ad Council nonprofit and the US National Highway Traffic Safety Administration began running public service announcements telling Americans that “friends don’t let friends drive drunk.” This helped normalize the simple act of stepping in to stop a friend from getting behind the wheel when they’re intoxicated, and it led to a 10% decrease in alcohol-related fatalities the next year — the largest one-year decrease ever recorded.

Beyond merely normalizing plant-based proteins, nudge interventions can potentially result in carnivores actually developing a taste for non-meat alternatives — although this can cut both ways, Green cautions.

“Suppose that we have a plant-based nudge at lunch, and the meal rules. Like, it’s the greatest plant-based dish you ever had in your life,” he says. “You might actually eat more plant-based in the future, because you’ve had this positive update that plant-based food is yummy.”

But if the meal is bad, you might conclude that “tofu sucks,” and avoid plant-based foods in the future. This is yet another reason why implementation of plant-based defaults requires careful attention and planning to be successful.

The selling point of plant-based nudges is that they’re both effective and cheap to implement. But in Green’s eyes, it’s “really, really hard and rare” for any one policy change to actually be both effective and cheap at once.

If you devote time and resources to train each individual dining institution on how to effectively facilitate plant-based nudges, the program may be effective, but it won’t be cheap. If you forgo that training and simply implement a change in how meals are offered, the program will be cheap, but it might not be very effective.

Nudges can be valuable in laying the groundwork for widespread dietary change, Green says, but actually bringing about that change will require doing the exact kind of hard work that nudge theory seeks to avoid: Changing people’s minds.

“The actual, uncomfortable thing I want to confront people with,” Green says, “is that we need to convince people [of meat’s downsides], and that’s really hard. But I spend a lot of time thinking about that, instead of thinking about how we can manipulate them into eating less of it.”