It seems like stating the obvious to say that most people think of vegetarianism as a diet. After all, it's defined by what food you will and won't consume. Eat meat? You're not a vegetarian. Don't eat meat, for whatever reason? Then you are.

The problem with this definition, though, is that it doesn't hold up in practice: Several studies have found that the majority of self-identified vegetarians eat meat at least occasionally. Does that mean they aren't really vegetarians? Or does it mean that vegetarianism is about something else, something more than simply the food you put in your body?

In a paper recently published in the journal Appetite, my colleague Anthony Burrow and I argue that it's the latter — that eating a vegetarian diet and identifying as a vegetarian aren't interchangeable. Based on our research, we make the case that vegetarianism is best understood not as a series of food choices, but rather as a way of understanding yourself, an element that makes up a core part of a person's identity.

To understand where we're coming from, it's helpful to start with a process called social categorization. Through social categorization, our minds automatically sort people into various groups based on attributes like race, gender, and age. A similar phenomenon can occur with the food we eat: Those who don't eat meat can be perceived as a different social group than those who do.

But identifying as part of a non-meat-eating group represents just one way in which people engage with a vegetarian identity. The label "vegetarian" captures a wide variety of ways that people think, feel, and behave in relation to plant-based dieting. Plenty of psychological research highlights that vegetarians are a diverse group in terms of their dietary motivations and the importance they place on following their diets. To illustrate this diversity systematically, Burrow and I proposed a theory, called the Unified Model of Vegetarian Identity (UMVI), that outlines 10 dimensions of a vegetarian identity.

The first three of these dimensions — historical embeddedness, timing, and duration — emphasize that social contexts largely shape how we see ourselves as eaters. Timing and duration refer to when, and for how long, a person identifies as a vegetarian over the course of their lifetime, while historical embeddedness refers to the fact that expectations about how and what we eat can vary drastically by time period. One can imagine, for instance, that Benjamin Franklin likely had quite a different experience as a vegetarian in the 1700s than vegetarians have today.

The next four dimensions outline how people incorporate plant-based dieting into their perceptions of themselves. One of these dimensions is motivation, which captures why people make plant-based food choices — for example, whether they're spurred on by health concerns or moral ones. Another dimension, regard, measures how positively or negatively people feel about not only their own food choices but also others' food choices. (Some vegetarians — particularly those with a strong sense of moral motivation — experience negative emotions and heightened feelings of disgust from seeing people eat meat, a trait we call "low omnivorous regard.") The dimensions of salience and centrality, meanwhile, have to do with how much of a role the vegetarian identity plays in a person's overall self-concept.

The last three dimensions — label, dietary pattern, and strictness — all describe the behavioral components of vegetarian identity. All plant-based dieters, whether they call themselves vegetarian or vegan, follow a particular dietary pattern: a set of animal products they typically avoid. But the details can vary from person to person — maybe someone's a vegan except for eggs, or a vegetarian who eats fish. And people also vary in the extent to which they adhere to their dietary patterns (hence the finding that many self-identified vegetarians eat meat occasionally).

These last three dimensions of vegetarian identity can sometimes seem to contradict one another, but if you look at them in the context of our larger framework, it becomes clear that they can all coexist as parts of one coherent self-understanding. Ultimately, being a vegetarian isn't just a reflection of a person's food choices; it's a way of reflecting on yourself and your relations with others. To advance our understanding of vegetarianism, veganism, and why people make the food choices that they do, it's important to think of plant-based dieting as something that involves a range of thoughts, feelings, and behaviors within social contexts.

This understanding can also help guide future research in many unexplored territories. While psychological research in recent years has generated a comprehensive body of literature on vegetarianism, there's plenty that we still don't know — for example, research has yet to explore identity differences between people raised on a plant-based diet from birth and those who adopt the diet later in life, or fully explain why some strict plant-based dieters don't identify as vegetarian or vegan. As researchers work to answer questions like these, they can use our framework to think about plant-based food choices more holistically, seeing vegetarianism for what it truly is: an identity.

Science of Us is a smart but playful window into the latest science on human behavior, with the goal of enlightening, entertaining, and providing useful information that can be applied to everyday life.