Most of us never wonder why we eat some animals but not others, and that's no accident.

A fast-growing field studying the psychology of eating animals is catalyzing change among psychologists.

Research shows we justify eating animals with the "three Ns:" it's normal, natural, and necessary.

Throughout history, psychologists have played a critical role in both enabling and challenging injustice. For example, in 1912, psychologist Henry Goddard claimed that social problems were rooted in inherited low intelligence, helping to justify the forced sterilization of tens of thousands of people deemed "unfit" to have children. Later, in 1973, psychologists' research helped lead to the declassification of homosexuality as a mental illness.

Today, psychologists are again challenging harmful norms, this time those that sustain one of the most entrenched institutions: big animal agriculture. Apart from being a leading driver of climate change, public health crises, and human rights abuses, animal agriculture is responsible for the slaughter of more animals in a single day than the total number of people killed in all wars throughout history. A key reason this industry persists is that the invisible mentality that drives it is as entrenched as the industry itself.

Carnism and the Carnistic Mentality

Since my book Why We Love Dogs, Eat Pigs, and Wear Cows was published in 2010, an entire research field has emerged. My early research had led me to identify what I call carnism, the invisible belief system that conditions people to eat certain animals. Carnism is sustained by a problematic mentality, which has flown under the radar of most psychologists because it's so normal it seems unremarkable.

The "carnistic mentality" exists because humans are naturally inclined to feel empathy for others, including animals, and most of us are opposed to animals being subjected to needless suffering. Yet most of us also eat animals—not because we need to, but because we've always eaten animals and because we like how they taste. The result is cognitive dissonance, which we manage with unconscious psychological strategies, or "carnistic defenses," constituting the carnistic mentality. Carnistic defenses hide the contradictions between our values and behaviors, so that we unknowingly make exceptions to what we would normally consider unethical.

Consider the following scenario: You're biting into a juicy hamburger when your dining companion tells you that the meat is actually made from a golden........

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