Vegetarianism and veganism

Utilitarianism is closely linked to vegetarianism and veganism, and many utilitarians are vegetarians or vegans. The most prominently known connection between the two concepts is probably that of Peter Singer's utilitarian argument in favour of vegetarianism, put forward in his 1975 book Animal Liberation. However, concern for nonhuman animals amongst utilitarians goes back to Jeremy Bentham, the 18th Century British philosopher regarded as the founder of modern utilitarianism.

Utilitarian arguments in favour of vegetarianism
The vast majority of scientists acknowledge that the nonhuman animals that many humans eat are sentient; that is, they can feel pain and suffer. Furthermore, during the production of meat, nonhuman animals almost invariably suffer at some stage, for example in factory farms, during transportation or during the slaughter itself. A utilitarian philosophy requires that we reduce the pain and suffering in the world, and also requires that we equally consider the interests of every being, including the interests of nonhuman animals not to suffer, as it would be irrational to discount their interests simply because they are different to us. As Jeremy Bentham put it, when considering what makes a being worth protecting,

"What else is it that should trace the insuperable line? Is it the faculty of reason or perhaps the faculty of discourse? But a full-grown horse or dog, is beyond comparison a more rational, as  well as a more conversable animal, than an infant of a day or a week or  even a month, old. But suppose the case were otherwise, what would it avail? The question is not, Can they reason? nor, Can they talk? but, Can they suffer?"

Buying meat contributes to the demand for meat products and therefore the supply of meat products, therefore abstaining from consuming animal products reduces the supply of meat products and thus the number of nonhuman animals going through the meat production process and suffering.