Vegetarian, pescatarian, flexitarian and vegan – all are no- or limited-meat diets, so what's the difference? And why do we need all of them?

They all revolve around eating a plant-based diet, but there are notable differences when it comes to what specific food groups each includes.

Even though only 3 percent of Americans identified as vegan and 5 percentsaid they were vegetarian in a recent Gallup Poll, Nielsen reports that 39 percent of Americans in 2017 were actively trying to eat more plant-based foods.

A 2018 report by food consultants Baum and Whiteman also showed that more than 30 percent of Americans have meat-free days, more than 50 percent of adults drink nondairy milk and about 83 percent are adding more plant-based foods to their diets.

While being on a plant-based diet has been shown to help people lose weight, that's not the only reason some people choose to go that route. Some people refrain from eating meat due to ethical reasons because they believe eating animals is morally wrong. Other people decide to lead a plant-based lifestyle to reduce their carbon footprint and greenhouse gas emissions.

And it's important to note that just because you're a vegetarian or vegan doesn't automatically mean you eat a "healthy" diet.

Check out the differences between these diets below, so you don't accidentally and embarrassingly offer a vegan a mozzarella stick instead of turkey meatballs because they "don't eat meat."

Vegetarian diet

Probably the most familiar of them all: the vegetarian.

A vegetarian is someone who refrains from eating all types of meat, whether it be poultry, red meat or fish (including shellfish). They don't eat anything that has been made from the body of a living or dead animal.

Their diet consists mostly of grains, vegetables, fruits, nuts, legumes, dairy and practically anything else that doesn't involve the body parts of an animal.

Pescatarian diet

A pescatarian follows the same dietary guidelines as a vegetarian, except they eat fish.

The word pescatarian comes from combining "pesce," which means "fish" in Italian and "vegetarian."

Why fish? It really just depends on the person's preference. As with vegetarians, it could be for environmental or health reasons. Some pescatarians choose to allow fish and seafood in their diet so that they can add more protein and other nutrients they might be missing from eating an all-around plant-based diet.

Flexitarian diet

A flexitarian is someone who is a part-time vegetarian.

What?

Flexitarians eat a vegetarian diet but without completely removing meat. Their diet consists of adding more plant-based foods while eating things like red meat and poultry sparingly.

It's the most flexible of diets (ha, get it? Flexitarian = flexible). You get the best of both worlds, and there are no hard rules about what you're allowed to eat and what you can't.

It was made popular by Dawn Jackson Blatner, a registered dietitian, who wrote the book "The Flexitarian Diet." The diet boasts adding new healthy foods to your diet, rather than taking food away.

More:Beyonce promotes plant-based diet by offering tickets to her concerts for life

Vegan diet

A vegan is someone who refrains from eating all animal products. So while some vegetarians eat things such as eggs, cheese and yogurt, vegans do not eat dairy or any animal byproducts, like gelatin.

Sometimes veganism extends beyond the person's diet and into their lifestyle, with some choosing not to wear leather or silk and even feeding their pets a vegan diet. It just depends on the individual.

More:The pegan diet — a hybrid of paleo and vegan — could be the next big thing