From Beyoncé and Jay Z, to former Man v. Food host Adam Richman, the vegan diet seems to be becoming the diet rule rather than the exception. A 2014 infographic put together by TopRNtoBSN.com found the number of vegans has doubled since 2009, with a little more than 69 percent of the 8,000 Americans surveyed being vegan. It’s no surprise, then, PETA tends to be the diet’s biggest advocate.

But what exactly does it mean when someone says they’re vegan? More importantly, how is it different from simply going vegetarian? Here, we break down each diet, their believed pros and cons, and how each one could work for you.

Vegan Diet

U.S. News & World Report ranked the vegan diet No. 19 on its list of best diets overall. It also ranks in the top 10 for best weight-loss diets, best-heart-healthy diets, and best diabetes diets.

Basically, vegans eliminate all animal and dairy products (also eggs) from their diet. U.S. News cited this includes anything made with gelatin, “which comes from animal bones and hooves.” Dieters instead load up on fruits, vegetables, leafy greens, whole grains, nuts, seeds, and legumes.

Since animal products are the most convenient sources of protein and iron, vegans have a hard time getting an equal fix, which isn’t to say it’s impossible. PETA cited a cup of cooked lentils and a cup of cooked black beans each pack 18 grams of protein; a veggie burger patty packs 13g of protein; while 4 ounces of firm tofu packs 11g of protein.

Soybeans blackstrap molasses, lentils, beans, and Swiss chard are all rich in the mineral. PETA added iron absorption increases when foods rich in iron are paired with foods rich in vitamin C, such as leafy vegetables and citrus.

One study published in BMJ Open found a low-carb vegan diet reduces cholesterol levels, plus risk for developing heart disease. Eating mostly plants has also been associated with a better sex life. But in addition to this, and protecting the animals, a major draw to veganism is the impact it has on the environment — or rather, lack thereof.

The Washington Post reported one cow’s annual output of the greenhouse gas methane is “equivalent to the emissions generated by a car burning 235 gallons of gasoline.” And when reporters did the feed conversation, 6 pounds of feed amounted to 1 pound of beef; nearly 4 pounds of feed for pork; and 2 pounds for chicken.

Vegans, on the other hand, don’t emit as much greenhouse gas than their meat-eating counterparts. Slate calculated the difference between the two diets equals around 1.5 metric tons of carbon dioxide (CO2) per year.  CO2, like methane, traps heat and warms the planet, hence global warming. In 2013, CO2 represented Mother Nature Network reported “84 percent of all greenhouse gases emitted by humans.”

Vegetarian Diet

Vegetarians eliminate animal products, too, but the dairy can stay if the dieter wants. U.S. News ranked the vegetarian diet No. 11 — eight spots ahead of the vegan diet— on their list of best overall diets, as well as in the top 10 best heart-healthy diets, best diabetes diets, and best plant-based diets.

Like vegans, vegetarians eat a lot of fruits and vegetables, leafy greens, whole grains, nuts, seeds, and legumes. But unlike vegans, The American Heart Association said “there is no single vegetarian eating pattern.”

For example, a lactovegetarian eats plant-based foods, cheese, and dairy, while a lacto-ovovegetarian (lacto-ovo) eats all of the above and eggs. There are also semi-vegetarians, or people who don’t eat red meat but eat chicken and fish with their plant-based foods, dairy, and eggs. Most vegetarians, U.S. News said, are lacto-ovo.

Vegetarians have long been hailed as the healthiest eaters. A study published in the American Heart Association Meeting Report Abstract found people who mostly adhere to a pro-vegetarian diet (70 percent of food intake is derived from plants) were less likely to die from cardiovascular disease. And a slew of other research have associated this particular diet with reduced risk for certain types of cancer, high blood pressure, and early death.

And again, like vegans, maintaining a mostly plant-based diet is beneficial to the environment.

"Dietary greenhouse gas emissions in self-selected meat-eaters are approximately twice as high as those in vegans,” researchers from the Oxford Martin Programme on the Future of Food and the British Heart Foundation Centre said in a statement. “It is likely that reductions in meat consumption would lead to reductions in dietary greenhouse gas emissions."

Researchers added 70 percent of Amazon rainforest have been destroyed in Latin America in order to make more room for raising livestock.

Diet Do’s And Don’ts

PETA and science would agree vegan and vegetarian diets are beneficial to humans, animals, and the environment. They’re also nutritionally sound: Eating more fruits and vegetables, as well as whole grains and legumes, generously increases a person’s daily dose of healthy vitamins, protein, and fiber.

That said, there’s a lot to consider when mulling over either one of these diets. For one, veganism is very restrictive. While protein and iron can be otherwise sourced, vitamin B12 — another vitamin rich in animal products — is harder to get. Health reported B12 supplements “keeps the body’s nerve and blood cells healthy and…make DNA, so deficiencies can lead to tiredness, weakness ... nerve problems, and depression.”

There’s also a tendency for meat-free eaters to fill the animal void with processed foods. It may be less to think about, but Health added these options aren’t as nutritionally sound and can cause a person to feel hungrier and grumpier.

And a study published in the Humane Research Council found 10 percent of vegans and vegetarians will abandon their diet. Former vegetarians told the HRC they disliked their diet for making them stick out in a crowd, preventing them from interacting with others, maintaining a diet different from their own.

The trick, as experts like Mark Bittman would tell you, is not to go all-vegan or all-vegetarian at once; gradually phase meat out of your diet, while adding more vegan- and vegetarian-friendly options; Meatless Mondays are a great way to do this. Don't forget, too, to note the vitamins and nutrients you'll have to work a little harder to get without meat.