Taco Bell is one of the best fast-food chains for vegans, but some of its offerings are a lot better than others. Business Insider/Jessica Tyler

Fast-food menus tend to have pretty limited options for people who follow vegan diets.

But veganism is a rapidly growing trend — Nielsen data shows that nearly 40% of Americans are trying to incorporate more plant-based foods into their diets.

Though there still isn't a ton to choose from, major chains are slowly starting to add more vegan options to their menus.

Of every major fast-food chain, Taco Bell is likely the best for those on a vegan diet. Here's how some of the most popular vegan items from the chain rank.

Vegan fast food — free from meat, dairy, egg, or other animal products and byproducts — is not easy to come by. fast food — free from meat, dairy, egg, or other animal products and byproducts — is not easy to come by.

The population of vegans, vegetarians, and people who are simply trying to eat less meat is growing rapidly. Restaurant consultancy group Baum+Whiteman expects plant-based foods to be the top trend of 2018. A study by the Plant Based Foods Association from September 2016 found that the plant-based food industry — which includes meat, dairy, and egg alternatives — generates over $13 billion in sales annually throughout the US economy.

Currently, Nielsen data shows that nearly 40% of Americans are trying to incorporate more plant-based foods into their diets. According to Baum+Whiteman, 58% of adults choose to drink non-dairy milk instead of dairy milk, yet most fast-food chains don't carry any alternatives to dairy milk. In the past year alone, Google has seen a 90% increase in vegan-related searches.

Many major chains are slowly starting to catch on to the trend. White Castle now serves the plant-based Impossible Burger, and Costco and Ikea both recently added vegan items to their food-court menus.

But out of every fast-food chain, Taco Bell is likely the most vegan-friendly there is. On its website, it has instructions for ordering vegan at the chain along with a list of all of its American Vegetarian Association-certified vegan ingredients. As it turns out, almost anything on the Taco Bell menu can be made vegan with a few substitutions.

We tried some of the most popular vegan meals from Taco Bell. Here's how we ranked them: