It's nearly impossible to get a substantial vegan meal at most fast-food chains.

A study by the Plant Based Foods Association shows that the plant-based food industry — which includes meat and dairy alternatives, tofu, egg replacements, and other animal-product alternatives — generates over $13 billion in sales annually throughout the US economy.

By not adapting to the increasing demand for vegan food, fast-food chains are missing out on a huge opportunity.

I recently tried to survive a week eating nothing but vegan food from popular fast-food chains.

Unsurprisingly, it was a failed experiment. Over the span of three days, I ate under 2,000 calories and nearly 70 grams of sugar. My options were, for the most part, limited to french fries, sugary oatmeal, and plain salads. I couldn't get enough protein to make it through one day, let alone three.

While I've been vegan for quite a while, this experiment opened my eyes to one of the fast-food industry's biggest shortcomings: a failure by most chains to offer even one substantial vegan meal.

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.

In addition to consumers opting for meat and dairy alternatives, many food companies are betting on the growing vegan market. Nestle acquired vegan meat supplier Sweet Earth in September, Campbell recently acquired Pacific Foods, which makes non-dairy milks, and McDonald's even launched the McVegan burger in Sweden and Finland to meet increased demand for more vegetarian and vegan options, though the brand has made no such attempts in the US.

Despite the obviously increasing demand for non-meat and non-dairy products, it remains nearly impossible to get a substantial vegan meal from a fast food restaurant. Taco Bell and White Castle seem to be the only two chains that are shifting towards meeting the increasing demand for vegan options, while other-fast food restaurants are missing out on a growing market.