To find out what the most commonly purchased food was in the US, we asked America's largest retailer — Walmart — what its top-selling item was in 2015.

The answer? Bananas.

Dorn Wenninger, vice president of produce and floral for Walmart US, told Tech Insider that the company sold over 1.5 billion pounds of bananas last year.

"Imagine all the logistics and processes," he said, "to move 1.5 billion pounds of a perishable item from seven countries in Latin America to over 4,000 stores in the US."

From the time the bananas are packed into containers on farms in Mexico, Central America, and the top of South America, to the time they reach Walmart stores, they are kept at 56 degrees Fahrenheit. This process takes anywhere from two to 3.5 weeks, Wenninger said.

The sale of organic bananas has more than tripled over the last year, he said. Sales of organics overall, he said, are growing over twice as fast as sales of non-organic produce.

But bananas aren't the only healthy food that's increasing in popularity. Wenninger said foods perceived as "superfoods" are also on the rise.

"Cauliflower has been hot and really on trend. High color fruits and vegetables, which have high levels of antioxidants — blackberries, blueberries, cranberries, kale — all are growing faster than the total produce industry as a whole," he said.

So far, nothing has unseated the humble banana from its No. 1 spot. But because all bananas are clones, and a new fungal disease is threatening to wipe out the fruit, that might soon change.