Data from Perfect Price, a company with a database of millions of credit card transactions, shows that consumers spend the most money on groceries at Costco. Priceonomics takes a look at the data and explains how Whole Foods may be more expensive, but people spend more money at big-box stores such as Costco and Sam's Club.
The distribution of spending between Walmart and Whole Foods show the similar amounts that people spend grocery shopping at these stores:
Slightly more people spend less than $25 on a trip to Whole Foods, and slightly more spend between $25-$100 at Walmart, but overall, the distribution of how much people spend on trips to these stores are remarkably alike. Of course, Whole Foods prices are generally much higher than at Walmart, so this similarity is primarily a function of people making smaller trips to Whole Foods.