Japan is famous for its convenience stores, and the foods there are fast and easy. But nutritious? Not so much.

The ideal would be to buy all our foods from specialists and, admittedly, Japan is still a good place to find such niche purveyors: baked goods from bakeries, fish from fishmongers, meat from butchers, and fruits and vegetables from greengrocers, where, in season, you find fresh produce from the prefectures they are mainly grown. The system is perfect — until you factor in the time and money it takes.

We all think we’re being efficient when we do “a big shop” at a supermarket. The issue here is the business model — have you ever noticed the price volatility of big chain stores? The prices of certain products can differ wildly from day to day. You may think you’re getting a deal when that head of broccoli goes on sale, but those daily specials are often what is known as “loss leaders.” Supermarkets take a hit on one product to get you through the front door, but other prices are inflated to make sure that the company always comes out on top. You’re being gouged, but behavioral models show that an average customer will continue shopping in a store after procuring some bargains even if other prices are inflated.