"A boring diet is a slimming diet," Barnett said.
It goes back to the concept of diminishing returns. To use Barnett's example, if you eat a single Oreo, you're going to really enjoy it. "If you eat a full bag of Oreos, by the time you eat the last one, you're not going to get nearly as much happiness or utility out of it."
He added: "If you restrict your food choices day in and day out, no matter what kind of preferences you have for food, you're going to get bored with it."
Both Barnett and Payne said they eat a salad for lunch every weekday. ("I've gotten to like salads over the years, but I don't have the urge to overeat a salad," Payne said.) When Payne goes to Starbucks, he orders an Americano with a dash of nonfat milk.
What's more, when you do allow yourself to splurge, depending on your specific meta-rules, you'll enjoy it that much more.