What to Eat When: The Science Behind How You Eat

In each of their medical careers, Cleveland Clinic chief wellness officer and New York Times best-selling author Michael Roizen, M.D., and Johns Hopkins faculty member and medical director for The Dr. Oz Show Michael Crupain, M.D., have emphasized the medicinal power of food. In their new book What to Eat When (National Geographic, 2019), the doctors tap into the science of food and how the food choices you make each day—and when you make them—can affect your health, your energy, your sex life, your waistline, your attitude and the way you age.

What alerted you to the importance of adding time as a variable to healthy eating?

Crupain: The collective diet industry has spent a lot of time addressing the “what” part of eating: fruits versus fries, nuts versus chips, etc. But we’ve spent little time on the “when.” Mike and I are both on the board of HealthCorps [a health-education charity founded by Dr. Mehmet Oz], and a few years ago I told Mike I wanted to come to the Cleveland Clinic and work on a project with him. He said, “Let’s write a book together.”

Roizen: The data on the effects of when you eat started accumulating about 10 years ago in animals, three to four years ago in humans. As we took a closer look, we decided that we needed to write about it. There was enough data to make people understand that this really is very important to how long and how well you live.

Describe the “When Way” of eating.

Roizen: By eating in tune with your circadian rhythm [a natural process that regulates your sleep-wake cycle], you get an advantage to your energy level, your health level, your sleep and to maintaining a normal weight.

Crupain: We came up with four guidelines for the When Way: 1) Eat when the sun is out—sync with your circadian rhythm, because the whole point of circadian rhythm is to make us efficient, for our body to do the right thing at the right time; 2) Eat more food early, less later—aim to consume 75 percent of your daily calories before 2 p.m.; 3) Try to be consistent with your day-to-day eating; and 4) Don’t stereotype foods—who says you can’t have eggs or oatmeal for dinner or a black-bean burger or salad for breakfast?

You write that “our body’s internal environment is always changing—and how you feed it during those changes matters.” Is that why you came up with the “What’s the Situation” section for what to eat in different life scenarios, such as when you’re stressed and hangry, when you can’t sleep, when you have a job interview?

Crupain: Yes. Life isn’t the same every day, so you have to be ready to deal with those things. These scenarios came from all over: experiences in our lives, with other people, things we know are important. We wanted them to be a wide variety. Some are very serious; some are less serious; some are in the middle.

Roizen: These are things that patients have asked us about. I’m a science nerd, and there was also data that took us to this variety of situations.

You offer a 31-day plan. After one gets through that, what’s next?

Crupain: You just keep going. Our plan helps to gradually get people to a different way of eating, because biologically it’s better to make changes gradually. The first 15 days focus on adjusting the size and time of meals. The second half is focused on the what: Eat more plants and less sugar. By the end of 31 days, your body should be ready to keep doing this forever. But if it’s not, that’s OK too. You can go back and try again or take longer.