Soon after Daphne Miller, M.D., began practicing medicine in San Francisco, she realized that so many of her patients' woes—heart disease, diabetes, cancer—could be traced back to a poor diet. But she often wondered: what foods could prevent these diseases? Then while working as a medical volunteer in the Amazon, she realized why Angela, one of her patients back in California, felt better every time she returned from visiting her tiny home village. "In Brazil, Angela's meals focused on local ingredients—plantains, beans, free-range chickens, fresh-caught fish and fruit," says Miller. She was eating a diet that had helped villagers keep modern diseases at bay for centuries. "These meals were different from the processed foods that she ate in San Francisco." The epiphany prompted Miller to spend the next two years studying eating habits common to indigenous communities with low rates of chronic diseases, such as heart disease, diabetes, breast cancer and depression. She compiled her findings in The Jungle Effect: A Doctor Discovers the Healthiest Diets from Around the World (Collins), out in paperback this June. We recently caught up with Dr. Miller, a family physician and associate professor at the University of California, San Francisco.