Eating a wide range of fresh fruits and vegetables, legumes, and whole grains is essential to a healthy microbiome. You should aim for at least the government recommendation of 38 grams of fiber a day, with a focus on raw, crunchy greens like broccoli. Leach thinks you should eat more than that, consuming 30 to 40 different plants a week. "Forage a little farther than you usually do," he says. Make sure you eat the crunchy parts – for instance, the ends of the broccoli spears – and seek out foods with high concentrations of the compound inulin: onions, garlic, leeks, celery.