Why do some kids get allergies and not others? Why do some patients respond better to cancer treatment? Why do some men get erectile dysfunction while others are potent into their 90s? Why do some people have an easier time losing weight? The bridge between many 21st-century health epidemics may be found in the trillions of microorganisms that live harmoniously in your body. The biopharma and nutrition juggernauts are in a race to reveal how your gut bacteria can influence everything from your prostate cancer to your diabetes to your behavior. Whether you're an entrepreneur, a philanthropist, or just a concerned parent, gut microbes should be on your radar as the key to good health and disease treatment.