How to Quickly and Easily Boost Your Immune System Against Internal and External Stressors* Your immune system is a complicated yet amazing defense system -- 80% of it lives right in your digestive tract. It helps keep you healthy and strong -- protecting your body from all sorts of internal and external stressors.* Unfortunately, even if you eat wholesome and preferably organic foods, exercise regularly, and get proper amounts of sleep, your immune system can be overrun by free radicals and environmental stressors. This is particularly true as you age.