How is bacteria beneficial to your body?

Bacteria are about balance in the environment or body. For example, to maintain proper digestion of foods, you need good bacteria. If there are not enough good bacteria, then you do not digest your food or obtain as much nourishment from your foods. Each region of the world has a different balance of good bacteria. That is why the water in one region of the world doesn't necessarily make the native inhabitants of the area sick, but might make you sick if you travel there.