
There's actually a TON of truth to that statement.
Most bothersome yet harmless bugs like the cold can easily be prevented from gaining a foothold in your body by keeping your immune system in peak condition - which requires a body in good health.
Not everyone can do much about the state of their immune system, of course, but most people can improve their immune system simply by eating better and staying active.
What that all entails, I won't get into - that would turn this short post into a novel. I don't feel like typing that up right now.
