To take something (or someone) with "a pinch of salt" means to not accept it unquestioningly, or don't automatically believe in it. Be a bit skeptical about it, do some research, and make your own conclusion.
The "rat race" is the daily chore of going to work and earning money so that you can survive. Working long hours, trying to do better than the person next to you, etc., can lead to stress, high blood pressure and other ills. That's why jogging is much healthier!
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