How much Really do our eating, exercise habits, or even bad habits effect who we truly are?

Basically what I mean is, I see people who smoke cigarettes for instance, are usually a little bit more on the anxious side. Now please don’t misunderstand me, I’m not trying to set stereotypes. I am just going off of my own personal experience and a little observation. I used to be a smoker for 10 years myself. After I quit I felt less anxiety and in general, more healthy and motivated all around. This is only one example of a bad habit. How about a persons eating or daily diet regimen for example. A person, who say, eats more fried foods than fresh, baked ect... How much does our eating, exercise, and daily habits really effect our mental decisions, and even spiritual life?