My wife is a doctor, most of of our friends have at least one, often both as doctors. Most of them are living healthily, but that may be also due to location - Geneva, Switzerland which has strong French influence. Meaning good high quality food is default, portions smaller than US, tons of physical exercise is a default here, we have beautiful nature and mountains at our doorsteps so that helps. My banking IT colleagues fall into exactly same category.
But then there are the rest, which have various issues like eating crap, overweight, no sports etc. Yet they know fully darn well where it leads to. Either they make some mental bypass like smokers 'it won't happen to me', or they are at peace and enjoy themselves.
Proper knowledge of consequences is not enough to persuade everybody, regardless of their IQ. Also, even healthily folks that are say anxious go sometimes on regretful binging spree when things get tougher.