My personal, layman's view is that, once again, Dr. McDougall is right: There are three key steps: Healthy diet, moderate (but frequent) exercise, and low stress.
I know that stress affects the body. In my case it means more rapid heart rate (not good), shallower breathing (not good), and probably a stream of possibly damaging hormones or other substances (such as adrenaline).
I have been successful at diet and exercise. I have not been as successful at stress reduction. First, I haven't devoted as much attention to it. Second, reducing stress can be very difficult for some. It requires changing habits and attitudes we might have developed as a child. I have made progress. I have not arrived at the end point.
The most important question in dealing with stress is this: What is stress?
My definition is that stress is the body's physical response to a physical or mental demand placed on a person.
The key to stress reduction, I have found (so far), is to deal with true (fact-based) demands and reject as unworthy other demands. If I am cold, I respond my adding more clothes or turning up the heat. If someone calls on the phone and tries to pressure me into doing something about X, I need to decide whether I should. If I should, then I make a plan and take action (which reduces stress).