I can tell you from personal experience having been a physical fitness health nut and also having gone through prolong periods of enormous stress that the two are undeniably linked. When you're under stress, you have fight or flight response. Several chemicals such as cortisol and adrenaline are produced in your body. When you're under chronic stress, you have this type of constant sense of this. It depletes resources in your body differently than when you're relaxed. It also causes you to store more body fat because when we were in the wild the environment stress response could be associated with food scarcity.
The time in my life when I was in the best shape of my life was when I was under the least amount of stress. I had low blood pressure, cholesterol, LDL/HDL, triglycerides, everything. My GP was cheering me on.
Get your stress under control and focus on having a healthy lifestyle and everything else will sort itself out. The problem in America is that we are a culture that pushes inordinate amounts of stress on our citizens. Where UK citizens would take a month long holiday every year because of the generous vacation time afforded by most European countries, the United States doesn't guarantee any paid vacation or sick time. And then we wonder why compared to other countries our citizens are significantly more tired, burnt out and less healthy.