My comment: Here's the answer to the question => What's the least I have to do? Answer: the more you do the better. Fitness & Fatness independently important.
“We found that adding low amounts of physical activity to one’s daily routine, such as 75 minutes of brisk walking per week, was associated with increased longevity: a gain of 1.8 years of life expectancy after age 40, compared with doing no such activity"
We all know that exercise is good for you, but how good? While previous studies have shown the link between physical activity and a lower risk of premature mortality, the number of years of life expectancy gained among persons with different activity levels has been unclear — until now.
In a new study from Harvard-affiliated Brigham and Women’s Hospital (BWH), in collaboration with the National Cancer Institute, researchers have quantified how many years of life are gained by being physically active at different levels, among all individuals as well as among various groups having different body mass indexes (BMI).