Plan for life long fitness
As a health conscious individual you do what you need to do to be fit and healthy. You plan your diet cautiously you engage in regular exercising.
So far so good, but problem is most of the people do not change their diet as per their lifestyle change or modify their exercise routine as per the change in daily activity level.
If you plan to maintain lifelong fitness you need to closely watch your lifestyle changes, and modify your diet and exercise routine to compensate for the changes.
An example may come handy here: a sales person who does lots of field work gets promoted and now his work needs him to be at his desk for most of the day. Now if he continues his 2000 kcal as before there is chance he will start gaining weight.
He can either step up his workout level or bring down calorie intake to be in shape.
Even if every thing remains equal increased age can bring body’s calorie requirement down [because of reduction of the lean muscle percentage minimum calorie requirement of the body while at rest reduces]. For women few more things like pregnancy, breast feeding etc. get added to the mix other than age and activity level.
Persons with long term view of fitness need to keep all these factors in mind while planning diet and exercise routine.