This is the key when it comes to losing weight. Basal metabolism has to be active constantly because in that situation, energy will be spent all the time and that of course, requires constant input of energy. This is where fat burning process starts, because with controlled eating, energy needed for the metabolism cannot be satisfied from taken food, so some additional sources are needed. In most cases, this source is glycogen, but since it is depleted quickly, next source is used and that is fat tissue. The problem in some situations when fast diets are used is that instead of fat tissue, muscle tissue is used. How is this possible? This is because our body does not know the difference between intentional and unintentional food cutting. So, when the intake of food is greatly reduced, the body turns its defensive mechanism on and actually saves the fat instead of eliminating it! This is a paradox people have to be aware of when dieting, and in order to prevent it, some amount of all nutrients must be taken with food.
To keep the basal metabolism always up and running, exercising should be performed as much as possible. It does not have to be some intensive training session done 5 times a week, and in most cases, brisk walks from home to work, from home to grocery store and back, to the nearest park and back are needed. Nothing more than that is needed, but it is advisable that it happens as often as possible. Used strength level is low so there will not be exhaustion of the body muscles and the activity can be performed for quite some time. This is important to know because by some statistics, intensive fat burning process starts after about 30 minutes of exercising.
People have to be active no matter what age we talk about here. Even in their 70's, actually, especially at that age, people should exercise. Of course, it has to be something appropriate for the overall physical condition of the practitioner, but it has to be present.