Most people know the score by now. Our rates of obesity are rising all the time in spite of all knowledge, low fat foods and a preoccupation with dieting. So if I told you the odds are good that you will probably end up more fat and out of shape from dieting than if you had not bothered in the first place, you would probably not be very surprised.  After losing weight on a diet, approximately 95% of people gained the weight back in a few years, many within the first year and many gained an extra 5lb. If you want to gain weight, especially as you get older, go on a diet. 

Here are some of the problems.

You go on a diet restricting your caloric intake, certainly your body will respond by burning body fat, all good so far, however your body will also take a relatively large amount of protein from your muscles.  If you loose 40 lb about 15lb will be muscle loss. Now, if you gradually gain back the weight (remember the percentage of those that do). You do not gain back the lost muscle mass it's all fat. Now you are in worse shape than even. You are back to your original weight, (if you are lucky you’re not heavier). But you have less musle mass.

Muscle is active tissue it burns calories, you now have a lower percentage of muscle mass and you now burn less calories at the same body weight. When you diet,  you lose muscle mass at a faster rate, which leaves you even more vulnerable to weight gain.

 The loss of muscle mass is already one of the biggest problems affecting us as we age. It starts around age 30. By age 50, you've lost about 10 percent of your muscle mass.” After that it speeds up about 2 percent per year, by 80, you could have a 40 percent loss of muscle Mass.” it becomes increasingly difficult to avoid weight gain as you get older. 

Our bodies will store almost unlimited amounts of fat. And when we gain fat, we tend to become less sensitive to the hormone that makes us feel satisfied when we eat. the heavier we get, the more likely we are to overeat.

Humans have also developed an adaptation to times of famine, when there is a shortage of food the body tends s to hang on to those fat stores,the body does not know you want to burn off those extra pounds when dieting, so it slows the metabolism.

Big key: Exercise speeds the metabolism, especial strength training. Certainly you will burn more calories during cardio but you metabolism is raised higher and for longer after strength training,you get an after burn effect.

If you are doing resistance training while losing weight, you can virtually eliminate loss of muscle.You certainly can maintain the muscle mass you have.

For older adults I would recommend weight bearing exercises as they also help to maintain bone density, walking, out side or in on a treadmill is great  but ellipticals are also excellent.  Add some upper body strength exercises  and you have a good stratergy to help fight the loss of muscle mass and stoke  up your metabolism.  The evidence shows that no matter what age you are, you can increase muscle mass.

It doesn't take much of an increase in exercise to produce improvement, because your resting metabolic rate is with you 24 hours a day. A small increase over a year makes a huge difference. Even if you maintain the same food intake, you won't be as likely to gain weight if your working out.