The focus shouldn't all be on weight loss, and you should also focus on maintaining a reasonable weight.
Starting diets, losing weight, and then stopping the diet and putting the weight back on is also harmful to your body.
You should emphasize lifestyle changes to keep weight off instead of jumping from diet to diet causing your weight to fluctuate.
To get a rough idea of what your ideal body weight, you can use the following formula:
110 pounds for men, or 99 pounds for women, plus 5 pounds for every inch of height over five feet.
Staying within 10% of that number will keep you in good shape.
As always, this is just an estimate, and you should always consult your doctor about your ideal weight.
And remember, it's not just exercise that keeps your weight under control; diet also plays a huge role.
Exercising and maintaining a healthy diet are great ways to protect your spine as time goes by.