Once you reach 50, flattening your stomach becomes a greater challenge than it might have been even a decade earlier. Your metabolism and hormone levels will be lower than they once were, and your injury susceptibility will be higher. As such, you'll be well served to take a modified approach to improving your abdominals.
Consult Your Doctor
At this age, it's especially important to consult your doctor before beginning a new diet or fitness routine. Explain that you're aiming to flatten your stomach, and she may provide you with specific, personal dietary or physical restrictions. Additionally, consider asking your doctor about hormone replacement therapy options for your age group; since low testosterone is directly associated with accumulation of abdominal fat, this will help you towards your goal.
Reduce Your Calories
To flatten your midsection, you'll need to prevent the deposit of more fat in the area. To do this, reduce your caloric intake. Take an inventory of your current food and drink intake, and refer to the relevant nutritional information to develop an estimate how many calories you're taking in each day. Depending on the amount of fat you have to lose, reduce this figure by between 500 and 1,000 calories. According to MayoClinic.com, this will prevent new fat from depositing and allow you to lose between 1 and 2 lbs. per week. To reach this deficit, start by cutting out junk food. If that's insufficient, reduce your portion sizes at meals as required.
Do Cardiovascular Exercise
There's no such thing as spot reduction of fat. So, if you're looking to reduce fat through exercise, you'll have to do cardio to reduce fat all over your body. Aim for at least three weekly sessions of cardiovascular activity; appropriate choices include running, biking, swimming or anything else that consistently raises your heart rate. At first, complete each session in as few as 30 minutes. As your fitness improves, increase the frequency and duration of your sessions up to one hour daily.
Train Your Abdominals
While direct abdominal training won't eliminate fat, it will develop the underlying muscles, creating the appearance of increased leanness and tone. Train your abdominals at least twice each week, performing five exercises for each session. Because of your age, back injury is a serious concern. As such, it's best if you use the following exercises, all of which have been demonstrated to exert little pressure on the spine: traditional crunch, feet-anchored crunch, bicycle crunch, captain's chair and hanging leg raise. Perform each of these exercises for two sets of as many repetitions as you can manage without sacrificing good form. Rest as desired between sets.