Your muscle mass has the greatest impact on your metabolism. The more muscle you have, the more calories you burn. Less muscle equals fewer calories burned throughout the day. To add another wrench in your weight and heart health struggle, metabolism decreases as you age. The rate of decrease is about 2% every 10 years beginning at age 30. You can counteract this decline by being active and maintaining your muscle mass.
Building an extra 5 pounds of muscle will boost your metabolism by ~100 calories each day.
Speak with your MD before beginning a fitness regime.