People who exercise and continue to smoke may be putting themselves at risk for a heart attack. Smoking limits your blood's oxygen-carrying capacity and constricts your coronary arteries, so there may not be enough oxygen available to your muscles and your heart. Exercise can be a positive factor in helping you to quit smoking. Smokers do weigh an average of three to five pounds less than nonsmokers because nicotine increases the body's metabolism and decreases appetite. However, not everyone gains weight after quitting. Exercise can help curb both nicotine and food cravings. It also helps relieve stress and tension, which cause some people to smoke in the first place, as well as overeat. Even if you do gain some weight after quitting, exercising, along with eating sensibly, can help you lose those pounds within a few months. Consult a healthcare professional about exercise and smoking, especially if you've been diagnosed with heart disease or other health problems.