Obesity, physical fitness and nutrition each play a large role in causing a heart attack (myocardial infarction).

Obesity
Heart attacks are more likely to occur in obese people. This is partly due to the way obesity contributes to high blood pressure and makes diabetes and cholesterol problems more likely.

Even when it has not caused other health problems, obesity raises the risk for a heart attack. Doctors are not able to explain all the reasons for this extra risk.

We do know that obesity may increase risk by causing a thickening (hypertrophy) of the heart muscle and by increasing the chance that you will have sleep apnea. Sleep apnea is a condition in which breathing is interrupted many times during sleep. This can cause heart stress.

Several studies have estimated the risk for obese people compared with people of normal weight. One example is the Nurses' Health Study. It found that non-smoking women who had a body mass index (BMI) at or above 32 had a quadrupled risk for dying of a heart attack compared to thin women with a BMI below 19.

Physical fitness
Exercise improves blood pressure, cholesterol, and weight. Even in modest amounts, exercise protects against heart attacks. Experts have blamed poor exercise for about 12% of the total risk for heart attack across the world. (This came from a study of 52 countries.)

Physical fitness can be measured by exercise tolerance in treadmill studies. And this can predicts a person's risk for a heart attack. To evaluate peak exercise capacity, a study divided men into groups based on the number of metabolic equivalents (METs) they could reach. Looking at how each group did over time, researchers found that every increase of one MET in exercise capacity was linked to a 12% improvement in survival.

Nutrition
A diet low in salt and high in fruits and vegetables appears to reduce your risk for a heart attack. Getting enough fiber seems helpful, too. The amount of salt in the diet seems to be one of the greatest factors in heart risk. Most Americans eat about two teaspoons of salt in a day. Men take in 10.4 grams (g) of salt, and women consume 7.3g.

If all American adults over age 35 cut their salt intake by 3g per day, a computer simulation predicts that during the next decade we would see 54,000 to 99,000 fewer heart attacks per year, and 32,000 to 66,000 fewer strokes per year.