One of the ways health providers indirectly measure body fat is by calculating your body mass index, or BMI. The measurement indicates whether you have underweight, a healthy weight, overweight or obesity.
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Average BMI for Americans
BMI is an indirect calculation of body fat based on height and weight. The formula for BMI is weight / (height x height) x 703. Weight is calculated in pounds and height in inches. For example, the calculation for a person weighing 190 pounds and standing 6 feet tall is 190 divided by 5,184 multiplied by 703, which equals a BMI of 25.7.
The average adult male and female in the United States has a BMI of around 26.5, according to the National Health and Nutrition Survey. A BMI between 18.4 and 24.9 is considered healthy, while 25 to 29.9 is described as having overweight. A BMI of 30 or above falls in the obesity category.
That said, BMI on its own is not a useful measurement for determining a person's overall health. BMI is often not an accurate measurement of body fatness because people have varying levels of muscle mass, which can contribute to a heavier weight.
Risks of Overweight and Obesity
Excess weight may cause elevated blood cholesterol, high blood pressure and raised blood sugar, which are signs of health conditions. Carrying extra pounds puts more stress on joints and cartilage, too. Having overweight or obesity puts you at a higher risk for heart disease, certain cancers, stroke, hypertension, type-2 diabetes, sleep apnea, fatty liver disease and osteoarthritis.
People with a higher BMI have a bigger waist circumference, another marker for chronic disease risk. The largest and longest study to evaluate the health risks of excess abdominal fat, also known as visceral fat, is the Nurses' Health Study. Researchers found that independent of BMI, having a higher waist circumference puts you at a significantly increased risk of death from heart disease, cancer and all causes. The study was published in the April 2008 issue of the journal Circulation.
Visceral fat is dangerous because it's deeper in the abdomen and accumulates around your organs, promoting inflammation and negatively affecting surrounding organs. For example, visceral fat accumulating around the liver is a key factor in fatty liver disease, according to a report published in the Journal of Gastroenterology in May 2006. To reduce your risk of chronic disease, aim for a waist circumference of less than 40 inches for men and less than 35 inches for women.
The good news is, losing 5 to 10 percent of body weight decreases the risk of problems such as heart disease. If you weigh 180 pounds, that's a weight loss of 9 to 18 pounds.
Know Your Target Health Numbers
Aside from BMI, it's critical to know the goal numbers for other health parameters. Healthy blood pressure is 120/80 or less, while a goal blood sugar is less than 100 milligrams per deciliter. Having glucose and blood pressure in the target range helps to keep your heart and other organs healthy.
For cholesterol, aim for a total number of less than 200 milligrams per deciliter, consisting of less than 100 for low-density lipoprotein, or LDL -- the "bad" cholesterol -- and less than 150 for triglycerides. The goal for high-density lipoprotein, or HDL, the "good" cholesterol, is more than 40 milligrams per deciliter for men and greater than 50 for women. Cholesterol can build up in your arteries and cause them to narrow, increasing the risk of heart attack or stroke.
Losing Weight to Improve BMI
Improving your body composition is pivotal to improving your health and lowering your BMI. This means increasing the amount of lean muscle in your body and reducing the amount of fat you carry. One of the first steps is to cut back on foods that provide excess calories. Some of the main culprits in the typical diet are sugar-sweetened drinks, dairy desserts, sugary snacks, pizza and fatty processed meats such as sausage and bacon. Often, cutting back on these foods and getting more physical activity is enough to improve your BMI. Aim to choose mostly fresh whole foods such as fruits and vegetables, lean meats and seafood, whole grains, milk and yogurt, nuts, seeds and unsaturated oils like olive, sesame and flaxseed.
- Centers for Disease Control and Prevention: Healthy Weight, Overweight, and Obesity Among U.S. Adults
- National Institute of Diabetes and Digestive and Kidney Diseases: Do You Know Some of the Risks of Being Overweight?
- American Heart Association: Sugar 101
- Circulation: Abdominal Obesity and the Risk of All-Cause, Cardiovascular, and Cancer Mortality: Sixteen Years of Follow-Up in US Women
- Journal of Gastroenterology: Visceral Fat Accumulation and Insulin Resistance Are Important Factors in Nonalcoholic Fatty Liver Disease
- Centers for Disease Control: About Adult BMI