Body Fat - The Scale or the Tape Measure

Not all fat is the same. So it’s not just how much fat you have that’s important for your health. It’s where that fat is located.

Most of our body fat sits under the skin. This fat, called subcutaneous fat, is that extra flab that stares at us in the morning. It makes up about 90 percent of body fat in most people.

The fat you can't see is the fat that surrounds the organs in our body, especially the organs inside our belly. Doctors use the fancy term viscera for organs, hence the name visceral fat. Visceral fat is not so obvious. It lies out of reach, deep within the belly, where it pads the spaces between our stomach, intestines and other organs.

People who have more subcutaneous fat have a greater chance of having more visceral fat. But the opposite is often not true. Many people who have a body weight in the normal range have too much visceral fat. In fact, as much as one-fourth of a person’s total body fat may be visceral fat.

Even thin people who carry more extra visceral fat have a higher risk of type 2 diabetes and heart disease. And women with more visceral fat have a higher risk for breast cancer and gallbladder problems.

Hopping on a scale and comparing your weight to the so-called “norm” is a crude measurement of how much fat you carry. You can refine this number by calculating your body mass index (BMI). This is just your weight adjusted for height. (For a BMI calculator, click here.)

BMI has become the most frequently used method of determining whether a person is overweight. A BMI between 25 and 30 indicates that someone is overweight. A BMI higher than 30 means that someone is obese. But BMI alone is not a good predictor of visceral fat.

You can spend a little more money for a scale that also tells what percent of your weight is fat. You just step on the pads and a safe electrical signal goes into one foot, up the leg to the body, and down the other leg. Fat slows down the current’s travel time, and using that information the scale can tell how much of your body is made up of fat versus other tissues. In a few seconds, you get a percent body fat reading. Knowing what percent of your weight is body fat helps some, but it still doesn’t tell you how much of that fat is visceral fat.

More accurate assessments of visceral fat require imaging the body with a CT scan or MRI. But these tests are not practical for everyday use. Both are rather expensive, especially MRIs. And CT scanning does use x-ray, which exposes your body to radiation, so you wouldn’t want to get repeated CT scans to see what’s happening to your visceral fat over time.

The cheapest proxy we have for visceral fat is the tape measure. And it actually does a reasonable job at predicting whether we have too much visceral fat.

To give you a sense of whether you have too much visceral fat, first measure your waist size by putting the tape around your waist at the height of your belly button. Then measure your hip size by wrapping the tape measure around the thickest part of your hips, before they start to taper toward your legs. Now you can calculate your waist-to-hip ratio: just divide your waist size by your hip size.

Men should have a waist size less than 37 inches, for women it should be less than 32 inches. Ideally, you want your waist-to-hip ratio to be 0.8 or less. Either reading in the abnormal range means you probably have too much visceral fat.

If both are out of range, your first thought might be liposuction. While the idea may seem rationale, when put to the test it doesn’t work. It can remove the fat under the skin but doesn’t get rid of the visceral fat.

And don’t start a crash diet. This works against you. You might lose a good bit of weight initially but your body goes into a starvation mode. The moment you start eating a little more, the fat rapidly starts to come back.

Exercise is the most effective way to get rid of visceral fat. While you still need to watch the calories and avoid bad fats, physical activity should be your top priority.

How much exercise do you need to decrease visceral fat? Researchers at Duke University Medical Center have provided some guidance. They compared non-exercising adults with adults who exercised at different intensities. After six months, the non-exercisers experienced a nearly 9% gain in visceral fat. People who walked or jogged about 12 miles per week put on no visceral fat. Those who jogged about 20 miles per week lost both visceral and subcutaneous fat.

Translating this into time, you need at least 30 minutes of moderate-intensity exercise every day. If you can exercise for 60 minutes a day, you're sure to be attacking your visceral fat.

Here’s my personal advice: Don’t be obsessed with the scale. Start with some exercise and slowly ramp it up, cut a few calories, and pull out the tape measure once a month to check on your progress.

Howard LeWine, M.D., is a hospitalist at Brigham and Women’s Hospital in Boston, where he practices and teaches Internal Medicine. He is the Chief Medical Editor of Internet Publishing at Harvard Health Publications.

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