Excess body fat has serious consequences for health. It' associated with high levels of LDL ("bad") cholesterol and triglycerides and low levels of HDL ("good") cholesterol. It impairs the body's responsiveness to insulin, raising blood sugar and insulin levels. Excess body fat contributes to major causes of death and disability, including heart attacks, strokes, high blood pressure, cancer, diabetes, osteoarthritis, fatty liver, and depression.
Faced with these risks, it's no wonder that you want to know how much you should weigh. But this common and important question is actually the wrong question. For health, the issue is not how much you weigh, but how much abdominal fat you have.
Methods have changed over the years. But when scientists recognized that what matters is not body weight but body fat, standards began to change. The body mass index (BMI), remains enshrined as the standard way to diagnose overweight and obesity.
Beyond the BMI
The BMI provides a good estimate of body fat, and it's more accurate than skinfold measurements. Although the BMI is the official standard, it has several flaws. For one thing, highly trained athletes with big muscles can have BMIs of 30, with little body fat. At the other extreme, the BMI may fail to accurately reflect body fatness in adults who have lost substantial amounts of muscle mass. But the most important problem is that the BMI reflects total body fat without regard to how the fat is distributed. And although no excess fat is good, one type of excess fat is much more dangerous than the others. Research shows that abdominal fat is the worst of the worst.
The inside story
What makes abdominal fat so harmful? Scientists don't know for sure, but research is providing strong clues. To understand these clues, you must first understand that abdominal fat comes in two different forms. Some of it is located in the fatty tissue just beneath the skin. This subcutaneous fat behaves like the fat elsewhere in the body; it's no friend to health, but it's no special threat either.
Fat inside the abdomen is another story. This visceral fat is located around the internal organs, and it's the true villain of the piece. One of the earliest explanations for this was that visceral obesity was linked to overactivity of the body's stress response mechanisms, which raise blood pressure, blood sugar levels, and cardiac risk.
A newer explanation relies on the concept of lipotoxicity. Unlike subcutaneous fat, visceral fat cells release their metabolic products directly into the portal circulation, which carries blood straight to the liver. As a result, visceral fat cells that are enlarged and stuffed with excess triglycerides pour free fatty acids into the liver. Free fatty acids also accumulate in the pancreas, heart, and other organs. In all these locations, the free fatty acids accumulate in cells that are not engineered to store fat. The result is organ dysfunction, which produces impaired regulation of insulin, blood sugar, and cholesterol, as well as abnormal heart function.
These explanations are not mutually exclusive; all may help account for the hazards of visceral fat. All in all, clinical observations and basic research results agree that excessive fat inside the abdomen is a major contributor to cardiovascular disease.
Evaluating abdominal obesity
The most accurate method is to use computed tomography (CT) or magnetic resonance imaging (MRI) to measure the amount of visceral fat. But they're expensive and require sophisticated equipment.
A far simpler method is to determine the waist-to-hip ratio. With your abdomen relaxed, measure your waist at the navel. Next, measure your hips at their widest point, usually at the bony prominences. Finally, divide your waist size by your hip size:
Waist (in inches) / Hips (in inches) = ratio
How does your ratio translate into health risk? The chance of suffering a heart attack or stroke increases steadily as a man's ratio rises above 0.95; for women, risk begins to rise above 0.85.
The waist-to-hip ratio is a very useful tool. But many experts are now turning to an even simpler technique: waist circumference. Because it involves one measurement instead of two, it's more accurate and reproducible than the waist-to-hip ratio.
To measure your waist circumference properly, take your shoes off and stand with your feet together. Be sure your belly is bare. Relax and exhale. Using a cloth measuring tape that can't be stretched, not the stiff metal tape from your toolbox, measure your waist at the navel. Be sure to keep the tape parallel to the ground. Record the measurement to the nearest one-tenth of an inch.
Table 2: Interpreting your waist circumference
|Low risk||37 inches and below||31.5 inches and below|
|Intermediate risk||37.1–39.9 inches||31.6–34.9 inches|
|High risk||40 inches and above||35 inches and above|
Measuring your waist to learn if you have abdominal obesity and excess visceral fat is easy — but doing something about it is much harder.
Remember the basics. The only way to reduce visceral fat is to lose weight — and the only way to do that is to burn up more calories with exercise than you take in from food. Sustained weight loss requires both caloric restriction and increased exercise.
BMI vs. waist circumference
The BMI is more complex, but waist measurement is more prone to errors than measuring height and weight. So for the time being, you should use both standards. Your BMI will give you the best estimate of your total body fatness, while your waist measurement will give you the best estimate of your visceral fat and risk of obesity-related disease.