Belly fat and the expanding American waistline

In a previous post I described the distinction between visceral (or belly) fat and subcutaneous fat. Visceral fat is located in your abdominal cavity between your inner organs such as the stomach, liver, kidneys, and intestines. Subcutaneous fat (about 80% of all fat) is located directly beneath the skin and can be measured by pinching the skin or more quantitatively using skin-fold calipers. The fat in the thighs and buttocks is subcutaneous fat.

You can estimate belly fat by calculating your waist-to-hip ratio (WHR), which is the ratio of the circumference of the waist to that of the hips. The idea is that the hip size depends on subcutaneous fat whereas the waist size depends on both subcutaneous and visceral fat. Abdominal obesity is defined as a waist–hip ratio above 0.95 for males and above 0.80 for females, although the exact classification values can vary.

Alternatively you can estimate belly fat from your waist size alone (see below), which is simpler i.e. requires only a single measurement but perhaps not as informative.

Belly fat (abdominal obesity) is one of the five risk factors that defines metabolic syndrome, which is a condition of elevated risk for heart disease and diabetes. Note that belly fat adds risk even beyond your BMI (i.e. measure of overall obesity). One study has shown that the risk of dying was 2.1 times higher for those with normal BMI but high WHR than for people with normal BMI and normal WHR, and was also higher than the risk for people categorized as obese by BMI but with normal WHR.

Interestingly according to a new study, BMI has been relatively constant over the last 13 years among Americans, but waistlines are increasing (NYTimes):

"Average waist circumference — but not body mass index— increased significantly in the United States between 1999 and 2012, a new study reports.

After adjusting for age, the overall mean waist circumference increased to 38.7 inches in 2012 from 37.5 in 1999.

In 2012, 54.2 percent of Americans had abdominal obesity (defined as an age-adjusted waist circumference of more than 40 inches for men and more than 34.6 for women) compared with 46.4 percent in 1999. The study was published in JAMA."

This is not a good trend. Even though total obesity (measured by BMI) has been relatively constant, the increase in abdominal obesity indicates that Americans are less healthy than before.

How can you decrease belly fat and abdominal obesity? Glad you asked. As you might suspect exercise and diet are important (HarvardHealth):

"The starting point for bringing weight under control, in general, and combating abdominal fat, in particular, is regular moderate-intensity physical activity — at least 30 minutes per day (and perhaps up to 60 minutes per day) to control weight. [...]

Diet is also important. Pay attention to portion size, and emphasize complex carbohydrates (fruits, vegetables, and whole grains) and lean protein over simple carbohydrates such as white bread, refined-grain pasta, and sugary drinks. Replacing saturated fats and trans fats with polyunsaturated fats can also help."

Note that sit-ups are not specifically recommended. You want to burn calories, and sit-ups are not necessarily the most efficient way of obtaining 30-60 minutes of moderately vigorous exercise per day. I will expand upon this point in a future post.

Thus, reducing your waistline (if you have belly fat) is not just important for fitting in your jeans (Figure 1); it is important for your health.

Figure 1. Abdominal obesity (aka belly fat). Make sure to check your waistline along with your weight.