Using body mass index (BMI) as a metric of healthy weight has become a matter of dispute. But there’s little argument that belly fat is the worst kind of fat. A new study questions the validity of BMI by finding that risk of death increases significantly with a waist-to-hip ratio padded with belly fat, even with a so-called normal BMI.
Waist to hip ratio
Body mass index is calculated using a person’s height and weight. A BMI between 18.5 and 24.9 is considered normal. However, BMI doesn’t take into account muscle mass or fat distribution. Using BMI alone overlooks unhealthy fat distribution and labels most athletes and many fit, healthy people as overweight.
A more representative metric of a person’s health may be waist-to-hip ratio. Waist-to-hip ratio is calculated by dividing the circumference of the waist just above the navel with the circumference of the hips at their widest point. Women with waist-to-hip ratios above 0.8 are at increased health risk because of excess fat in the abdominal region. For men, the tipping point for belly fat is 1.0.
Dangerous fat distribution
New research from the Mayo Clinic has found that people with a normal BMI and a high waist-to-hip ratio had the greatest risk of cardiovascular-related death and the highest death risk from any cause.
The study analyzed a representative sample of the U.S. population including more than 12,000 adults over age 18. Surveys collected information about BMI, waist-to-hip ratio, socioeconomic status, illnesses and medical tests. Baseline data was compared to the National Death Index 14 years later.
After removing people with chronic obstructive pulmonary disease (COPD) and cancer from the analysis, researchers found that for people with normal BMI and high waist-to-hip ratio, risk of cardiovascular death was 2.75 times higher and risk of death from all causes was 2.08 times higher compared to people with normal BMI and a normal waist-to-hip ratio.
Deadly visceral fat
The increased death risk was due to visceral fat, indicated by the high waist-to-hip ratio. Visceral fat lurks below the belly fat often characterized by love handles. It accumulates under the abdominal muscles and around the organs. Visceral fat has been linked to a litany of health consequences, including heart disease, type 2 diabetes, dementia, high blood pressure, and some cancers.
Apple shape vs. pear shape
Discussions about waist-to-hip ratio often refer to apples and pears. Women with a waist-to-hip ratio above 0.8 and men above 1.0 are classified as “apple shaped.” Those below those thresholds are “pear shaped.”
If you happen to be apple shaped, you’re carrying around visceral fat and should change your diet and pay closer attention to your cholesterol, blood pressure and blood-sugar levels—even if your BMI is in the normal range.
Lose visceral fat
A study by Wake Forest researchers found that the best way to lose visceral fat was to eat more soluble fiber from vegetables, fruit and beans, and engage in moderate physical activity.
The study found that for every 10-gram increase in soluble fiber per day, visceral fat was reduced by 3.7 percent over five years. Adding moderate activity boosted the decrease to 7.4 percent over the same time period.
According to the researchers, an example of 10 grams of soluble fiber includes two small apples, one cup of green peas and one-half cup of pinto beans. Their definition of moderate physical activity was exercising vigorously for 30 minutes, two to four times a week.