Where does your body fat reside?
Belly fat predicts higher mortality risk
Subcutaneous fat occurs just beneath the skin. Visceral fat occurs within the abdominal cavity. Researchers used data from 3,001 participants in the Framingham Heart Study Offspring and Third-Generation cohorts to determine links between these types of fat and metabolic risk factors, such as type 2 diabetes. CAT scans measured the amounts of visceral and subcutaneous fat in each participant.
Visceral fat explained more of the variation of risk factors than did subcutaneous fat after controlling for body-mass index (BMI) and waist circumference. For example, only about 1 percent of normal weight women in the lowest quartile of visceral fat had the metabolic syndrome, compared to about 70 percent of obese women in the highest quartile of visceral fat. The amounts of both types of fat tended to run in families. Heritability values for visceral and subcutaneous fat were 36 and 57 percent, respectively. Visceral fat appears to be more pathogenic than subcutaneous fat.
Public health guidelines for obesity prevention are based on BMI values. BMI does not, however, account for body shape or body fat distribution. Interestingly, persons with normal BMI can have central obesity, namely excess belly fat. A new study investigated links between six combinations of BMI and belly fat (measured as waist circumference) and risk of mortality. Participants included 156,624 post-menopausal women.
Compared to normal weight women with normal waist circumference, normal weight women with high waist circumference (more than 34.6 inches) had a 31 percent higher risk of all-cause mortality over an average follow-up of 17.9 years. This risk level accounted for a host of confounding factors. High waist circumference consistently predicted higher risk of all-cause, cardiovascular-related, and cancer mortality, regardless of BMI. A normal waist circumference cut the risk of death for overweight or obese women. Thus, the current public health emphasis on losing weight to reduce obesity and improve health may be misdirected. Reducing belly fat may be more healthful.
In 2010, the American Heart Association published the Life’s Simple 7 metrics to assess and promote cardiovascular health. The seven factors included 1) smoking, 2) physical activity, 3) BMI, 4) diet, 5) total serum cholesterol, 6) blood pressure, and 7) fasting blood glucose. Subsequent research suggested revisions to three of the metrics to better predict cardiovascular and cancer mortality. Waist-to-hip ratio replaced BMI. The Healthy Eating Index-2000 provided the diet score. The ideal blood pressure dropped from 130/80 mm Hg to 120/80 mm Hg. For both versions of Life’s Simple Seven, scores ranged from zero (worst) to 7 (best). Researchers used data from the National Health and Nutrition Examination Surveys to evaluate the revised Life’s Simple Seven.
Compared to participants with revised scores of 0 or 1, participants with revised scores of 5 or more had 54 percent lower risk of all-cause mortality, 58 percent lower risk of cancer mortality, and 63 percent lower risk of cardiovascular mortality. Interestingly, overweight participants (BMI less than 30) but without central obesity (waist-to-hip ratio less than 0.9 for men and 0.8 for women) had lower risk of all-cause and cardiovascular disease mortality. Fat location is a better predictor of cardiovascular disease than fat amount. The revised Life’s Simple Seven provided more information than the original Life’s Simple Seven, especially for cancer mortality. Alas, only about 1 percent of participants achieved ideal values of the revised Life’s Seven Simple metrics.