YOUR HEALTH IS MORE THAN YOUR BMI

Body weight corrected for height, or BMI (body mass index), is a common measurement used by doctors and the public alike to gauge overall health and to predict heart disease and mortality. But BMI isn’t good at predicting the health of many people, especially women. If you want a clearer picture of your disease risk, it’s time to look at body composition.

Why BMI is problematic

Studies have failed to show that increased weight or BMI is associated with increased mortality in older adults. In fact, there is a paradoxical increased longevity in people with higher BMI. What is going on? Aren’t we sure that being “heavy” isn’t good for us? 

Our weight on the scale measures the water, fat, and muscle in our bodies. Changes in the scale weight–and subsequent changes in measurements like BMI–do not account for body composition. And whether we’re carrying our weight as muscle or fat matters a lot for our health. But the BMI measurement was developed in 1832 to compare populations–not individuals–primarily made up of white, European men. So using BMI as a one-size fits all for non-male and non-white bodies simply doesn’t tell us what’s healthy for each person. 

Fat measurement is problematic too. Fat can be found on the trunk, such as subcutaneous fat we see around our waists and hips. Or it can surround our organs, as visceral fat. The distribution of fat on the body varies a lot, particularly in women. The impact of fat accumulation on health and heart disease depends on where it accumulates.

There’s a paradox of lower all-cause mortality in older adults with higher BMI. Why? Because higher muscle mass–which leads to a higher BMI–is good for our health. Higher BMI also occurs in many women with subcutaneous fat, which is associated with better cardiovascular health.

Measuring body composition

Two conclusions we can draw from this: High muscle mass is good, and high visceral fat is something to work on. High visceral adipose tissue, or VAT, is associated with metabolic syndrome, inflammatory markers, and mortality. So knowing not just your BMI but the composition of your muscle mass and fat are crucial in understanding your health risks.

These parameters are tricky to measure. For estimating visceral fat, waist circumference is a good place to start. By adding impedance measurements from each arm and leg, as with the SECA scale we use at CFC, you can get an estimate of muscle mass, fat mass, and visceral fat mass. A DXA scan, often performed for bone density measurement, can provide these measurements as well; this technique has been used for research studies. MRI studies can measure visceral fat accurately, but is not often used for this purpose. 

Body composition in men and women, and pre- or post-menopause

Measurements of body weight and BMI are misleading because they do not differentiate muscle from fat, nor do they differentiate the type or location of fat accumulation.

The types and distribution of fat in our bodies make things complicated when using weight to predict heart disease in women. High muscle mass and low fat mass is the best-case scenario for heart health in both men and women. But premenopausal women with high muscle mass and high fat mass are a close second. Estrogen distributes fat in the legs and hips, which is actually protective for the development of heart disease. After the menopause transition, stored fat is increasingly the VAT, visceral, kind, as it is in men. Excess visceral fat inside the abdomen and on the heart promotes cardiovascular disease in both men and women.

The Breakdown

• High muscle mass + Low fat mass = Best case scenario for men and women. 
• High muscle mass + High fat mass = Second best case for women.
• Low muscle mass + Low fat mass = Better for men than women.
• Low muscle mass + High fat mass = Worst case scenario for men and women.