I recently watched a documentary on people who live in jungles worldwide called The Human Planet: Jungles. A theme I noticed from theBayaka of the Congo,Awa Guaja of the eastern Amazon and theKorowai of Papua New Guinea was that the men were extremely lean and muscular but many of the women were not. Indeed some of the women were almost chubby, especially around the waist.
I don’t know enough about these people to know whether this belly fat is the result of a more modern diet, low activity levels and frequent childbirth or some other factors. But I do wonder, is this belly fat healthy and normal? Is the American obsession with the flat stomach simply a cultural vanity, or does belly fat have implications for health?
Waist to height ratio is measured by taking the circumference of the waist just above the iliac crests after exhaling (without sucking in) and dividing this by height. If you have a 36 inch waist and are 72 inches tall your waist-to-height ratio is 0.5.
A systematic review and meta-analysis on waist-to-height ratio as a predictor ofcardiometabolic risk factors was published in Obesity Reviews in May of 2012.1Margaret Ashwell and her team reviewed thirty one studies with a combined sample size of over 300,000 including people from five continents, and ethnic groups such as Australian Aborigines. An African American population was included but no native African populations were included. Twenty-six of the studies were cross-sectional and five were prospective.
The ability of BMI, waist-to height and waist circumference to predict present or future disease was assessed by comparing the area under a receiver operating characteristic curve (ROC-curve). An area under the curve of 70% means a test can predict present or future disease 70% of the time
In the meta-analysis waist-to-height ratio performed better than BMI and waist circumference at predicting diabetes, dyslipidemia (women only), metabolic syndrome (women only), cardiovascular disease, and all outcomes combined. How much better? In most cases waist-to-height was 4-5% percent better but in some cases it was no better than BMI. For example, BMI can identify people have diabetes or who will develop diabetes 70% of the time while waist-to-height ratio can identify them 75% of the time.
The studies included in this review, assessed risk on a continuous basis1, but a previous systematic review established a waist-to height ratio of 0.5 as a useful cutoff value for cardiometabolic risk in diverse populations.2 When your waist circumference is more than half your height you are at risk for cardiovascular disease and diabetes.
So it seems that having a large waist, i.e. excess belly fatis indeed a sign of poor health. This may be because a large waistline can be partly due to fat in and around internal organs.
The circumference of your waist can also be increased artificially by the presence of food and air in your GI tract, as well as by long relaxed abdominal muscles and a posture of lumbar lordosis. I am impressed by the ability of waist-to-height ratio to predict cardiometabolic risk as well as it does despite these confounding variables.
So are the women in the tribes I mentioned above at risk for heart disease and diabetes? While I can’t calculate waist-to-height ratio from video, it seems that some of them are.
At this point I think it is very important to pay attention to the cutoff values in waist to height ratio. Less than half your height might not be as skinny as you think. Measure yourself today and find out.
Last of all and perhaps most importantly, remember that fitness is much better indicator of long term health than fatness.3 The fat and fit have better long term health than people who are skinny but out of shape.3
1. Ashwell M, Gunn P, Gibson S. Waist-to-height ratio is a better screening tool than waist circumference and BMI for adult cardiometabolic risk factors: Systematic review and meta-analysis. Obesity Reviews. 2012.
2. Browning LM, Hsieh SD, Ashwell M. A systematic review of waist-to-height ratio as a screening tool for the prediction of cardiovascular disease and diabetes: 0· 5 could be a suitable global boundary value. Nutrition research reviews. 2010;23(2):247.
3. Hellénius ML, Sundberg CJ. Physical activity as medicine: Time to translate evidence into clinical practice. Br J Sports Med. 2011;45(3):158-158.