|Waist-to-Hip Ratio, Waist Circumference and BMI: What to Use for Health Risk Indication and Why?
Len Kravitz, Ph.D.
The ever-increasing worldwide obesity epidemic poses increased risk for coronary heart disease, hypertension, abnormal cholesterol, diabetes mellitus, sleep apnea and certain cancers (Hainer, Toplak, and Mitrakou, 2008). However, the increased risks associated with obesity are of greater concern depending on the pattern of fat distribution in the body (e.g., in the torso and abdomen versus the hips, thighs and buttocks) (Srikanthan, Seeman, and Karlamangla, 2009). Torso and abdominal fat, referred to as visceral, central or intra-abdominal fat, is related to health abnormalities including insulin resistance and abnormal blood lipid levels, escalating the risk of diabetes mellitus and cardiovascular disease, respectively (Ness-Abramof and Apovian, 2008). Presently, body mass index (BMI), waist circumference, and waist-to-hip ratio are employed for classifying obesity and the risks of abdominal fat accumulation. For exercise professionals, the important question is, in addition to the body composition technique (skinfolds, bioelectrical impedence, hydrostatic weighing) they use to track body fat and muscle change, which anthropometric assessment is most suitable to use with their clients for detecting cardiovascular and metabolic risk?
Special Focus: Insulin Resistance
A) With effectual glucose metabolism, insulin reacts with receptors on muscle, fat and the liver, like a 'key fitting into a lock', opening the passageway for glucose to enter and be used by the cell.
B) Insulin resistance is a condition in which the body produces insulin but the muscle, fat, and liver cells do not react with it, and the glucose cannot enter the cell. The pancreas unsuccessfully tries to resolve the problem by producing more insulin. Excess glucose builds up in the bloodstream, which is an antecedent for diabetes. Thus, most people with insulin resistance have high levels of insulin and glucose circulating in their blood.
Source: U.S. Department of Health and Human Services (2008).
Why is Abdominal Fat Risk Such a Health Risk?
In the human body, fat can be divided into two main compartments: visceral (torso) and subcutaneous (under the skin). As well, fat is stored in smaller amounts in the heart, pancreas, liver and within muscle, referred to as intramuscular fat (which is used for fuel during exercise). Visceral body fat helps to maintain free fatty acid (free fatty acids are the triglyceride molecules separated from their glycerol 'backbone') levels in the blood, and facilitates in the regulation of blood insulin (Ness-Abramof and Apovian, 2008). Visceral fat may be infiltrated by specific immune cells (known as macrophages), which will trigger insulin resistance, a precursor for pre-diabetes and diabetes (Attie and Scherer, 2009). It is meaningful to note that walking 30 minutes a day for 5 days a week and/or losing 5 to 7 percent of body weight (if overweight or obese) prevents or delays diabetes by nearly 60 percent (U.S. Department of Health and Human Services, 2008).
Fat cells, once considered to be solely energy depots, are now known to be busy endocrine (hormone secreting) organs. They secrete a number of specialized proteins known as cytokines, which regulate responses to infection, immune reactions, inflammation and trauma. In regards to inflammation regulation (i.e., the response of the body to injury or irritation), fat cells secrete pro-inflammatory (causing inflamation) and anti-inflammatory (inhibiting inflammation) cytokines (Dinarello, 2000). Some of the cytokines promoting inflammation are tumor necrosis, interlukin-6, and C-reactive protein. These pro-inflammatory cytokines can damage arterial walls when chronically elevated in the circulatory system, such as from high blood pressure, and become the starting point for atherosclerotic plaque build-up. Elevated C-reactive protein is positively correlated to cardiovascular disease and relatively easy to test for in a blood assay. Personal trainers should encourage clients to have their C-reactive protein assessed at that same time they have their cholesterol checked.
Fat cells also produce and secrete adiponectin, a specialized protein that improves insulin sensitivity (the cells ability to use glucose) and protects against atherosclerosis. Unfortunately, with visceral fat obesity accumulation, adiponectin levels are reduced, thus leading to a higher cardiometabolic (e.g., heart disease and diabetes) health risk (Ness-Abramof and Apovian, 2008).
Importantly, elevated levels of blood cortisol intensify central fat deposition. Cortisol is a stress hormone, and thus chronic stress can directly increase visceral fat accumulation. This is a good reason why mind/body classes, which help to neutralize stress, can directly counteract central fat accumulation.
Anthropometric Measurement: BMI, Waist Circumference and Waist-to-Hip Ratio
The BMI is calculated as weight in kg divided by the square of height (in meters). Another simple BMI calculation is body weight in pounds multiplied by 703 and then divided by height in inches. Keenly, there are many BMI calculators on the web. The World Health Organization has established guidelines for normal (18.5 - 24.9 kg/m2), overweight (25-29.9 kg/m2) and obese (>30 kg/m2) adults. One of the drawbacks of BMI use in fitness populations is that a muscular person will score higher, producing an inaccurate assessment of overweight or obese. Ness-Abramof and Apovian (2008) also indicate that older populations tend to have a loss in muscle mass, possibly leading to an underestimate of the BMI. Srikanthan, Seeman, and Karlamangla (2009) add that aging results in decreases of standing posture that can inaccurately increase BMI by 1.5 kg/m2 in men and 2.5 kg/m2 in women, despite minimal change in body weight. To finish, BMI is a weak predictor of weight-related health problems among some racial and ethnic groups, such as African-American and Hispanic-American women (National Institute of Diabetes and Digestive and Kidney Diseases, 2008).
The precise measurement of visceral fat requires the use of magnetic resonance imaging or tomography, which are scientific techniques that visually depict the internal tissue compositions. Waist circumference is a substitute technique for these scientific assessments. A waist circumference >35 inches (88 cm) in women and >40 inches (102 cm) in men is associated with higher cardiometabolic risk (Ness-Abramof and Apovian, 2008). Welborn and Dhaliwal (2007) indicate that waist circumference is superior to BMI in predicting cardiovascular disease risk. One practical question is how should waist circumference be measured? Landmarks include 1) the umbilicus, 2) the midpoint between the lowest rib and the iliac crest, and 3) just above the iliac crest. Advantageously, Ross et al. (2008) showed that all these waist circumference landmarks are equally effective in identifying all-cause mortality, cardiovascular disease and diabetes risk. So, exercise professionals are encouraged to use the anatomical landmark that works best with their clients.
Make sure the measurement is taken at the END of expiration, when the diaphragm is in its neutral position; during an inspiration the diaphragm descends into the abdominal cavity, enlarging the waist circumference measurement. Exercise professionals are advised to use a spring loaded tape measure (just do a find on any web search engine to attain), as these simple and inexpensive tape measures provide a constant tension for consistency with all anthropometric measurements.
With the waist-to-hip ratio, the waist is measured at the narrowest part of the waist, between the lowest rib and iliac crest, and the hip circumference is taken at the widest area of the hips at the greatest protuberance of the buttocks. Then simply divide the waist measurement by the hip measurement. The WHO defines the ratios of >9.0 in men and >8.5 in women as one of the decisive benchmarks for metabolic syndrome. Welborn and Dahlia (2007) and Srikanthan, Seeman, and Karlamangla (2009) confirm, and cite several other investigations that show waist-to-hip ratio being the superior clinical measurement for predicting all cause and cardiovascular disease mortality. Welborn and Dhaliwal add that the hip circumference indicates a lower risk for body fat accumulation, and thus including it into the waist-to-hip equation enhances the accuracy of this measurement technique.
Wait! Is there is Useful Anthropometric Technique to Identify Risk in Overweight Children?
Although there are age-specific table cutoffs for youth with waist circumference, Maffeis, Banzato, and Talamini (2008) recommend the use of waist-to-height ratio with &Mac178;5.0 being normal and >5.0 being an increased metabolic and cardiovascular risk. Waist-to-height ratio is calculated by dividing a person's waist measurement (inches) by their height (inches). Waist is measured at the narrowest point of one's midsection between the bottom rib and the top of the hipbone.
It is inspiring to highlight that there is a plethora of research on these anthropometric measurements. BMI is a reliable way to tell if body weight is putting a person at generalized health risk. Waist circumference and waist-to-hip ratio are measures of central adiposity that appear to predict cardiovascular and diabetes risk better than BMI (Srikanthan, Seeman, and Karlamangla 2009). Much research denotes that the waist-to-hip ratio is the superior health risk-categorizing indicator. Many exercise professionals are highly skilled at body composition measure techniques, such as skinfolds. In completing and explaining the anthropometric and body composition measures for clients, personal trainers can provide supplementary educational information about reducing cardiometabolic health risks and improving quality of life.
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National Institute of Diabetes and Digestive and Kidney Diseases, (2008). Weight and waist measurement: Tools for adults: http://win.niddk.nih.gov/publications/tools.htm#circumf
Retrieved June 26, 2010
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Srikanthan, P., Seeman, T.E., and Karlamangla, A.S. (2009). Waist-hip-ratio as a predictor of all-cause mortality in high-functioning older adults. Annals of Epidemiology, 19, 724-731.
Ross, R., Berentzen, T., Bradshaw, A.J., Janssen, I., et al. (2008). Does the relationship between waist circumference, morbidity and mortality depend on measurement protocol for waist circumference? Obesity Reviews, 9(4), 312-326.
U.S. Department oF Health and Human Services. National Institutes of Health (2008). Insulin Resistance and Diabetes. NIH Publication No. 09-4893
Welborn, T.A. and Dhaliwal, S.S. (2007). Preferred clinical measures of central obesity for predicting mortality. European Journal of Clinical Nutrition, 61, 1373-1379.
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Retrieved June 26, 2010
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@Bio:Len Kravitz, PhD, is the program coordinator of exercise science and a researcher at the University of New Mexico, Albuquerque, where he won the Outstanding Teacher of the Year award. Len was recently honored with the 2009 Canadian Fitness Professional Specialty Presenter of the Year award and chosen as the American Council on Exercise 2006 Fitness Educator of the Year. He has also received the prestigious Can-Fit-Pro Lifetime Achievement Award and the Aquatic Exercise Association Global Award.