Paul Ribisl, Ph.D., published an article in ACSM's Health & Fitness Journal® in the July/August 2004 issue where he made a case that waist circumference is a good index for assessing abdominal obesity or visceral fat. In his article, he encourages the use of both waist circumference and sagittal abdominal diameters (SADs) as an adjunct to other standard measures in health examinations. He also discussed the association between visceral fat and increased risk to obesity-related comorbidities. The current article expands on Dr. Ribisl's suggestions by providing a practical field test to measure abdominal visceral fat.
Obesity has been recognized as a national epidemic. According to The U.S. Department of Health and Human Services (2000), 64% of Americans are either overweight or obese (1). The problems of obesity have been well established and involve an increased risk for several comorbidities, including high blood lipids, insulin resistance, hypertension, type 2 diabetes, and cardiovascular disease (2, 3). In addition to medical care costs, Americans spend millions of dollars on weight loss interventions while seeking fitness professionals for support and guidance. Fitness instructors and personal trainers provide support and guidance using body composition to assess health risk and to demonstrate body composition changes resulting from weight loss or conditioning.
Recently, studies have shown that the site of fat distribution is more important than total body fat because abdominal obesity is associated with an increased risk for several comorbidities. The National Institutes of Health's publication, Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults (4), encourages more research on the relationship between various body fat compartments and risk of disease. The guidelines also recommend that weight loss intervention programs include measurements of abdominal fat to better assess health improvements. Dr. Ribisl (5) published an article in the July/August 2004 issue of ACSM's Health & Fitness Journal® describing the importance of assessing abdominal visceral fat and supported the use of SADs. Our goal is to provide an easy way to implement measurements of visceral fat using SADs.
Assessment Using Sagittal Abdominal Diameter
Regional obesity describes the storage of fat tissue in specific locations in the body. Abdominal fat stores (upper body obesity) carry a higher risk than gluteal-femoral fat stores (lower body obesity). Abdominal obesity is composed of visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT). VAT has been linked to the increased health risk; therefore, assessment of visceral fat change with weight change is important for fitness instructors and personal trainers when motivating and counseling their clients for weight loss.
Abdominal fat compartments are best measured by radiological imaging techniques of computed tomography (CT), magnetic resonance imaging, and dual-energy X-ray absorptiometry; however, imaging is expensive and not always available. Measures of SAD are predictive of VAT in both men and women and have been validated with imaging techniques such as CT scans (6-9). Previous studies have found SAD measurements to be reliable (9, 10). Williamson et al. (10) demonstrated good reproducibility when SAD was measured indirectly with a sliding-beam caliper.
Measurement of SAD is a noninvasive, practical, and easy-to-perform procedure used to predict visceral and SAT. SADs are able to distinguish between abdominal fat layers because, in the supine position, VAT elevates the abdomen in the sagittal plane, whereas SAT compresses the abdomen (7). The abdominal sagittal diameter is a measure of the horizontal distance between the abdomen and the lower back. Figure 1 shows abdominal fat location and distinguishes between abdominal visceral and subcutaneous fat from a CT scan. VAT is the mesenteric, omental, and retroperitoneal fat within the abdominal cavity formed by the back and abdominal wall musculature. Abdominal SAT is the fat between the skin and the back and abdominal musculature (11).
How to Measure Visceral Fat
Sagittal abdominal diameters are taken with the subject in the supine position on a hard stable surface. A carpenter's level is placed across the abdomen at the level of the umbilicus. Measures are taken from the bottom of the carpenter's level to the top of the table once the subject performs a normal expiration (7). The average of three measurements is used to calculate visceral fat volume, expressed in liters. Figure 2 shows the position of the level when measuring SAD.
An equation by Kvist et al. (6) predicted VAT from the average of the three SAD measurements. The calculation of total adipose tissue (TAT) of the body is based on the subject's height-to-weight ratio in another predictive equation by Kvist et al. (6). SAT of the body is then derived by subtracting the calculated VAT from the calculated TAT of the body (6).
Three Equations to Predict Abdominal Fat Distribution
1. VAT is predicted from an equation based on the measured distance (in centimeters) from the carpenter's level to the table (6).
2. A calculation of TAT of the body is obtained by using the subject's height-to-weight ratio in another predictive equation (6).
3. SAT of the body is then derived by subtracting the calculated VAT from the calculated TAT (6).
Practical Application of Visceral Fat Assessment
We measured VAT using the SAD technique in a hospital-based community weight loss program to (1) enhance an understanding of regional fat distribution and to (2) improve motivation by monitoring visceral fat changes associated with weight loss. This weight loss program provided a service to the community and a source of subjects for study. We wanted to know if there was a significant difference in reduction of visceral and subcutaneous fat associated with total body weight loss. We used indirect anthropometric measures of SAD to derive VAT and SAT.
The Plan to Lose
The eight-week weight loss program included pretest and posttest SAD measurements. The intervention included a low-calorie diet (1,200 Kcal/day) and an exercise protocol. The exercise program was intended to expedite weight loss by promoting a greater caloric deficit while maintaining lean body mass. All participants followed a daily exercise regimen of light-to-moderate activity (4 to 6 METs) where walking was recommended; however, participants were given the option to choose from a variety of self-directed, moderate-intensity activities. Exercise sessions progressed from 20 minutes per day to 60 minutes per day. Participants were encouraged to exercise seven days a week to establish a routine of physical activity.
Participants were provided with ACCUSPLIT Eagle pedometers to assist in self-monitoring their daily exercise. Pedometers counted the number of steps taken, which were used to determine miles covered and calories burned based on individual stride length and body weight. Step data were used as a motivational device and not reported.
Did It Work?
The results show significant changes in visceral fat. Figure 3 shows absolute and relative weight loss as well as changes in regional fat distribution. Absolute weight loss is the total amount lost in pounds. Relative weight loss is the relationship between pretest and posttest measurements expressed as a percentage. Participants lost an average of 11.0 lbs of weight, representing 5.4% of initial body weight. TAT of the body decreased 9.9 lbs, accounting for 90% of the total weight loss (p < 0.05). There also were significant (p < 0.05) changes in both VAT (1.6 lbs) and SAT (8.3 lbs) of the body as a result of the eight-week study. Participants lost more VAT than SAT in relative terms as expressed as the percentage lost from pretest to posttest.
What Is the Importance?
The principal finding was a significant difference between the amount of VAT loss and SAT loss after the eight-week weight loss intervention. VAT decreased 16.8% from pretest to posttest measures, whereas SAT decreased 8.5%. The absolute loss of VAT was less than SAT; however, a greater percentage of VAT was lost. These results support previous findings that weight loss leads to a significant reduction in abdominal fat stores and, more importantly, that VAT decreases relatively more than SAT in people losing weight (11, 12). These changes in VAT are estimated and not directly measured; therefore, their interpretation should be used with caution. However, the practical application of using SAD measurements to educate about the risk of abdominal fat and its potential in motivating positive behavior change is especially important.
Through group counseling, these clients became aware of the importance of regional fat distribution, especially the role of visceral fat. Motivation was improved as clients reviewed their posttest data to find substantial decreases in VAT.
Summing It Up
In summary, weight loss is associated with significant reductions in abdominal fat. Benefits from a reduction in VAT of the abdomen include a reduced risk for comorbidities related to metabolic syndrome, specifically cardiovascular disease and type 2 diabetes (2, 3).
Changes in VAT associated with weight loss can motivate and enhance continued weight loss. Because of the obesity epidemic, there is an increased demand for health and fitness professionals to provide counseling for weight management. Health clubs and fitness centers should strongly consider assessing regional abdominal fat changes, in addition to total weight and fat loss.
Condensed Version and Bottom Line
The problems of obesity have escalated in recent years. Regional fat distribution is of particular concern because VAT, a component of abdominal fat stored around the viscera, is associated with increased health risk. Previously, researchers have suggested assessing visceral fat during body composition evaluations. Health professionals are encouraged to measure abdominal fat distribution using SAD. It is a practical measurement that health care professionals can use to assess risk. Three simple equations predict abdominal fat distribution, while three easy steps predict visceral fat in pounds. Educating clients about fat distribution and monitoring visceral fat during weight management may improve motivation and increase adherence.
1. U.S. Department of Health and Human Services. National Health and Nutrition Examination Survey: Healthy Weight, Overweight, and Obesity
Among U.S. Adults. U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. Publication no. 03-0260, 2003. Available at http://www.cdc.gov/nchs/data/nhanes/databriefs/adultweight.pdf
. Accessed July 12, 2004.
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. The Journal of the American Medical Association
5. Ribisl P.M. Clinical Applications. Toxic "waist" dump: our abdominal visceral fat
. ACSM's Health & Fitness Journal
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7. Stunkard A.J. and T.A. Wadden. Obesity: theory and therapy
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9. Zamboni M., E. Turcato, F. Armellini, et al. Sagittal abdominal diameter as a practical predictor of visceral fat. International Journal of Obesity and Related Metabolic Disorders
10. Williamson D.F., H.S. Kahn, C.M. Worthman, et al. Precision of recumbent anthropometry. American Journal of Human Biology
11. Stallone D.D., A.J. Stunkard, T.A. Wadden, et al. Weight loss and body fat distribution: a feasibility study using computed tomography. International Journal of Obesity
12. Van der Kooy K., R. Leenen, J.C. Seidell, et al. Waist-hip ratio is a poor predictor of changes in visceral fat. The American Journal of Clinical Nutrition
Keywords:© 2006 American College of Sports Medicine
Sagittal Abdominal Diameters; Abdominal Visceral Fat; Weight Management; Obesity; Body Composition