Info

Overweight—increased health risks

>30

Obesity—high health risks

Conicity Index

The conicity index was formulated by Valdez (35) to estimate abdominal fat, based on the theory that leaner subjects have a body shape similar to a cylinder, but as fat is accumulated around the abdomen, the body shape changes towards that of a double cone (two cones with a common base at the waist). With the assumption that the average human body density is 1.05 kg/m3, the equation was derived as:

Conicity index =

Waist

(0.109 x ^weight/height)

The conicity index is theorized to have a built-in adjustment for height and weight so that abdominal adiposity can be compared across different populations of varying heights and weights (36). The index is related to the ratio of intra-abdominal fat/extraabdominal fat mass similarly to waist-to-hip ratio, and may be useful when hip measurement is not available. Valdez et al. (36) found the conicity index to be correlated to cardiovascular risk factors similarly to that of waist-to-hip ratio in different countries. A drawback is that the index has not been cross-validated to ensure applicability.

Waist-to-thigh Ratio

In some studies waist-to-thigh ratio has been used as an index for fat distribution to relate to metabolic risk factors (34). This ratio is also influenced by abdominal fat as well as fat mass, muscle mass and bone structures of the thigh, which may be a strong indicator of certain health conditions involving both abdominal fat accumulation and skeletal muscle wasting such as NIDDM.

Sagittal Abdominal Diameter

The use of sagittal diameter of the waist has been proposed as an index of abdominal fatness based on a theory that fat deposition in the anteroposterior axis is more 'dangerous' than lateral fat deposition. This index has not been validated in an independent population. Sagittal diameter can be measured using a pelviometer in the standing position, or a more sophisticated instrument that is modified from a sliding stadiometer in the supine position (37). Gadgets are on sale with a back plate which is j

Male 0.90 Waist to hip ratio 1.10 Male

Female 0.70 Waist to hip ratio 1.20 Female

Figure 4.7 Silhouette photographs showing variation in human body fat distribution flexible, thereby introducing enormous errors. The measurement of sagittal diameter of the waist has not been used very widely. This method has recently been validated by CT scanning and found to have high reproducible results.

Abdominal Cross-sectional Area

Abdominal cross-sectional area (CSAa) has also been proposed by van der Kooy et al. (38) as an index of abdominal fat and is calculated from waist sagittal (WSD) and waist transverse diameters (WTD) as: CSAa = (4 x WSD x WTD)/n, but this more complicated method is not likely to be much different from a circumference or a single measurement of waist diameter.

Waist Circumference

Recent proposals for the use of waist circumference as a single measurement of body fat and fat distribution have now been adopted by several major public health promotion agencies and organizations (8,9,21).

Waist circumference has been suggested as a simple measurement to identify individuals with high BMI or high waist-to-hip ratio. Waist circumference correlates significantly with BMI (both men and women: r = 0.89; P < 0.001). Lean et al. (39) have derived the 'action levels' for weight management based on the waist circumference of over 2000 men and women (Table 4.3). Action level 1: Waist circumference of > 94 cm in men or > 80 cm in women identifies as overweight with increased health risks, those with BMI > 25 kg/m2 and high waist-to-hip ratio ( > 0.95 for men; > 0.80 for women). These subjects are advised not to gain further body weight and to increase physical activity. Action level 2: Waist circumference of > 102 cm in men or > 80 cm in women identifies as overweight with high health risks, those with BMI > 30 kg/m2 and high waist-to-hip ratio ( > 0.95 in men and > 0.80 in women). Weight loss and consultation of health professionals are recommended for these individuals. These action levels for weight management have a sensitivity (correctly identifies individuals who need weight management by waist circumference above action levels) and a specificity (correctly identifies individuals who do not need weight management by waist circumference below action levels) of more than 96% for identifying overweight and obese subjects with high waist-to-hip ratio. Waist circumference is not importantly influenced by height (40) (Figure 4.9), thus it is not necessary to divide waist by height when using waist circumference as an index of adiposity. To avoid problems with over-tightening during waist measurement, a specially designed 'Waist Watcher' spring-loaded tape measure has been produced with three colour bands based on cut-offs of the waist circumference action levels (Figure 4.10).

ANTHROPOMETRIC INDICES OF OBESITY Table 4.3 Action levels to identify overweight and obese men and women with increased abdominal fat

Waist circumference

Approximate equivalents

Action level

Body mass Waist-to-hip index ratio Classification of health risks

Weight management

Women

Increased health risks High health risks

Increased health risks High health risks

Prevent further weight gain, try to get down to below action level 1 (94 cm) Seek advice to lose weight, aim for 5-10% weight loss permanently

Prevent further weight gain, try to get down to below action level 1 (80 cm) Seek advice to lose weight, aim for 5-10% weight loss permanently cm

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