The authors have declared that no competing interests exist.
Conceived and designed the experiments: JPW JAS. Performed the experiments: JPW BF. Analyzed the data: JPW AMK BF JAS. Contributed reagents/materials/analysis tools: JPW AMK BF JAS. Wrote the paper: JPW AMK JAS. Critical revision for important intellectual content: JPW BF AMK JAS.
Body shape is a known risk factor for diabetes and mortality, but the methods estimating body shape, BMI and waist circumference are crude. We determined whether a novel body shape measure, trunk to leg volume ratio, was independently associated with diabetes and mortality.
Data from the National Health and Nutritional Examination Survey 1999–2004, a study representative of the US population, were used to generate dual-energy X-ray absorptiometry-derived trunk to leg volume ratio and determine its associations to diabetes, metabolic covariates, and mortality by BMI category, gender, and race/ethnicity group.
The prevalence of pre-diabetes and diabetes increased with age, BMI, triglycerides, blood pressure, and decreased HDL level. After adjusting for covariates, the corresponding fourth to first quartile trunk to leg volume ratio odds ratios (OR) were 6.8 (95% confidence interval [CI], 4.9–9.6) for diabetes, 3.9 (95% CI, 3.0–5.2) for high triglycerides, 1.8 (95% CI, 1.6–2.1) for high blood pressure, 3.0 (95% CI, 2.4–3.8) for low HDL, 3.6 (95% CI, 2.8–4.7) for metabolic syndrome, and 1.76 (95% CI, 1.20–2.60) for mortality. Additionally, trunk to leg volume ratio was the strongest independent measure associated with diabetes (P<0.001), even after adjusting for BMI and waist circumference. Even among those with normal BMI, those in the highest quartile of trunk to leg volume ratio had a higher likelihood of death (5.5%) than those in the lowest quartile (0.2%). Overall, trunk to leg volume ratio is driven by competing mechanisms of changing adiposity and lean mass.
A high ratio of trunk to leg volume showed a strong association to diabetes and mortality that was independent of total and regional fat distributions. This novel body shape measure provides additional information regarding central adiposity and appendicular wasting to better stratify individuals at risk for diabetes and mortality, even among those with normal BMI.
Body shape is a known risk factor for mortality and diabetes, which is a major global health problem associated with reduced life span, increased morbidity, and significant financial burdens on individuals and health care systems
Total body volume is the solid volume of an individual and the metric used to measure body density and estimate body composition
Dual energy X-ray absorptiometry (DXA) is a highly prevalent medical imaging modality. Typical outputs of a DXA scan report include whole body and regional measures of fat mass, lean mass, bone mineral content (BMC), and bone mineral density. In the last ten years, ratios of regional DXA mass compartments (like trunk to peripheral fat mass and android to gynoid fat mass) have also been used to stratify risk for metabolic diseases
While ratios of DXA-reported fat masses have been used to distinguish certain groups, they are not as intuitive as body shape itself. We have recently developed a technique to measure solid body volume using DXA-reported fat, lean, and BMC values
In this study, we derived an easily interpretable body shape measure from whole body DXA data, the ratio of trunk volume to leg volume, and tested its association to diabetes, metabolic covariates, and subsequent mortality in a representative United States population. We hypothesized that participants with a higher trunk to leg volume ratio would have higher rates of diabetes, its metabolic covariates, and mortality.
We performed a retrospective analysis of the publicly accessible NHANES 1999–2004 datasets to determine the association of body shape to diabetes, metabolic covariates, and mortality. NHANES is a population-based study of the non-institutionalized US population. In addition to DXA scan output, NHANES 1999–2004 contains self-reported survey responses (including gender, race/ethnicity, diabetes status, physical activity level, family size, family income level, various medication usage) and laboratory-based results (including weight, height, BMI, waist circumference, fasting plasma glucose, insulin, triglycerides, high-density lipoprotein (HDL), systolic blood pressure, and diastolic blood pressure). There were a total of 10,673 adult subjects (age > = 20 years) with DXA scan output data available from the public study website
We generated whole body and regional (arms, legs, and trunk) volume measures from the DXA scan output by using the calibration equation described in a previous reporting
We analyzed the distribution of demographic variables by BMI category and tested for differences between these groups by the Bonferroni-adjusted t-test. We examined the prevalence of pre-diabetes (fasting plasma glucose levels between 100–125 mg/dL) and diabetes (defined by self- reported diagnosis or a fasting glucose ≥126 mg/dL) by gender, race/ethnicity, age category, BMI category, weight quartile, DXA total percent fat quartile, trunk to leg volume ratio quartile, waist circumference category, triglyceride level, HDL-cholesterol level, and blood pressure category. To avoid the confounding effect of medication use of individuals with diabetes on their lipids and blood pressure, we used quartile cut points derived from the population excluding those with diabetes. We used the 2005 NCEP guidelines to define cut points for BMI categories, high waist circumference, high triglyceride levels, high blood pressure, low HDL levels, and metabolic syndrome
We used sequential logistic regression models to determine the association between trunk to leg volume ratio and metabolic outcomes (diabetes, high triglycerides, low HDL-cholesterol levels, high blood pressure, and metabolic syndrome) and mortality. For each model, we determined the order of variable significance, area under the receive-operator characteristic curve (AUC), odds ratio per standard deviation increase of trunk to leg volume ratio, and odds ratios for trunk to leg volume quartile (compared to the first quartile). We first adjusted for age alone; in the second stage covariate model, we also included gender, race/ethnicity, continuous BMI, continuous waist circumference, self-reported activity level, continuous poverty index ratio. To adjust for other DXA-derived measures of body fat, we created a second covariate model that also adjusted for the ratio of trunk fat mass to leg fat mass. The full model (used only for diabetes) included all covariates above and further adjusted for fasting insulin, triglycerides, HDL, systolic and diastolic blood pressure. We finally created a second full model (used only for diabetes) that also adjusted for the ratio of trunk fat mass to leg fat mass. All statistical analysis was done using SAS software, version 9.2 (SAS Institute, Inc., Cary, NC).
To investigate the driving forces of fat mass and lean mass behind trunk to leg volume ratio, we generated several height-normalized variables: trunk fat mass index (kg/m2), trunk lean mass index (kg/m2), trunk volume index (L/m2), leg fat mass index (kg/m2), leg lean mass index (kg/m2), and leg volume index (L/m2). To determine what body composition variables affected trunk to leg volume the most, we compared mean values of these height-normalized variables, trunk to leg fat mass ratio, and trunk to leg lean mass ratio to trunk to leg volume ratio quartile.
Demographic | Underweight | Normal | Overweight | Obese | Total |
Female | 102 | 1645 | 1572 | 1496 | 4815 |
Male | 67 | 1612 | 2251 | 1131 | 5061 |
Mexican American | 17 | 627 | 994 | 699 | 2337 |
Non-Hispanic Black | 35 | 520 | 647 | 569 | 1771 |
Non-Hispanic White | 100 | 1799 | 1860 | 1193 | 4952 |
Other Race/Ethnicity | 17 | 311 | 322 | 166 | 816 |
Age (yr) | 43.7±20.2 | 47.1±19.6 | 51.4±17.9 | 49.4±16.7 | 49.3±18.3 |
BMI (kg/m2) | 17.5±0.9 | 22.5±1.7 | 27.4±1.4 | 33.7±3.2 | 27.3±5.0 |
Weight (kg) | 48.8±6.6 | 63.6±9.0 | 77.9±10.1 | 93.2±13.1 | 76.8±16.0 |
Waist Circumference (cm) | 70.2±5.2 | 83.1±7.7 | 96.3±7.6 | 108.5±8.9 | 94.8±13.0 |
Triglycerides (mg/dL) |
96±64 | 117±87 | 160±151 | 173±182 | 148±144 |
HDL (mg/dL) | 61.3±16.8 | 56.7±16.5 | 49.4±14.7 | 46.8±12.8 | 51.4±15.5 |
Systolic BP (mmHg) |
119±24 | 122±21 | 128±20 | 128±19 | 126±21 |
Diastolic BP (mmHg) |
70±12 | 69±13 | 72±13 | 73±13 | 71±13 |
DXA Total Fat (%) | 22.9±6.2 | 29.0±7.7 | 33.5±7.3 | 39.8±7.2 | 33.5±8.6 |
Trunk to Leg Fat Mass Ratio |
1.04±0.31 | 1.30±0.43 | 1.61±0.47 | 1.63±0.45 | 1.50±0.48 |
Trunk to Leg Volume Ratio |
1.40±0.17 | 1.46±0.22 | 1.57±0.24 | 1.57±0.26 | 1.53±0.24 |
BMI categories were defined as follows: underweight BMI (<18.5 kg/m2), normal BMI (> = 18.5 kg/m2 and <25 kg/m2), overweight BMI (> = 25 kg/m2 and <30 kg/m2), and obese BMI (> = 30 kg/m2). All measures displayed were significantly different (P<0.05) for each BMI category (by Bonferroni-adjusted t-test) unless otherwise noted.
Differences between Overweight & Obese were not significantly significant.
Differences between Underweight & Normal were not significantly significant.
Differences between Underweight & Overweight were not significantly significant.
Measure | Value | N | % Pre-Diabetes | % Diabetes |
Gender | Female | 4815 | 10.0 | 10.2 |
Male | 5061 | 15.7 | 10.4 | |
Race/Ethnicity | Mexican American | 2337 | 14.9 | 13.7 |
Non-Hispanic Black | 1771 | 8.7 | 11.8 | |
Non-Hispanic White | 4952 | 13.6 | 7.9 | |
Other | 816 | 12.3 | 12.0 | |
Age (yr) |
<50 | 5246 | 9.5 | 3.2 |
50–70 | 2901 | 16.0 | 17.6 | |
>70 | 1729 | 18.1 | 19.5 | |
BMI (kg/m2) |
Underweight (<18.5) | 169 | 8.3 | 3.0 |
Normal (18.5–25) | 3257 | 9.4 | 6.0 | |
Overweight (25–30) | 3823 | 15.2 | 11.4 | |
Obese (>30) | 2627 | 14.3 | 14.5 | |
Weight (kg) |
<64.8 kg (Q1) | 2380 | 8.6 | 7.5 |
≥64.8 kg & <75.2 kg (Q2) | 2447 | 11.8 | 9.7 | |
≥75.2 kg & <86.7 kg (Q3) | 2512 | 15.5 | 11.1 | |
≥86.7 kg (Q4) | 2537 | 15.5 | 12.7 | |
DXA Total Fat (%) |
<26.9% (Q1) | 2334 | 11.4 | 6.2 |
≥26.9% & <32.8% (Q2) | 2466 | 15.2 | 10.6 | |
≥32.8% & <40.3% (Q3) | 2517 | 12.7 | 11.3 | |
≥40.3(Q4) | 2559 | 12.4 | 12.8 | |
Trunk to Leg Volume Ratio |
<1.34 (Q1) | 2282 | 6.1 | 2.9 |
≥1.34 & <1.50 (Q2) | 2339 | 10.0 | 5.3 | |
≥1.50 & <1.66 (Q3) | 2401 | 15.6 | 7.8 | |
≥1.66 (Q4) | 2854 | 18.5 | 22.4 | |
Waist Circumference (cm) | ≤102 (M) or ≤88 (F) (Low) | 5257 | 14.7 | 15.1 |
>102 (M) or >88 (F) (High) | 4619 | 11.3 | 6.0 | |
Triglycerides (mg/dL) | <150 (Low) | 3089 | 23.8 | 8.0 |
≥150 (High) | 1578 | 33.5 | 19.8 | |
HDL (mg/dL) | <40 (M) or <50 (F) (Low) | 2207 | 15.7 | 14.5 |
≥40 (M) or ≥50 (F) (High) | 4114 | 13.0 | 7.4 | |
Blood Pressure (mmHg) | <130 (S) & <85 (D) (Low) | 5944 | 11.0 | 6.8 |
≥130 (S) or ≥85 (D) (High) | 3715 | 16.0 | 15.6 |
Quartile cut points (Q1–Q4) were based on individuals without diabetes. For waist circumference and HDL levels, there were separate cutoffs by gender, so ‘M’ is male and ‘F’ is female. Systolic blood pressure is shown as ‘S’, and diastolic blood pressure is shown as ‘D’.
Pre-Diabetes P-for-trend <0.05.
Diabetes P-for-trend <0.05.
The prevalence of diabetes (A), high triglycerides (B), low HDL (C), and high blood pressure (D) versus trunk to leg volume ratio quartile for normal BMI (> = 18.5 kg/m2 and <25 kg/m2), overweight BMI (> = 25 kg/m2 and <30 kg/m2), obese BMI (> = 30 kg/m2), and total population in NHANES 1999–2004 are shown below. All data displayed had a significant trend (P-for-trend <0.001) in prevalence versus quartile of trunk to leg volume ratio. There was a significant (P<0.001) interaction (trunk to leg volume ratio quartile & BMI category) in the prevalence of diabetes and high blood pressure.
The prevalence of diabetes (A), high triglycerides (B), low HDL (C), and high blood pressure (D) versus trunk to leg volume ratio quartile for race/ethnicity in NHANES 1999–2004 are shown below. All data displayed had a significant trend (P-for-trend <0.001) in prevalence versus quartile of trunk to leg volume ratio. There was a significant (P<0.05) interaction term (trunk to leg volume ratio quartile & race/ethnicity) in the prevalence of diabetes and high blood pressure.
There was a significant increasing trend (P-for-trend<0.001) in the prevalence of diabetes, high triglycerides, low HDL, and high blood pressure by trunk to leg volume ratio quartile for both men and women.
The prevalence of metabolic syndrome versus trunk to leg volume ratio quartile is displayed below for (A) BMI category, (B) gender, (C) race/ethnicity, and (D) age group in NHANES 1999–2004. (A) All data displayed by BMI category had a significant trend (P-for-trend<0.001) in metabolic syndrome versus trunk to leg volume ratio quartile; there was also a significant interaction (P-for-interaction<0.001) between trunk to leg volume ratio quartile and BMI category for metabolic syndrome. (B) All data displayed by gender had a significant trend (P-for-trend <0.001) in mortality versus trunk to leg volume ratio quartile; there was also a significant interaction (P-for-interaction<0.001) between trunk to leg volume ratio quartile and gender for metabolic syndrome. (C) All data displayed by race/ethnicity had a significant trend (P-for-trend<0.001) in metabolic syndrome versus trunk to leg volume ratio quartile; there was also a significant interaction (P-for-interaction<0.05) between trunk to leg volume ratio quartile and race/ethnicity for metabolic syndrome. (D) All data displayed by age group had a significant trend (P-for-trend<0.001) in metabolic syndrome versus trunk to leg volume ratio quartile; there was also a significant interaction (P-for-interaction<0.001) between trunk to leg volume ratio quartile and age group for metabolic syndrome.
Mortality versus trunk to leg volume ratio quartile is displayed below for (A) BMI category, (B) gender, (C) race/ethnicity, and (D) age group in NHANES 1999–2004. (A) All data displayed by BMI category had a significant trend (P-for-trend<0.001) in mortality versus trunk to leg volume ratio quartile; there was also a significant interaction (P-for-interaction<0.01) between trunk to leg volume ratio quartile and BMI category for mortality. (B) All data displayed by gender had a significant trend (P-for-trend <0.001) in mortality versus trunk to leg volume ratio quartile. (C) All data displayed by race/ethnicity had a significant trend (P-for-trend<0.001 for Mexican American, Non-Hispanic Black, and Non-Hispanic White; P-for-trend<0.05 for Other Race)) in mortality versus trunk to leg volume ratio quartile. (D) Only individuals >70 years displayed a significant trend (P-for-trend <0.01) in mortality versus trunk to leg volume ratio quartile.
Odds Ratios for Trunk to Leg Volume Ratio Quartile | |||||||
Condition | Model | AUC | Per SD Increase | Q1 | Q2 | Q3 | Q4 |
Diabetes | Age |
0.796 | 2.2 (2.0–2.3) | 1.0 | 1.6 (1.2–2.2) | 2.1 (1.6–2.8) | 5.7 (4.4–7.4) |
Covariate |
0.839 | 2.3 (2.1–2.5) | 1.0 | 2.0 (1.4–2.8) | 2.6 (1.9–3.7) | 6.8 (4.9–9.6) | |
Covariate 2 |
0.839 | 2.3 (2.1–2.5) | 1.0 | 1.6 (1.1–2.2) | 1.6 (1.1–2.3) | 2.6 (1.7–4.0) | |
Full |
0.868 | 1.9 (1.6–2.3) | 1.0 | 1.1 (0.6–2.0) |
1.4 (0.8–2.5) |
3.9 (2.2–7.0) | |
Full 2 |
0.868 | 1.9 (1.6–2.3) | 1.0 | 0.9 (0.5–1.8) |
1.1 (0.6–2.0) |
2.2 (1.0–4.7) | |
High TG | Age | 0.703 | 2.1 (1.9–2.2) | 1.0 | 2.1 (1.7–2.7) | 4.0 (3.2–5.0) | 6.8 (5.5–8.5) |
Covariate | 0.722 | 1.8 (1.6–1.9) | 1.0 | 1.7 (1.4–2.2) | 2.8 (2.2–3.7) | 3.9 (3.0–5.2) | |
Covariate 2 | 0.538 | 0.8 (0.7–0.9) | 1.0 | 0.9 (0.8–1.1) |
0.8 (0.7–1.0) | 0.7 (0.6–0.9) | |
Low HDL | Age | 0.628 | 1.7 (1.6–1.8) | 1.0 | 1.6 (1.3–1.8) | 2.1 (1.8–2.4) | 3.6 (3.0–4.2) |
Covariate | 0.705 | 1.6 (1.5–1.7) | 1.0 | 1.5 (1.2–1.8) | 2.0 (1.6–2.4) | 3.0 (2.4–3.8) | |
Covariate 2 |
0.709 | 1.2 (0.7–2.4) |
1.0 | 1.2 (1.0–1.5) |
1.2 (1.0–1.5) |
1.3 (0.9–1.7) |
|
High BP | Age | 0.768 | 1.2 (1.1–1.3) | 1.0 | 1.1 (0.9–1.3) |
1.3 (1.1–1.4) |
1.6 (1.4–1.8) |
Covariate | 0.781 | 1.3 (1.2–1.3) | 1.0 | 1.2 (1.0–1.4) | 1.4 (1.2–1.7) | 1.8 (1.6–2.1) | |
Covariate 2 |
0.782 | 1.9 (1.1–3.2) | 1.0 | 1.1 (1.0–1.4) |
1.2 (1.0–1.5) | 1.4 (1.1–1.8) | |
MetS | Age | 0.747 | 1.9 (1.8–2.1) | 1.0 | 1.6 (1.3–2.0) | 2.5 (2.0–3.0) | 4.9 (4.0–6.1) |
Covariate | 0.840 | 1.8 (1.6–1.9) | 1.0 | 1.5 (1.2–2.0) | 2.2 (1.7–2.9) | 3.6 (2.8–4.7) | |
Covariate 2 |
0.840 | 1.4 (1.2–1.6) | 1.0 | 1.2 (1.0–1.6) |
1.5 (1.1–2.0) | 1.6 (1.1–2.3) | |
Mortality | Age | 0.830 | 1.2 (1.1–1.3) | 1.0 | 1.4 (1.0–2.0) | 1.4 (1.1–2.0) | 1.7 (1.2–2.3) |
Covariate | 0.862 | 1.2 (1.1–1.4) | 1.0 | 1.3 (0.9–1.9) |
1.4 (1.0–2.1) |
1.8 (1.2–2.6) | |
Covariate 2 | 0.863 | 1.8 (1.5–2.3) | 1.0 | 1.3 (0.9–1.9) |
1.4 (1.0–2.1) |
1.8 (1.2–2.6) |
AUC is the area under the receiver-operator characteristic curve. Odds ratios are displayed as odds ratio (95% confidence interval). Quartile cut points (Q1-Q4) were based on individuals without diabetes.
Age model adjusts for age.
Covariate model adjusts for gender, race/ethnicity, age, BMI, waist circumference, self-reported activity level, and poverty index ratio.
Covariate 2 model adjusts for gender, race/ethnicity, age, BMI, waist circumference, self-reported activity level, poverty index ratio, and trunk to leg fat mass ratio.
Full model adjusts for all variables in b and insulin, triglycerides, HDL, systolic blood pressure, and diastolic blood pressure.
Full 2 model adjusts for all variables in d and trunk to leg fat mass ratio.
Odds ratio not significant.
Forward selection turned off because trunk to leg volume ratio quartile wasn’t significant enough to remain in the model otherwise.
In a fully adjusted model, individuals in the highest quartile of trunk to leg volume ratio were 3.9 times as likely to have diabetes compared to the lowest quartile, but the odds of diabetes in the second or third quartiles were not significantly different than the lowest quartile. Additionally, trunk to leg volume ratio was the most significant variable, followed by age, in the fully-adjusted model (P<0.001). Even after adjusting for DXA-derived trunk to leg fat mass ratio in the Full 2 model, we found that individuals in the highest quartile of trunk to leg volume ratio were 2.2 times as likely to have diabetes compared to the lowest quartile.
For mortality, the association with waist circumference was not significant. Individuals in the highest quartile of trunk to leg volume ratio had increased odds of mortality (OR = 1.8, 95% CI 1.2–2.6) compared to those in the lowest quartile while there was a decreased odds of mortality with each SD increase in BMI (OR = 0.7, 95% CI 0.7–0.8). For several of the models that also adjusted for trunk to leg fat mass ratio (Covariate 2), forward selection of variables was turned off to ensure that both trunk to leg fat mass ratio and trunk to leg volume ratio remained in the model.
Each ROC curve displays the sensitivity versus one minus specificity for each logistic regression model that is used to distinguish those individuals with diabetes in NHANES 1999–2004. The trunk to leg volume ratio only model (AUC = 0.748) includes only the variable of trunk to leg volume ratio. The age model (AUC = 0.796) includes the variables of age and trunk to leg volume ratio. The covariate model (AUC = 0.839) includes the variables of gender, race/ethnicity, age, BMI, waist circumference, self-reported activity level, poverty index ratio, and trunk to leg volume ratio. The full model (AUC = 0.796) includes the variables of race/ethnicity, age, waist circumference, poverty index ratio, insulin, triglycerides, systolic blood pressure, diastolic blood pressure, and trunk to leg volume ratio; gender, BMI, self-reported activity level, and HDL level were dropped from the final model because the coefficients were not significant (P<0.05).
(A) Mean height-normalized trunk fat mass index (kg/m2), trunk lean mass index (kg/m2), and trunk volume index (L/m2) values are stratified by quartile of trunk to leg volume ratio. The increase in trunk volume is attributed mainly to the increase in trunk fat. (B) Mean height-normalized leg fat mass index (kg/m2), leg lean mass index (kg/m2), and leg volume index (L/m2) values are stratified by quartile of trunk to leg volume ratio. There is an overall decrease in leg volume primarily driven by a decrease in leg fat mass. (C) Mean trunk to leg fat mass ratio, trunk to leg lean mass ratio, and trunk to leg volume ratio are stratified by quartile of trunk to leg volume ratio. Trunk to leg fat mass ratio increases more dramatically than trunk to leg lean mass ratio.
The prevalence of diabetes, high triglycerides, low HDL, high blood pressure, metabolic syndrome, and subsequent mortality significantly increased with each trunk to leg volume ratio quartile. Among traditionally low-risk individuals in the normal BMI category, prevalence of these conditions increased dramatically as trunk to leg volume ratio increased. Even after adjusting for several covariates in the pathway between body shape and the metabolic outcome including the fat distribution measure of trunk to leg fat mass ratio, individuals in the fourth versus first quartile of trunk to leg volume ratio had significantly increased odds of having diabetes, high triglycerides, low HDL, high blood pressure, metabolic syndrome, and subsequent mortality. Additionally, the driving force behind increased trunk to leg volume ratio was primarily increases in both the fat and lean compartments of the trunk with decreases in the legs. Even after adjustments for other measures of body shape (BMI or waist circumference), trunk to leg volume ratio was an independent marker of diabetes, metabolic covariates, and mortality in a representative sample of the United States.
While simplistic shape measures of BMI and waist circumference are associated to diabetes status, our results show that trunk to leg volume ratio provides additional information beyond these measures. Most studies use BMI and waist circumference as surrogates for total percent fat and central adiposity, respectively
Because of the compounding effects of obesity and diabetes, trunk to leg volume ratio could potentially be used as a screening assessment that seems more promising than BMI or waist circumference. Mokdad et al. reported similar trends in diabetes prevalence by age and BMI category in the 2001 Behavioral Risk Factor Surveillance System
Our study used DXA as a tool of convenience because of the availability of a large dataset for retrospective analysis. Because all DXA scans in NHANES 1999–2004 were taken on the same type of DXA system, no cross calibration between systems was necessary. While this project looks at regional DXA measures from the trunk and leg, we have previously developed a method to look at DXA-derived body shape on pixel-by-pixel basis that could be employed to generate advanced measures of shape beyond ratios of regional volume
Despite no statistically significant difference in mean trunk to leg volume ratio between overweight and obese individuals (in
Our initial hypothesis held true. Increased trunk to leg volume ratio was due to competing effects of adiposity and lean mass in the trunk and legs. We also hypothesized that increased trunk volume was due primarily to increased central adiposity, and that decreased leg volume was due to muscle wasting. However, we did not see changes in leg lean mass driving the trunk to leg volume ratio. Our data suggests that high visceral mass for both fat and lean accompanied with a low subcutaneous adiposity is the strongest driver of body shape risk irrespective of muscularity represented by leg lean mass.
Our study had several limitations. NHANES 1999–2004 didn’t include hip circumference measurements, so we were not able to do a direct comparison of trunk to leg volume ratio to waist to hip ratio, a surrogate of body shape used more in research than in clinical care. To compensate, we looked at the most similar measure we could generate (waist to thigh circumference ratio); this ratio was highly correlated to but did not perform as well as trunk to leg volume ratio. In 2012, two major DXA system manufacturers (Hologic and GE-Lunar) released feature updates to quantify visceral fat from their DXA scans
We conclude that this novel trunk to leg volume ratio derived from whole body DXA scans in a representative sample of the US population showed strong associations with diabetes, high triglycerides, low HDL, high blood pressure, metabolic syndrome and mortality. These associations were also strong for individuals in the normal BMI category, which is typically considered low risk for diabetes. Trunk to leg volume ratio provides an independent marker that intuitively describes body shape and stratifies diabetes and mortality more accurately than currently available body shape measures of BMI and waist circumference. A large ratio of trunk versus leg volume is a strong indicator of poor health, with increased prevalence of diabetes, poor metabolic profiles, and elevated mortality even in individuals not considered overweight.