Reliability tests and guidelines for B-mode ultrasound assessment of central adiposity

Ultrasound-based measurement of central adiposity: Key considerations and guidelines

Central adiposity, which is visceral and subcutaneous adiposity in the abdominal region, is a known risk factor for developing chronic cardiometabolic diseases. Central adiposity can be measured relatively inexpensively using ultrasound. Ultrasound has been shown to be precise and reliable, with measurement accuracy comparable to computed tomography and magnetic resonance. Despite the advantages conferred by ultrasound, widespread adoption has been hindered by lack of reliable standard operating procedures. To consolidate the literature and bring clarity to the use of ultrasound-derived measures of central adiposity, this review outlines (i) the [patho]physiological importance of central adiposity to cardiometabolic disease risk; (ii) an overview of the history and main technical aspects of ultrasound methodology; (iii) key measurement considerations, including transducer selection, subject preparation, image acquisition, image analysis, and operator training; and (iv) guidelines for standardized ultrasound protocols for measuring central adiposity.

Characterization and prevalence of obesity among normal weight college students

Normal weight obesity (NWO) describes individuals who have a normal weight body mass index (BMI), but have an unhealthy amount of body fat. Based on the life-long habits that develop during college, exploring NWO among a college-aged population may be essential in identifying and preventing obesity that develops in early adulthood. This study aimed to characterize NWO among young adults with normal weight BMI. 94 college students (Mean ± SD: Age: 19.6 ± 1.5 yrs; BMI: 21.9 ± 1.8 kg/m²) enrolled during the Fall semester (Aug-Oct) were assessed for body composition by dual energy X-ray absorptiometry to determine body fat percentage, fat mass, lean mass and trunk fat; lifestyle habits were characterized from validated questionnaires. Mean arterial pressure and metabolic biomarkers [total cholesterol, high density lipoproteins, non-high density lipoproteins, and glucose] were evaluated for cardiometabolic health. NWO was defined using data from the National Health and Nutrition Examination Survey (NHANES) for body fat percentage. Data was analyzed by group (NWO vs NWL) and sex. with independent t-tests to investigate continuous data, and chi-square test of independence for categorical data. Rates of NWO for the total sample were 13.8%. Males (n=30) had a higher rate of NWO (26.7%) compared to females (n=64; 7.8%). NWO individuals had higher fat mass (p=0.024), trunk fat (p<0.001), and larger waist to hip ratio (p<0.001) than normal weight lean. NWO also engaged in less vigorous physical activity (p=0.043). The occurrence of NWO among otherwise healthy college students is evident. Identification of these individuals may be an effective component for obesity prevention and treatment. Determining feasible methods to measure body fat in this population is essential, as BMI may mask obesity in a young adult population.

Evaluation of ultrasound measurements of abdominal fat for the prediction of gestational diabetes in the first and second trimesters of pregnancy

OBJECTIVE

To evaluate whether ultrasound abdominal fat measurements in the first and second trimesters can predict adverse gestational outcomes, particularly gestational diabetes mellitus (GDM), and identify early patients at higher risk for complications.

METHODS

A prospective cohort study of 126 pregnant women at 11-14 and 20-24 weeks of gestation with normal fasting glucose levels during early pregnancy. From 126 participants with complete data, 13.5% were diagnosed with GDM, based on the cutoffs established for the peripherical blood glucose. Subcutaneous, visceral, and maximum preperitoneal abdominal fat were measured using ultrasound techniques. GDM status was determined by oral glucose tolerance test (OGTT) with 75 g glucose overload, and the following values were considered abnormal: fasting glucose ≥92 mg/dl and/or 1 h after overload ≥180 mg/dl and/or 2 h after overload ≥153 mg/dl. The receiver operator characteristic (ROC) curve was used to determine the optimal threshold to predict GDM.

RESULTS

Maximum preperitoneal fat measurement was predictive of GDM, and subcutaneous and visceral abdominal fat measurements did not show significant differences in the prediction of GDM. According to the ROC curve, a threshold of 45.25 mm of preperitoneal fat was identified as the optimal cutoff point, with 87% sensitivity and 41% specificity to predict GDM. The raw and adjusted odds ratios for age and pre-pregnancy body mass index were 0.730 (95% confidence interval [CI], 0.561-0.900) and 0.777 (95% CI, 0.623-0.931), respectively.

CONCLUSION

The use of a 45.25 mm threshold for maximum preperitoneal fat, measured by ultrasound to predict the risk of GDM, appears to be a feasible, inexpensive, and practical alternative to incorporate into clinical practice during the first trimester of pregnancy.

Metabolic effects of menopause: a cross-sectional characterization of body composition and exercise metabolism

OBJECTIVES

To evaluate body composition, fat distribution, and metabolism at rest and during exercise in premenopausal, perimenopausal, and postmenopausal women.

METHODS

This cross-sectional study in 72 women ages 35 to 60 years evaluated body composition via a fourcompartment model, fat distribution using dual-energy x-ray absorptiometry-derived android to gynoid ratio, metabolic measures via indirect calorimetry, and lifestyle factors using surveys. One-way analyses of variance and one-way analyses of covariance covaried for age and hormone levels (estrogen and progesterone) were used to compare groups.

RESULTS

Body fat percent was significantly lower in premenopausal than perimenopausal women (mean difference ± standard error: - 10.29 ± 2.73%, P = 0.026) despite similarities in fat mass and fat-free mass between groups (P≥0.217). Android to gynoid ratio was significantly lower in premenopausal than perimenopausal women (MD ± SE: -0.16 ± 0.05 a.u., P = 0.031). Resting energy expenditure was similar between groups (P = 0.999). Fat oxidation during moderate intensity cycle ergometer exercise was significantly greater in premenopausal than postmenopausal women (MD ± SE: 0.09 ± 0.03 g/min, P = 0.045). The change in respiratory exchange ratio between rest and moderate intensity exercise was significantly lower in premenopausal women than peri- (MD ± SE: -0.05 ± 0.03 a.u., P = 0.035) and postmenopausal women (MD ± SE: -0.06 ± 0.03 a.u., P = 0.040). Premenopausal women reported significantly fewer menopause symptoms than peri- (MD ± SE: -6.58 ± 1.52 symptoms, P = 0.002) and postmenopausal participants (MD ± SE: -4.63 ± 1.52 symptoms, P = 0.044), while similarities between groups were observed for lifestyle factors including diet and physical activity (P>0.999).

CONCLUSIONS

Perimenopause may be the most opportune window for lifestyle intervention, as this group experienced the onset of unfavorable body composition and metabolic characteristics.

VIDEO SUMMARY

http://links.lww.com/MENO/A932.

High-Fat Breakfast Meal Replacement in Overweight and Obesity: Implications on Body Composition, Metabolic Markers, and Satiety

The purpose of this paper was to determine the effect of replacing breakfast with a high-fat drink on fat mass (FM), lean mass (LM), percent body fat (%BF), visceral fat (VAT), resting metabolic rate (RMR), fuel utilization (RER), blood lipids and satiety in overweight and obese adults. Healthy adults (n = 42; 21 Females; body mass index (BMI): 32.8 ± 4.6 kg·m-2) were randomized to control (CON; n = 21) or meal replacement (MRP; n = 22) groups. Body composition was measured using a four-compartment model; RMR and RER were assessed from indirect calorimetry. The MRP (70% fat) was consumed once daily for eight weeks. For males, there was no change (p > 0.05) in FM (mean difference (MD) = 0.41 ± 1.19 kg], %BF MD = 0.50 ± 1.09%, LM MD = -0.64 ± 1.79 kg, or VAT MD = -0.31 ± 1.36 cm for MRP versus CON. Similarly, no differences for females for FM MD = -0.73 ± 1.37 kg, %BF MD = -0.57 ± 1.26%, LM MD = 0.31 ± 1.37 kg, or VAT MD: -0.83 ± 1.2 cm. HDL was significantly reduced in the MRP group for females (adjusted mean change: -6.41 ± 4.44 units, p = 0.018). There was no effect on RMR or RER. Satiety increased in the afternoon for MRP (p = 0.021). Despite high fat, no negative impact on lipids resulted; increased satiety may be beneficial for controlling afternoon cravings, but does not affect body composition.

Measurement of mean subcutaneous fat thickness: eight standardised ultrasound sites compared to 216 randomly selected sites

Ultrasound (US) provides the most accurate technique for thickness measurements of subcutaneous adipose tissue (SAT) layers. This US method was recently standardised using eight sites to capture SAT patterning and allows distinguishing between fat and embedded fibrous structures. These eight sites chosen for fat patterning studies do not represent the mean SAT thickness measured all over the body that is necessary for determining subcutaneous fat mass. This was obtained by SAT measurements at 216 sites distributed randomly all over the body. Ten participants with BMI below 28.5kgm-2 and SAT means (from eight sites) ranging from 3 mm to 10 mm were selected. The means from eight sites overestimated the means obtained from 216 sites (i.e. 2160 US measurements in the ten participants); the calibration factor of 0.65 corrects this; standard deviation (SD) was 0.05, i.e. 8%. The SD of the calibration factor transforms linearly when estimating the error range of the whole body's SAT volume (body surface area times the calibrated mean SAT thickness). The SAT masses ranged from 3.2 to 12.4 kg in this group. The standard deviations resulting from solely the calibration factor uncertainty were ±0.3 and ±1.0 kg, respectively. For these examples, the SAT percentages were 4.9(±0.4)% and 13.3(±1.0)%.

Preperitoneal fat as a non-invasive marker of increased risk of severe non-alcoholic fatty liver disease in patients with type 2 diabetes

BACKGROUND AND AIM

Fat distribution may have prognostic value in the evaluation of non-alcoholic fatty liver disease. This study was conducted to evaluate associations of magnetic resonance imaging-measured abdominal fat areas with steatosis, steatohepatitis, and fibrosis, assessed histopathologically, in patients with type 2 diabetes.

METHODS

This prospective study included 66 patients with type 2 diabetes (12 males, 54 females, age 26-68 years), without chronic liver disease of other causes. Axial dual-echo magnetic resonance images were acquired. Visceral, subcutaneous, and preperitoneal fat areas were measured using Osirix software. Liver biopsy specimens were obtained from all patients and examined histopathologically to evaluate steatosis, steatohepatitis, and fibrosis. Linear (for steatosis) and logistic (for steatohepatitis and fibrosis) regression models were fitted for the outcomes. R2 was used as a measure of how much model variance the predictors explained and to compare different predictors of the same outcome.

RESULTS

Visceral and preperitoneal fat areas correlated well with histopathologically determined liver steatosis grade (both P = 0.004) and liver fibrosis (P = 0.008 and P = 0.037, respectively). All fat areas correlated well with steatohepatitis (P ≤ 0.002). Preperitoneal and visceral fat areas were the best predictors of steatohepatitis (R2 = 0.379) and fibrosis (R2 = 0.181), respectively.

CONCLUSIONS

Visceral fat area was the best predictor of fibrosis in patients with type 2 diabetes. Preperitoneal fat area was the best predictor of steatohepatitis and is a potential new non-invasive marker for use in the screening of these patients to detect more aggressive forms of non-alcoholic fatty liver disease.

Metabolic characterization of overweight and obese adults

OBJECTIVES

Traditional evaluations of metabolic health may overlook underlying dysfunction in individuals who show no signs of insulin resistance or dyslipidemia. The purpose of this study was to characterize metabolic health in overweight and obese adults using traditional and non-traditional cardiometabolic variables. A secondary purpose was to evaluate differences between overweight/obese and male/female cohorts, respectively.

METHODS

Forty-nine overweight and obese adults (Mean ± SD; Age = 35.0 ± 8.9 yrs; Body mass index = 33.6 ± 5.2 kg·m-2; Percent body fat [%fat] = 36.7 ± 7.9%) were characterized. Body composition (fat mass [FM], lean mass [LM], %fat) was calculated using a 4-compartment model; visceral adipose tissue (VAT) was quantified using B-mode ultrasound. Resting metabolic rate (RMR) and respiratory exchange ratio (RER) were evaluated using indirect calorimetry. Fasted blood and saliva samples were analyzed for total cholesterol (TC), high-density lipoproteins (HDL), low-density lipoproteins (LDL), triglycerides (TRG), glucose (GLUC), insulin, leptin, estradiol, and cortisol.

RESULTS

The prevalence of individuals with two or more cardiometabolic risk factors increased from 13%, using traditional risk factors (GLUC, TRG, HDL), to 80% when non-traditional metabolic factors (VAT, LM, RMR, RER, TC, LDL, HOMA-IR) were considered. Between overweight/obese, there were no significant differences in %fat (p = 0.152), VAT (p = 0.959), RER (p = 0.493), lipids/GLUC (p > 0.05), insulin (p = 0.143), leptin (p = 0.053), or cortisol (p = 0.063); obese had higher FM, LM, RMR, and estradiol (p < 0.01). Males had greater LM, RMR, and TRG (p < 0.01); females had greater %fat, and leptin (p < 0.001). There were no significant sex differences in RER, estradiol, insulin, or cortisol (p > 0.05).

CONCLUSIONS

Evaluating metabolic health beyond BMI and traditional cardiometabolic risk factors can give significant insights into metabolic status. Due to high variability in metabolic health in overweight and obese adults and inherent sex differences, implementation of body composition and visceral fat measures in the clinical setting can improve early identification and approaches to disease prevention.