The objective of this study was to examine the influence of persistence of the MetS (MetS) and its individual components over a 3-year period on carotid intima media thickness (CIMT) in overweight Latino children.
Ninety-seven healthy male and female overweight Latino children (mean age at baseline: 11.0±1.8 yrs) were assessed for MetS on four annual evaluations and classified according to the persistence of MetS: NEVER (0 annual visits with the MetS, n=53), INTERMITTENT (1 or 2 visits with the MetS, n=28), and PERSISTENT (3 or 4 visits with the MetS, n=16). CIMT was measured with high-resolution B-mode ultrasound (7.9±0.7 months after the most recent MetS assessment; mean age: 14.6±1.8 yr).
PERSISTENT MetS was associated with significantly higher CIMT (0.647mm±0.018 compared to (0.600mm±0.007 in those who NEVER had MetS, p<0.01). This difference remained significant after controlling for gender, baseline age, total fat mass, total lean tissue mass and insulin sensitivity. PERSISTENT high waist circumference and PERSISTENT high blood pressure were also significantly associated with higher mean CIMT, but these differences were no longer significant after controlling for total fat and lean tissue mass. Baseline systolic blood pressure and 2-hour glucose were significantly related to CIMT independent of all other MetS components (p<0.05).
Persistence of the MetS over a 3-year period was uniquely associated with increased CIMT during childhood. Children with hypertension, persistent abdominal adiposity and impaired glucose tolerance may also be at higher risk for elevated CIMT.
CIMT; obesity; children; MetS
To assess carotid artery intima media thickness (CIMT) change over two years in overweight Latino adolescents and examine its relationship to cardiometabolic risk.
72 healthy overweight male and female Latino adolescents (mean age: 14.5±1.7 yrs; mean BMI: 31.5±6.9 kg/m2) were evaluated at baseline and 2 years later for: CIMT by high resolution B-mode ultrasound, the metabolic syndrome and its features, body composition by DEXA and MRI, and glucose/insulin measures by fasting blood, and oral and intravenous glucose tolerance tests.
Baseline CIMT did not differ from 2-year follow-up; however 38 participants increased CIMT (0.017±0.003mm; +2.8%) and 34 decreased (-0.019±0.002mm; −3.1%). ANCOVA analyses showed that participants with CIMT progression had higher baseline LDL-cholesterol and total cholesterol (91.3±3.4 and 150.3±3.9mg/dL) compared with those with CIMT regression (78.1±3.6 and 135.6±4.2mg/dL, p<0.05), independent of sex, baseline CIMT, age, and height. In multivariate regression, LDL-cholesterol was the sole predictor of CIMT progression, but the effect was small (odds of CIMT progression increased by 3% for each 1 mg/dL higher baseline LDL-cholesterol [95% CI: 1.004-1.006, p=0.03].
These results indicate a high variability in the magnitude of CIMT change in growing overweight Latino youth and support the use of LDL-cholesterol to assess sub-clinical atherosclerosis risk in this population.
Obesity; Cardiovascular disease risk; Ultrasound imaging
Purpose of review
To summarize recent findings that have examined dietary, genetic and gene–diet interactions that contribute to fat accumulation in the liver during growth and development, with particular focus on contributions relating to dietary carbohydrate and sugar consumption. In addition, this review highlights how some of these contributions to liver fat vary across the population in terms of ethnic-specific effects.
Dietary carbohydrate, and especially sugars contribute to increased liver fat accumulation due to the lipogenic potential of fructose during liver metabolism. In addition, recent genome-wide studies have identified several polymorphisms that contribute to increased liver fat accumulation, with some of these genes relating to dietary carbohydrate and sugar consumption. In particular, the patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene, which is highly prevalent in Hispanics, contributes to excessive liver fat beginning at a young age, especially in the context of high sugar consumption.
Dietary sugar contributes to liver fat accumulation, with this being explained by de-novo lipogenesis from fructose in the liver. Certain genetic factors, including PNPLA3, glucokinase regulatory protein and APOC3 contribute to increased liver fat accumulation, with these effects being manifested at an early age. Hispanics in particular are at elevated risk for liver fat accumulation because of the higher frequency of genetic variants such as PNPLA3 and glucokinase regulatory protein as well as an interaction between the PNPLA3 and dietary sugar.
fatty liver; genetic; obesity; sugar
Characteristics associated with low socioeconomic status neighborhoods may put children at risk for unique chronic stressors that affect cortisol levels. This research sought to explore whether neighborhood stressor exposure affected serum cortisol levels among children.
A total of 148 African and European American children with an average age of 8.28 years participated in a longitudinal study evaluating ethnic differences in body composition and disease risk. A total of five waves of data were included in analyses. Mixed modeling was used to explore neighborhood stressors, which was a composite index of five items for zip code level poverty and physical disorder, and serum cortisol outcomes for the full sample, by race/ethnicity and gender. Adjustments were made for individual level correlates age, pubertal status, gender, and total fat mass.
Neighborhood disorder was predictive of lower serum cortisol levels among African American children (p<.05), such that higher neighborhood stressor exposure resulted in lower serum cortisol over time compared to individuals in socially ordered neighborhoods. Neighborhood disorder was marginally significant and predictive of higher serum cortisol among European American children (p <.10). Transition to a higher pubertal status, nested in age was also predictive of lower serum cortisol levels (p<.01) among European American children.
Children who are exposed to negative socioenviornmental climates over time are more likely to have altered serum cortisol levels. This may be an adaptive mechanism to cope with stress; however, disrupted cortisol levels may have negative effects on general physical and mental health.
Neighborhood; cortisol; children
To examine whether persistent Metabolic syndrome (MetS) was associated with risk for type 2 diabetes in overweight Latino children.
73 participants (age 11.0±1.7 years) from a longitudinal study were classified as: NEVER (negative for MetS at all 3 visits); INTERMITTENT (positive for MetS at 1 or 2 visits); or PERSISTENT (positive for MetS at all 3 visits). Measures included DEXA, MRI, 2-h oral glucose tolerance test, and frequently sampled intravenous glucose tolerance test.
The PERSISTENT group had a faster rate of fat mass gain than the NEVER group (20% vs. 15% gain of baseline value, p<0.05 for time*group interaction (time= visit)). Independent of body composition, the PERSISTENT group increased by 70% in insulin incremental area under the curve, and the other groups decreased (p<0.05 for time*group interaction). Despite no time*group interactions for insulin sensitivity, acute insulin response, or disposition index, the PERSISTENT maintained 43% lower insulin sensitivity (p<0.01) and by visit 2 had a 25% lower disposition index (p<0.05) compared with the NEVER group.
Participants with persistent MetS had accelerated fat gain, increasing insulin response to oral glucose, and lower insulin sensitivity and beta cell function, indicators of progressively greater risk for type 2 diabetes.
longitudinal; beta cell function; insulin sensitivity; insulin resistance; insulin IAUC
This study assessed the changes in time spent in moderate to vigorous physical activity (MVPA) on fat depots, insulin action, and inflammation. Longitudinal data were generated from 66 Hispanic adolescents (15.6±1.1 yr; BMI percentile 97.1±3.0) who participated in a 16-wk nutrition or nutrition+exercise intervention. There were no effects of the intervention on PA, but there were inter-individual changes in PA. For purposes of this analysis, all intervention groups were combined to assess how changes in PA during 16 wk affected changes in adiposity, insulin action, and markers of inflammation. MVPA was assessed by 7-day accelerometry, total body fat via DXA, liver fat by MRI, and insulin, glucose and HOMA-IR via a fasting blood draw. A repeated measures ANCOVA was used to assess the effect of MVPA on fat depots, insulin action, and inflammatory markers. Sixty-two percent of participants increased MVPA (mean increase, 19.7±16.5 min/day) and 38% decreased MVPA (mean decrease, 10.7±10.1 min/day). Those who increased MVPA by as little as 20 min per day over 16 wk, compared to those who decreased MVPA, had significant reductions in liver fat (−13% vs. +3%; P=0.01), leptin levels (−18% vs. +4%; P=0.02), and fasting insulin (−23% vs. +5%; P=0.05). These findings indicate that a modest increase in MVPA can improve metabolic health in sedentary overweight Hispanic adolescents.
Moderate-to-Vigorous Physical Activity; Obesity
Purpose. It is unclear whether sociocultural and socioeconomic factors are directly linked to type 2 diabetes risk in overweight/obese ethnic minority children and adolescents. This study examines the relationships between sociocultural orientation, household social position, and type 2 diabetes risk in overweight/obese African-American (n = 43) and Latino-American (n = 113) children and adolescents. Methods. Sociocultural orientation was assessed using the Acculturation, Habits, and Interests Multicultural Scale for Adolescents (AHIMSA) questionnaire. Household social position was calculated using the Hollingshead Two-Factor Index of Social Position. Insulin sensitivity (SI), acute insulin response (AIRG) and disposition index (DI) were derived from a frequently sampled intravenous glucose tolerance test (FSIGT). The relationships between AHIMSA subscales (i.e., integration, assimilation, separation, and marginalization), household social position and FSIGT parameters were assessed using multiple linear regression. Results. For African-Americans, integration (integrating their family's culture with those of mainstream white-American culture) was positively associated with AIRG (β = 0.27 ± 0.09, r = 0.48, P < 0.01) and DI (β = 0.28 ± 0.09, r = 0.55, P < 0.01). For Latino-Americans, household social position was inversely associated with AIRG (β = −0.010 ± 0.004, r = −0.19, P = 0.02) and DI (β = −20.44 ± 7.50, r = −0.27, P < 0.01). Conclusions. Sociocultural orientation and household social position play distinct and opposing roles in shaping type 2 diabetes risk in African-American and Latino-American children and adolescents.
To determine, in an overweight pediatric population, if an A1C-determined high risk, pre-diabetic state (A1C ≥6.0–6.4%) is associated with decreased insulin sensitivity and β-cell dysfunction, known factors in the pathogenesis of type 2 diabetes.
We divided 206 healthy overweight Latino adolescents (124 male/82 female; age 13.1±2.0 yrs), into 2 groups: Lower Risk (LR, n=179) had A1C <6.0%; and High Risk (HR, n=27) had A1C 6.0–6.4%. Measures included A1C; OGTT fasting & 2-hr glucose and insulin; insulin sensitivity (SI), acute insulin response (AIR), and disposition index (DI, an index of β-cell function) by frequently sampled FSIVGTT with minimal modeling. Body fat was determined by DEXA.
Compared with the LR group, the HR group had 21% lower SI (1.21±0.06 vs. 1.54±0.13, p<0.05), 30% lower AIR (928±102 vs. 1342±56, p<0.01), and 31% lower DI (1390±146 vs. 2023±83, p=0.001) after adjusting for age and total percent body fat.
These data provide clear evidence of greater impairment of β-cell function in those overweight Latino children with A1C 6.0–6.4%, and would thereby support the adoption of the International Expert Committee A1C-determined definition of high risk state for overweight children at risk for type 2 diabetes.
Obesity; Prediabetes; A1c; beta cell function; insulin sensitivity
To assess the effects of a maintenance program (monthly newsletters versus monthly group classes and telephone behavioral sessions) on obesity and metabolic disease risk at one year in overweight minority adolescents.
After a 4-month nutrition and strength training intervention, 53 overweight Latino and African American adolescents (15.4 ±1.1 yrs) were randomized into one of two maintenance groups for 8 months: monthly newsletters (n=23) or group classes (n=30; monthly classes + individualized behavioral telephone sessions). The following outcomes were measured at months 4 (immediately following the intense intervention) and month 12: height, weight, blood pressure, body composition via BodPod™, lipids and glucose/insulin indices via frequently sampled intravenous glucose tolerance test (FSIVGTT).
There were no significant group by time interactions for any of the health outcomes. There were significant time effects in several outcomes for both groups from month 4 to 12: bench press and leg press decreased by 5% and 14% (p=0.004 & p=0.01), fasting insulin and acute insulin response decreased by 26% and 16% (p<0.001 & p=0.046); while HDL cholesterol and insulin sensitivity improved by 5% and 14% (p=0.042 and p=0.039).
Newsletters as opposed to group classes may suffice as follow-up maintenance programs to decrease type 2 diabetes and cardiovascular risk in overweight minority adolescents.
Maintenance; Obesity Intervention; Type 2 Diabetes; Cardiovascular risk factors; Latino and African American adolescents
A genome-wide study of adults identified a variant of PNPLA3 (rs738409) associated with ∼twofold higher liver fat. The purpose of this study was to examine the influence of PNPLA3 genotype on liver fat and other related metabolic outcomes in obese Hispanic children and adolescents.
RESEARCH DESIGN AND METHODS
Three hundred and twenty-seven Hispanics aged 8–18 years were genotyped for rs738409. One hundred and eighty-eight subjects had measures of visceral (VAT) and subcutaneous (SAT) adipose tissue volume and hepatic (HFF) and pancreatic (PFF) fat fraction by magnetic resonance imaging. One hundred and thirty-nine subjects did not have HFF measures but had extensive measures of insulin sensitivity and fasting lipids.
Liver fat in GG subjects was 1.7 and 2.4 times higher than GC and CC (11.1 ± 0.8% in GG vs. 6.6 ± 0.7% in GC and 4.7 ± 0.9% in CC; P < 0.0001), and this effect was observed even in the youngest children (8–10 years of age). The variant was not associated with VAT, SAT, PFF, or insulin sensitivity or other glucose/insulin indexes. However, Hispanic children carrying the GG genotype had significantly lower HDL cholesterol (40.9 ± 10.9 in CC vs. 37.0 ± 8.3 in CG vs. 35.7 ± 7.4 in GG; P = 0.03) and a tendency toward lower free fatty acid levels (P = 0.06).
These results provide new evidence that the effect of the PNPLA3 variant is apparent in Hispanic children and adolescents, is unique to fat deposition in liver as compared with other ectopic depots examined, and is associated with lower HDL cholesterol.
To develop a magnetic resonance imaging (MRI)-based approach for quantifying absolute fat mass in organs, muscles, and adipose tissues, and to validate its accuracy against reference chemical analysis (CA).
Chemical-shift imaging can accurately decompose water and fat signals from the acquired MRI data. A proton density fat fraction (PDFF) can be computed from the separated images, and reflects the relative fat content on a voxel-by-voxel basis. The PDFF is mathematically closely related to the fat mass fraction and can be converted to absolute fat mass in grams by multiplying by the voxel volume and the mass density of fat. In this validation study, 97 freshly excised and unique samples from four pigs, comprising of organs, muscles, and adipose and lean tissues were imaged by MRI and then analyzed independently by CA. Linear regression was used to assess correlation, agreement, and measurement differences between MRI and CA.
Considering all 97 samples, a strong correlation and agreement was obtained between MRI and CA-derived fat mass (slope = 1.01, intercept = 1.99g, r2 = 0.98, p < 0.01). The mean difference d between MRI and CA was 2.17±3.40g. MRI did not exhibit any tendency to under or overestimate CA (p > 0.05). When considering samples from each pig separately, the results were (slope = 1.05, intercept = 1.11g, r2 = 0.98, d = 2.66±4.36g), (slope = 0.99, intercept = 2.33g, r2 = 0.99, d = 1.88±2.68g), (slope = 1.07, intercept = 1.52g, r2 = 0.96, d = 2.73±2.50g), and (slope=0.92, intercept=2.84g, r2 = 0.97, d = 1.18±3.90g), respectively.
Chemical-shift MRI and PDFF provides an accurate means of determining absolute fat mass in organs, muscles, and adipose and lean tissues.
fat quantification; body fat composition; pigs; validation; MRI
The purpose of this study was to examine interrelationships between IGF-I, IGF binding proteins (IGFBPs), and adiposity in 49 African American and 77 Latino obese adolescents (15.3±0.1 and 15.4±0.2 yr; body mass index: 33.0±0.7 and 35.0±1.0 kg/m2, respectively). Immunoradiometric assays were used to measure IGF-I, IGFBP-I, and IGFBP-3. Total fat and soft lean tissue were measured by DEXA and visceral adipose tissue (VAT), subcutaneous abdominal adipose tissue (SAAT), and hepatic fat fraction (HFF) were measured by MRI. IGF-I levels were 23.1% higher and IGFBP-I were 40.4% higher in African Americans compared to Latinos after adjustment for total lean and total fat mass. IGF-I and IGFBP-I were inversely correlated with BMI, total fat mass, VAT, and HFF (r = −0.20 to −0.33, p<0.05) while IGFBP-I was inversely correlated with SAAT (r = −0.22, p<0.05). These relationships did not differ by ethnicity, however, the relationship between IGF-I and SAAT, as well as IGFBP-I and HFF, differed by ethnicity. Predicted mean IGF-I levels were 30.7% higher for African Americans at the 75th compared to 25th percentile of SAAT and only 11.7% higher for Latinos. Predicted mean IGFBP-I levels were 158% higher for African Americans at the 25th compared to the 75th percentile of HFF while IGFBP-I levels were 1.7% higher for Latinos at the 75th compared to the 25th percentile. These results demonstrate that the relationship between IGF-I and SAAT as well as IGFBP-I and HFF are different in African American and Latino adolescents and may contribute to the higher IGF-I levels in African Americans.
Insulin-Like Growth Factors; Insulin-Like Growth Factor Binding Proteins; Ethnicity Differences; Obesity; Minorities
To examine in obese young adults the influence of ethnicity and subcutaneous adipose tissue (SAT) inflammation on hepatic fat fraction (HFF), visceral adipose tissue (VAT) deposition, insulin sensitivity (SI), β-cell function, and SAT gene expression.
RESEARCH DESIGN AND METHODS
SAT biopsies were obtained from 36 obese young adults (20 Hispanics, 16 African Americans) to measure crown-like structures (CLS), reflecting SAT inflammation. SAT, VAT, and HFF were measured by magnetic resonance imaging, and SI and β-cell function (disposition index [DI]) were measured by intravenous glucose tolerance test. SAT gene expression was assessed using Illumina microarrays.
Participants with CLS in SAT (n = 16) were similar to those without CLS in terms of ethnicity, sex, and total body fat. Individuals with CLS had greater VAT (3.7 ± 1.3 vs. 2.6 ± 1.6 L; P = 0.04), HFF (9.9 ± 7.3 vs. 5.8 ± 4.4%; P = 0.03), tumor necrosis factor-α (20.8 ± 4.8 vs. 16.2 ± 5.8 pg/mL; P = 0.01), fasting insulin (20.9 ± 10.6 vs. 9.7 ± 6.6 mU/mL; P < 0.001) and glucose (94.4 ± 9.3 vs. 86.8 ± 5.3 mg/dL; P = 0.005), and lower DI (1,559 ± 984 vs. 2,024 ± 829 ×10−4 min−1; P = 0.03). Individuals with CLS in SAT exhibited upregulation of matrix metalloproteinase-9 and monocyte antigen CD14 genes, as well as several other genes belonging to the nuclear factor-κB (NF-κB) stress pathway.
Adipose tissue inflammation was equally distributed between sexes and ethnicities. It was associated with partitioning of fat toward VAT and the liver and altered β-cell function, independent of total adiposity. Several genes belonging to the NF-κB stress pathway were upregulated, suggesting stimulation of proinflammatory mediators.
This study aimed to test the effects of a circuit training (CT; aerobic + strength training) program, with and without motivational interviewing (MI) behavioral therapy, on reducing adiposity and type 2 diabetes risk factors in Latina teenagers.
Thirty-eight Latina adolescents (15.8 ± 1.1 yr) who are overweight/obese were randomly assigned to control (C; n = 12), CT (n = 14), or CT + MI (n = 12). The CT classes were held twice a week (60–90 min) for 16 wk. The CT + MI group also received individual or group MI sessions every other week. The following were measured before and after intervention: strength by one-repetition maximum; cardiorespiratory fitness (V̇O2max) by submaximal treadmill test; physical activity by accelerometry; dietary intake by records; height, weight, waist circumference; total body composition by dual-energy x-ray absorptiometry; visceral adipose tissue, subcutaneous adipose tissue, and hepatic fat fraction by magnetic resonance imaging; and glucose/insulin indices by fasting blood draw. Across-intervention group effects were tested using repeated-measures ANOVA with post hoc pairwise comparisons.
CT and CT + MI participants, compared with controls, significantly increased fitness (+16% and +15% vs −6%, P = 0.03) and leg press (+40% vs +20%, P = 0.007). Compared with controls, CT participants also decreased waist circumference (−3% vs +3%; P < 0.001), subcutaneous adipose tissue (−10% vs 8%, P = 0.04), visceral adipose tissue (−10% vs +6%, P = 0.05), fasting insulin (−24% vs +6%, P = 0.03), and insulin resistance (−21% vs −4%, P = 0.05).
CT may be an effective starter program to reduce fat depots and improve insulin resistance in Latino youth who are overweight/obese, whereas the additional MI therapy showed no additive effect on these health outcomes.
VISCERAL FAT; CIRCUIT TRAINING INTERVENTION; OVERWEIGHT LATINA ADOLESCENTS; FASTING INSULIN AND INSULIN RESISTANCE; MOTIVATIONAL INTERVIEWING
The purpose of this study was to examine the relationship between changes in insulin sensitivity and subsequent changes in fat mass in obese Hispanic children over 3 consecutive years.
RESEARCH DESIGN AND METHODS
In a longitudinal research design, insulin sensitivity (Si) of 96 research participants was determined at baseline and 1 year later. Body adiposity was assessed at four assessments.
The change in Si during the first year of the study was a significant predictor of further fat mass development (P < 0.05). Considering different directions of Si change, Si was a strong predictor for further fat mass development only in the group that decreased their Si (P < 0.05).
The results show that the direction of change in insulin sensitivity at an early age is an important independent predictor for further fat mass development and emphasize the importance of insulin sensitivity as a primary target for long-term obesity prevention, as well as the significance of early age intervention.
OBJECTIVE—To examine changes in risk factors in overweight and obese Hispanic children at high risk of developing type 2 diabetes.
RESEARCH DESIGN AND METHODS—We recruited 128 overweight/obese Hispanic children with a family history of type 2 diabetes primarily from clinics in East Los Angeles. Children were evaluated annually for 4 years with an oral glucose tolerance test, applying American Diabetes Association criteria to define diabetes and pre-diabetes. Insulin sensitivity (Si), acute insulin response (AIR) to glucose, and β-cell function (BCF) were determined from frequently sampled intravenous glucose tolerance tests, and total body fat by dual-energy X-ray absorptiometry and intra-abdominal and subcutaneous abdominal adipose tissue (IAAT and SAAT) by magnetic resonance imaging were assessed in years 1, 2, and 4.
RESULTS—No subjects developed type 2 diabetes, 40% never had pre-diabetes, 47% had intermittent pre-diabetes with no clear pattern over time, and 13% had persistent pre-diabetes. At baseline, those with persistent pre-diabetes had lower BCF and higher IAAT. In repeated measures, Si deteriorated regardless of pre-diabetes, and there was a significant effect of pre-diabetes on AIR (42% lower in pre-diabetes; P = 0.01) and disposition index (34% lower in pre-diabetes; P = 0.021) and a significant interaction of pre-diabetes and time on IAAT (greater increase over time in those with pre-diabetes; P = 0.034).
CONCLUSIONS—In this group of Hispanic children at high risk of type 2 diabetes, 1) pre-diabetes is highly variable from year to year; 2) the prevalence of persistent pre-diabetes over 3 years is 13%; and 3) children with persistent pre-diabetes have lower BCF, due to a lower AIR, and increasing visceral fat over time.
Interventions for obese adolescents in real-world, clinical settings need to be evaluated because most weight management care occurs in this context.
To determine whether a lifestyle intervention that includes motivational interviewing and cognitive behavioural therapy (Health Initiatives Program [HIP]) leads to weight management that is superior to a similar lifestyle intervention (Youth Lifestyle Program [YLP]) that does not include these techniques; and to determine whether the HIP and YLP interventions are superior to a wait list control (WLC) group.
Obese adolescents were randomly assigned to a YLP (n=15), HIP (n=17) or WLC (n=14) group. The YLP and HIP were 16-session, one-on-one interventions. The primary outcome was the percentage change of body mass index z-score.
Completers-only analyses revealed 3.9% (YLP) and 6.5% (HIP) decreases in the percentage change of body mass index z-score compared with a 0.8% (WLC) increase (P<0.001). Levels of attrition did not differ among groups, but were relatively high (approximately 20% to 40%).
Lifestyle interventions delivered in a real-world, clinical setting led to short-term improvements in the obesity status of adolescents.
Adolescent; Intervention; Obesity
As the prevalence of obesity continues to rise, rapid and accurate tools for assessing abdominal body and organ fat quantity and distribution are critically needed to assist researchers investigating therapeutic and preventive measures against obesity and its comorbidities. Magnetic resonance imaging (MRI) is the most promising modality to address such need. It is non-invasive, utilizes no ionizing radiation, provides unmatched 3D visualization, is repeatable, and is applicable to subject cohorts of all ages. This article is aimed to provide the reader with an overview of current and state-of-the-art techniques in MRI and associated image analysis methods for fat quantification. The principles underlying traditional approaches such as T1-weighted imaging and magnetic resonance spectroscopy as well as more modern chemical-shift imaging techniques are discussed and compared. The benefits of contiguous 3D acquisitions over 2D multi-slice approaches are highlighted. Typical post-processing procedures for extracting adipose tissue depot volumes and percent organ fat content from abdominal MRI data sets are explained. Furthermore, the advantages and disadvantages of each MRI approach with respect to imaging parameters, spatial resolution, subject motion, scan time, and appropriate fat quantitative endpoints are also provided. Practical considerations in implementing these methods are also presented.
MRI; fat imaging; organ fat; body fat quantification; adipose tissue
The purpose of this study was to examine ethnic differences in the metabolic responses to a 16-week intervention designed to improve insulin sensitivity (SI), adiposity, and inflammation in obese African-American and Latino adolescents. A total of 100 participants (African Americans: n = 48, Latino: n = 52; age: 15.4 ± 1.1 years, BMI percentile: 97.3 ± 3.3) were randomly assigned to interventions: control (C; n = 30), nutrition (N; n = 39, 1×/week focused on decreasing sugar and increasing fiber intake), or nutrition + strength training (N+ST; n = 31, 2×/week). The following were measured at pre- and postintervention: strength, dietary intake, body composition (dual-energy X-ray absorptiometry/magnetic resonance imaging) and glucose/insulin indexes (oral glucose tolerance test (OGTT)/intravenous glucose tolerance test (IVGTT)) and inflammatory markers. Overall, N compared to C and N+ST reported significant improvements in SI (+16.5% vs. −32.3% vs. −6.9% respectively, P < 0.01) and disposition index (DI: +15.5% vs. −14.2% vs. −13.7% respectively, P < 0.01). N+ST compared to C and N reported significant reductions in hepatic fat fraction (HFF: −27.3% vs. −4.3% vs. 0% respectively, P < 0.01). Compared to N, N+ST reported reductions in plasminogen activator inhibitor-1 (PAI-1) (−38.3% vs. +1.0%, P < 0.01) and resistin (−18.7% vs. +11.3%, P = 0.02). There were no intervention effects for all other measures of adiposity or inflammation. Significant intervention by ethnicity interactions were found for African Americans in the N group who reported increases in total fat mass, 2-h glucose and glucose incremental areas under the curve (IAUC) compared to Latinos (P’s < 0.05). These interventions yielded differential effects with N reporting favorable improvements in SI and DI and N+ST reporting marked reductions in HFF and inflammation. Both ethnic groups had significant improvements in metabolic health; however some improvements were not seen in African Americans.
To examine the relationship of fasting indicators of insulin sensitivity with a more invasive measure of insulin sensitivity (frequently sampled intravenous glucose tolerance test [FSIVGTT]) and the effect of Tanner stage and ethnicity on that relationship.
RESEARCH DESIGN AND METHODS
Data were analyzed from 149 overweight girls (97 Hispanic and 52 African American) who were either in the early stages of maturation defined by Tanner stages 1 or 2 (52 Hispanic and 18 African American) or in the later stages of maturation defined by Tanner stages 4 and 5 (45 Hispanic and 34 African American). Fasting indicators of insulin sensitivity (IS) included fasting insulin and glucose and the homeostasis model assessment of insulin resistance (HOMA-IR). IS was derived from an FSIVGTT with minimal modeling.
In Tanner stages 1 and 2, all fasting indicators were significantly associated with IS: (fasting insulin: r = −0.67, P < 0.01; HOMA: r = −0.66, P < 0.01) with no significant influence of ethnicity on these relationships. In Tanner stages 4 and 5, however, all fasting indicators were associated with IS in African American girls (fasting insulin: r = −0.55, P < 0.01; HOMA: r = −0.47, P < 0.01), but none of the indicators were significantly associated with IS in Hispanic girls.
Fasting indicators were reflective of IS for girls in Tanner stages 1 and 2, regardless of ethnicity and may provide a clinical measure of future risk for type 2 diabetes. In the latter stages of maturation, however, more invasive measures are warranted to adequately determine IS in clinical practice.
To examine the prevalence of the metabolic syndrome in overweight Hispanic youth according to three published pediatric definitions. Furthermore, the relationship of each definition to directly measured insulin resistance was examined.
Secondary data analysis of 218 overweight Hispanic youth with a family history of type 2 diabetes. The metabolic syndrome was defined as ≥ three of the following; elevated triglycerides, low HDL-cholesterol, elevated blood pressure, abdominal obesity, and hyperglycemia. The cut-points were derived from updated definitions of Cook et al(1), Cruz et al(2), and Weiss et al(3). Insulin sensitivity was determined via the insulin-modified frequently sampled intravenous glucose tolerance test.
Prevalence of the metabolic syndrome ranged from 25.7% to 39% with moderate to substantial agreement between definitions (kappa=0.52−0.7). Regardless of definition, an inverse relationship between metabolic risk and insulin sensitivity was noted such that children with the metabolic syndrome had 51−60% lower insulin sensitivity compared to those without any risk factors (p≤0.001 for all definitions).
The metabolic syndrome is prevalent in overweight Hispanic youth and may provide pediatricians with additional clinical insight for identifying the most metabolically at-risk children. Working towards a uniform and practical definition of the metabolic syndrome may improve its clinical implementation.
Insulin resistance; Obesity; Child; Latino; Metabolic syndrome
To examine changes in insulin sensitivity (SI), compensatory acute insulin response (AIR) and β-cell function/disposition index (DI) across puberty in overweight Latino boys and girls.
253 Latino children followed annually for up to 5 years. Longitudinal modeling was used to examine changes in SI, AIR, DI and fasting and 2-hr glucose and insulin across Tanner stage.
In boys, SI decreased in early puberty with a recovery by late puberty. The compensatory increase in AIR was appropriate in early maturation, but after Tanner 3, AIR declined by more than that predicted from the recovery in SI. For girls, SI decreased in early puberty and across all stages of maturation. In early maturation, there was an appropriate compensatory increase in AIR, but after Tanner 3 AIR decreased. Thus, DI deteriorated across puberty in boys and girls.
In overweight Hispanic youth, compensatory changes in insulin secretion fails after Tanner 3 in both sexes, indicating β-cell deterioration during this critical period of development, thus increasing risk for Type 2 diabetes.
Insulin resistance; Beta cell function; puberty; longitudinal; Latino
Visceral adipose tissue (VAT) and hepatic fat are associated with insulin resistance and vary by sex and ethnicity. Recently, pancreatic fat fraction (PFF) has also been linked with increasing obesity. Our aim was to assess ethnic and sex differences in PFF and its relationship to other fat depots, circulating free fatty acids (FFA), insulin secretion and sensitivity, and inflammation in obese adolescents and young adults.
RESEARCH DESIGN AND METHODS
We examined 138 (40 males, 98 females) obese Hispanics and African Americans (13–25 years). Subcutaneous adipose tissue and VAT volumes, hepatic fat fraction (HFF), and PFF were determined by magnetic resonance imaging. Insulin sensitivity and β-cell function were assessed during an intravenous glucose tolerance test.
Hispanics had higher PFF than African Americans (7.3 ± 3.8 vs. 6.2 ± 2.6%, P = 0.03); this ethnic difference was higher in young adults compared with children and adolescents (ethnicity × age: P = 0.01). Males had higher PFF than females (P < 0.0001). PFF was positively correlated with VAT (r = 0.45, P < 0.0001), HFF (r = 0.29, P < 0.0001), and FFA (r = 0.32, P = 0.001). PFF positively correlated with inflammatory markers but lost significance when adjusted for VAT. In multiple stepwise regression analysis, VAT and FFA were the best predictors of PFF (adjusted R2 = 0.40). There were no significant correlations between PFF and markers of insulin sensitivity or β-cell function.
PFF is higher in Hispanics than African Americans, and this difference increases with age. In young obese individuals, PFF is related to VAT, HFF, and circulating FFA, thus possibly contributing to their increased risk for type 2 diabetes and related metabolic disorders.
Intramyocellular lipid (IMCL) has been inversely associated with insulin sensitivity in some, but not all, studies. This study utilized fast, high-resolution, magnetic resonance spectroscopic imaging (MRSI) to: investigate relationships between muscle lipids (IMCL and extramyocellular lipid (EMCL)) and insulin sensitivity in muscles of varying oxidative capacity, explore ethnic differences in these relationships, and determine whether a eucaloric, low-fat dietary intervention would reduce IMCL and increase insulin sensitivity. Subjects were 30 healthy, African-American (AA; n=14) and European-American (EA; n=16) males, BMI 26.49 (±5.57) kg/m2, age 21.80 (±7.84) yrs. Soleus and tibialis anterior muscle lipids were quantified using MRSI. Insulin sensitivity was assessed via intravenous glucose tolerance test. A 2-week, eucaloric, low-fat diet intervention was conducted in a sub-group (n=12) subjects with assessments at baseline and post-intervention. Neither IMCL nor EMCL levels differed between ethnicities. In the total group, and within EA (but not AA), both tibialis anterior IMCL and EMCL were inversely associated with insulin sensitivity (P<0.05 for both); soleus muscle lipids were not associated with insulin sensitivity. Soleus, but not tibialis anterior, IMCL declined in both ethnic groups (average 25.3%; p<0.01) following dietary intervention; insulin sensitivity was unchanged. Results suggest that an association of muscle lipids with insulin sensitivity may be influenced by the oxidative capacity of the muscle group studied and may vary with ethnicity.
Muscle lipids; intramyocellular lipid; MRSI; ethnicity; insulin sensitivity