Sex-associated differences in free fatty acid flux of obese adolescents

CONTEXT

In obesity, increases in free fatty acid (FFA) flux can predict development of insulin resistance. Adult women release more FFA relative to resting energy expenditure (REE) and have greater FFA clearance rates than men. In adolescents, it is unknown whether sex differences in FFA flux occur.

OBJECTIVE

Our objective was to determine the associations of sex, REE, and body composition with FFA kinetics in obese adolescents.

PARTICIPANTS

Participants were from a convenience sample of 112 non-Hispanic white and black adolescents (31% male; age range, 12-18 years; body mass index SD score range, 1.6-3.1) studied before initiating obesity treatment.

MAIN OUTCOME MEASURES

Glucose, insulin, and FFA were measured during insulin-modified frequently sampled iv glucose tolerance tests. Minimal models for glucose and FFA calculated insulin sensitivity index (SI) and FFA kinetics, including maximum (l0 + l2) and insulin-suppressed (l2) lipolysis rates, clearance rate constant (cf), and insulin concentration for 50% lipolysis suppression (ED50). Relationships of FFA measures to sex, REE, fat mass (FM), lean body mass (LBM) and visceral adipose tissue (VAT) were examined.

RESULTS

In models accounting for age, race, pubertal status, height, FM, and LBM, we found sex, pubertal status, age, and REE independently contributed to the prediction of l2 and l0 + l2 (P < .05). Sex and REE independently predicted ED50 (P < .05). Sex, FM/VAT, and LBM were independent predictors of cf. Girls had greater l2, l0 + l2 and ED50 (P < .05, adjusted for REE) and greater cf (P < .05, adjusted for FM or VAT) than boys.

CONCLUSION

Independent of the effects of REE and FM, FFA kinetics differ significantly in obese adolescent girls and boys, suggesting greater FFA flux among girls.

Effects of metformin on body weight and body composition in obese insulin-resistant children: a randomized clinical trial

OBJECTIVE

Metformin can decrease adiposity and ameliorate obesity-related comorbid conditions, including abnormalities in glucose homeostasis in adolescents, but there are few data evaluating the efficacy of metformin among younger children. Our objective was to determine whether metformin treatment causes weight loss and improves obesity-related comorbidities in obese children, who are insulin-resistant.

RESEARCH DESIGN AND METHODS

This study was a randomized double-blind placebo-controlled trial consisting of 100 severely obese (mean BMI 34.6 ± 6.6 kg/m(2)) insulin-resistant children aged 6-12 years, randomized to 1,000 mg metformin (n = 53) or placebo (n = 47) twice daily for 6 months, followed by open-label metformin treatment for 6 months. All children and their parents participated in a monthly dietitian-administered weight-reduction program.

RESULTS

Eighty-five percent completed the 6-month randomized phase. Children prescribed metformin had significantly greater decreases in BMI (difference -1.09 kg/m(2), CI -1.87 to -0.31, P = 0.006), body weight (difference -3.38 kg, CI -5.2 to -1.57, P < 0.001), BMI Z score (difference between metformin and placebo groups -0.07, CI -0.12 to -0.01, P = 0.02), and fat mass (difference -1.40 kg, CI -2.74 to -0.06, P = 0.04). Fasting plasma glucose (P = 0.007) and homeostasis model assessment (HOMA) insulin resistance index (P = 0.006) also improved more in metformin-treated children than in placebo-treated children. Gastrointestinal symptoms were significantly more prevalent in metformin-treated children, which limited maximal tolerated dosage in 17%. During the 6-month open-label phase, children treated previously with placebo decreased their BMI Z score; those treated continuously with metformin did not significantly change BMI Z score further.

CONCLUSIONS

Metformin had modest but favorable effects on body weight, body composition, and glucose homeostasis in obese insulin-resistant children participating in a low-intensity weight-reduction program.

A pilot study of interpersonal psychotherapy for preventing excess weight gain in adolescent girls at-risk for obesity

OBJECTIVE

Interpersonal psychotherapy (IPT) is effective at reducing binge episodes and inducing weight stabilization in obese adults with binge eating disorder.

METHOD

We piloted the administration of IPT to girls at-risk for excess weight gain (BMI 75th-97th percentile; IPT-WG) with and without loss of control (LOC) eating. Thirty-eight girls (12-17 years) were randomized to IPT-WG or a standard-of-care health education group.

RESULTS

All 38 girls completed the programs and all follow-up visits through 6 months. Thirty-five of 38 returned for a complete assessment visit at 1 year. Among girls with baseline LOC (n = 20), those in IPT-WG experienced greater reductions in such episodes than girls in health education (p = .036). Regardless of LOC status, over 1 year girls in IPT-WG were less likely to increase their BMI as expected for their age and BMI percentile (p = .028).

DISCUSSION

IPT-WG is feasible and acceptable to adolescent girls at-risk for adult obesity and may prevent excess weight gain over 1 year.

Prediction of maximal oxygen uptake by bioelectrical impedance analysis in overweight adolescents

AIM

Maximal oxygen uptake (VO(2max)), the gold standard for measurement of cardiorespiratory fitness, is frequently difficult to assess in overweight individuals due to physical limitations. Reactance and resistance measures obtained from bioelectrical impedance analysis (BIA) have been suggested as easily obtainable predictors of cardiorespiratory fitness, but the accuracy with which ht(2)/Z can predict VO(2max) has not previously been examined in overweight adolescents.

METHODS

The impedance index was used as a predictor of VO(2max) in 87 overweight girls and 47 overweight boys ages 12 to 17 with mean BMI of 38.6 + or - 7.3 and 42.5 + or - 8.2 in girls and boys respectively. The Bland Altman procedure assessed agreement between predicted and actual VO(2max).

RESULTS

Predicted VO(2max) was significantly correlated with measured VO(2max) (r(2)=0.48, P<0.0001). Using the Bland Altman procedure, there was significant magnitude bias (r(2)=0.10; P<0.002). The limits of agreement for predicted relative to actual VO(2max) were -589 to 574 mL O(2)/min.

CONCLUSIONS

The impedance index was highly correlated with VO(2max) in overweight adolescents. However, using BIA data to predict maximal oxygen uptake over-predicted VO(2max) at low levels of oxygen consumption and under-predicted VO(2max) at high levels of oxygen consumption. This magnitude bias, along with the large limits of agreement of BIA-derived predicted VO(2max), limit its usefulness in the clinical setting for overweight adolescents.

Insulin resistance, hyperinsulinemia, and energy intake in overweight children

OBJECTIVE

To examine the relationship between energy intake during a buffet meal and indexes of insulin dynamics in overweight children.

STUDY DESIGN

Ninety-five nondiabetic, overweight (body mass index > or = 95th percentile) children (age 10.3 +/- 1.4 years) selected lunch from a 9835-kcal buffet eaten ad libitum after an overnight fast. The associations between energy intake and measures of insulin dynamics, in the postabsorptive state and during a 2-hour hyperglycemic clamp, were determined. Covariates in the statistical model included race, sex, skeletal age, fat-free mass, fat mass, socioeconomic status, and number of foods in the buffet rated as acceptable.

RESULTS

Energy intake was positively associated with the fasting homeostasis model assessment for insulin resistance index (beta = 0.24, P = .042), fasting insulin/glucose ratio (beta = 0.24, P = .044), first-phase insulin (beta = 0.23, P = .032), and first-phase C-peptide (beta = 0.21, P = .046); energy intake was negatively associated with clamp-derived insulin sensitivity (beta = -0.29, P = .042). Each 10% decrease in clamp-derived insulin sensitivity predicted a 27-kcal greater energy intake.

CONCLUSIONS

Insulin resistance and hyperinsulinemia are associated with greater energy intake after an overnight fast in overweight children. These associations suggest mechanisms whereby insulin resistance may contribute to excessive weight gain in children.

Preventing excessive weight gain in adolescents: interpersonal psychotherapy for binge eating

The most prevalent disordered eating pattern described in overweight youth is loss of control (LOC) eating, during which individuals experience an inability to control the type or amount of food they consume. LOC eating is associated cross-sectionally with greater adiposity in children and adolescents and seems to predispose youth to gain weight or body fat above that expected during normal growth, thus likely contributing to obesity in susceptible individuals. No prior studies have examined whether LOC eating can be decreased by interventions in children or adolescents without full-syndrome eating disorders or whether programs reducing LOC eating prevent inappropriate weight gain attributable to LOC eating. Interpersonal psychotherapy, a form of therapy that was designed to treat depression and has been adapted for the treatment of eating disorders, has shown efficacy in reducing binge eating episodes and inducing weight stabilization among adults diagnosed with binge eating disorder. In this paper, we propose a theoretical model of excessive weight gain in adolescents at high risk for adult obesity who engage in LOC eating and associated overeating patterns. A rationale is provided for interpersonal psychotherapy as an intervention to slow the trajectory of weight gain in at-risk youth, with the aim of preventing or ameliorating obesity in adulthood.

Children's descriptions of the foods consumed during loss of control eating episodes

Binge and loss of control (LOC) eating appear to be common among youth; however, little is known about the foods consumed during such eating episodes. Two-hundred forty-nine children, age 6-18 years, were interviewed to determine if they engaged in eating episodes with LOC over the past month. In the absence of reported LOC eating, overeating episodes or normal meals without LOC were recorded. Participants were asked to describe the type and quantity of foods eaten during an episode. Eighty-one children reported LOC eating episodes and 168 reported no such episodes (No LOC). Although total energy intake did not differ between LOC and No LOC episodes, LOC episodes consisted of a lower percentage of calories from protein (14.2+/-0.7 v. 18.0+/-0.7%, p<.001) and a higher percentage from carbohydrates (49.8+/-1.6 v. 45.2+/-1.1%, p<.05). Specifically, LOC episodes consisted of a higher percentage of calories from snacks (13.2+/-2.7 v. 7.4+/-1.2%, p<.05) and desserts (18.1+/-3.1 v. 12.8+/-1.5%, p<.05). The quality of LOC episodes may help explain why LOC eating promotes excessive weight gain among children who report such episodes.

Reduced methylprednisolone clearance causing prolonged pharmacodynamics in a healthy subject was not associated with CYP3A5*3 allele or a change in diet composition

The influence of diet and genetics was investigated in a healthy white person who had distinctly low methylprednisolone clearance. Pharmacokinetic and pharmacodynamic parameter values were similar on 2 occasions during the consumption of a low-carbohydrate diet and a Weight Watchers diet, indicating that the decreased clearance was unlikely attributable to a change in diet composition. Although the subject was found to be homozygous for CYP3A5*3, genetic findings were not significant for a number of other CYP3A4 and CYP3A5 allelic variants. Because of the high prevalence of CYP3A5*3/*3 in whites and because 5 of 7 white control subjects are also homozygous for CYP3A5*3, this genotype cannot fully explain the reduced metabolism of the drug. Other genetic or contributing factors might have been involved. New polymerase chain reaction-based genotyping methods for functionally defective CYP3A5*6, *8, *9, and *10 alleles were developed in this study. These assays will be useful for CYP3A5 genotype analysis in future clinical studies.