Effects of dietary macronutrient intake on insulin sensitivity and secretion and glucose and lipid metabolism in healthy, obese adolescents

Glycemia and Gluconeogenesis With Metformin and Liraglutide: A Randomized Trial in Youth-onset Type 2 Diabetes

OBJECTIVE

Elevated rates of gluconeogenesis are an early pathogenic feature of youth-onset type 2 diabetes (Y-T2D), but targeted first-line therapies are suboptimal, especially in African American (AA) youth. We evaluated glucose-lowering mechanisms of metformin and liraglutide by measuring rates of gluconeogenesis and β-cell function after therapy in AA Y-T2D.

METHODS

In this parallel randomized clinical trial, 22 youth with Y-T2D-age 15.3 ± 2.1 years (mean ± SD), 68% female, body mass index (BMI) 40.1 ± 7.9 kg/m2, duration of diagnosis 1.8 ± 1.3 years-were randomized to metformin alone (Met) or metformin + liraglutide (Lira) (Met + Lira) and evaluated before and after 12 weeks. Stable isotope tracers were used to measure gluconeogenesis [2H2O] and glucose production [6,6-2H2]glucose after an overnight fast and during a continuous meal. β-cell function (sigma) and whole-body insulin sensitivity (mSI) were assessed during a frequently sampled 2-hour oral glucose tolerance test.

RESULTS

At baseline, gluconeogenesis, glucose production, and fasting and 2-hour glucose were comparable in both groups, though Met + Lira had higher hemoglobin A1C. Met + Lira had a greater decrease from baseline in fasting glucose (-2.0 ± 1.3 vs -0.6 ± 0.9 mmol/L, P = .008) and a greater increase in sigma (0.72 ± 0.68 vs -0.05 ± 0.71, P = .03). The change in fractional gluconeogenesis was similar between groups (Met + Lira: -0.36 ± 9.4 vs Met: 0.04 ± 12.3%, P = .9), and there were no changes in prandial gluconeogenesis or mSI. Increased glucose clearance in both groups was related to sigma (r = 0.63, P = .003) but not gluconeogenesis or mSI.

CONCLUSION

Among Y-T2D, metformin with or without liraglutide improved glycemia but did not suppress high rates of gluconeogenesis. Novel therapies that will enhance β-cell function and target the elevated rates of gluconeogenesis in Y-T2D are needed.

Macronutrients modified dietary intervention in the management of overweight/obese children and adolescents: a systematic review

The prevalence of obesity in adults and children is rapidly increasing worldwide. Obesity is among the main causes of chronic diseases and various problems, including economic consequences and they can also be affected by genetic, environmental, psychological, and socioeconomic factors. Dietary modification is a well-known and important factor in weight control, in particular, dietary macronutrient composition, food selection, dietary patterns, and energy restriction can affect weight reduction. Therefore, this systematic review aims to provide basic evidence for identifying the optimal macronutrient composition for managing obesity in Korean children and adolescents. We searched literature through an international database, studies were selected using our eligibility criteria and quality was assessed via a risk of bias tool. In our results, several studies have demonstrated that dietary macronutrient modifications affect body composition and metabolic markers in children and adolescents. In contrast, hypocaloric diets, regardless of macronutrient composition, are reportedly effective for weight loss in obese children. However, these findings were based on intervention studies that examined the association between dietary macronutrient composition and obesity in non-Korean children and adolescents. Therefore, in the future, more intervention studies are needed to elucidate this relationship and evidence between macronutrients and obesity in Korean children and adolescents.

Do macronutrient intakes affect obesity indices in Jordanian adults?

OBJECTIVE

To determine whether macronutrient intake is associated with novel obesity indices, including the conicity index (CI), body adiposity index (BAI), abdominal volume index (AVI), body roundness index (BRI), and weight-adjusted-waist index (WWI).

METHODOLOGY

A cross-sectional survey was conducted with 491 adults (344 males and 147 females) working at different universities in Jordan (July-December 2019). Daily intake of energy (kcal), carbohydrates (g), protein (g), and fat (g) was obtained using 24-h recalls collected over 2 days. Additionally, obesity indices were calculated.

RESULTS

Regardless of sex, energy, and carbohydrate intakes had a moderately significant positive association, whereas protein and fat intakes had a weakly significant association with BAI, AVI, and BRI. CI and WWI showed a weakly significant association with all macronutrients in males, a moderate correlation with energy and carbohydrate intake, and a weak association with fat and protein intake in females. Male participants had significant increases in the CI (T1 = 1.29 ± 0.01 vs. T3 = 1.36 ± 0.01, p = .018), AVI (T1 = 17.96 ± 0.52 vs. T3 = 22.81 ± 0.57, p = .011), and WWI (T1 = 10.72 ± 0.11 vs. T3 = 11.29 ± 0.09, p = .047) indices scores through the carbohydrate intake tertiles. Additionally, there was a significant increase in scores of AVI (T1 = 18.60 ± 0.56 vs. T3 = 21.42 ± 0.46, p = .048) and an almost significant increase in CI (T1 = 1.30 ± 0.01vs. T3 = 1.33 ± 0.01, p = .056) through the tertiles of protein intake.

CONCLUSION

Macronutrients were significantly associated with all indices. The effect of macronutrients on obesity indices is sex-based. Among men, CI, AVI, and WWI were the indices most affected by carbohydrate and protein intakes. Future studies should further investigate food sources and macronutrient quality.

Roles of hepatic atypical protein kinase C hyperactivity and hyperinsulinemia in insulin-resistant forms of obesity and type 2 diabetes mellitus

Diet-induced obesity, the metabolic syndrome, type 2 diabetes (DIO/MetS/T2DM), and their adverse sequelae have reached pandemic levels. In mice, DIO/MetS/T2DM initiation involves diet-dependent increases in lipids that activate hepatic atypical PKC (aPKC) and thereby increase lipogenic enzymes and proinflammatory cytokines. These or other hepatic aberrations, via adverse liver-to-muscle cross talk, rapidly impair postreceptor insulin signaling to glucose transport in muscle. The ensuing hyperinsulinemia further activates hepatic aPKC, which first blocks the ability of Akt to suppress gluconeogenic enzyme expression, and later impairs Akt activation, further increasing hepatic glucose production. Recent findings suggest that hepatic aPKC also increases a proteolytic enzyme that degrades insulin receptors. Fortunately, all hepatic aberrations and muscle impairments are prevented/reversed by inhibition or deficiency of hepatic aPKC. But, in the absence of treatment, hyperinsulinemia induces adverse events, some by using "spare receptors" to bypass receptor defects. Thus, in brain, hyperinsulinemia increases Aβ-plaque precursors and Alzheimer risk; in kidney, hyperinsulinemia activates the renin-angiotensin-adrenal axis, thus increasing vasoconstriction, sodium retention, and cardiovascular risk; and in liver, hyperinsulinemia increases lipogenesis, obesity, hepatosteatosis, hyperlipidemia, and cardiovascular risk. In summary, increases in hepatic aPKC are critically required for development of DIO/MetS/T2DM and its adverse sequelae, and therapeutic approaches that limit hepatic aPKC may be particularly effective.

Metabolic flexibility across the spectrum of glycemic regulation in youth

BACKGROUNDMetabolic flexibility (MF) refers to the relative ability to utilize lipid and carbohydrate substrates and to transition between them. It is not clear whether MF is impaired in obese youth and what the determining factors are.METHODSWe investigated the determinants of MF (increased respiratory exchange ratio [ΔRER] under insulin-stimulated conditions) in pubertal youth (n = 104; 15.6 ± 1.8 years) with obesity across the spectrum of glucose tolerance compared with normal weight (NW) controls, including body composition (fat-free mass [FFM], %body fat), visceral adipose fat (VAT) (MRI), glycemia, and insulin sensitivity (IS) [3-hour hyperinsulinemic-euglycemic clamp with measurement of lipolysis ([2H5] glycerol), free fatty acids (FFAs), and RER (indirect calorimetry)].RESULTSYouth with prediabetes and type 2 diabetes had lower ΔRER and oxidative and nonoxidative glucose disposal compared with NW, with no significant difference in ΔRER between NW and obese with normal glucose tolerance. In multiple regression analysis, ISFFM (β = 0.4, P = 0.004), percentage suppression of FFAs (r = 0.26, P = 0.007), and race/ethnicity (β = -0.23, P = 0.02) contributed to the variance in ΔRER (R2 = 0.30, P < 0.001) independent of percentage body fat (or VAT), sex, Tanner stage, and hemoglobin A1c.ConclusionMF is defective at the extreme of the metabolic phenotype in obese youth with dysglycemia related to a defect in IS limiting substrate utilization.FUNDINGUSDA/ARS Project Number 3092-51000-057.

Impacts of Dietary Macronutrient Pattern on Adolescent Body Composition and Metabolic Risk: Current and Future Health Status-A Narrative Review

Obesity, particularly in childhood and adolescence, is one of the serious public health problems worldwide. According to the World Health Organization, 10% of young people aged 5-17 years are obese, which is rapidly increasing around the world. Furthermore, approximately 80% of adolescents who become obese develop bodyweight-related health problems in adulthood. Eating habits and lifestyles play important roles in forming body composition and metabolic status. Changes in body composition in adolescence, the period in which secondary sex characteristics begin to develop, can alter hormonal and metabolic status, can consequently affect health status and the risk of developing chronic diseases in adulthood, and moreover may have an impact on probable body composition and metabolic status in the next generation. Here, we reviewed cross-sectional and interventional studies to analyze the role of dietary patterns focusing on macronutrient intake in growth, body composition, and metabolic changes in adolescents. These findings provide insights into optimal dietary guidelines for healthy growth with accretion of adequate body composition in adolescence, and provide an effective strategy for preventing and managing the risk of obesity-related metabolic disease in adulthood, with the additional benefit of providing potential benefits for the next generation's health.

Dietary Carbohydrates and Insulin Resistance in Adolescents from Marginalized Areas of Chiapas, México

Evidence of the role that dietary carbohydrates (total carbohydrates, dietary fiber, total sugars, dietary glycemic index (GI) and glycemic load (GL)) exerts on insulin levels in adolescents is controversial. Thus, the aim of this study was to assess the association between dietary carbohydrates and insulin resistance in adolescents from Chiapas, México. A cross-sectional study was conducted in 217 adolescents. Sociodemographic, anthropometric, dietary and biochemical data were obtained. Total carbohydrates, dietary fiber, total sugars, dietary GI and GL were calculated from 24 h recalls. Two validated cut-off points for the homeostasis model assessment of insulin resistance (HOMA-IR) were used as surrogates of insulin resistance. Fasting insulin levels ≥ 14.38 μU/mL were considered as abnormal. Multivariate logistic regression models were fitted to assess the association between tertiles of dietary carbohydrates and insulin resistance or hyperinsulinemia. In our study, adolescents with the highest dietary fiber intake had lower odds of HOMA-IR > 2.97 (OR = 0.34; 95% CI: 0.13-0.93) when adjusted for sex, age, body fat percentage and saturated fatty acids intake. No significant associations were found for the rest of the carbohydrate variables. In summary, high-fiber diets reduce the probability of insulin resistance in adolescents from marginalized areas of Chiapas, México.

Obesity-Related Metabolic Risk in Sedentary Hispanic Adolescent Girls with Normal BMI

Hispanic adolescent girls with normal BMI frequently have high body fat %. Without knowledge of body fat content and distribution, their risk for metabolic complications is unknown. We measured metabolic risk indicators and abdominal fat distribution in post-pubertal Hispanic adolescent girls with Normal BMI (N-BMI: BMI < 85th percentile) and compared these indicators between girls with Normal BMI and High Fat content (N-BMI-HF: body fat ≥ 27%; n = 15) and Normal BMI and Normal Fat content (N-BMI-NF: body fat < 27%; n = 8). Plasma concentrations of glucose, insulin, adiponectin, leptin and Hs-CRP were determined. Insulin resistance was calculated using an oral glucose tolerance test. Body fat % was measured by DXA and subcutaneous, visceral and hepatic fat by MRI/MRS. The N-BMI-HF girls had increased abdominal and hepatic fat content and increased insulin resistance, plasma leptin and Hs-CRP concentrations (p < 0.05) as compared to their N-BMI-NF counterparts. In N-BMI girls, insulin resistance, plasma insulin and leptin correlated with BMI and body fat % (p < 0.05). This research confirms the necessity of the development of BMI and body fat % cut-off criteria per sex, age and racial/ethnic group based on metabolic risk factors to optimize the effectiveness of metabolic risk screening procedures.

Nutrition from the Inside Out

Nearly 50 years ago, I set out to investigate the clinical problem of hypoglycemia in children with illnesses that limited their food intake. My goal was to gather accurate and precise measurable data. At the time, I wasn't interested in nutrition as a discipline defined in its more general or popular sense. To address the specific problem that interested me required development of entirely new methods based on stable, nonradioactive tracers that satisfied the conditions of accuracy and precision. At the time, I had no inclination of the various theoretical and practical problems that would have to be solved to achieve this goal. Some are briefly described here. Nor did I have the slightest idea that developing the field would result in a fundamental change in how human clinical investigation was conducted, with the eventual replacement of radiotracers with stable isotopically labeled ones, even for adult clinical investigation. Additionally, I had no inclination that the original questions would open avenues to much broader questions of practical nutritional relevance. Moreover, only much later as the editor of The American Journal of Clinical Nutrition did I appreciate the policy implications of how nutritional data are presented in the scientific literature. At least in part, less accurate and precise measurements and less than full transparency in reporting nutritional data have resulted in widespread debate about the public policy recommendations and guidelines that are the intended result of collecting the data in the first place. This article provides a personal recollection (with all the known faults of self-reporting and retrospective memory) of the journey that starts with measurement certainty and ends with policy uncertainty.

Can metabolic function and physical fitness improve without weight loss for inactive, obese, Hispanic adolescents? A feasibility study

INTRODUCTION

A case series that examines the effects of a 12-week combined resistance and aerobic training program for four sedentary obese, Hispanic adolescents without weight loss.

SUBJECTS/METHODS

Baseline and post-intervention anthropometric, metabolic and physical fitness measures were obtained. Body composition, hepatic, visceral, and intramuscular fat contents were analyzed via imaging. Fasting levels of alanine transaminase (ALT), insulin, glucose, free fatty acids, triglycerides, high- and low-density lipoproteins (LDL), and C-reactive protein were obtained via blood samples.

RESULTS

Two subjects decreased their glucose levels by 1.86% and 4.06%. Subjects 1, 3, and 4 increased their lean body mass by 4.12%, 9.70%, and 5.48%. ALT was reduced 13.0%, 16.0%, and 35.7% for subjects 2, 3, and 4, respectively. LDLs were reduced by 37.7%, 4.5%, and 7.5% for subjects 1, 2, and 3. Triglycerides were reduced by 25.4%, 37.8%, and 4.6% for subjects 1, 2, and 3. Visceral fat reductions by 16.5%, 14.2%, and 13.0% occurred for subjects 1, 2, and 3. C-reactive protein was reduced for subjects 1, 2, and 3 by 19.4%, 16.3%, and 32.0%.

CONCLUSION

Expected directions of change were made for most indicators of metabolic function and body composition, but measures of physical fitness improved for all four subjects.

Review: Obesity and cardiometabolic syndrome in children

The cardiometabolic syndrome is highly prevalent among overweight youth. The risk of developing the cardiometabolic syndrome is likely triggered or exacerbated by concurrent obesity, unhealthy lifestyle/eating habits, and hormonal changes (puberty). Current screening recommendations include measurement of blood pressure, fasting insulin and glucose, and total cholesterol. However, limiting assessments to these measures underestimates cardiometabolic risk in overweight youth, particularly minorities. Early identification of cardiometabolic risk in its incipient stages may justify early and more aggressive intervention to prevent progression and complications. This review provides rationale for additional assessments to determine cardiometabolic risk in overweight youth and recommends treatment options.

Measurements of Gluconeogenesis and Glycogenolysis: A Methodological Review

Gluconeogenesis is a complex metabolic process that involves multiple enzymatic steps regulated by myriad factors, including substrate concentrations, the redox state, activation and inhibition of specific enzyme steps, and hormonal modulation. At present, the most widely accepted technique to determine gluconeogenesis is by measuring the incorporation of deuterium from the body water pool into newly formed glucose. However, several techniques using radioactive and stable-labeled isotopes have been used to quantitate the contribution and regulation of gluconeogenesis in humans. Each method has its advantages, methodological assumptions, and set of propagated errors. In this review, we examine the strengths and weaknesses of the most commonly used stable isotopes methods to measure gluconeogenesis in vivo. We discuss the advantages and limitations of each method and summarize the applicability of these measurements in understanding normal and pathophysiological conditions.

BMI-related progression of atypical PKC-dependent aberrations in insulin signaling through IRS-1, Akt, FoxO1 and PGC-1α in livers of obese and type 2 diabetic humans

Information on insulin resistance in human liver is limited. In mouse diet-induced obesity (DIO), hepatic insulin resistance initially involves: lipid+insulin-induced activation of atypical protein kinase C (aPKC); elevated Akt activity/activation but selective impairment of compartmentalized Akt-dependent FoxO1 phosphorylation; and increases in gluconeogenic and lipogenic enzymes. In advanced stages, e.g., in hepatocytes of type 2 diabetes (T2D) humans, insulin activation of insulin receptor substrate-1(IRS-1) and Akt fails, further increasing FoxO1-dependent gluconeogenic/lipogenic enzyme expression. Increases in hepatic PGC-1α also figure prominently, but uncertainly, in this scheme. Here, we examined signaling factors in liver samples harvested from human transplant donors with increasing BMI, 20→25→30→35→40→45. We found, relative to lean (BMI=20-25) humans, obese (BMI>30) humans had all abnormalities seen in early mouse DIO, but, surprisingly, at all elevated BMI levels, had decreased insulin receptor-1 (IRS-1) levels, decreased Akt activity, and increased expression/abundance of aPKC-ι and PGC-1α. Moreover, with increasing BMI, there were: progressive increases in aPKC activity and PKC-ι expression/abundance; progressive decreases in IRS-1 levels, Akt activity and FoxO1 phosphorylation; progressive increases in expression/abundance of PGC-1α; and progressive increases in gluconeogenic and lipogenic enzymes. Remarkably, all abnormalities reached T2D levels at higher BMI levels. Most importantly, both "early" and advanced abnormalities were largely reversed by 24-hour treatment of T2D hepatocytes with aPKC inhibitor. We conclude: hepatic insulin resistance in human obesity is: advanced; BMI-correlated; and sequentially involves increased aPKC-activating ceramide; increased aPKC levels and activity; decreases in IRS-1 levels, Akt activity, and FoxO1 phosphorylation; and increases in expression/abundance of PGC-1α and gluconeogenic and lipogenic genes.

Increased gluconeogenesis in youth with newly diagnosed type 2 diabetes

AIMS/HYPOTHESIS

The role of increased gluconeogenesis as an important contributor to fasting hyperglycaemia at diabetes onset is not known. We evaluated the contribution of gluconeogenesis and glycogenolysis to fasting hyperglycaemia in newly diagnosed youths with type 2 diabetes following an overnight fast.

METHODS

Basal rates (μmol kg(FFM) (-1) min(-1)) of gluconeogenesis ((2)H2O), glycogenolysis and glycerol production ([(2)H5] glycerol) were measured in 18 adolescents (nine treatment naive diabetic and nine normal-glucose-tolerant obese adolescents).

RESULTS

Type 2 diabetes was associated with higher gluconeogenesis (9.2 ± 0.6 vs 7.0 ± 0.3 μmol kg(FFM) (-1) min(-1), p < 0.01), plasma fasting glucose (7.0 ± 0.6 vs 5.0 ± 0.2 mmol/l, p = 0.004) and insulin (300 ± 30 vs 126 ± 31 pmol/l, p = 0.001). Glucose production and glycogenolysis were similar between the groups (15.4 ± 0.3 vs 12.4 ± 1.4 μmol kg(FFM) (-1) min(-1), p = 0.06; and 6.2 ± 0.8 vs 5.3 ± 0.7 μmol kg(FFM) (-1) min(-1), p = 0.5, respectively). After controlling for differences in adiposity, gluconeogenesis, glycogenolysis and glucose production were higher in diabetic youth (p ≤ 0.02). Glycerol concentration (84 ± 6 vs 57 ± 6 μmol/l, p = 0.01) and glycerol production (5.0 ± 0.3 vs 3.6 ± 0.5 μmol kg(FFM) (-1) min(-1), p = 0.03) were 40% higher in youth with diabetes. The increased glycerol production could account for only ~1/3 of substrate needed for the increased gluconeogenesis in diabetic youth.

CONCLUSION/INTERPRETATIONS

Increased gluconeogenesis was a major contributor to fasting hyperglycaemia and hepatic insulin resistance in newly diagnosed untreated adolescents and was an early pathological feature of type 2 diabetes. Increased glycerol availability may represent a significant source of new carbon substrates for increased gluconeogenesis but would not account for all the carbons required to sustain the increased rates.

Habitually higher dietary glycemic index during puberty is prospectively related to increased risk markers of type 2 diabetes in younger adulthood

OBJECTIVE

Carbohydrate nutrition during periods of physiological insulin resistance such as puberty may affect future risk of type 2 diabetes. This study examined whether the amount or the quality (dietary glycemic index [GI], glycemic load [GL], and added sugar, fiber, and whole-grain intake) of carbohydrates during puberty is associated with risk markers of type 2 diabetes in younger adulthood.

RESEARCH DESIGN AND METHODS

The analysis was based on 226 participants (121 girls and 105 boys) from the Dortmund Nutritional and Anthropometric Longitudinally Designed Study (DONALD) with an average of five 3-day weighed dietary records (range 2-6) during puberty (girls, age 9-14 years; boys, age 10-15 years) and fasting blood samples in younger adulthood (age 18-36 years) (average duration of follow-up 12.6 years). Multivariable linear regression was used to analyze the associations between carbohydrate nutrition and homeostasis model assessment-insulin resistance (HOMA-IR) as well as the liver enzymes alanine aminotransferase (ALT) and γ-glutamyltransferase (GGT) (n = 214).

RESULTS

A higher dietary GI was prospectively related to greater values of HOMA-IR (P(trend) = 0.03), ALT (P(trend) = 0.02), and GGT (P(trend) = 0.04). After adjustment for sex, adult age, baseline BMI, and early life and socioeconomic factors as well as protein and fiber intake, predicted mean HOMA-IR values in energy-adjusted tertiles of GI were 2.37 (95% CI 2.16-2.60), 2.47 (2.26-2.71), and 2.59 (2.35-2.85). The amount of carbohydrates, GL, and added sugar, fiber, and whole-grain intake were not related to the analyzed markers.

CONCLUSIONS

Our data indicate that a habitually higher dietary GI during puberty may adversely affect risk markers of type 2 diabetes in younger adulthood.

Acute effect of Fatmax exercise on the metabolism in overweight and nonoverweight girls

INTRODUCTION

Acute exercise can reduce postprandial insulin concentrations and increase fat oxidation in adults, which may have important implications for insulin resistance and weight control. However, similar studies with young people or comparing overweight (OW) and nonoverweight (NO) individuals are sparse. Therefore, the acute effect of Fatmax exercise on glucose, insulin, and fat oxidation was examined in 12 OW and 15 NO girls.

METHODS

Participants completed two 2-d conditions in a counterbalanced order. On day 1, participants either expended 2.09 MJ (500 kcal) during treadmill exercise at individual Fatmax (EX) or 0.47 MJ (112 kcal) during rest (CON). On day 2, capillary blood and expired air samples were taken in the fasting state and at regular intervals for 2 h after high-glycemic-index breakfast consumption. Subsequently, blood glucose and plasma insulin concentrations were determined, and fat oxidation was estimated.

RESULTS

Blood glucose was similar between conditions in both groups (P > 0.05). Fasting plasma insulin (P = 0.047) and total area under the 2-h curve (P = 0.049) were reduced for EX compared with CON in the NO, but not OW girls (P > 0.05). Fasting fat oxidation was higher for EX than for CON in the NO girls (P = 0.036) and fat oxidation total area under the 2-h curve was higher for EX in both groups of girls (P ≤ 0.05).

CONCLUSIONS

A bout of Fatmax exercise performed ~16 h before high-glycemic-index breakfast consumption reduced fasting and postprandial insulin concentrations in NO girls and increased fat oxidation in both OW and NO girls. The higher postintervention energy and CHO intake in the OW compared with the NO girls or differences in metabolism between the two groups may have compromised potential exercise-induced reductions in insulin the OW girls.

Sex-specific interactions between the IRS1 polymorphism and intakes of carbohydrates and fat on incident type 2 diabetes

BACKGROUND

The minor T allele of rs2943641 near the gene encoding for insulin receptor substrate 1 (IRS1) has been associated with decreased risk of type 2 diabetes (T2D) and adiposity in genome-wide association studies. Dietary intake can influence the regulation of IRS1, and studies have indicated sex-specific associations between IRS1 and adiposity.

OBJECTIVE

The objective was to examine the interaction between IRS1 rs2943641 and macronutrient intakes on incident T2D and percentage body fat in the Malmö Diet and Cancer cohort.

DESIGN

The study included 15,227 women and 9614 men aged 45-74 y without prevalent diabetes. Dietary data were collected with a modified diet history method. During 12 y of follow-up, 1567 incident T2D cases were identified.

RESULTS

The T allele was associated with lower incidence of T2D (P-trend = 0.003) and, in men, with higher percentage body fat (P-trend = 0.00002). We observed 3-way interactions between sex, rs2943641, and carbohydrate intake (P = 0.01) as well as between sex, rs2943641, and fat intake (P = 0.01) on incident T2D. Among women, the T allele was associated with decreased risk only in the lower tertiles of carbohydrate intake (P-trend = 0.01, P-interaction = 0.01). In contrast, among men, the T allele was associated with decreased risk in the lowest tertile of fat intake (P-trend = 0.01, P-interaction = 0.02). No interaction was observed between macronutrient intakes and rs2943641 on percentage body fat.

CONCLUSIONS

Our results indicate that IRS1 rs2943641 interacts with carbohydrate and fat intakes on incident T2D in a sex-specific fashion. A protective association between the rs2943641 T allele and T2D was restricted to women with low carbohydrate intake and to men with low fat intake.

Low-carbohydrate diets: a matter of love or hate

Low-carbohydrate diets (LChD) have become very popular among the general population. These diets have been used to lose body weight and to ameliorate various abnormalities like diabetes, nonalcoholic fatty liver disease, polycystic ovary syndrome, narcolepsy, epilepsy, and others. Reports suggest that body weight reduction and glycemic control could be attained while following LChD. However, these advantages are more notably found in short periods of time consuming an LChD. Indeed, the safety and efficacy of the latter diets in the long term have not been sufficiently explored. In contrast to what has been proposed, other mentioned pathologies are not improved or are even worsened by carbohydrate restriction. Therefore, the aim of this review is to define the concept of LChD and to explain their clinical effects in the short and long term, their influence on metabolism, and the opinion of nutrition or health authorities. Finally, evincing the research gaps of LChD that are here exposed will later allow us to reach a consensus with regard to their utilization.

Gluconeogenesis is not regulated by either glucose or insulin in extremely low birth weight infants receiving total parenteral nutrition

OBJECTIVE

To determine potential factors regulating gluconeogenesis (GNG) in extremely low birth weight infants receiving total parenteral nutrition.

STUDY DESIGN

Seven infants (birth weight, 0.824 ± 0.068 kg; gestational age, 25.4 ± 0.5 weeks; postnatal age, 3.3 ± 0.2 days) were studied for 11 hours, with parenteral lipid and amino acid therapy continued at prestudy rates. Glucose was supplied at prestudy rates for the first 5 hours (period 1) and was then reduced to 6 mg/kg·min for 1 hour and further to ~3 mg/kg·min for 5 hours (period 2). A total of 2.5 mg/kg·min of the glucose was replaced by [U-(13)C]glucose throughout the study for measurements of glucose production and GNG. Concentrations of glucose, insulin, glucagons, and cortisol were determined.

RESULTS

GNG and glucose production remained unchanged (2.12 ± 0.23 vs. 1.84 ± 0.25 mg/kg·min [P = NS] and 2.44 ± 0.27 vs. 2.51 ± 0.31 mg/kg·min [P = NS], respectively), despite a 60% reduction of the glucose infusion rate and subsequent 30% (124.7 ± 10.8 to 82.6 ± 8.9 mg/dL; P = .009) and 70% (26.9 ± 4.7 to 6.6 ± 0.4 μU/mL; P = .002) decreases in glucose and insulin concentrations, respectively. Cortisol and glucagon concentrations remained unchanged.

CONCLUSION

In extremely low birth weight infants receiving total parenteral nutrition, GNG is a continuous process that is not affected by infusion rates of glucose or concentrations of glucose or insulin.

Metabolic flexibility and obesity in children and youth

The concept of metabolic flexibility describes the ability of skeletal muscle to switch between the oxidation of lipid as a fuel during fasting periods to the oxidation of carbohydrate during insulin stimulated period. Alterations in energy metabolism in adults with obesity, insulin resistance and/or type 2 diabetes induce a state of impaired metabolic flexibility, or metabolic inflexibility. Despite the increase in the prevalence of type 2 diabetes in obese children and youth, less is known about the factors involved in the development of metabolic inflexibility in the paediatric population. Metabolic flexibility is conditioned by nutrient partitioning in response to feeding, substrate mobilization and delivery to skeletal muscle during fasting or exercising condition, and skeletal muscle oxidative capacity. Our aim in this review was to identify among these factors those making obese children at risk of metabolic inflexibility. The development of ectopic rather than peripheral fat storage appears to be a factor strongly linked with a reduced metabolic flexibility. Tissue growth and maturation are determinants of impaired energy metabolism later in life but also as a promising way to reverse metabolic inflexibility given the plasticity of many tissues in youth. Finally, we have attempted to identify perspectives for future investigations of metabolic flexibility in obese children that will improve our understanding of the genesis of metabolic diseases associated with obesity.

Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth

INTRODUCTION

Data on the metabolic effects of resistance exercise (strength training) in adolescents are limited.

PURPOSE

The objective of this study was to determine whether a controlled resistance exercise program without dietary intervention or weight loss reduces body fat accumulation, increases lean body mass, and improves insulin sensitivity and glucose metabolism in sedentary obese Hispanic adolescents.

METHODS

Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 h·wk, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques.

RESULTS

All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (∼80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05).

CONCLUSIONS

We conclude that a controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.

Twelve weeks of moderate aerobic exercise without dietary intervention or weight loss does not affect 24-h energy expenditure in lean and obese adolescents

BACKGROUND

Exercise might have a persistent effect on energy expenditure and fat oxidation, resulting in increased fat loss. However, even without weight loss, exercise results in positive metabolic effects. The effect of an aerobic exercise program on 24-h total energy expenditure (TEE) and its components-basal (BEE), sleep (SEE), and awake sedentary (SEDEE) energy expenditure and substrate oxidation-has not been studied in lean and obese adolescents.

OBJECTIVE

The objective was to test the hypothesis that 24-h energy expenditure and fat oxidation increase in lean and obese adolescents after 12 wk of moderate aerobic exercise without dietary intervention and weight loss.

DESIGN

Twenty-eight postpubertal Hispanic adolescents (13 lean [mean +/- SE: age, 15.3 +/- 0.3 y; body mass index (BMI; in kg/m(2)), 20.2 +/- 0.7; body fat, 18.7 +/- 1.6%] and 15 obese [age, 15.6 +/- 0.3 y; BMI, 33.1 +/- 0.9; body fat, 38.1 +/- 1.4%]) completed a 12-wk aerobic exercise program (4 x 30 min/wk at > or =70% of VO(2 peak)) without weight loss. Energy expenditure and substrate oxidation were quantified by 24-h room calorimetry at baseline and postexercise.

RESULTS

This aerobic exercise program did not affect 24-h TEE, BEE, SEE, or SEDEE in lean or obese participants. In obese adolescents, respiratory quotient (RQ) and substrate oxidation also did not change. In lean adolescents, 24-h RQ and RQ during SEE decreased (both P < 0.01) and fat oxidation increased (P < 0.01).

CONCLUSIONS

A 12-wk aerobic exercise program did not increase TEE, BEE, SEE, or SEDEE in either lean or obese sedentary adolescents. Furthermore, 24-h fat oxidation did not change in the obese adolescents, whereas it increased in the lean adolescents.

A 12-week aerobic exercise program reduces hepatic fat accumulation and insulin resistance in obese, Hispanic adolescents

The rise in obesity-related morbidity in children and adolescents requires urgent prevention and treatment strategies. Currently, only limited data are available on the effects of exercise programs on insulin resistance, and visceral, hepatic, and intramyocellular fat accumulation. We hypothesized that a 12-week controlled aerobic exercise program without weight loss reduces visceral, hepatic, and intramyocellular fat content and decreases insulin resistance in sedentary Hispanic adolescents. Twenty-nine postpubertal (Tanner stage IV and V), Hispanic adolescents, 15 obese (7 boys, 8 girls; 15.6 +/- 0.4 years; 33.7 +/- 1.1 kg/m(2); 38.3 +/- 1.5% body fat) and 14 lean (10 boys, 4 girls; 15.1 +/- 0.3 years; 20.6 +/- 0.8 kg/m(2); 18.9 +/- 1.5% body fat), completed a 12-week aerobic exercise program (4 x 30 min/week at > or =70% of peak oxygen consumption (VO(2)peak)). Measurements of cardiovascular fitness, visceral, hepatic, and intramyocellular fat content (magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS)), and insulin resistance were obtained at baseline and postexercise. In both groups, fitness increased (obese: 13 +/- 2%, lean: 16 +/- 4%; both P < 0.01). In obese participants, intramyocellular fat remained unchanged, whereas hepatic fat content decreased from 8.9 +/- 3.2 to 5.6 +/- 1.8%; P < 0.05 and visceral fat content from 54.7 +/- 6.0 to 49.6 +/- 5.5 cm(2); P < 0.05. Insulin resistance decreased indicated by decreased fasting insulin (21.8 +/- 2.7 to 18.2 +/- 2.4 microU/ml; P < 0.01) and homeostasis model assessment of insulin resistance (HOMA(IR)) (4.9 +/- 0.7 to 4.1 +/- 0.6; P < 0.01). The decrease in visceral fat correlated with the decrease in fasting insulin (R(2) = 0.40; P < 0.05). No significant changes were observed in any parameter in lean participants except a small increase in lean body mass (LBM). Thus, a controlled aerobic exercise program, without weight loss, reduced hepatic and visceral fat accumulation, and decreased insulin resistance in obese adolescents.

Aerobic exercise increases peripheral and hepatic insulin sensitivity in sedentary adolescents

CONTEXT

Data are limited on the effects of controlled aerobic exercise programs (without weight loss) on insulin sensitivity and glucose metabolism in children and adolescents.

OBJECTIVE

To determine whether a controlled aerobic exercise program (without weight loss) improves peripheral and hepatic insulin sensitivity and affects glucose production (GPR), gluconeogenesis and glycogenolysis in sedentary lean and obese Hispanic adolescents.

PATIENTS AND DESIGN

Twenty-nine post-pubertal adolescents (14 lean: 15.1 +/- 0.3 y; 20.6 +/- 0.8 kg/m(2); 18.9+/-1.5% body fat and 15 obese: 15.6 +/- 0.4 y; 33.2 +/- 0.9 kg/m(2); 38.4 +/- 1.4% body fat) (mean +/- SE), completed a 12 wk aerobic exercise program (4 x 30 min/week at >or=70% of VO(2) peak). Peripheral and hepatic insulin sensitivity and glucose kinetics were quantified using GCMS pre- and post-exercise.

RESULTS

No weight loss occurred. Lean and obese participants complied well with the program ( approximately 90% of the exercise sessions attended, resulting in approximately 15% increase in fitness in both groups). Peripheral and hepatic insulin sensitivity were higher in lean than obese adolescents but increased in both groups; peripheral insulin sensitivity by 35 +/- 14% (lean) (p < 0.05) and 59 +/- 19% (obese) (p < 0.01) and hepatic insulin sensitivity by 19 +/- 7% (lean) (p < 0.05) and 23 +/- 4% (obese) (p < 0.01). GPR, gluconeogenesis and glycogenolysis did not differ between the groups. GPR decreased slightly, 3 +/- 1% (lean) (p < 0.05) and 4 +/- 1% (obese) (p < 0.01). Gluconeogenesis remained unchanged, while glycogenolysis decreased slightly in the obese group (p < 0.01).

CONCLUSION

This well accepted aerobic exercise program, without weight loss, is a promising strategy to improve peripheral and hepatic insulin sensitivity in lean and obese sedentary adolescents. The small decrease in GPR is probably of limited clinical relevance.

Effect of dietary macronutrient composition under moderate hypocaloric intake on maternal adaptation during lactation

BACKGROUND

No evidence-based recommendations exist concerning what dietary macronutrient composition optimizes weight loss during lactation while maintaining milk production.

OBJECTIVES

The study was designed to test the following hypotheses: compared with a reduced-calorie, high-carbohydrate (H-CHO) diet, an isonitrogenous, isocaloric high-fat (H-F) diet will decrease milk production and carbohydrate oxidation, increase gluconeogenesis and hexoneogenesis, and not affect energy balance.

DESIGN

Seven healthy lactating mothers and their infants were studied on 2 occasions in random order for 8 d separated by 1-2 wk. On one occasion, the subjects received the H-F (30% of energy as carbohydrate and 55% as fat) diet and on the other occasion received the H-CHO (60% of energy as carbohydrate and 25% as fat) diet. Milk production, infant intakes, and substrate and hormone concentrations were measured. Glucose rates of appearance, production, gluconeogenesis, glycogenolysis, and hexoneogenesis were measured by using stable-isotope gas chromatography-mass spectrometric techniques, and energy expenditure and substrate oxidation were measured by using indirect calorimetry.

RESULTS

Milk volume, lactose, and protein concentrations were unaffected. Milk fat, energy, and infant intakes were higher (P < 0.05) during the H-F diet. Neither gluconeogenesis nor hexoneogenesis was different. During the H-F diet, energy expenditure and fat and protein oxidation rates were higher (P < 0.05), and the daily energy balance deficit was greater (P < 0.01).

CONCLUSIONS

Milk fat, energy output, and energy expenditure were higher during the H-F diet, which resulted in a greater negative energy balance. The lactating mothers adapted to a low carbohydrate intake by decreasing carbohydrate oxidation. Additional studies are warranted to determine whether a hypocaloric H-F diet might promote weight loss to a greater extent than the H-CHO diet while maintaining milk production.

beta-Cell function and insulin sensitivity in adolescents from an OGTT

Given the increase in the incidence of insulin resistance, obesity, and type 2 diabetes in children and adolescents, it would be of paramount importance to assess quantitative indices of insulin secretion and action during a physiological perturbation, such as a meal or an oral glucose-tolerance test (OGTT). A minimal model method is proposed to measure quantitative indices of insulin secretion and action in adolescents from an oral test. A 7 h, 21-sample OGTT was performed in 11 adolescents. The C-peptide minimal model was identified on C-peptide and glucose data to quantify indices of beta-cell function: static phi(s) and dynamic phi(d) responsivity to glucose from which total responsivity phi was also measured. The glucose minimal model was identified on glucose and insulin data to estimate insulin sensitivity, S(I), which was compared to a reference measure, S(I)(ref), provided by a tracer method. Disposition indices, which adjust insulin secretion for insulin action, were then calculated. Indices of beta-cell function were phi(s) = 51.35 +/- 8.89 x 10(-9)min(-1), phi(d) = 1,392 +/- 258 x 10(-9), and phi = 82.09 +/- 17.70 x 10(-9)min(-1). Insulin sensitivity was S(I) = 14.19 +/- 2.73 x 10(-4), not significantly different from S(I)(ref) = 14.96 +/- 3.04 x 10(-4) dl/kg.min per microU/ml, and well correlated: r = 0.98, P < 0.0001, thus indicating that S(I) can be accurately measured from an oral test. Disposition indices were DI(s) = 1,040 +/- 201 x 10(-14) dl/kg/min(2) per pmol/l, DI(d) = 33,178 +/- 10,720 x 10(-14) dl/kg/min per pmol/l, DI = 1,844 +/- 522 x 10(-14) dl/kg/min(2) per pmol/l. Virtually the same minimal model assessment was obtained with a reduced 3 h, 9-sample protocol. OGTT interpreted with C-peptide and glucose minimal model has the potential to provide novel insight regarding the regulation of glucose metabolism in adolescents, and to evaluate the effect of obesity and interventions such as diet and exercise.

Relationships between reported macronutrient intake and insulin dynamics in a multi-ethnic cohort of early pubertal children

BACKGROUND

Racial/ethnic differences in the pediatric population in insulin dynamics have been documented. Additionally, girls tend to be more insulin resistant than boys. Although the mechanism driving these differences is unclear, diet may be a contributor.

OBJECTIVE(S)

The objective of this study was to evaluate the contribution of reported macronutrient intake on insulin dynamics and determine if diet composition may account for racial/ethnic and sex differences in insulin response/action.

METHODS

Participants were 250 African- (n=84), European- (n=105), or Hispanic-American (n=61) children 7-12 years, pubertal stage < or =3. An intravenous glucose tolerance test was used to derive the insulin sensitivity index and acute insulin response to glucose (AIRg) diet by two 24 h recalls, and body composition by dual-energy x-ray absorptiometry (DXA).

RESULTS

Reported energy intake from fat was positively related to fasting insulin (P < 0.05) and AIRg (P=0.05). Reported energy from carbohydrate was inversely associated with fasting insulin (P < 0.05), and reported energy from protein was inversely associated with AIRg (P < 0.05). The interaction terms between ethnicity and diet, and sex and diet were not significant for any outcome variables.

CONCLUSION

Dietary intake influences insulin dynamics; however, the racial/ethnic and sex differences in insulin dynamics in this population are not accounted for by macronutrient intake. Pubertal status is likely to play a role in the interaction between diet, race/ethnicity, sex and insulin dynamics. Longitudinal studies are needed to determine if the contribution of diet to insulin dynamics strengthens with reproductive maturation.

Short-term high dietary fructose intake had no effects on insulin sensitivity and secretion or glucose and lipid metabolism in healthy, obese adolescents

There is virtually no information on the metabolic impact of dietary fructose intake in adolescents despite their high fructose consumption, particularly via sweetened beverages.

AIM

To determine the short-term metabolic effects of dietary fructose intake in obese adolescents.

METHODS

Six volunteers (3 M/3 F; 15.2 +/- 0.5 yr; 35 +/- 2 kg/m2; 39 +/- 2% body fat) were studied twice following 7 d of isocaloric, isonitrogenous high carbohydrate (60% CHO; 25% fat) diets with fructose accounting for 6% and 24% of total energy intake, respectively (random order). Insulin sensitivity and secretion were analyzed by the stable labeled intravenous glucose tolerance test and glucose and lipid kinetics using GCMS.

RESULTS

A fourfold increase in dietary fructose intake did not affect insulin sensitivity or secretion, glucose kinetics, lipolysis or glucose, insulin, C-peptide, triglycerides, HDL- and LDL-cholesterol concentrations.

CONCLUSIONS

In the short term, when energy intake is constant, dietary fructose per se is not a contributor to insulin resistance and hypersecretion in obese adolescents.

Measurement of gluconeogenesis using glucose fragments and mass spectrometry after ingestion of deuterium oxide

We report a new method to measure the fraction of glucose derived from gluconeogenesis using gas chromatography-mass spectrometry and positive chemical ionization. After ingestion of deuterium oxide by subjects, glucose derived from gluconeogenesis is labeled with deuterium. Our calculations of gluconeogenesis are based on measurements of the average enrichment of deuterium on carbon 1, 3, 4, 5, and 6 of glucose and the deuterium enrichment in body water. In a sample from an adult volunteer after ingestion of deuterium oxide, fractional gluconeogenesis using the "average deuterium enrichment method" was 48.3 +/- 0.5% (mean +/- SD) and that with the C-5 hexamethylenetetramine (HMT) method by Landau et al. (Landau BR, Wahren J, Chandramouli V, Schumann WC, Ekberg K, Kalhan SC; J Clin Invest 98: 378-385, 1996) was 46.9 +/- 5.4%. The coefficient of variation of 10 replicate analyses using the new method was 1.0% compared with 11.5% for the C-5 HMT method. In samples derived from an infant receiving total parenteral nutrition, fractional gluconeogenesis was 13.3 +/- 0.3% using the new method and 13.7 +/- 0.8% using the C-5 HMT method. Fractional gluconeogenesis measured in six adult volunteers after 66 h of continuous fasting was 83.7 +/- 2.3% using the new method and 84.2 +/- 5.0% using the C-5 HMT method. In conclusion, the average deuterium enrichment method is simple, highly reproducible, and cost effective. Furthermore, it requires only small blood sample volumes. With the use of an additional tracer, glucose rate of appearance can also be measured during the same analysis. Thus the new method makes measurements of gluconeogenesis available and affordable to large numbers of investigators under conditions of low and high fractional gluconeogenesis ( approximately 10 to approximately 90) in all subject populations.

Glucose fluxes during OGTT in adolescents assessed by a stable isotope triple tracer method

Virtually no information is available on glucose fluxes during a meal or glucose ingestion in adolescents.

AIM

To use a triple tracer approach to measure rates of appearance of ingested glucose (Ra(ogtt)), endogenous glucose production (EGP) and glucose disappearance (Rd) following an oral glucose bolus in adolescents.

METHODS

Eleven adolescents (4 M/7 F, 15 +/- 1 yr; 67.3 +/- 4.7 kg; 24 +/-2 kg/m2) underwent a frequent sampled oral glucose tolerance test (OGTT) (labelled with [6,6-2H2]glucose) combined with intravenous infusion of [1-(13)C]glucose and [U-(13)C6]glucose following an overnight fast. Formulas were developed to estimate glucose fluxes using one- or two-compartment models.

RESULTS

During the 7 h following the OGTT bolus, 9.8 +/- 2.3% of the ingested glucose was extracted by the liver, EGP was suppressed by 45 +/- 4% and Rd increased by 21 +/- 5%.

CONCLUSIONS

The triple tracer method provided accurate assessment of Ra(ogtt), EGP and Rd fluxes during an OGTT in adolescents. Thus, this method might provide novel insight on postprandial glucose fluxes in children/adolescents under various conditions.

The potential role of olive oil-derived MUFA in insulin sensitivity

Dietary fatty acids play an important role in the development of insulin resistance, the prelude to type 2 diabetes mellitus. This review addresses the potential role of olive oil-derived MUFA in insulin sensitivity, particularly how dietary fat interacts with insulin resistance looking at whole body metabolic measures, as well as molecular effects. The review focuses on the role of non-esterified fatty acids, fatty acid composition in vivo and dietary fat modification on insulin resistance in the metabolic syndrome. Particular emphasis is placed on the role of olive oil within the context of dietary modification to improve insulin sensitivity and for the prevention of the metabolic syndrome.

Development of insulin resistance and its relation to diet in the obese child

The incidence rate of obesity in youth has continued to increase worldwide and about 30% of obese children display insulin resistance (IR) and other metabolic abnormalities. The present study reviews the mechanisms for development of IR in the obese child and possible links between IR and dietary factors in childhood and adolescence. Although increased concentrations of plasma free fatty acids (FFA) and their counter part at intracellular level, long-chain acyl-coenzyme A (LC acyl-CoA), have been related to the early onset of IR in childhood obesity, a new endocrine paradigm states that adipose tissue secretes a wide variety of hormones and cytokines that regulate lipid energy metabolism. These hormonal changes precede any changes in metabolites such as FFA and glucose and appear to be associated with early IR in childhood. Excessive caloric intake increases IR in children; opposite, substantial reduction of overweight achieved by a hypocaloric diet decreases it. Elevated consumption of animal protein, particularly in early life, as well as diets rich in saturated, trans, and n-6 polyunsaturated fatty acids, and diets with a high carbohydrate to fat ratio, besides a high glycaemic and low-fiber diet also appear to exacerbate adiposity and IR.

Effects of intravenous glucose on dopaminergic function in the human brain in vivo

Dopamine is known to regulate food intake by modulating food reward via the mesolimbic circuitry of the brain. The objective of this study was to compare the effects of high energy input (i.v. glucose) on striatal and thalamic dopamine release in overweight and lean individuals. We hypothesized that glucose would induce dopamine release and positive ratings (e.g., satiety) in Behavioral Analog Scales, particularly in food-deprived lean subjects. [(11)C]raclopride PET was performed for 12 lean (mean BMI = 22 kg/m(2)) and 12 overweight (mean BMI = 33 kg/m(2)) healthy subjects. Each subject was imaged twice in a blinded counter-balanced setting, after 300 mg/kg i.v. glucose and after i.v. placebo. Dopamine D2 receptor binding potentials (BPs) were estimated. The voxel-based analysis of the baseline scans indicated lower striatal BPs in the overweight group and a negative correlation between BMIs and BPs. Intravenous glucose did not have a significant effect on BPs in overweight or lean subjects (male and female groups combined). However, BP changes were opposite in the two gender groups. In male subjects, significant BP reductions after glucose were seen in the right and left caudate nucleus, left putamen, and right thalamus. In female subjects, increases in BP secondary to glucose were seen in the right caudate nucleus and right and left putamen. The sexually dimorphic effect of glucose was seen in both overweight and lean subjects. Although gender differences were not among the a priori hypotheses of the present study and, therefore, they must be considered to be preliminary findings, we postulate that this observation is a reflection of an interaction between glucose, sex steroids (estrogen), leptin, and dopamine.

Metabolic inflexibility in substrate use is present in African-American but not Caucasian healthy, premenopausal, nondiabetic women

CONTEXT

There is an increased prevalence of obesity and insulin resistance in African-American compared with Caucasian females. Metabolic inflexibility (MI) is the inability to switch the use of lipids and carbohydrates in the peripheral tissue (i.e. muscle) based upon substrate availability.

OBJECTIVE

We examined whether MI exists in African-American females. MAIN OUTCOME MEASURES AND DESIGN: We measured substrate use differences during eucaloric, macronutrient-manipulated diets [high fat (50% fat, 35% carbohydrate, 15% protein) vs. low fat (30% fat, 55% carbohydrate, 15% protein)] between Caucasian and African-American women. We also compared differences in substrate use in response to insulin infusion during two-step pancreatic-euglycemic clamps and epinephrine infusion during lipolysis studies. In each study, similar groups of Caucasian and African-American women were compared.

RESULTS

Caucasians had significantly higher fat oxidation (FO) (P = 0.01) and lower carbohydrate oxidation (P < 0.01) during the high-fat vs. low-fat diet, whereas no significant differences were observed in African-Americans. The African-American women also failed to significantly suppress FO during the second step of the pancreatic-euglycemic clamp despite a doubling of their fasting plasma insulin and failed to increase their FO or decrease their carbohydrate oxidation in response to epinephrine infusion as much as Caucasian women did. The response of free fatty acid turnover rates to insulin and epinephrine stimulation was similar between races.

CONCLUSION

The impaired substrate use observed in African-American women during these three studies demonstrates the existence of MI and may contribute to their greater prevalence of obesity and insulin resistance.

Urinary C-peptide excretion in free-living healthy children is related to dietary carbohydrate intake but not to the dietary glycemic index

This study first examined whether urinary C-peptide (UCP), stored at -20 degrees C, remains stable over the long term, and second, whether the dietary glycemic index (GI) and the glycemic load (GL: GI x g carbohydrates) are related to the 24-h UCP excretion of healthy children. Participants in the Dortmund Nutrition and Anthropometric Longitudinally Designed Study with 24-h urine collections and a simultaneously completed weighed dietary record were included. From these, 3 comparable groups of 7- to 8-y-old children (n = 40 each) from 1990, 1996, and 2002 were randomly selected (total n = 120). C-peptide was measured with a 1-site ELISA. A GI value was assigned to all recorded foods containing carbohydrates (CHO). Statistical equivalence tests corroborated that UCP excretion in the 3 sampling periods was equivalent when corrected for body weight and protein intake (P < 0.05). UCP excretion was associated with the GL after adjustment for body weight, protein, and fiber intake [mean UCP (95% CI) in GL tertiles 1-3: 6.19 (5.37, 7.14) vs. 7.82 (6.77, 9.02) vs. 7.76 (6.71, 8.97) nmol/d, P for difference 0.04]. GI was not significantly related to UCP excretion [adjusted means (95% CI): 7.27 (6.28, 8.41) vs. 6.51 (5.64, 7.51) vs. 7.94 (6.86, 9.18), P for difference 0.2]. In conclusion, UCP retrospectively measured with a 1-site ELISA remained stable for up to 12 y (from 1990 until 2002). The observed positive relation of UCP with GL appears to result largely from its association with the amount of CHO, whereas dietary GI may be relevant only at higher intake levels.