Prediabetes in obese youth: a syndrome of impaired glucose tolerance, severe insulin resistance, and altered myocellular and abdominal fat partitioning

Cardiovascular complications of type 2 diabetes in youth

The prevalence of type 2 diabetes mellitus (T2DM) in youth has increased dramatically over the past decades. The literature also suggests that the progression from an impaired glucose tolerance state to established T2DM is more rapid in youth, compared to adults. The presence of significant cardiovascular complications in youth with T2DM, including cardiac, macrovascular, and microvascular remodeling, is another major issue in this younger cohort and poses a significant threat to the healthcare system. However, this issue is only now emerging as a major public health concern, with few data to support optimal treatment targets and strategies to reduce cardiovascular disease (CVD) risk in youth with T2DM. Accordingly, the purpose of this minireview is to better understand the cardiovascular complications in youth with T2DM. We briefly describe the pathophysiology from youth studies, including oxidative stress, inflammation, renin-angiotensin aldosterone system, and epigenetics, which link T2DM and CVD. We also describe the literature concerning the early signs of CVD in youth and potential treatment options to reduce cardiovascular risk.

Effects of recombinant human growth hormone (rhGH) administration on body composition and cardiovascular risk factors in obese adolescent girls

Background

Obesity is associated with a relative deficiency of growth hormone, which is predictive of greater visceral fat and markers of cardiovascular risk. The study’s purpose was to use recombinant human growth hormone (rhGH) as a physiologic probe to assess the effects of reversing obesity-related GH deficiency on body composition, cardiovascular risk markers, and insulin resistance.

Methods

22 obese girls 13–21 years old were followed for a randomized 6-month trial of rhGH vs. placebo/no treatment. At baseline and 6-months, DXA was performed for body composition, MRI to measure visceral, subcutaneous and total adipose tissue (VAT, SAT and TAT), and fasting blood drawn for IGF-1, inflammatory cardiovascular risk markers [soluble intercellular adhesion molecule (sICAM), high sensitivity CRP], lipids and HbA1C. An oral glucose tolerance test (OGTT) was performed. Twelve girls completed the 6-month visit. Baseline and mean 6-month change were compared between the groups using the Student t-test and the relationship between variables was determined through multiple regression analysis.

Results

After 6-months, the rhGH group maintained IGF-1 levels, and had decreases in total cholesterol (p = 0.03), sICAM-1 (p = 0.04) and HbA1C (p = 0.03) compared to placebo/no treatment. The rhGH group trended towards greater decreases in LDL and 2-hour OGTT glucose. Glucose tolerance did not worsen with rhGH administration.

Conclusions

Administering rhGH in small doses is able to stabilize IGF-1 levels in obesity. We have also shown that rhGH administration leads to an improvement in some markers of cardiovacular risk with without adversely affecting glucose tolerance.

Trial registration

Clinical Trial Registration Number: NCT01169103.

A low disposition index in adolescent offspring of mothers with gestational diabetes: a risk marker for the development of impaired glucose tolerance in youth

AIMS/HYPOTHESIS

With the increase in gestational diabetes mellitus (GDM), there is a growing need to understand the effects of intrauterine glucose exposure on the newborn at birth and later in life. The risk of developing impaired glucose tolerance (IGT) in individuals exposed to diabetes in utero has not been adequately investigated.

METHODS

We studied 255 obese adolescents with normal glucose tolerance. All of them were investigated for in utero exposure to GDM and underwent an OGTT, which was repeated after approximately 2.8 years.

RESULTS

210 (82.3%) participants were not exposed to GDM (NGDM group), and 45 (17.7%) were exposed to GDM (EGDM group). In the NGDM group, only 8.6% (n = 18) developed either IGT or type 2 diabetes compared with 31.1% (n = 14) of the EGDM group who developed either IGT or type 2 diabetes (p < 0.001). Exposure to GDM was the most significant predictor of developing IGT or type 2 diabetes (OR 5.75, 95% CI 2.19, 15.07, p < 0.001). At baseline and at follow-up, the EGDM group showed a reduction in beta cell function determined by the oral disposition index (p = 0.03 and p = 0.01, respectively), and, at follow-up, they also displayed a reduction in insulin sensitivity compared with the NGDM group (p = 0.05).

CONCLUSIONS/INTERPRETATION

Obese youth exposed in utero to GDM show early inability of the beta cell to compensate adequately in response to decreasing levels of insulin sensitivity.

β-cell function, incretin effect, and incretin hormones in obese youth along the span of glucose tolerance from normal to prediabetes to type 2 diabetes

Using the hyperglycemic and euglycemic clamp, we demonstrated impaired β-cell function in obese youth with increasing dysglycemia. Herein we describe oral glucose tolerance test (OGTT)-modeled β-cell function and incretin effect in obese adolescents spanning the range of glucose tolerance. β-Cell function parameters were derived from established mathematical models yielding β-cell glucose sensitivity (βCGS), rate sensitivity, and insulin sensitivity in 255 obese adolescents (173 with normal glucose tolerance [NGT], 48 with impaired glucose tolerance [IGT], and 34 with type 2 diabetes [T2D]). The incretin effect was calculated as the ratio of the OGTT-βCGS to the 2-h hyperglycemic clamp-βCGS. Incretin and glucagon concentrations were measured during the OGTT. Compared with NGT, βCGS was 30 and 65% lower in youth with IGT and T2D, respectively; rate sensitivity was 40% lower in T2D. Youth with IGT or T2D had 32 and 38% reduced incretin effect compared with NGT in the face of similar changes in GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) in response to oral glucose. We conclude that glucose sensitivity deteriorates progressively in obese youth across the spectrum of glucose tolerance in association with impairment in incretin effect without reduction in GLP-1 or GIP, similar to that seen in adult dysglycemia.

Metabolic syndrome in pediatrics

The ever growing prevalence of childhood obesity is being accompanied by an increase in the pediatric population of diseases once believed to be exclusive of the adulthood such as the metabolic syndrome (MS). The MS has been defined as the link between insulin resistance, hypertension, dyslipidemia, impaired glucose tolerance, and other metabolic abnormalities associated with an increased risk of atherosclerotic cardiovascular diseases in adults. In this review, we will discuss the peculiar aspects of the pediatric MS and the role of novel molecules and biomarkers in its pathogenesis.

Chemical-genetic induction of Malonyl-CoA decarboxylase in skeletal muscle

Background

Defects in skeletal muscle fatty acid oxidation have been implicated in the etiology of insulin resistance. Malonyl-CoA decarboxylase (MCD) has been a target of investigation because it reduces the concentration of malonyl-CoA, a metabolite that inhibits fatty acid oxidation. The in vivo role of muscle MCD expression in the development of insulin resistance remains unclear.

Results

To determine the role of MCD in skeletal muscle of diet induced obese and insulin resistant mouse models we generated mice expressing a muscle specific transgene for MCD (Tg-fMCD^Skel) stabilized posttranslationally by the small molecule, Shield-1. Tg-fMCD^Skel and control mice were placed on either a high fat or low fat diet for 3.5 months. Obese and glucose intolerant as well as lean control Tg-fMCD^Skel and nontransgenic control mice were treated with Shield-1 and changes in their body weight and insulin sensitivity were determined upon induction of MCD. Inducing MCD activity >5-fold in skeletal muscle over two weeks did not alter body weight or glucose intolerance of obese mice. MCD induction further potentiated the defects in insulin signaling of obese mice. In addition, key enzymes in fatty acid oxidation were suppressed following MCD induction.

Conclusion

Acute induction of MCD in the skeletal muscle of obese and glucose intolerant mice did not improve body weight and decreased insulin sensitivity compared to obese nontransgenic controls. Induction of MCD in skeletal muscle resulted in a suppression of mitochondrial oxidative genes suggesting a redundant and metabolite driven regulation of gene expression.

Effects of exercise and lifestyle modification on fitness, insulin resistance, skeletal muscle oxidative phosphorylation and intramyocellular lipid content in obese children and adolescents

BACKGROUND

Obesity is associated with poor fitness and adverse metabolic consequences in children.

OBJECTIVE

To investigate how exercise and lifestyle modification may improve fitness and insulin sensitivity in this population.

DESIGN AND SUBJECTS

Randomized controlled trial, 21 obese (body mass index ≥ 95% percentile) subjects, ages 10 to 17 years.

METHODS

Subjects were given standardized healthful lifestyle advice for 8 weeks. In addition, they were randomized to an in-home supervised exercise intervention (n = 10) or control group (n = 11).

MEASUREMENTS

Fasting laboratory studies (insulin, glucose, lipid profile) and assessments of fitness, body composition, skeletal muscle oxidative phosphorylation and intramyocellular lipid content (IMCL), were performed at baseline and study completion.

RESULTS

Subjects were 13.0 ± 1.9 (standard deviation) years old, 72% female and 44% non-white. Exercise improved fitness (P = 0.03) and power (P = 0.01), and increased IMCL (P = 0.02). HOMA-IR decreased among all subjects in response to lifestyle modification advice (P = 0.01), regardless of exercise training assignment. In univariate analysis in all subjects, change in cardiovascular fitness was associated with change in HOMA-IR. In exploratory analyses, increased IMCL was associated with greater resting energy expenditure (r = 0.78, P = 0.005) and a decrease in fasting respiratory quotient (r = -0.70, P = 0.02) (n = 11).

CONCLUSIONS

Change in fitness was found to be related to change in insulin resistance in response to lifestyle modification and exercise in obese children. IMCL increased with exercise in these obese children, which may reflect greater muscle lipid oxidative capacity.

Links between ectopic fat and vascular disease in humans

The average of overweight individual can have differential fat depots in target organs or specific compartments of the body. This ectopic fat distribution may be more of a predictive factor for cardiovascular risk than obesity. Abdominal visceral obesity, a representative ectopic fat, is robustly associated with insulin resistance and cardiovascular risk. Fat depots in the liver and muscle tissue cause adverse cardiometabolic risk by affecting glucose and lipid metabolism. Pericardial fat and perivascular fat affect coronary atherosclerosis, cardiac function, and hemodynamics. Fat around the neck is associated with systemic vascular resistance. Fat around the kidney may increase blood pressure and induce albuminuria. Fat accumulation in or around the pancreas alters glucose metabolism, conferring cardiovascular risk. Ectopic fat may act as an active endocrine and paracrine organ that releases various bioactive mediators that influence insulin resistance, glucose and lipid metabolism, coagulation, and inflammation, which all contribute to cardiovascular risk. Because both obese and apparently lean individuals can have ectopic fat, regional fat distribution may play an important role in the development of cardiovascular diseases in both nonobese and obese people.

Role of diacylglycerol activation of PKCθ in lipid-induced muscle insulin resistance in humans

Muscle insulin resistance is a key feature of obesity and type 2 diabetes and is strongly associated with increased intramyocellular lipid content and inflammation. However, the cellular and molecular mechanisms responsible for causing muscle insulin resistance in humans are still unclear. To address this question, we performed serial muscle biopsies in healthy, lean subjects before and during a lipid infusion to induce acute muscle insulin resistance and assessed lipid and inflammatory parameters that have been previously implicated in causing muscle insulin resistance. We found that acute induction of muscle insulin resistance was associated with a transient increase in total and cytosolic diacylglycerol (DAG) content that was temporally associated with protein kinase (PKC)θ activation, increased insulin receptor substrate (IRS)-1 serine 1101 phosphorylation, and inhibition of insulin-stimulated IRS-1 tyrosine phosphorylation and AKT2 phosphorylation. In contrast, there were no associations between insulin resistance and alterations in muscle ceramide, acylcarnitine content, or adipocytokines (interleukin-6, adiponectin, retinol-binding protein 4) or soluble intercellular adhesion molecule-1. Similar associations between muscle DAG content, PKCθ activation, and muscle insulin resistance were observed in healthy insulin-resistant obese subjects and obese type 2 diabetic subjects. Taken together, these data support a key role for DAG activation of PKCθ in the pathogenesis of lipid-induced muscle insulin resistance in obese and type 2 diabetic individuals.

Not only type 2 diabetes but also prediabetes is associated with portal inflammation and fibrosis in patients with non-alcoholic fatty liver disease

AIMS

Growing evidence suggests that not only type 2 diabetes (T2D) but also prediabetes (PD) is common in patients with non-alcoholic fatty liver disease (NAFLD). However, few data exist on how PD impacts the histological characteristics of NAFLD patients. In this exploratory study, we sought to investigate the associations of PD and T2D with the severity of the histological features in patients with NAFLD.

METHODS

The population consisted of 280 patients with biopsy-proven NAFLD. The associations of PD and T2D with the severity of histological features of NAFLD were analyzed using multiple logistic (or ordinal logistic) regression models after adjustment for confounding factors.

RESULTS

PD and T2D was noted in 102 (36.4%) and 92 (32.8%) of patients, respectively. Of the 92 patients with T2D, ten (10.9%) were diagnosed de novo after the OGTT. PD and T2D were significantly associated with more severe portal inflammation (P<0.01); the adjusted odds ratios (ORs) of PD and T2D for having a higher grade of portal inflammation were 1.8 [95% CI, 1.1, 3.2] and 2.6 [95% CI, 1.3, 5.8]), respectively. A similar relationship was observed for liver fibrosis (P<0.001); specifically, the adjusted ORs of PD and T2D for having a higher grade of hepatic fibrosis were 2.4 [95% CI, 1.3, 3.7] and 3.8 [95% CI, 1.9, 6.1]), respectively.

CONCLUSION

Not only T2D but also PD is independently associated with portal inflammation and fibrosis in NAFLD patients. PD may be useful as a clinical indicator of patients who are likely to have already more severe histological findings.

The relative contributions of the abdominal visceral and subcutaneous fat depots to cardiometabolic risk in youth

The aim of this study was to evaluate the association of abdominal visceral and subcutaneous fat, independent of total body fat, with cardiometabolic risk factors and insulin resistance among youth. Visceral and subcutaneous fat, percentage total body fat, insulin resistance (adjusted for lean body mass: Mlbm), blood pressure, glucose, insulin and lipids were obtained in 472 youth ages 6-18 years. Linear regression, adjusted for age, sex, race, Tanner stage and percentage total body fat, was used to evaluate associations of visceral and subcutaneous fat with cardiometabolic risk factors. Visceral fat was associated inversely with Mlbm (P = 0.003) and positively with fasting insulin (P = 0.002) and triglycerides (P = 0.002). Visceral fat levels above the mean were associated inversely with high-density lipoprotein (HDL) cholesterol (P = 0.002), and positively with systolic blood pressure (P < 0.0001) and non-HDL cholesterol (P < 0.0001). Subcutaneous fat was associated inversely with Mlbm (P = 0.003) and HDL cholesterol (P < 0.05), and positively with fasting glucose (P < 0.05), fasting insulin (P = 0.0003), systolic blood pressure (P = 0.005) and triglycerides (P = 0.003). Subcutaneous fat levels above the mean were associated with non-HDL cholesterol (P = 0.0002). These findings suggest that there may be a threshold level of visceral and subcutaneous fat (regardless of total body fat), that when exceeded in childhood, is more likely to be associated with many cardiometabolic risk factors. Triglycerides and insulin resistance appear to be associated with these fat depots at even lower thresholds of abdominal adiposity.

Use of a simple liquid meal test to evaluate insulin sensitivity and beta-cell function in children

Insulin sensitivity and β-cell function are useful indices of metabolic disease risk but are difficult to assess in young children because of the invasive nature of commonly used methodology. A meal-based method for assessing insulin sensitivity and β-cell function may at least partially alleviate concerns. The objectives of this study were to: (i) determine the association of insulin sensitivity assessed by liquid meal test with that determined by an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT); (ii) examine the association of insulin sensitivity derived from each test with measures of body composition, fat distribution and metabolic health (lipids, fasting insulin and glucose, and surrogate indices of insulin sensitivity); and (iii) examine the associations of indices of β-cell function derived from each test with total and regional adiposity. Forty-seven children (7-12 years) underwent both a liquid meal test and an FSIGT. The insulin sensitivity index derived from the meal test (SI-meal) was positively associated with that from the FSIGT (SI-FSIGT; r = 0.63; P < 0.001), and inversely with all measures of insulin secretion derived from the meal test. Both SI-meal and SI-FSIGT were associated with measures of total and regional adiposity. SI-meal, but not SI-FSIGT, was associated with triglycerides and fasting insulin, after adjusting for ethnicity, gender, pubertal stage and fat mass. Basal insulin secretion measured during the meal test was positively associated with all measures of adiposity, independent of insulin sensitivity. In conclusion, a liquid meal offers a valid and sensitive means of assessing insulin sensitivity and β-cell responsivity in young children.

The many faces of diabetes: a disease with increasing heterogeneity

Diabetes is a much more heterogeneous disease than the present subdivision into types 1 and 2 assumes; type 1 and type 2 diabetes probably represent extremes on a range of diabetic disorders. Both type 1 and type 2 diabetes seem to result from a collision between genes and environment. Although genetic predisposition establishes susceptibility, rapid changes in the environment (ie, lifestyle factors) are the most probable explanation for the increase in incidence of both forms of diabetes. Many patients have genetic predispositions to both forms of diabetes, resulting in hybrid forms of diabetes (eg, latent autoimmune diabetes in adults). Obesity is a strong modifier of diabetes risk, and can account for not only a large proportion of the epidemic of type 2 diabetes in Asia but also the ever-increasing number of adolescents with type 2 diabetes. With improved characterisation of patients with diabetes, the range of diabetic subgroups will become even more diverse in the future.

The prevention and control the type-2 diabetes by changing lifestyle and dietary pattern

Type-2 diabetes is a major, non-communicable disease with increasing prevalence at a global level. Type-2 diabetes results when the body does not make enough insulin or the body cannot use the insulin it produces. Type-2 diabetes is the leading cause of premature deaths. Improperly managed, it can lead to a number of health issues, including heart diseases, stroke, kidney disease, blindness, nerve damage, leg and foot amputations, and death. Type-2 diabetes or adult-onset diabetes is most common type of diabetes, usually begins when a person is in his or her mid-50s, but diabetes is not inevitable. Minor changes in your lifestyle can greatly reduce your chances of getting this disease. Therefore, in order to prevent this condition, action should be taken regarding the modifiable factors that influence its development-lifestyle and dietary habits. However, with proper testing, treatment and lifestyle changes, healthy eating as a strategy, promote walking, exercise, and other physical activities have beneficial effects on human health and prevention or treatment of diabetes, promoting adherence to this pattern is of considerable public health importance.

Therapeutic interventions for hypertension in metabolic syndrome: a comprehensive approach

Hypertension is a major component of the metabolic syndrome and a major cardiovascular risk factor. Both disorders are rapidly increasing in frequency, with hypertension affecting nearly 60 million Americans and over 1 billion people worldwide, and metabolic syndrome affecting 44% of the US population above the age of 60 years. Sedentary lifestyle, together with obesity and aging of the population, are the major contributing factors for this growing epidemic. Hypertension in metabolic syndrome possesses unique pathophysiological aspects that have considerable implications on therapy of this disease. In this article, we review the pathophysiology and provide a rationale for the current therapeutic options in light of the most recent clinical trials in the field.

Maternal and in utero determinants of type 2 diabetes risk in the young

The global prevalence of diabetes mellitus has reached epidemic proportions. In 2010, it was estimated that 6.4 % of the adult population (285 million) have diabetes. In recent years, the incidence of type 2 diabetes (T2D), a condition traditionally associated with aging, has been steadily increasing among younger individuals. It is now a well-established notion that the early-life period is a critical window of development and that influences during this period can "developmentally prime" the metabolic status of the adult. This review discusses the role of maternal and in utero influences on the developmental priming of T2D risk. Both human epidemiological studies and experimental animal models are beginning to demonstrate that early dietary challenges can accelerate the onset of age-associated metabolic disturbances, including insulin resistance, T2D, obesity, hypertension, and cardiovascular disease. These findings show that poor maternal nutrition can prime a prediabetes phenotype, often manifest as insulin resistance, by very early stages of life. Thus, the maternal diet is a critical determinant of premature T2D risk. While the mechanisms that link early nutrition to age-associated metabolic decline are currently unclear, preliminary findings suggest perturbations in a number of processes involved in cellular aging, such as changes in longevity-associated Sirtuin activity, epigenetic regulation of key metabolic genes, and mitochondrial dysfunction. Preliminary studies show that pharmacological interventions in utero and dietary supplementation in early postnatal life may alleviate insulin resistance and reduce T2D risk. However, further studies are warranted to fully understand the relationship between the early environment and long-term effects on metabolism. Such mechanistic insights will facilitate strategic interventions that prevent accelerated metabolic decline and the premature onset of T2D in the current and future generations.

Programming of glucose-insulin homoeostasis: long-term consequences of pre-natal versus early post-natal nutrition insults. Evidence from a sheep model

AIM

Exposure to adverse intra-uterine conditions can predispose for metabolic disorders later in life. By using a sheep model, we studied (i) how programming of glucose-insulin homoeostasis during late gestation is manifested later in life depending on the early post-natal dietary exposure and (ii) whether dietary alteration in obese individuals can prevent adverse outcomes of early life programming.

METHODS

During late gestation, twin-pregnant sheep were fed 100% (NORM) or 50% (LOW) of energy and protein requirements. After birth, offspring were exposed to a moderate (CONV) or high-carbohydrate-high-fat (HCHF) diet until around puberty. Offspring remaining thereafter (exclusively females) were fed a moderate diet until young adulthood.

RESULTS

LOW lambs had increased insulin secretory responses during intravenous glucose tolerance tests indicative of reduced insulin sensitivity. HCHF lambs were hypertriglyceridaemic, 75% had mild pancreatic collagen infiltration, and their acute insulin secretory response and insulin clearance during intravenous glucose and insulin tolerance tests, respectively, were reduced. However, NORM-HCHF in contrast to LOW-HCHF lambs had normal glucose tolerance, indicating that later health outcomes are highly influenced by pre-natal nutrition. Dietary alteration normalized glucose-insulin homoeostasis in adult HCHF females, whereas late-gestation undernutrition (LOW) permanently depressed insulin sensitivity.

CONCLUSION

Maintenance of glucose tolerance in sheep exposed to pre-natal undernutrition relied on pancreatic hypersecretion of insulin to compensate for reduced insulin sensitivity. A mismatching high-fat diet in early post-natal life interfered with this pancreatic hypersecretion resulting in reduced glucose tolerance. Early post-natal, but not late pre-natal, impacts on glucose-insulin homoeostasis could be reversed by dietary correction later in life.

Aerobic exercise but not resistance exercise reduces intrahepatic lipid content and visceral fat and improves insulin sensitivity in obese adolescent girls: a randomized controlled trial

It is unclear whether regular exercise alone (no caloric restriction) is a useful strategy to reduce adiposity and obesity-related metabolic risk factors in obese girls. We examined the effects of aerobic (AE) vs. resistance exercise (RE) alone on visceral adipose tissue (VAT), intrahepatic lipid, and insulin sensitivity in obese girls. Forty-four obese adolescent girls (BMI ≥95th percentile, 12-18 yr) with abdominal obesity (waist circumference 106.5 ± 11.1 cm) were randomized to 3 mo of 180 min/wk AE (n = 16) or RE (n = 16) or a nonexercising control group (n = 12). Total fat and VAT were assessed by MRI and intrahepatic lipid by proton magnetic resonance spectroscopy. Intermuscular AT (IMAT) was measured by CT. Insulin sensitivity was evaluated by a 3-h hyperinsulinemic (80 mU·m(2)·min(-1)) euglycemic clamp. Compared with controls (0.13 ± 1.10 kg), body weight did not change (P > 0.1) in the AE (-1.31 ± 1.43 kg) and RE (-0.31 ± 1.38 kg) groups. Despite the absence of weight loss, total body fat (%) and IMAT decreased (P < 0.05) in both exercise groups compared with control. Compared with control, significant (P < 0.05) reductions in VAT (Δ-15.68 ± 7.64 cm(2)) and intrahepatic lipid (Δ-1.70 ± 0.74%) and improvement in insulin sensitivity (Δ0.92 ± 0.27 mg·kg(-1)·min(-1) per μU/ml) were observed in the AE group but not the RE group. Improvements in insulin sensitivity in the AE group were associated with the reductions in total AT mass (r = -0.65, P = 0.02). In obese adolescent girls, AE but not RE is effective in reducing liver fat and visceral adiposity and improving insulin sensitivity independent of weight loss or calorie restriction.

Type 2 diabetes mellitus in pediatrics: a new challenge

BACKGROUND

The increased prevalence of childhood obesity in the last few years has been accompanied by the increase in prevalence of type 2 diabetes in pediatrics. In this paper, we will review the risk factors and the pathogenic determinants leading to type 2 diabetes in youth.

DATA SOURCES

We searched on PubMed with the key words: obesity, type 2 diabetes, children, adolescents, youth, non-alcoholic fatty liver disease, genes and selected those publications written in English that we judged to be relevant to the topic of the review.

RESULTS

Based on the data present in the literature, we reviewed the following three topics: 1) the role of ectopic fat deposition, in particular of fatty liver, in the pathogenesis of pediatric type 2 diabetes; 2) the progression to type 2 diabetes in pediatrics and how it differs from adults, and 3) current theraputic options.

CONCLUSION

Type 2 diabetes in youth is a complex disease, creating new challenges in treatment and prevention.

Ectopic fat and cardiometabolic and vascular risk

Given that the variation in how regional adipose tissue handles and stores excess dietary energy has substantial cardiometabolic implications, ectopic fat distribution might be an important predictor of cardiometabolic and vascular risk, in addition to overall obesity itself. Conceptually, ectopic fat depots may be divided into systemically acting fat depots and locally acting fat depots. Systemically acting fat depots include visceral fat, fat in the liver, muscle, or neck, and subcutaneous fat. Accumulation in the abdominal visceral area, compared with overall obesity, has an equally or more important role in the development of cardiometabolic risk. Fat depots in liver/muscle tissue cause adverse cardiometabolic effects by affecting energy metabolism. Fat depots in lower-body subcutaneous areas may be protective regarding cardiometabolic risk, by trapping remnant energy. Fat accumulation in the neck is a unique type of fat depot that may increase cardiovascular risk by increasing insulin resistance. Locally acting fat depots include pericardial fat, perivascular fat, and renal sinus fat. These fat depots have effects primarily on adjacent anatomic organs, directly via lipotoxicity and indirectly via cytokine secretion. Pericardial fat is associated with coronary atherosclerosis. Perivascular fat may play an independent role in adverse vascular biology, including arterial stiffness. Renal sinus fat is a unique fat depot that may confer additional cardiometabolic risk. Thus, ectopic fat depots may contribute to the understanding of the link between body composition and cardiometabolic risk. In this review, we focus on the role and clinical implications of ectopic fat depots in cardiometabolic and vascular risk.

Cardiorespiratory fitness and adiposity in metabolically healthy overweight and obese youth

OBJECTIVE

Controversy exists surrounding the contribution of fitness and adiposity as determinants of the Metabolically Healthy Overweight(MHO) phenotype in youth. This study investigated the independent contribution of cardiorespiratory fitness and adiposity to the MHO phenotype among overweight and obese youth.

METHODS

This cross-sectional study included 108 overweight and obese youth classified as MHO (no cardiometabolic risk factors) or non-MHO (≥1 cardiometabolic risk factor), based on age- and gender specific cut-points for fasting glucose, triglycerides, high-density lipoprotein cholesterol, systolic and diastolic blood pressure, and hepaticsteatosis.

RESULTS

Twenty-five percent of overweight and obese youth were classified as MHO. This phenotype was associated with lower BMIz-score (BMI z-score: 1.8 ± 0.3 vs 2.1 ± 0.4, P = .02) and waist circumference (99.7 ± 13.2 vs 106.1 ± 13.7 cm, P = .04) compared with non-MHO youth. When matched for fitness level and stratified by BMI z-score (1.6 ± 0.3 vs 2.4 ± 0.2), the prevalence of MHO was four fold higher in the low BMI z-score group (27% vs 7%; P = .03).Multiple logistic regression analyses revealed that the best predictor of MHO was the absence of hepatic steatosis even after adjusting for waist circumference (odds ratio 0.57, 95% confidence interval 0.40–0.80) or BMI z-score (odds ratio 0.59, 95% confidence interval 0.43–0.80).

CONCLUSIONS

The MHO phenotype was present in 25% of overweight and obese youth and is strongly associated with lower levels of adiposity,and the absence of hepatic steatosis, but not with cardiorespiratory fitness.

Circulating levels of FGF-21 in obese youth: associations with liver fat content and markers of liver damage

OBJECTIVE

Fibroblast growth factor (FGF)-21 is highly expressed in the liver and regulates glucose and lipid metabolism in rodents. The effects of obesity and fatty liver on circulating FGF-21 levels have been described mainly in adults. Herein, we measured plasma FGF-21 levels in lean and obese adolescents with low and high hepatic fat content (HFF% <5.5% and HFF% ≥ 5.5%, respectively) and explored their relationship with hepatic fat content, measures of hepatic apoptosis, and insulin sensitivity.

METHODS

A total of 217 lean and obese adolescents with both low and high HFF% (lean = 31; obese low HFF% = 107; and obese high HFF% = 79) underwent an oral glucose tolerance test, a fast gradient magnetic resonance imaging to measure the %HFF and abdominal fat distribution. Cytokeratin 18 levels were measured as a biomarker of liver apoptosis. A subset of adolescents underwent a 2-step hyperinsulinemic-euglycemic clamp, and a liver biopsy (N = 14), to assess insulin sensitivity and steatohepatitis, respectively.

RESULTS

Compared to controls, FGF-21 levels were higher in obese youth, especially in those with high HFF (P < .001). FGF-21 significantly correlated with adiposity indexes (P < .001), visceral fat (r² = 0.240, P < .001), hepatic fat content (r² = 0.278, P < .001), cytokeratin 18 (r² = 0.217, P < .001), and alanine aminotransferase (r² = .164, P < .001). In subjects with steatoheaptitis, FGF-21 levels significantly correlated with the nonalcoholic fatty liver disease activity score (r² = 0.27, P = .04). Stepwise regression analysis indicated that these relationships are independent of body mass index, visceral fat, and insulin sensitivity. An inverse correlation was documented with insulin, hepatic resistance indexes, and adipose resistance indexes, which disappeared after adjusting for hepatic fat content.

CONCLUSIONS

Plasma FGF-21 levels are increased in obese adolescents, particularly in those with fatty liver. FGF-21 concentrations significantly and independently correlate with hepatic fat content and markers of hepatic apoptosis in obese youths.

The predictive ability of triglycerides and waist (hypertriglyceridemic waist) in assessing metabolic triad change in obese children and adolescents

BACKGROUND

The metabolic triad [fasting insulin, apolipoprotein B, and low-density lipoporotein (LDL) peak particle density] is characteristic of increased intra-abdominal adipose tissue and insulin resistance and can be predicted by the simple and adoptable screening tool, the hypertriglyceridemic waist. The associations between hypertriglyceridemic waist components [fasting triglycerides (TG) and waist circumference cut-points derived from a child-specific metabolic syndrome definition] with the metabolic triad were examined in obese youth before and after weight loss.

METHODS

A continuous metabolic triad score (MTS) was calculated as a cumulative and standardized residual score of fasting insulin, apolipoprotein B, and LDL peak particle density (z-scores of the metabolic triad variables regressed onto age and sex). The predictive ability of TG and waist in assessing metabolic triad change was undertaken in 75 clinically obese boys and girls, aged 8-18, body mass index (BMI) 34.2±6.4 kg/m(2) before and after weight loss.

RESULTS

Fasting TG concentrations (r(2)=0.216, P<0.0001) and waist circumference (r(2)=0.049, P=0.019) were both significant independent predictors of the cumulative MTS, together accounting for 26.5% of its total variance. All cardiometabolic risk factors [except a reduction in high-density lipoprotein cholesterol (HDL-C)] were favorably modified following weight loss. Fasting TG change was the only significant predictor of the MTS change (r(2)=0.177, P<0.0001). Waist circumference was not a significant predictor of MTS change.

CONCLUSION

The reduction in fasting TG concentration (but not waist circumference) was the only significant predictor of MTS change. Fasting TG may be the most important metabolic syndrome component to best characterize the metabolic heterogeneity in obese cohorts and the changes in metabolic risk in clinically obese youth.

An evaluation of early cardiometabolic risk factors in children and adolescents with Turner syndrome

BACKGROUND AND OBJECTIVES

Turner syndrome (TS) confers increased lifetime risk of type 2 diabetes mellitus and cardiovascular disease. We compared cardiometabolic risk factors and measures of subcutaneous, visceral adipose tissue and intra-myocellular lipid between young TS girls and an age- and BMI-standard deviation scores (SDS)-matched healthy female cohort.

PATIENTS AND METHODS

A cross-sectional cohort study was conducted at the Hospital for Sick Children, Toronto. Nineteen TS and 17 control girls (13.7 ± 2.5 vs 12.7 ± 3.4 years of age, respectively, P = 0.30). Multiple-sample oral glucose tolerance test with measurement of fasting insulin, LDL, HDL, triglycerides, adiponectin and highly sensitive C-reactive protein (hsCRP) was performed. Subcutaneous adipose tissue, visceral adipose tissue intramyocellular lipid levels evaluated by magnetic resonance techniques. Insulin secretion (IS), sensitivity (Si) and the insulin secretion-sensitivity index (ISSI-2) were calculated from oral glucose tolerance test data.

RESULTS

Five TS and no controls had impaired fasting glucose or impaired glucose tolerance; none had type 2 diabetes mellitus. Insulin sensitivity and insulin secretion were similar between groups; ISSI-2 was lower in TS (923.5 ± 307.3 vs 659.1 ± 387.3; P = 0.03). TS girls had higher blood pressure (82.5 ± 13.6 vs 73.5 ± 5.5 mmHg; P = 0.0146), waist circumference (76.0 ± 11.8 vs 65.9 ± 9.7; P = 0.0087) and subcutaneous adipose tissue (135.6 ± 88.6 vs 69.3 ± 59.9; P = 0.01) than controls. Visceral adipose tissue, intramyocellular lipid levels and adiponectin were not different between groups. TS girls also had higher triglycerides (1.1 ± 0.6 vs 0.7 ± 0.3; P = 0.003), total cholesterol (4.4 ± 0.7 vs 3.9 ± 0.4; P = 0.02) and hsCRP (2.0 ± 1.9 vs 0.8 ± 0.3; P = 0.01).

CONCLUSIONS

TS girls exhibit more cardiometabolic risk factors and reduced beta cell function compared with age- and BMI-SDS-matched girls. Increased awareness of early risk of type 2 diabetes mellitus and hypertension in TS girls is needed.

Pathophysiology of prediabetes and treatment implications for the prevention of type 2 diabetes mellitus

Type 2 diabetes and other non-communicable diseases (NCD) are a growing public health challenge globally. An estimated 285 million people, corresponding to 6.4 % of the world's adult population has diabetes. This is expected to reach 552 million by 2030, 7.8 % of the adult population, with the African region expected to experience the greatest increase. A much larger segment of the world's population, approximating 79 million individuals in the US alone, has prediabetes. Multiple factors including genetic predisposition, insulin resistance, increased insulin secretory demand, glucotoxicity, lipotoxicity, impaired incretin release/action, amylin accumulation, and decreased β-cell mass play a causative role in the progressive β-cell dysfunction characteristic of prediabetes. Interventions preventing progression to type 2 diabetes should therefore delay or prevent β-cell failure. This article will first review the principal pathophysiological mechanisms underlying prediabetes and subsequently address treatment considerations based on these in the prevention of type 2 diabetes. In view of long-standing safety data with demonstrated efficacy and cost-effectiveness in the prevention of type 2 diabetes in high-risk individuals, metformin should be considered as initial therapy for those unable to comply with or lifestyle modification or where the latter has been ineffective in decreasing progression to type 2 diabetes.

Insulin resistance: an emerging link in Alzheimer's disease

Relentless progression of Alzheimer's disease (AD) poses a grave situation for the biomedical community to tackle. Agents starting as hot favorites in clinical trials have failed in later stages and it is time we reconsidered our approaches to intervene the disease. Quite some interesting work in the last decade has introduced a new school of thought which factors in neuronal glycemic imbalance as a major component for the development of AD. Insulin resistance in the brain has brought forward subsequent sequelae which might work towards amyloid accretion and/or tau hyperphosphorylation. It is also pointed out that insulin works by distributing iron to neuronal tissue and an insulin resistant state throws it off gear leading to iron overloading of neurons which is ultimately detrimental. A relatively recent investigation finds the role of c-Jun-N-terminal kinase (JNK3) in AD which also seems to bear a link with insulin resistance.

Metabolic syndrome in youth: current insights and novel serum biomarkers

Paralleling the worldwide epidemic in childhood obesity, in the last decade we have observed a rise in the prevalence of metabolic syndrome (MetS) in pediatrics. The MetS comprises a cluster of cardiovascular risk factors. Multiple definitions have been proposed for the syndrome in the pediatric age group, but they are very difficult to test and validate. Thus, in this paper we will discuss the current knowledge in pediatric MetS and the potential role of novel biomarkers in the pathogenesis and diagnosis of MetS.

Associations of β-cell function and insulin resistance with youth-onset type 2 diabetes and prediabetes among Asian Indians

AIM

This study examined β-cell function and insulin resistance (homeostasis model assessment-insulin resistance [HOMA-IR]) in Asian Indian youth with type 2 diabetes mellitus (T2DM-Y) and prediabetes.

SUBJECTS AND METHODS

Eighty-two subjects with non-insulin-requiring type 2 diabetes and age of onset below 25 years were recruited within 18 months of diagnosis and compared with age- and sex-matched subjects with prediabetes (n=31) and normal glucose tolerance (NGT) (n = 83). Body mass index (BMI) and waist circumference were measured, and blood samples were taken in the fasting state and after 30, 60, 90, and 120 min of an oral glucose load for assessment of plasma glucose and insulin levels. Insulin sensitivity/resistance measures was calculated by using the reciprocal of the fasting insulin, the HOMA-IR equation, and the composite whole body insulin sensitivity index (Matsuda Index), and β-cell function was calculated by the oral disposition index (DIo).

RESULTS

T2DM-Y and prediabetes subjects had higher BMI, waist circumference, and fasting insulin than NGT subjects (P<0.05 for each). The 30-min insulin levels were lower in T2DM-Y and higher in prediabetes subjects compared with NGT (57 and 140 vs. 129 μIU/mL, P<0.001). The T2DM-Y group had greater insulin resistance (HOMA-IR, 1.87 vs. 0.97; P<0.05) and lower β-cell function (DIo, 0.36 vs. 3.28; P<0.001) than NGT. In separate models, the Matsuda Index and DIo were independently associated with prediabetes and T2DM-Y (P<0.05). However, when both were included together, only DIo remained associated with T2DM-Y, whereas both DIo and Matsuda Index were associated with prediabetes (P<0.05). When controlled for adiposity (BMI and waist circumference), an association was observed but in opposite directions, with waist being positively associated with prediabetes (P = 0.016) and BMI negatively associated with T2DM-Y (P = 0.009).

CONCLUSIONS

Among Asian Indians, β-cell dysfunction appears to be more strongly associated with T2DM-Y than insulin resistance.

Development of type 2 diabetes mellitus in the obese adolescent: a growing challenge

OBJECTIVE

To describe the metabolic phenotype of type 2 diabetes mellitus in youth and possible metabolic defects leading to its development with particular emphasis on fatty liver.

METHODS

We present data gathered from studies performed in obese adolescents across the spectrum of glucose tolerance to assess both alterations in insulin sensitivity and secretion. Discussion regarding treatment options is presented using the data from the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) study.

RESULTS

As the number of children with obesity continues to grow, the health implications of the condition are becoming increasingly evident. An unprecedented phenomenon rarely seen before has emerged: type 2 diabetes mellitus. At the time of diabetes diagnosis, cardiovascular disease may already be present, even in young adults. The progression from normal glucose tolerance to type 2 diabetes in adults occurs through an intermediate phase of altered glucose metabolism known as impaired glucose tolerance or prediabetes. Previous studies from our group and others reported a high prevalence of impaired glucose tolerance among children and adolescents with marked obesity. Cross-sectional studies demonstrate that impaired glucose tolerance in obese youth is associated with severe insulin resistance, β-cell dysfunction, and altered abdominal and muscle fat partitioning. We end briefly by discussing the current data available on treatment of this condition from the TODAY study, the largest clinical trial ever performed in youth with type 2 diabetes.

CONCLUSION

The observed rapid progression of the glucose homeostasis alterations in adolescents underlines the importance of focusing attention on the earliest stages of the disease before the onset of any alterations in glucose tolerance.

Decreased transcription of ChREBP-α/β isoforms in abdominal subcutaneous adipose tissue of obese adolescents with prediabetes or early type 2 diabetes: associations with insulin resistance and hyperglycemia

Insulin resistance associated with altered fat partitioning in liver and adipose tissues is a prediabetic condition in obese adolescents. We investigated interactions between glucose tolerance, insulin sensitivity, and the expression of lipogenic genes in abdominal subcutaneous adipose and liver tissue in 53 obese adolescents. Based on their 2-h glucose tests they were stratified in the following groups: group 1, 2-h glucose level <120 mg/dL; group 2, 2-h glucose level between 120 and 140 mg/dL; and group 3, 2-h glucose level >140 mg/dL. Liver and adipose tissue insulin sensitivity were greater in group 1 than in group 2 and group 3, and muscle insulin sensitivity progressively decreased from group 1 to group 3. The expression of the carbohydrate-responsive element-binding protein (ChREBP) was decreased in adipose tissue but increased in the liver (eight subjects) in adolescents with impaired glucose tolerance or type 2 diabetes. The expression of adipose ChREBPα and ChREBPβ was inversely related to 2-h glucose level and positively correlated to insulin sensitivity. Improvement of glucose tolerance in four subjects was associated with an increase of ChREBP/GLUT4 expression in the adipose tissue. In conclusion, early in the development of prediabetes/type 2 diabetes in youth, ChREBPβ expression in adipose tissue predicts insulin resistance and, therefore, might play a role in the regulation of glucose tolerance.

Obesity, metabolic syndrome, and insulin resistance in urban high school students of minority race/ethnicity

OBJECTIVES

To determine the point prevalences of metabolic syndrome (MetS) and its components among healthy weight, overweight, and obese inner-city public high school students, to compare the prevalences of MetS when using 2 different definitions (one with the impaired fasting glucose [IFG] level and the other with a homeostasis model assessment of insulin resistance [HOMA-IR] of 3.99 or higher to define the glucose regulation component), and to compare the degree to which HOMA-IR and fasting glucose level are associated with the other MetS components.

DESIGN

Cross-sectional analysis.

SETTING

Two New York City public high schools, from April 2008 through August 2011.

PARTICIPANTS

Convenience sample of 1185 high school youth, comprising predominantly Hispanic and African American students from low-income households, participating in The Banishing Obesity and Diabetes in Youth Project, a medical screening and education program.

MAIN OUTCOME MEASURES

Prevalences of the following individual MetS components: IFG threshold, HOMA-IR, hypertension, central adiposity, hypertriglyceridemia, and low high-density lipoprotein cholesterol. Rates of MetSIFG and MetSHOMA-IR were also assessed.

RESULTS

MetSIFG and MetSHOMA-IR point prevalences were both 0.3% in the healthy weight group; they were 2.6% and 5.9%, respectively, in the overweight group and were 22.9% and 35.1%, respectively, in the obese group (P < .05 for both). An IFG threshold of 100 mg/dL or higher was found in 1.0% of participants, whereas a HOMA-IR of 3.99 or higher was found in 19.5% of participants.

CONCLUSIONS

An elevated HOMA-IR is much more sensitive than an IFG threshold in identifying adolescents with metabolic dysregulation. Using a HOMA-IR threshold of 3.99 identifies more youth with MetS than using an IFG threshold of 100 mg/dL. In addition to increasing the sensitivity of MetS detection, HOMA-IR has a much higher association with the other MetS components than the IFG threshold and may better reflect a unified underlying pathologic process useful to identify youth at risk for disease.

Prevalence of child and youth obesity in Spain in 2012

INTRODUCTION AND OBJECTIVES

Obesity is a major cardiovascular risk factor. In Spain, few studies have physically measured height and weight to estimate the magnitude of the problem. The aim of this study was to determine the prevalence of child and adolescent obesity in Spain in 2012.

METHODS

We performed a cross-sectional probability sample of 1018 children, representative of the Spanish population aged between 8 and 17 years old, with objectively measured height and weight, along with other sociodemographic variables. We calculated the prevalence of overweight and obesity according to the criteria of the World Health Organization, the International Obesity Task Force, and the enKid study.

RESULTS

In the group aged 8 to 17 years old, the prevalence of overweight and obesity was 26% and 12.6%, respectively; 4 in 10 young people were overweight or obese. Excess weight was found in 45% of the group aged 8 to 13 years and in 25.5% of that aged 14 to 17 years. This cardiovascular risk factor was associated with lower social class and lower educational level.

CONCLUSIONS

The prevalence of overweight and obesity in children and adolescents in Spain remains high (close to 40%), but has not increased in the last 12 years.

Progression of β-cell dysfunction in obese youth

The epidemic of childhood obesity has led to a remarkable increase in the prevalence of type 2 diabetes (T2D) among youth worldwide. The decreasing age at onset of T2D has alarming public health implications. In particular, the longer duration of the disease, as well as the faster onset and progression of T2D related complications, will present a considerable burden for young adults and a strain on public health. Therefore, it is important to understand the pathophysiology of early phases of disruption of glucose tolerance and identify those critical points in which diabetes may be prevented. β-Cell dysfunction has been shown to represent one of the key pathogenetic defects underlying the progression to diabetes in obese youth. In the present review, we describe longitudinal and cross-sectional studies of changes in insulin sensitivity and secretion across the spectrum of glucose tolerance in obese adolescents. Further, the role of ectopic fat accumulation is discussed in relation to its association with both β-cell dysfunction and insulin resistance.

Etiology of insulin resistance in youth with type 2 diabetes

Type 2 diabetes (T2DM), historically an adult disease, is now increasingly prevalent in obese youth. Poor diet and increased sedentary behavior contribute to the increasing rates of obesity in youth, yet not all obese children develop T2DM. In general, T2DM is characterized by both insulin resistance (IR) and pancreatic beta-cell insufficiency. In children, IR is related to elevated body mass index (BMI) and pubertal hormones, along with abnormal fat partitioning, elevated free fatty acids, inflammation, and/or mitochondrial dysfunction. Hyperglycemia and T2DM develop when the pancreas cannot match the increased insulin demands resulting from IR. Unique to youth, IR varies with stage of pubertal development, and some children may have resolution of hyperglycemia post-puberty once the IR of puberty resolves. Further understanding of IR, the progression to T2DM in youth, and later outcomes as adults will help direct future therapies and interventions for youth at risk.

Longitudinal effects of MRI-measured hepatic steatosis on biomarkers of glucose homeostasis and hepatic apoptosis in obese youth

OBJECTIVE

We used fast-gradient magnetic resonance imaging (MRI) to determine the longitudinal associations between the hepatic fat content (HFF), glucose homeostasis, and a biomarker of hepatocellular apoptosis in obese youth.

RESEARCH DESIGN AND METHODS

Baseline and longitudinal liver and abdominal MRI were performed with an oral glucose tolerance test in 76 obese youth followed for an average of 1.9 years. Cytokeratin-18 (CK-18) was measured at baseline and follow-up as a biomarker of hepatic apoptosis. The relationship between baseline HFF and metabolic parameters and circulating levels of CK-18 at follow-up were assessed using a bivariate correlation.

RESULTS

At baseline, 38% had hepatic steatosis based on %HFF ≥5.5% with alterations in indices of insulin sensitivity and secretion. At follow-up, BMI increased in both groups and baseline %HFF correlated strongly with the follow-up %HFF (r = 0.81, P < 0.001). Over time, markers of insulin sensitivity and 2-h glucose improved significantly in the group without fatty liver, in contrast with the persistence of the insulin resistance and associated correlates in the fatty liver group. Baseline HFF correlated with 2-h glucose (r = 0.38, P = 0.001), whole-body insulin sensitivity (r = -0.405, P = 0.001), adiponectin (r = -0.44, P < 0.001), CK-18 levels, (r = 0.63, P < 0.001), and disposition index (r = -0.272, P = 0.021) at follow-up. In a multivariate analysis, we showed that baseline HFF is an independent predictor of 2-h glucose and whole-body insulin sensitivity.

CONCLUSIONS

In obese youth, the phenotype of MRI-measured hepatic steatosis is persistent. Baseline HFF strongly modulates longitudinally 2-h blood glucose, biomarkers of insulin resistance, and hepatocellular apoptosis.

Adiposity, fat patterning, and the metabolic syndrome among diverse youth: the EPOCH study

OBJECTIVES

To assess fat distribution, prevalence of obesity, and the metabolic syndrome among diverse 6-13-year-old Colorado youth to better understand racial/ethnic influences on adiposity and metabolic syndrome.

STUDY DESIGN

We measured body mass index, subscapular-to-triceps skinfold ratio, waist circumference, dietary fat, and physical activity in 422 youth (47% non-Hispanic White, 44% Hispanic, and 9% African-American). Visceral adipose tissue, subcutaneous adipose tissue, and intramyocellular lipid were measured with magnetic resonance techniques. Multiple-linear regression was used to assess associations between race/ethnicity and adiposity patterns.

RESULTS

Hispanic and African-American youth had a higher prevalence of obesity and metabolic syndrome compared with non-Hispanic White youth. Both groups displayed a more centralized fat distribution and larger volumes of subcutaneous tissue, compared with non-Hispanic White youth. After controlling for body mass index, these differences were attenuated, and for a given body size, African-American youth showed significantly lower visceral adipose tissue than non-Hispanic White youth. However, both Hispanic and African-American youth showed higher intermyocellular lipid in skeletal muscle compared with non-Hispanic Whites, independent of body size.

CONCLUSIONS

Racial/ethnic minorities experience higher overall adiposity, and may also have an increased risk for early development of metabolic syndrome relative to non-Hispanic White youth, beyond their increased obesity risk.

Trends in general and abdominal obesity among Chinese children and adolescents 1993-2009

OBJECTIVE

This study aimed to examine the secular trends in body mass index (BMI) and waist circumference (WC), and the prevalence of general and abdominal obesity among Chinese children and adolescents from 1993 to 2009.

METHODS

Data were obtained from the China health and nutrition survey conducted from 1993 to 2009. 9693 children and adolescents aged 6-17 years were included in this study, with their height, weight and WC measured. General obesity was defined using the BMI cut-offs for overweight recommended by the International Obesity Task Force, and abdominal obesity was assessed when a WC is above the 90th percentile for gender and age.

RESULTS

Among the total participants, mean BMI and WC increased significantly over the period 1993-2009: BMI increased from 17.6 to 17.8 kg m(-2) , and WC increased from 61.4 to 63.1 cm (both increases P < 0.001). The prevalence of general obesity and abdominal obesity increased significantly over the period: general obesity (including overweight) rose from 6.1% to 13.1% and abdominal obesity from 4.9% to 11.7% (both increases P < 0.001). WC and abdominal obesity increased at a relatively higher rate than BMI and general obesity. Upward trends in the prevalence of general and abdominal obesity were observed in all subgroups of gender, age and region (all increases P < 0.05), except for abdominal obesity in girls aged 13-17 years (P = 0.102).

CONCLUSION

General and abdominal obesity increased significantly over the past 17 years in Chinese children.

Islet function in obese adolescents

Concurrent with the epidemic of childhood obesity, an unprecedented increase in the prevalence of several adiposity-related complications in this age group has emerged. In particular, type 2 diabetes (T2D), once considered an illness restricted to adulthood, is progressively affecting more and more adolescents, and represents now roughly 20-45% of new-onset cases in this age group. To unravel the pathogenesis of diabetes development during adolescence, many studies have focused on defining early defects in both insulin sensitivity and secretion that might be implicated in the natural history of the disease. Although a lot still need to be clarified, studies have shown that the progression from normal glucose tolerance to T2D involves intermediate stages of impaired fasting glucose and/or impaired glucose tolerance, also known as prediabetes. Insulin resistance and β-cell dysfunction represent the two major key pathogenetic defects underlying the progression to diabetes in obese youth. In this review, we have sought to mainly describe the role of β-cell function in relation to the ambient insulin resistance in the development of T2D in obese adolescents.

Development of associations among central adiposity, adiponectin and insulin sensitivity from adolescence to young adulthood

OBJECTIVE

To examine associations of central adiposity, serum adiponectin and clamp-derived insulin sensitivity in a single longitudinal cohort from early adolescence to young adulthood.

METHODS

The cohort was examined three times at mean ages 15 years (n = 308), 19 years (n = 218) and 22 years (n = 163). Insulin sensitivity was measured with the euglycaemic hyperinsulinaemic clamp. Circulating adiponectin was measured by enzyme-linked immunosorbent assay. Computed tomography scans were used at mean age 22 to compute subcutaneous and visceral abdominal fat volume. Partial Pearson correlations and linear regression were used to examine cross-sectional associations at each examination.

RESULTS

The moderate negative correlation between waist circumference and adiponectin was significant and essentially unchanged from mean age 15 (-0.32, P < 0.0001) to mean age 22 (-0.29, P < 0.002), whereas the negative correlation between waist circumference and insulin sensitivity and the positive correlation between adiponectin and insulin sensitivity increased steadily in magnitude to mean age 22 (-0.29, P = 0.0002; and 0.32, P < 0.0001, respectively). In regression models including both visceral and subcutaneous fat, only visceral fat was significantly associated with insulin sensitivity, while only subcutaneous fat was nearly significantly associated with adiponectin.

CONCLUSIONS

This study shows that the significant negative relationship between waist circumference and adiponectin predated the development of significant relationships between insulin sensitivity and both waist circumference and adiponectin. It also shows that adiponectin is more closely related to subcutaneous fat and insulin sensitivity is more closely related to visceral fat in young adults.

Insulin resistance in type 2 diabetic youth

PURPOSE OF REVIEW

This review focuses on recent literature on insulin resistance in youth with type 2 diabetes mellitus (T2DM). Insulin resistance is associated with a variety of cardiometabolic problems leading to increased morbidity and mortality across the lifespan.

RECENT FINDINGS

Functional pancreatic β-cell changes play a role in the transition from obesity to impaired glucose tolerance (IGT). Insulin resistance drives islet cell upregulation, manifested by elevated glucagon and c-peptide levels, early in the transition to IGT. Surrogate measurements of insulin resistance and insulin secretion exist but their accuracy compared to clamp data is imperfect. Recent large longitudinal studies provide detailed information on the progression from normoglycemia to T2DM and on the phenotype of T2DM youth. Defining prediabetes and T2DM remains a challenge in youth. Lifestyle interventions do not appear as effective in children as in adults. Metformin remains the only oral hypoglycemic agent approved for T2DM in youth.

SUMMARY

New insights exist regarding the conversion from insulin resistance to T2DM, measurement of insulin resistance and phenotypes of insulin resistance youth, but more information is needed. Surrogate measurements of insulin resistance, additional treatment options for insulin resistance and individualization of treatment options for T2DM adolescents in particular require further investigation.

Use of MRI and CT for fat imaging in children and youth: what have we learned about obesity, fat distribution and metabolic disease risk?

Childhood obesity is a matter of great concern for public health. Efforts have been made to understand its impact on health through advanced imaging techniques. An increasing number of studies focus on fat distribution and its associations with metabolic risk, in interaction with genetics, environment and ethnicity, in children. The present review is a qualitative synthesis of the existing literature on visceral and subcutaneous abdominal, intrahepatic and intramuscular fat. Our search revealed 80 original articles. Abdominal as well as ectopic fat depots are prevalent already in childhood and contribute to abnormal metabolic parameters, starting early in life. Visceral, hepatic and intramuscular fat seem to be interrelated but their patterns as well as their independent contribution on metabolic risk are not clear. Some ethnic-specific characteristics are also prevalent. These results encourage further research in childhood obesity by using imaging techniques such as magnetic resonance imaging and computed tomography. These imaging methods can provide a better understanding of fat distribution and its relationships with metabolic risk, compared to less detailed fat and obesity assessment. However, studies on bigger samples and with a prospective character are warranted.

Main characteristics and participation rate of European adolescents included in the HELENA study

Background

Participation rate and response rate are key issues in a cross sectional large-scale epidemiological study. The objective of this paper is to describe the study population and to evaluate participation and response rate as well as the key nutritional status variables in male and female adolescents involved in the HELENA study.

Methods

A multi-stage random cluster sampling with a target sample of 3000 adolescents aged [12.5 to 17.5] years, stratified for geographical location and age, was carried out. Information for participants and non-participants (NP) was compared, and participation and response rates to specific questionnaires were discussed.

Results

3,865 adolescents aged [12.5 to 17.5] years (1,845 females) participated in the HELENA study, of whom 1,076 (568 females) participated in the blood sampling. 3,528 (1,845 females) adolescents were finally kept for statistical analysis. Participation rates for the schools and classes differed importantly between countries. The participation rate of pupils within the participating classes also differed importantly between countries. Sex ratio, mean age and BMI were similar between NP and participating adolescents within each centre, and in the overall sample. For all the questionnaires included in the database, the response rate of questionnaires was high (more than 80% of questions were completed).

Conclusion

From this study it could be concluded that participation rate differed importantly between countries, though no bias could be identified when comparing the key study variables between participants and non-participants. Response rate for questionnaires was very high. Future studies investigating lifestyle and health in adolescents can optimize their methods when considering the opportunities and barriers observed in the HELENA study.

Physical activity and cardiovascular risk factors in Spanish children aged 11-13 years

INTRODUCTION AND OBJECTIVES

The prevalence of childhood obesity has increased in recent decades. The aim was to determine whether a 3-month intervention on daily physical activity at school could affect body weight and cardiovascular risk factors associated with childhood obesity.

METHODS

A total of 137 children (12[1] years old) volunteered to participate in an observational cross-sectional study. Children were allowed to join one of the following groups: a) sedentary group (2h/week of physical education at school); b) active group (2h/week of physical education at school plus 3h/week extra physical activity), and c) sports group (2h/week of physical education at school plus 5h/week extra physical activity). Anthropometric characteristics, blood pressure, physical condition (estimated by the Course-Navette test), and biochemical parameters related with cardiovascular risk factors were determined.

RESULTS

Body weight, body mass index, waist circumference, sum of skinfold thickness, body fat percentage, and fat mass index of children were decreased with high physical activity level, whereas body water content significantly increased with activity. Parameters related with cardiovascular risk -triglycerides, insulin, systolic blood pressure, and homeostatic model assessment index- presented lower values in the sports group. Maximal oxygen uptake and maximum heart rate (Course Navette test) progressively increased with activity. Children participating in a total of 7h/week of physical activity presented significantly lower odds ratio of having high levels of the following cardiovascular risk factors: waist circumference, fat mass index, and homeostatic model assessment index.

CONCLUSIONS

Physical activity is important for metabolic health in children. Children with higher levels of physical activity presented better anthropometric and biochemical profiles.

Hepatic steatosis and low cardiorespiratory fitness in youth with type 2 diabetes

The purpose of this study was to examine the association between cardiorespiratory fitness, ectopic triglyceride accumulation, and insulin sensitivity among youth with and without type 2 diabetes. Subjects included 137 youth ages 13-18 years including 27 with type 2 diabetes, 97 overweight normoglycemic controls, and 13 healthy weight normoglycemic controls. The primary outcome measure was cardiorespiratory fitness defined as peak oxygen uptake indexed to fat free mass. Secondary outcomes included liver and muscle triglyceride content determined by (1)H-magnetic resonance spectroscopy and insulin sensitivity determined by frequently sampled intravenous glucose tolerance test. Despite similar measures of adiposity, peak oxygen uptake was 11% lower (38.9 ± 7.9 vs. 43.9 ± 6.1 ml/kgFFM/min, P = 0.002) and hepatic triglyceride content was nearly threefold higher (14.4 vs. 5.7%, P = 0.001) in youth with type 2 diabetes relative to overweight controls. In all 137 youth, cardiorespiratory fitness was negatively associated with hepatic triglyceride content (r = -0.22, P = 0.02) and positively associated with insulin sensitivity (r = 0.29, P = 0.002) independent of total body and visceral fat mass. Hepatic triglyceride content was also negatively associated with insulin sensitivity (r = -0.35, P < 0.001), independent of adiposity, sex, age, and peak oxygen uptake. This study demonstrated that low cardiorespiratory fitness and elevated hepatic triglyceride content are features of type 2 diabetes in youth. Furthermore, cardiorespiratory fitness and hepatic triglyceride are associated with insulin sensitivity in youth. Taken together, these data suggest that cardiorespiratory fitness and hepatic steatosis are potential clinical biomarkers for type 2 diabetes among youth.

Glycerolipid/free fatty acid cycle and islet β-cell function in health, obesity and diabetes

Pancreatic β-cells secrete insulin in response to fluctuations in blood fuel concentrations, in particular glucose and fatty acids. However, chronic fuel surfeit can overwhelm the metabolic, signaling and secretory capacity of the β-cell leading to its dysfunction and death - often referred to as glucolipotoxicity. In β-cells and many other cells, glucose and lipid metabolic pathways converge into a glycerolipid/free fatty acid (GL/FFA) cycle, which is driven by the substrates, glycerol-3-phosphate and fatty acyl-CoA, derived from glucose and fatty acids, respectively. Although the overall operation of GL/FFA cycle, consisting of lipolysis and lipogenesis, is "futile" in terms of energy expenditure, this metabolic cycle likely plays an indispensable role for various β-cell functions, in particular insulin secretion and excess fuel detoxification. In this review, we discuss the significance of GL/FFA cycle in the β-cell, its regulation and role in generating essential metabolic signals that participate in the lipid amplification arm of glucose stimulated insulin secretion and in β-cell growth. We propose the novel concept that the lipolytic segment of GL/FFA cycle is instrumental in producing signals for insulin secretion, whereas, the lipogenic segment generates signals relevant for β-cell survival/death and growth/proliferation.

Metabolic consequences of hepatic steatosis in overweight and obese adolescents

OBJECTIVE

To test the hypothesis that hepatic steatosis is associated with risk factors for type 2 diabetes in overweight and obese youth, mediated by cardiorespiratory fitness.

RESEARCH DESIGN AND METHODS

This was a cross-sectional study comparing insulin sensitivity between 30 overweight and obese adolescents with hepatic steatosis, 68 overweight and obese adolescents without hepatic steatosis, and 11 healthy weight adolescents without hepatic steatosis. Cardiorespiratory fitness was determined by a graded maximal exercise test on a cycle ergometer. Secondary outcomes included presence of metabolic syndrome and glucose response to a 75-g oral glucose challenge.

RESULTS

The presence of hepatic steatosis was associated with 55% lower insulin sensitivity (P = 0.02) and a twofold greater prevalence of metabolic syndrome (P = 0.001). Differences in insulin sensitivity (3.5 vs. 4.5 mU ⋅ kg(-1) ⋅ min(-1), P = 0.03), prevalence of metabolic syndrome (48 vs. 20%, P = 0.03), and glucose area under the curve (816 vs. 710, P = 0.04) remained between groups after matching for age, sex, and visceral fat. The association between hepatic steatosis and insulin sensitivity (β = -0.24, t = -2.29, P < 0.025), metabolic syndrome (β = -0.54, t = -5.8, P < 0.001), and glucose area under the curve (β = 0.33, t = 3.3, P < 0.001) was independent of visceral and whole-body adiposity. Cardiorespiratory fitness was not associated with hepatic steatosis, insulin sensitivity, or presence of metabolic syndrome.

CONCLUSIONS

Hepatic steatosis is associated with type 2 diabetes risk factors independent of cardiorespiratory fitness, whole-body adiposity, and visceral fat mass.