Metabolic adaptation to high-fat and high-carbohydrate diets in children and adolescents

Association Between Adipose Tissue Characteristics and Metabolic Flexibility in Humans: A Systematic Review

Adipose tissue total amount, distribution, and phenotype influence metabolic health. This may be partially mediated by the metabolic effects that these adipose tissue characteristics exert on the nearby and distant tissues. Thus, adipose tissue may influence the capacity of cells, tissues, and the organism to adapt fuel oxidation to fuel availability, i.e., their metabolic flexibility (MetF). Our aim was to systematically review the evidence for an association between adipose tissue characteristics and MetF in response to metabolic challenges in human adults. We searched in PubMed (last search on September 4, 2021) for reports that measured adipose tissue characteristics (total amount, distribution, and phenotype) and MetF in response to metabolic challenges (as a change in respiratory quotient) in humans aged 18 to <65 years. Any study design was considered, and the risk of bias was assessed with a checklist for randomized and non-randomized studies. From 880 records identified, 22 remained for the analysis, 10 of them measured MetF in response to glucose plus insulin stimulation, nine in response to dietary challenges, and four in response to other challenges. Our main findings were that: (a) MetF to glucose plus insulin stimulation seems inversely associated with adipose tissue total amount, waist circumference, and visceral adipose tissue; and (b) MetF to dietary challenges does not seem associated with adipose tissue total amount or distribution. In conclusion, evidence suggests that adipose tissue may directly or indirectly influence MetF to glucose plus insulin stimulation, an effect probably explained by skeletal muscle insulin sensitivity. Systematic Review Registration: PROSPERO [CRD42020167810].

Understanding the role of aerobic fitness, spatial learning, and hippocampal subfields in adolescent males

Physical exercise during adolescence, a critical developmental window, can facilitate neurogenesis in the dentate gyrus and astrogliogenesis in Cornu Ammonis (CA) hippocampal subfields of rats, and which have been associated with improved hippocampal dependent memory performance. Recent translational studies in humans also suggest that aerobic fitness is associated with hippocampal volume and better spatial memory during adolescence. However, associations between fitness, hippocampal subfield morphology, and learning capabilities in human adolescents remain largely unknown. Employing a translational study design in 34 adolescent males, we explored the relationship between aerobic fitness, hippocampal subfield volumes, and both spatial and verbal memory. Aerobic fitness, assessed by peak oxygen utilization on a high-intensity exercise test (VO2 peak), was positively associated with the volumetric enlargement of the hippocampal head, and the CA1 head region specifically. Larger CA1 volumes were also associated with spatial learning on a Virtual Morris Water Maze task and verbal learning on the Rey Auditory Verbal Learning Test, but not recall memory. In line with previous animal work, the current findings lend support for the long-axis specialization of the hippocampus in the areas of exercise and learning during adolescence.

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.

Snack selection influences glucose metabolism, antioxidant capacity and cholesterol in healthy overweight adults: A randomized parallel arm trial

Including carbohydrate/fructose-rich foods (predominantly fruit) in the diets of overweight individuals can improve chronic disease risk factors. We hypothesized dried plums (DP) would improve nutrient consumption, total antioxidant capacity (TAC), lipid and adipokine profiles, and would decrease adiposity and inflammation. To test this, we studied the effects of 8-weeks of twice-daily snacking of macronutrient-matched 100kcal servings of DP or refined carbohydrate-rich snack (low-fat muffins: LFM) on daily energy and nutrient consumption, and chronic disease risk factors in overweight adults. Body weight/composition, waist circumference, blood pressure, plasma glucose, insulin, c-peptide, lipids, TAC, adipokines and inflammation were measured at baseline and throughout the study. Postprandial glucose and insulin were assessed following assigned test foods at baseline and 8-weeks. Repeated measures ANOVAs were undertaken to examine group and time differences. Post-hoc independent and paired samples t-tests were conducted where necessary. DP increased (P<.05) overall intake of dietary fiber and potassium, and TAC, from baseline to 8-weeks. Baseline postprandial glycemia tended (P=.09) to be lower with DP versus LFM, while both groups had a decreased response after 8-weeks. Postprandial insulinemia was lower (P<.05) for DP at both time-points. No differences in body weight/composition, blood pressure, or fasting glucose, insulin, triglycerides, total cholesterol, HDL-C, inflammation or adipokines were detected. Low-density lipoprotein cholesterol (LDL-C) increased (P<.05) throughout the trial following LFM. Overall, DP lessened postprandial insulinemia, improved nutrient consumption and plasma TAC, and maintained plasma LDL-C compared to a macronutrient-matched refined carbohydrate snack, which could decrease chronic disease risk.

Effects of total fat intake on bodyweight in children

BACKGROUND

As part of efforts to prevent childhood overweight and obesity, we need to understand the relationship between total fat intake and body fatness in generally healthy children.

OBJECTIVES

To assess the effects and associations of total fat intake on measures of weight and body fatness in children and young people not aiming to lose weight.

SEARCH METHODS

For this update we revised the previous search strategy and ran it over all years in the Cochrane Library, MEDLINE (Ovid), MEDLINE (PubMed), and Embase (Ovid) (current to 23 May 2017). No language and publication status limits were applied. We searched the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov for ongoing and unpublished studies (5 June 2017).

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in children aged 24 months to 18 years, with or without risk factors for cardiovascular disease, randomised to a lower fat (30% or less of total energy (TE)) versus usual or moderate-fat diet (greater than 30%TE), without the intention to reduce weight, and assessed a measure of weight or body fatness after at least six months. We included prospective cohort studies if they related baseline total fat intake to weight or body fatness at least 12 months later.

DATA COLLECTION AND ANALYSIS

We extracted data on participants, interventions or exposures, controls and outcomes, and trial or cohort quality characteristics, as well as data on potential effect modifiers, and assessed risk of bias for all included studies. We extracted body weight and blood lipid levels outcomes at six months, six to 12 months, one to two years, two to five years and more than five years for RCTs; and for cohort studies, at baseline to one year, one to two years, two to five years, five to 10 years and more than 10 years. We planned to perform random-effects meta-analyses with relevant subgrouping, and sensitivity and funnel plot analyses where data allowed.

MAIN RESULTS

We included 24 studies comprising three parallel-group RCTs (n = 1054 randomised) and 21 prospective analytical cohort studies (about 25,059 children completed). Twenty-three studies were conducted in high-income countries. No meta-analyses were possible, since only one RCT reported the same outcome at each time point range for all outcomes, and cohort studies were too heterogeneous to combine.Effects of dietary counselling to reduce total fat intake from RCTsTwo studies recruited children aged between 4 and 11 years and a third recruited children aged 12 to 13 years. Interventions were combinations of individual and group counselling, and education sessions in clinics, schools and homes, delivered by dieticians, nutritionists, behaviourists or trained, supervised teachers. Concerns about imprecision and poor reporting limited our confidence in our findings. In addition, the inclusion of hypercholesteraemic children in two trials raised concerns about applicability.One study of dietary counselling to lower total fat intake found that the intervention may make little or no difference to weight compared with usual diet at 12 months (mean difference (MD) -0.50 kg, 95% confidence interval (CI) -1.78 to 0.78; n = 620; low-quality evidence) and at three years (MD -0.60 kg, 95% CI -2.39 to 1.19; n = 612; low-quality evidence). Education delivered as a classroom curriculum probably decreased BMI in children at 17 months (MD -1.5 kg/m2, 95% CI -2.45 to -0.55; 1 RCT; n = 191; moderate-quality evidence). The effects were smaller at longer term follow-up (five years: MD 0 kg/m2, 95% CI -0.63 to 0.63; n = 541; seven years; MD -0.10 kg/m2, 95% CI -0.75 to 0.55; n = 576; low-quality evidence).Dietary counselling probably slightly reduced total cholesterol at 12 months compared to controls (MD -0.15 mmol/L, 95% CI -0.24 to -0.06; 1 RCT; n = 618; moderate-quality evidence), but may make little or no difference over longer time periods. Dietary counselling probably slightly decreased low-density lipoprotein (LDL) cholesterol at 12 months (MD -0.12 mmol/L, 95% CI -0.20 to -0.04; 1 RCT; n = 618, moderate-quality evidence) and at five years (MD -0.09, 95% CI -0.17 to -0.01; 1 RCT; n = 623; moderate-quality evidence), compared to controls. Dietary counselling probably made little or no difference to HDL-C at 12 months (MD -0.03 mmol/L, 95% CI -0.08 to 0.02; 1 RCT; n = 618; moderate-quality evidence), and at five years (MD -0.01 mmol/L, 95% CI -0.06 to 0.04; 1 RCT; n = 522; moderate-quality evidence). Likewise, counselling probably made little or no difference to triglycerides in children at 12 months (MD -0.01 mmol/L, 95% CI -0.08 to 0.06; 1 RCT; n = 618; moderate-quality evidence). Lower versus usual or modified fat intake may make little or no difference to height at seven years (MD -0.60 cm, 95% CI -2.06 to 0.86; 1 RCT; n = 577; low-quality evidence).Associations between total fat intake, weight and body fatness from cohort studiesOver half the cohort analyses that reported on primary outcomes suggested that as total fat intake increases, body fatness measures may move in the same direction. However, heterogeneous methods and reporting across cohort studies, and predominantly very low-quality evidence, made it difficult to draw firm conclusions and true relationships may be substantially different.

AUTHORS' CONCLUSIONS

We were unable to reach firm conclusions. Limited evidence from three trials that randomised children to dietary counselling or education to lower total fat intake (30% or less TE) versus usual or modified fat intake, but with no intention to reduce weight, showed small reductions in body mass index, total- and LDL-cholesterol at some time points with lower fat intake compared to controls. There were no consistent effects on weight, high-density lipoprotein (HDL) cholesterol or height. Associations in cohort studies that related total fat intake to later measures of body fatness in children were inconsistent and the quality of this evidence was mostly very low. Most studies were conducted in high-income countries, and may not be applicable in low- and middle-income settings. High-quality, longer-term studies are needed, that include low- and middle-income settings to look at both possible benefits and harms.

Effects of total fat intake on bodyweight in children

BACKGROUND

As part of efforts to prevent childhood overweight and obesity, we need to understand the relationship between total fat intake and body fatness in generally healthy children.

OBJECTIVES

To assess the effects of total fat intake on measures of weight and body fatness in children and young people not aiming to lose weight.

SEARCH METHODS

For this update we revised the previous search strategy and ran it over all years in the Cochrane Library, MEDLINE (Ovid), MEDLINE (PubMed), and Embase (Ovid) (current to 23 May 2017). No language and publication status limits were applied. We searched the World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov for ongoing and unpublished studies (5 June 2017).

SELECTION CRITERIA

We included randomised controlled trials (RCTs) in children aged 24 months to 18 years, with or without risk factors for cardiovascular disease, randomised to a lower fat (30% or less of total energy (TE)) versus usual or moderate-fat diet (greater than 30%TE), without the intention to reduce weight, and assessed a measure of weight or body fatness after at least six months. We included prospective analytical cohort studies in these children if they related baseline total fat intake to weight or body fatness at least 12 months later. We duplicated inclusion decisions and resolved disagreement by discussion with other authors.

DATA COLLECTION AND ANALYSIS

We extracted data on participants, interventions or exposures, controls and outcomes, and trial or cohort quality characteristics, as well as data on potential effect modifiers, and assessed risk of bias for all included studies. We extracted outcome data using the following time point ranges, when available: RCTs: baseline to six months, six to 12 months, one to two years, two to five years and more than five years; cohort studies: baseline to one year, one to two years, two to five years, five to 10 years and more than 10 years. We planned to perform random-effects meta-analyses with relevant subgrouping, and sensitivity and funnel plot analyses where data allowed.

MAIN RESULTS

We included 24 studies comprising three parallel-group RCTs (n = 1054 randomised) and 21 prospective analytical cohort studies (about 25,059 children completed). Twenty-three were conducted in high-income countries. No meta-analyses were possible, since only one RCT reported the same outcome at each time point range for all outcomes, and cohort studies were too heterogeneous.For the RCTs, concerns about imprecision and poor reporting limited our confidence in our findings. In addition, the inclusion of hypercholesteraemic children in two trials raised concerns about applicability. Lower versus usual or modified total fat intake may have made little or no difference to weight over a six- to twelve month period (mean difference (MD) -0.50 kg, 95% confidence interval (CI) -1.78 to 0.78; 1 RCT; n = 620; low-quality evidence), nor a two- to five-year period (MD -0.60 kg, 95% CI -2.39 to 1.19; 1 RCT; n = 612; low-quality evidence). Compared to controls, lower total fat intake (30% or less TE) probably decreased BMI in children over a one- to two-year period (MD -1.5 kg/m2, 95% CI -2.45 to -0.55; 1 RCT; n = 191; moderate-quality evidence), with no other differences evident across the other time points (two to five years: MD 0.00 kg/m2, 95% CI -0.63 to 0.63; 1 RCT; n = 541; greater than five years; MD -0.10 kg/m2, 95% CI -0.75 to 0.55; 1 RCT; n = 576; low-quality evidence). Lower fat intake probably slightly reduced total cholesterol over six to 12 months compared to controls (MD -0.15 mmol/L, 95% CI -0.24 to -0.06; 1 RCT; n = 618; moderate-quality evidence), but may make little or no difference over longer time periods. Lower fat intake probably slightly decreased low-density lipoprotein (LDL) cholesterol over six to 12 months (MD -0.12 mmol/L, 95% CI -0.20 to -0.04; 1 RCT; n = 618, moderate-quality evidence) and over two to five years (MD -0.09, 95% CI -0.17 to -0.01; 1 RCT; n = 623; moderate-quality evidence), compared to controls. However, lower total fat intake probably made little or no difference to HDL-C over a six- to 12-month period (MD -0.03 mmol/L, 95% CI -0.08 to 0.02; 1 RCT; n = 618; moderate-quality evidence), nor a two- to five-year period (MD -0.01 mmol/L, 95% CI -0.06 to 0.04; 1 RCT; n = 522; moderate-quality evidence). Likewise, lower total fat intake probably made little or no difference to triglycerides in children over a six- to 12-month period (MD -0.01 mmol/L, 95% CI -0.08 to 0.06; 1 RCT; n = 618; moderate-quality evidence). Lower versus usual or modified fat intake may make little or no difference to height over more than five years (MD -0.60 cm, 95% CI -2.06 to 0.86; 1 RCT; n = 577; low-quality evidence).Over half the cohort analyses that reported on primary outcomes suggested that as total fat intake increases, body fatness measures may move in the same direction. However, heterogeneous methods and reporting across cohort studies, and predominantly very low-quality evidence, made it difficult to draw firm conclusions and true relationships may be substantially different.

AUTHORS' CONCLUSIONS

We were unable to reach firm conclusions. Limited evidence from three trials that randomised children to a lower total fat intake (30% or less TE) versus usual or modified fat intake, but with no intention to reduce weight, showed small reductions in body mass index, total- and LDL-cholesterol at some time points with lower fat intake compared to controls, and no consistent differences in effects on weight, high-density lipoprotein (HDL) cholesterol or height. Associations in cohort studies that related total fat intake to later measures of body fatness in children were inconsistent and the quality of this evidence was mostly very low. Twenty-three out of 24 included studies were conducted in high-income countries, and may not be applicable in low- and middle-income settings. High-quality, longer-term studies are needed, that include low- and middle-income settings and look at both possible benefits and risks.

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.

Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition

Weight changes are accompanied by imbalances between calorie intake and expenditure. This fact is often misinterpreted to suggest that obesity is caused by gluttony and sloth and can be treated by simply advising people to eat less and move more. Rather various components of energy balance are dynamically interrelated and weight loss is resisted by counterbalancing physiological processes. While low-carbohydrate diets have been suggested to partially subvert these processes by increasing energy expenditure and promoting fat loss, our meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure (26 kcal/d; P <.0001) and fat loss (16 g/d; P <.0001) were greater with lower fat diets. We review the components of energy balance and the mechanisms acting to resist weight loss in the context of static, settling point, and set-point models of body weight regulation, with the set-point model being most commensurate with current data.

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.

A review of the carbohydrate-insulin model of obesity

The carbohydrate-insulin model of obesity theorizes that diets high in carbohydrate are particularly fattening due to their propensity to elevate insulin secretion. Insulin directs the partitioning of energy toward storage as fat in adipose tissue and away from oxidation by metabolically active tissues and purportedly results in a perceived state of cellular internal starvation. In response, hunger and appetite increases and metabolism is suppressed, thereby promoting the positive energy balance associated with the development of obesity. Several logical consequences of this carbohydrate-insulin model of obesity were recently investigated in a pair of carefully controlled inpatient feeding studies whose results failed to support key model predictions. Therefore, important aspects of carbohydrate-insulin model have been experimentally falsified suggesting that the model is too simplistic. This review describes the current state of the carbohydrate-insulin model and the implications of its recent experimental tests.

Measuring the short-term substrate utilization response to high-carbohydrate and high-fat meals in the whole-body indirect calorimeter

The paper demonstrates that minute‐to‐minute metabolic response to meals with different macronutrient content can be measured and discerned in the whole‐body indirect calorimeter. The ability to discriminate between high‐carbohydrate and high‐fat meals is achieved by applying a modified regularization technique with additional constraints imposed on oxygen consumption rate. These additional constraints reduce the differences in accuracy between the oxygen and carbon dioxide analyzers. The modified technique was applied to 63 calorimeter sessions that were each 24 h long. The data were collected from 16 healthy volunteers (eight males, eight females, aged 22–35 years). Each volunteer performed four 24‐h long calorimeter sessions. At each session, they received one of four treatment combinations involving exercise (high or low intensity) and diet (a high‐fat or high‐carbohydrate shake for lunch). One volunteer did not complete all four assignments, which brought the total number of sessions to 63 instead of 64. During the 24‐h stay in the calorimeter, subjects wore a continuous glucose monitoring system, which was used as a benchmark for subject's postprandial glycemic response. The minute‐by‐minute respiratory exchange ratio (RER) data showed excellent agreement with concurrent subcutaneous glucose concentrations in postprandial state. The averaged minute‐to‐minute RER response to the high‐carbohydrate shake was significantly different from the response to high‐fat shake. Also, postprandial RER slopes were significantly different for two dietary treatments. The results show that whole‐body respiration calorimeters can be utilized as tools to study short‐term kinetics of substrate oxidation in humans.

Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men

BACKGROUND

The carbohydrate-insulin model of obesity posits that habitual consumption of a high-carbohydrate diet sequesters fat within adipose tissue because of hyperinsulinemia and results in adaptive suppression of energy expenditure (EE). Therefore, isocaloric exchange of dietary carbohydrate for fat is predicted to result in increased EE, increased fat oxidation, and loss of body fat. In contrast, a more conventional view that "a calorie is a calorie" predicts that isocaloric variations in dietary carbohydrate and fat will have no physiologically important effects on EE or body fat.

OBJECTIVE

We investigated whether an isocaloric low-carbohydrate ketogenic diet (KD) is associated with changes in EE, respiratory quotient (RQ), and body composition.

DESIGN

Seventeen overweight or obese men were admitted to metabolic wards, where they consumed a high-carbohydrate baseline diet (BD) for 4 wk followed by 4 wk of an isocaloric KD with clamped protein. Subjects spent 2 consecutive days each week residing in metabolic chambers to measure changes in EE (EEchamber), sleeping EE (SEE), and RQ. Body composition changes were measured by dual-energy X-ray absorptiometry. Average EE during the final 2 wk of the BD and KD periods was measured by doubly labeled water (EEDLW).

RESULTS

Subjects lost weight and body fat throughout the study corresponding to an overall negative energy balance of ∼300 kcal/d. Compared with BD, the KD coincided with increased EEchamber (57 ± 13 kcal/d, P = 0.0004) and SEE (89 ± 14 kcal/d, P < 0.0001) and decreased RQ (-0.111 ± 0.003, P < 0.0001). EEDLW increased by 151 ± 63 kcal/d (P = 0.03). Body fat loss slowed during the KD and coincided with increased protein utilization and loss of fat-free mass.

CONCLUSION

The isocaloric KD was not accompanied by increased body fat loss but was associated with relatively small increases in EE that were near the limits of detection with the use of state-of-the-art technology. This trial was registered at clinicaltrials.gov as NCT01967563.

Effect of Fructose on Established Lipid Targets: A Systematic Review and Meta-Analysis of Controlled Feeding Trials

Background

Debate over the role of fructose in mediating cardiovascular risk remains active. To update the evidence on the effect of fructose on established therapeutic lipid targets for cardiovascular disease (low-density lipoprotein cholesterol [LDL]-C, apolipoprotein B, non-high-density lipoprotein cholesterol [HDL-C]), and metabolic syndrome (triglycerides and HDL-C), we conducted a systematic review and meta-analysis of controlled feeding trials.

Methods and Results

MEDLINE, EMBASE, CINHAL, and the Cochrane Library were searched through July 7, 2015 for controlled feeding trials with follow-up ≥7 days, which investigated the effect of oral fructose compared to a control carbohydrate on lipids (LDL-C, apolipoprotein B, non-HDL-C, triglycerides, and HDL-C) in participants of all health backgrounds. Two independent reviewers extracted relevant data. Data were pooled using random effects models and expressed as mean difference with 95% CI. Interstudy heterogeneity was assessed (Cochran Q statistic) and quantified (I² statistic). Eligibility criteria were met by 51 isocaloric trials (n=943), in which fructose was provided in isocaloric exchange for other carbohydrates, and 8 hypercaloric trials (n=125), in which fructose supplemented control diets with excess calories compared to the control diets alone without the excess calories. Fructose had no effect on LDL-C, non-HDL-C, apolipoprotein B, triglycerides, or HDL-C in isocaloric trials. However, in hypercaloric trials, fructose increased apolipoprotein B (n=2 trials; mean difference = 0.18 mmol/L; 95% CI: 0.05, 0.30; P=0.005) and triglycerides (n=8 trials; mean difference = 0.26 mmol/L; 95% CI: 0.11, 0.41; P<0.001). The study is limited by small sample sizes, limited follow-up, and low quality scores of the included trials.

Conclusions

Pooled analyses showed that fructose only had an adverse effect on established lipid targets when added to existing diets so as to provide excess calories (+21% to 35% energy). When isocalorically exchanged for other carbohydrates, fructose had no adverse effects on blood lipids. More trials that are larger, longer, and higher quality are required.

Clinical Trials Registration

URL: https://www.clinicaltrials.gov/. Unique Identifier: NCT01363791.

Global metabolomic profiling targeting childhood obesity in the Hispanic population

BACKGROUND

Metabolomics may unravel important biological pathways involved in the pathophysiology of childhood obesity.

OBJECTIVES

We aimed to 1) identify metabolites that differ significantly between nonobese and obese Hispanic children; 2) collapse metabolites into principal components (PCs) associated with obesity and metabolic risk, specifically hyperinsulinemia, hypertriglyceridemia, hyperleptinemia, and hyperuricemia; and 3) identify metabolites associated with energy expenditure and fat oxidation.

DESIGN

This trial was a cross-sectional observational study of metabolomics by using gas chromatography-mass spectrometry and ultrahigh-performance liquid chromatography-tandem mass spectrometry analyses performed on fasting plasma samples from 353 nonobese and 450 obese Hispanic children.

RESULTS

Branched-chained amino acids (BCAAs) (Leu, Ile, and Val) and their catabolites, propionylcarnitine and butyrylcarnitine, were significantly elevated in obese children. Strikingly lower lysolipids and dicarboxylated fatty acids were seen in obese children. Steroid derivatives were markedly higher in obese children as were markers of inflammation and oxidative stress. PC6 (BCAAs and aromatic AAs) and PC10 (asparagine, glycine, and serine) made the largest contributions to body mass index, and PC10 and PC12 (acylcarnitines) made the largest contributions to adiposity. Metabolic risk factors and total energy expenditure were associated with PC6, PC9 (AA and tricarboxylic acid cycle metabolites), and PC10. Fat oxidation was inversely related to PC8 (lysolipids) and positively related to PC16 (acylcarnitines).

CONCLUSIONS

Global metabolomic profiling in nonobese and obese children replicates the increased BCAA and acylcarnitine catabolism and changes in nucleotides, lysolipids, and inflammation markers seen in obese adults; however, a strong signature of reduced fatty acid catabolism and increased steroid derivatives may be unique to obese children. Metabolic flexibility in fuel use observed in obese children may occur through the activation of alternative intermediary pathways. Insulin resistance, hyperleptinemia, hypertriglyceridemia, hyperuricemia, and oxidative stress and inflammation evident in obese children are associated with distinct metabolomic profiles.

The ecologic validity of fructose feeding trials: supraphysiological feeding of fructose in human trials requires careful consideration when drawing conclusions on cardiometabolic risk

Background

Select trials of fructose overfeeding have been used to implicate fructose as a driver of cardiometabolic risk.

Objective

We examined temporal trends of fructose dose in human controlled feeding trials of fructose and cardiometabolic risk.

Methods

We combined studies from eight meta-analyses on fructose and cardiometabolic risk to assess the average fructose dose used in these trials. Two types of trials were identified: (1) substitution trials, in which energy from fructose was exchanged with equal energy from other carbohydrates and (2) addition trials, in which energy from fructose supplemented a diet compared to the diet alone.

Results

We included 64 substitution trials and 16 addition trials. The weighted average fructose dose in substitution trials was 101.7 g/day (95% CI: 98.4–105.1 g/day), and the weighted average fructose dose in addition trials was 187.3 g/day (95% CI: 181.4–192.9 g/day).

Conclusion

Average fructose dose in substitution and addition trials greatly exceed national levels of reported fructose intake (49 ± 1.0 g/day) (NHANES 1977–2004). Future trials using fructose doses at real world levels are needed.

Moderate amounts of fructose- or glucose-sweetened beverages do not differentially alter metabolic health in male and female adolescents

BACKGROUND

Adolescents consume more sugar-sweetened beverages than do individuals in any other age group, but it is unknown how the type of sugar-sweetened beverage affects metabolic health in this population.

OBJECTIVE

The objective was to compare the metabolic health effects of short-term (2-wk) consumption of high-fructose (HF) and high-glucose (HG)-sweetened beverages in adolescents (15-20 y of age).

DESIGN

In a counterbalanced, single-blind fashion, 40 male and female adolescents completed two 2-wk trials that included 1) an HF trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g fructose/d and 15 g glucose/d) for 2 wk and 2) an HG trial in which they consumed 710 mL of a sugar-sweetened beverage/d (equivalent to 50 g glucose/d and 15 g fructose/d) for 2 wk in addition to their normal ad libitum diet. In addition, the participants maintained similar physical activity levels during each trial. The day after each trial, insulin sensitivity and resistance [assessed via Quantitative Insulin Sensitivity Check Index (QUICKI) and homeostatic model assessment of insulin resistance (HOMA-IR) index] and fasting and postprandial glucose, lactate, lipid, cholesterol, insulin, C-peptide, insulin secretion, and clearance responses to HF or HG mixed meals were assessed.

RESULTS

Body weight, QUICKI (whole-body insulin sensitivity), HOMA-IR (hepatic insulin resistance), and fasting lipids, cholesterol, glucose, lactate, and insulin secretion or clearance were not different between trials. Fasting HDL- and HDL₃-cholesterol concentrations were ∼10-31% greater (P < 0.05) in female adolescents than in male adolescents. Postprandial triacylglycerol, HDL-cholesterol, HDL₃-cholesterol, and glucose concentrations were not different between HF and HG trials. The lactate incremental area under the curve was ∼3.7-fold greater during the HF trial (P < 0.05), whereas insulin secretion was 19% greater during the HG trial (P < 0.05).

CONCLUSIONS

Moderate amounts of HF- or HG-sweetened beverages for 2 wk did not have differential effects on fasting or postprandial cholesterol, triacylglycerol, glucose, or hepatic insulin clearance in weight-stable, physically active adolescents.

Effects of high-fat and high-carbohydrate diets on fat and carbohydrate oxidation and plasma metabolites in healthy cats

High-fat (HF) or high-carbohydrate (HC) diets (30% fat, 18.9% carbohydrate; HF and 10% fat, 46.3% carbohydrate; HC) and lengths of adaptation were investigated in cats (Felis catus; 10 ± 2 months, 3.6 ± 0.3 kg). Cats randomly received each treatment for 14 days in a crossover design with a 14-day washout period between each diet. Three 22-h indirect calorimetry studies were conducted after acute (day 0), semichronic (day 4) and chronic (day 13) dietary exposure. Blood samples were collected after a 24-h fast on days 1, 5 and 14. When cats consumed the HC and HF diet, oxidation of the restricted nutrient exceeded intake while oxidation of the nutrient in excess matched intake. Mean max energy expenditure (EE) of cats consuming the HF and HC diet were 107 and 102 kcal/kg(0.67)/day and occurred at a mean of 4 and 12 h post-feeding respectively. Maximal fat (0.90 g/h) and carbohydrate (carbohydrate; 1.42 g/h) oxidation were attained at 26 min and 10.4 h post-feeding respectively. The changes observed in macronutrient oxidation and EE suggest that cats adapt whole-body nutrient metabolism in response to changes in dietary macronutrient content, but may require longer than 14 day to adapt to a macronutrient that is present at a lower concentration in the diet.

Metabolic and hormonal consequences of two different meals after a moderate intensity exercise bout in obese prepubertal children

BACKGROUND/OBJECTIVES

To investigate the relationship between postprandial nutrient balance, satiety and hormone changes induced by two different meals taken after a moderate intensity exercise bout.

SUBJECTS/METHODS

Ten prepubertal obese children participated in the study. The experiment was designed as a cross-over study for repeated measures. Each test period lasted five consecutive hours during which the children were under medical supervision. The effects of two isocaloric meals were compared after a moderate intensity exercise (4 multiples of resting metabolic rate, 30 min, cycling): a low-fat/high-carbohydrate meal (meal A) and a high-fat/low-carbohydrate meal (meal B). Pre and postprandial (3 h) substrate oxidation, biochemical parameters, gastrointestinal hormone concentrations and appetite were measured.

RESULTS

The main results were: (i) higher fat balance (5.1±5.0 vs -5.0±6.6 g, P=0.001) and lower carbohydrate balance after meal B than A (-9.7±13.3 vs 11.3±18.3 g, P<0.01); (ii) higher energy balance after meal B than after meal A (5.9±21.5 vs -13.9±20.2 kcal, P<0.05); (iii) higher plasma triglyceride concentrations (area under the curve) after meal B than after meal A (2962.5±2095.8 mg*180 min/dl vs -169.5±1633.7 mg*180 min/dl, P<0.01); (iv) higher serum glucagon-like peptide-1 concentrations after meal B than after meal A (1101.5±873.0 pmol*180 min/l vs 478.8±638.3 pmol*180 min/l, P<0.05).

CONCLUSIONS

After a bout of moderate intensity exercise, a meal with a high-fat/low-carbohydrate ratio had a less favorable metabolic impact than an isoenergetic, isoproteic low-fat/high-carbohydrate meal.

Food consumption and serum nutritional status of people living in the Kathmandu valley in Nepal

OBJECTIVE

The food consumption and serum nutritional status of people living in the Kathmandu valley, Nepal, were examined to obtain actual data for comparison with our previous findings.

METHODS

A dietary survey of 45 males and 60 females was carried out in March 1997 by the 24-hr dietary recall method and nutrient intake was calculated from food tables of India and Japan. Fasting venous blood samples were obtained and serum biochemical parameters were measured using clinical kits.

RESULTS

The mean body mass index values was at about the same level in both sexes, although the mean percentage body fat of females was higher than that of males, and vice versa for packed red cell volume. The main foods consumed by both sexes, were rice, potatoes, meats, milk & dairy products and vegetables, with a difference in the amounts consumed. Females did not drink alcoholic beverages. The mean daily intakes of energy, protein, lipids, iron and vitamin B group for the males were higher than those for the females, while those of vitamins A and C for the males were lower than those for the females. The mean values of serum biochemical parameters for both sexes were generally at the normal levels, but those of ALT and TG were at the higher end of the normal range. Differences of correlation between food groups and between serum parameters were observed depending on the sex, however, no clear relationship between food and nutrient intake and serum biochemical parameters were observed.

CONCLUSIONS

The present food intake study revealed that the amounts of food consumption for both sexes, especially for the females, were mostly insufficient although the serum parameters were at the normal levels. The energy intake of both sexes was lower than that of estimated requirements and those in Terai region. The relatively high serum TG level of the subjects may be due to the consumption of large amounts of cereals containing much carbohydrate. Our findings suggested a marked influence on food consumption by food price and income in spite of the easier food availability in the city, and also lack of knowledge about nutrients and health, thus there is need for improvement of the nutritional status of this group of people.

Effects of Dinner Composition on Postprandial Macronutrient Oxidation in Prepubertal Girls

OBJECTIVE

To see whether a fat-rich (50%) evening meal promoted fat oxidation and a different spontaneous food intake on the following day at breakfast than a meal with a lower fat content (20%) in 10 prepubertal obese girls.

RESEARCH METHODS AND PROCEDURES

The postabsorptive and postprandial (10.5 hours) energy expenditure after a low-fat (LF) (20% fat, 68% carbohydrate, 12% protein) and an isocaloric (2.1 MJ) and isoproteic high-fat (HF; 50% fat, 38% carbohydrate, 12% protein) meal were measured by indirect calorimetry.

RESULTS

Fat oxidation was not significantly different after the two meals [LF, 31 +/- 9 vs. HF, 35 +/- 9 g/10.5 hours, p = not significant (NS)]. The girls oxidized 1.8 +/- 0.9 times more fat than that ingested (11.1 grams) with the LF meal vs. 0.3 +/- 0.3 times more fat than that ingested (27.1 grams) with the HF meal (p < 0.001). Carbohydrate oxidation was significantly higher after an LF than an HF meal (39 +/- 12 vs. 29 +/- 9 g/10.5 hours, p < 0,05). At breakfast, the girls spontaneously ingested a similar amount of energy (1.5 +/- 0.7 vs. 1.5 +/- 0.6 MJ, p = NS) and macronutrient proportions (fat, 23% vs. 26%, p = NS; protein, 9% vs. 10%; carbohydrate, 68% vs. 64%,) independently of their having eaten an HF or an LF dinner.

DISCUSSION

An HF dinner did not stimulate fat oxidation, and no compensatory effect in spontaneous food intake was observed during breakfast the following morning. Cumulated total fat oxidation after dinner was higher than total fat ingested at dinner, but a much larger negative fat balance was observed after the LF meal. Spontaneous energy and nutrient intakes at breakfast were similar after LF and HF isocaloric, isoproteic dinners. This study points out the lack of sensitivity of short-term fat balance to subsequently readjust fat intake and emphasizes the importance of an LF meal to avoid transient positive fat imbalance.

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.

Higher intakes of energy and grain products at 4 years of age are associated with being overweight at 6 years of age

This study examined dietary factors associated with overweight in a population-based sample of 6-y-old children. Analyses of data from the Québec Longitudinal Study of Child Development (QLSCD) included a representative sample (n = 1014) of children born in 1998 in the province of Québec, Canada. Dietary intake was measured by using a 24-h dietary recall administered at 4 y of age. Weight and height were measured using a standard protocol at 6 y. Using logistic regression, higher daily energy intake at 4 y was significantly related to overweight at 6 y. After adjustment for confounding and overweight at 4 y, the relationship remained significant among girls (P = 0.04) but became marginally significant among boys (P = 0.07). Additionally, boys who consumed ≥5 servings of grain products/d at 4 y were more likely to be overweight at 6 y compared to those who did not [adjusted OR = 3.20 (95% CI): 1.72-5.97]. The association attenuated somewhat after adjustment for overweight at 4 y [OR = 1.82 (95% CI): 0.894-3.71; P = 0.09]. The findings provide support for the revisions made in the Canadian dietary guidelines for young children, which now recommend 4-7 servings of grain products daily for children aged 4-8 y rather than the excessive 5-12 servings of previous recommendations.

Energy prediction equations are inadequate for obese Hispanic youth

Assessing energy requirements is a fundamental activity in clinical dietetics practice. A study was designed to determine whether published linear regression equations were accurate for predicting resting energy expenditure (REE) in fasted Hispanic children with obesity (aged 7 to 15 years). REE was measured using indirect calorimetry; body composition was estimated with whole-body air displacement plethysmography. REE was predicted using four equations: Institute of Medicine for healthy-weight children (IOM-HW), IOM for overweight and obese children (IOM-OS), Harris-Benedict, and Schofield. Accuracy of the prediction was calculated as the absolute value of the difference between the measured and predicted REE divided by the measured REE, expressed as a percentage. Predicted values within 85% to 115% of measured were defined as accurate. Participants (n=58; 53% boys) were mean age 11.8±2.1 years, had 43.5%±5.1% body fat, and had a body mass index of 31.5±5.8 (98.6±1.1 body mass index percentile). Measured REE was 2,339±680 kcal/day; predicted REE was 1,815±401 kcal/day (IOM-HW), 1,794±311 kcal/day (IOM-OS), 1,151±300 kcal/day (Harris-Benedict), and, 1,771±316 kcal/day (Schofield). Measured REE adjusted for body weight averaged 32.0±8.4 kcal/kg/day (95% confidence interval 29.8 to 34.2). Published equations predicted REE within 15% accuracy for only 36% to 40% of 58 participants, except for Harris-Benedict, which did not achieve accuracy for any participant. The most frequently accurate values were obtained using IOM-HW, which predicted REE within 15% accuracy for 55% (17/31) of boys. Published equations did not accurately predict REE for youth in the study sample. Further studies are warranted to formulate accurate energy prediction equations for this population.

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.

Evidence-based review on the effect of normal dietary consumption of fructose on development of hyperlipidemia and obesity in healthy, normal weight individuals

In recent years, there has been episodic speculation that an increase in consumption of fructose from foods and beverages is an underlying factor responsible for the relatively recent increase in obesity and obesity-related diseases such as diabetes. Reports in support of this hypothesis have been published, showing that concentrations of triglycerides (TG) are higher and concentrations of insulin and hormones associated with satiety are lower in animals following the ingestion of fairly large quantities of fructose, compared to other carbohydrates. However, results from human studies are inconsistent. A possible reason for the inconsistent results is that they are dependent on the particular study population, the design of the studies, and/or the amount of fructose administered. A systematic assessment of the strength and quality of the studies and their relevance for healthy, normal weight humans ingesting fructose in a normal dietary manner has not been performed. The purpose of this review was to critically evaluate the existing database for a causal relationship between the ingestion of fructose in a normal, dietary manner and the development of hyperlipidemia or increased body weight in healthy, normal weight humans, using an evidence-based approach. The results of the analysis indicate that fructose does not cause biologically relevant changes in TG or body weight when consumed at levels approaching 95th percentile estimates of intake.

A high-fat vs. a moderate-fat meal in obese boys: nutrient balance, appetite, and gastrointestinal hormone changes

Meal composition is a contributing factor to fat gain. In this study, we investigated the relationship between postprandial nutrient balance, satiety, and hormone changes induced by a high-fat meal vs. a moderate-fat meal. Ten prepubertal obese boys (BMI z-score range: 1.3-3.0) were recruited. Two meals (energy: 590 kcal) were compared: (i) high-fat (HF) meal: 12% protein, 52% fat, 36% carbohydrates; (ii) moderate-fat (MF) meal: 12% protein, 27% fat, 61% carbohydrates. Pre- and postprandial (5 h) substrate oxidation (indirect calorimetry), appetite (visual analogue scale), biochemical parameters and gastrointestinal hormone concentrations were measured. Carbohydrate balance was significantly (P < 0.001) lower (31.3 (5.7) g/5 h vs. 66.9 (5.9) g/5 h) and fat balance was significantly (P < 0.001) higher (11.5 (3.3) g/5 h vs. -0.7 (2.9) g/5 h) after HF than MF meal. Appetite (area under the curve (AUC)) was significantly reduced after an MF than an HF meal (494 (55) cm.300 min vs. 595 (57) cm.300 min, P < 0.05). Postprandial triglyceride concentration (AUC) was significantly (P < 0.05) higher after an HF than an MF meal: 141.1 (30.3) mmol.300 min/l vs. 79.3 (23.8) mmol.300 min/l, respectively. Peptide YY (PYY), cholecystokinin (CCK), and ghrelin concentrations (AUC) were not significantly different after an HF and MF meal. Glucagon-like peptide-1 (GLP-1) was significantly (P < 0.05) higher after an HF than after an MF meal (72.3 (9.8) ng/ml vs. 22.7 (7.6) ng/ml, respectively), but it did not affect subjective appetite. In conclusion, an MF meal induced a better postprandial metabolic nutrient balance, triglyceride levels, and appetite suppression than an HF meal. Gastrointestinal hormones were not related to clinically assessed hunger suppression after both meals.

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.

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.

Nutritional status of people living in Dzong village, in the northern mountainous area of Nepal

A nutritional survey was carried out among residents (39 males and 46 females) of Dzong village in the northern area of the Gandaki region of Nepal. The results were compared with our previous findings. The mean body mass index value was under 21 for both sexes, but the mean percentage of body fat of females (17-19 years old, 25.8 +/- 9.4%; 20-29 years old, 31.0 +/- 8.4%) was higher than that of males (17-19 years old, 12.0 +/- 1.0%; 50-59 years old, 24.4 +/- 7.6%). Most serum nutritional markers for both sexes were generally at normal levels although the iron levels were lower and packed red cell volume levels were higher than normal. As determined by results of the 24-hr dietary recall survey, the main food groups consumed by both sexes were cereals, potatoes, pulses, meats and vegetables. The mean daily intake of nutrients was similar for both sexes, with a few exceptions. The relatively high serum TG levels of the subjects may have been due to the high consumption of carbohydrate-laden cereals. The amounts of food consumed were not adequate, resulting in a latent and chronic deficiency of nutrients, especially calcium and iron. These results suggest that improvements in the nutritional status of this group of people are necessary.

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.

Glycemic index, postprandial glycemia and cardiovascular disease

PURPOSE OF REVIEW

Several lines of evidence indicate that exaggerated postprandial glycemia puts individuals without diabetes at greater risk of developing cardiovascular disease. In large, prospective observational studies, including meta-analyses, higher 120 min post-load blood glucose and glycated hemoglobin (a measure of average blood glucose level over time) independently predict cardiovascular mortality and morbidity in individuals without diabetes. These findings imply that the glycemic nature of dietary carbohydrates may also be relevant. We aim to provide a clearer perspective on how the glycemic impact of carbohydrates may modulate development of cardiovascular disease.

RECENT FINDINGS

In ecological studies, average dietary glycemic index (a measure of the postprandial glycemic potential of carbohydrates) and glycemic load (average glycemic index x amount of carbohydrate) predicts coronary infarct and cardiovascular disease risk factors, including HDL cholesterol, triglycerides and C-reactive protein. In short-term intervention studies of overweight and hyperlipidemic patients, low glycemic index diets lead to improvements in cardiovascular disease risk factors, including reduced LDL cholesterol and improved insulin sensitivity, as well as greater body fat loss on energy-restricted diets. Molecular studies indicate that physiological hyperglycemia induces overproduction of superoxide by the mitochondrial electron-transport chain, resulting in inflammatory responses and endothelial dysfunction.

SUMMARY

Taken together, the findings suggest that conventional high-carbohydrate diets with their high glycemic index may be suboptimal, particularly in insulin-resistant individuals. Because around one in four adults has impairments in postprandial glucose regulation, the glycemic potential of carbohydrates warrants further investigation in cardiovascular disease prevention.

Substrate metabolism, nutrient balance and obesity development in children and adolescents: a target for intervention?

Obesity results from the organism's inability to maintain energy balance over a long term. Childhood obesity and its related factors and pathological consequences tend to persist into adulthood. A cluster of factors, including high energy density in the diet (high fat intake), low energy expenditure, and disturbed substrate oxidation, favour the increase in fat mass. Oxidation of three major macronutrients and their roles in the regulation of energy balance, particularly in children and adolescents, are discussed. Total glucose oxidation is not different between obese and lean children; exogenous glucose utilization is higher whereas endogenous glucose utilization is lower in obese compared with lean children. Carbohydrate composition of the diet determines carbohydrate oxidation regardless of fat content of the diet. Both exogenous and endogenous fat oxidation are higher in obese than in lean subjects. The influence of high fat intake on accumulation of fat mass is operative rather over a long term. Several future directions are addressed, such that a combination of increased physical activity and modification in diet composition, in terms of energy density and glycemic index, is recommended for children and adolescents.