Genetic Evidence That Carbohydrate-Stimulated Insulin Secretion Leads to Obesity

Using an Oral Sugar Test to Biologically Validate the Use of a Commercial Enzyme Immunoassay to Measure Salivary Insulin in Western Lowland Gorillas (Gorilla gorilla gorilla)

Noninvasive evaluations of hormones can contribute to the assessment of health and welfare of animals. Variations in insulin levels and sensitivity, for example, have been linked to health concerns in non-human and human primates including insulin resistance, diabetes, and heart disease, the leading cause of death in zoo-housed gorillas. Few published studies have assessed insulin concentrations in western lowland gorillas (Gorilla gorilla gorilla), and all did so using serum. Anesthesia is typically required to collect blood samples from zoo-housed gorillas, limiting sampling frequency and restricting samples to the fasted state. The ability to measure insulin levels in saliva would eliminate these constraints and provide a minimally invasive means for monitoring this hormone. The purpose of this study was to analytically and biologically validate the measurement of insulin in saliva of western lowland gorillas using a commercially available enzyme immunoassay. For validation, an oral sugar test was conducted on five adult gorillas residing at Cleveland Metroparks Zoo. Such assessments are common practice in both human and equine medicine to evaluate the body's insulin response to ingestion of sugars. The test involved measuring salivary insulin at timed intervals before and after gorillas consumed doses of sugar. Salivary insulin levels increased from 15 min post-sugar ingestion and peaked after 90 to 120 min. One female had a high response and peaked at 990.21 mU/L. The other four gorillas had peaks between 49.82 and 167.04 mU/L. The assessment provided a biological validation for the measurement of salivary insulin in western lowland gorillas.

Associations Between TCF7L2, PPARγ, and KCNJ11 Genotypes and Insulin Response to an Oral Glucose Tolerance Test: A Systematic Review

SCOPE

Insulin responses to standardized meals differ between individuals. This variability may in part be explained by genotype. This systematic review evaluates associations between genotype and insulin response to an oral glucose tolerance test (OGTT) in terms of insulin area under the curve (AUC).

METHODS AND RESULTS

Three electronic databases (Web of Science, Embase, PubMed) were searched for studies investigating associations between insulin AUC after an OGTT and single nucleotide polymorphisms (SNPs) belonging to the transcription factor 7 like 2 (TCF7L2) gene, the peroxisome proliferator-activated receptor gamma (PPARγ) gene, or the potassium inwardly rectifying channel subfamily J member 11 (KCNJ11) gene in persons without diabetes. A total of 5199 articles were identified, of which 38 were included. Among them were family-based studies (9), twin studies (2), and studies with unrelated participants (27). Seventeen articles investigated TCF7L2 (7 SNPs), 14 investigated PPARγ (1 SNP), and 8 investigated KCNJ11 (5 SNPs). For all investigated SNPs, at least half of the reports indicated no statistically significant association with postprandial insulin AUC.

CONCLUSION

No evidence was found for associations between TCF7L2, PPARγ, and KCNJ11 genotypes and insulin AUC after an OGTT. Future studies should investigate the effect of genetic risk scores on postprandial insulin.

Implicating type 2 diabetes effector genes in relevant metabolic cellular models using promoter-focused Capture-C

AIMS/HYPOTHESIS

Genome-wide association studies (GWAS) have identified hundreds of type 2 diabetes loci, with the vast majority of signals located in non-coding regions; as a consequence, it remains largely unclear which 'effector' genes these variants influence. Determining these effector genes has been hampered by the relatively challenging cellular settings in which they are hypothesised to confer their effects.

METHODS

To implicate such effector genes, we elected to generate and integrate high-resolution promoter-focused Capture-C, assay for transposase-accessible chromatin with sequencing (ATAC-seq) and RNA-seq datasets to characterise chromatin and expression profiles in multiple cell lines relevant to type 2 diabetes for subsequent functional follow-up analyses: EndoC-BH1 (pancreatic beta cell), HepG2 (hepatocyte) and Simpson-Golabi-Behmel syndrome (SGBS; adipocyte).

RESULTS

The subsequent variant-to-gene analysis implicated 810 candidate effector genes at 370 type 2 diabetes risk loci. Using partitioned linkage disequilibrium score regression, we observed enrichment for type 2 diabetes and fasting glucose GWAS loci in promoter-connected putative cis-regulatory elements in EndoC-BH1 cells as well as fasting insulin GWAS loci in SGBS cells. Moreover, as a proof of principle, when we knocked down expression of the SMCO4 gene in EndoC-BH1 cells, we observed a statistically significant increase in insulin secretion.

CONCLUSIONS/INTERPRETATION

These results provide a resource for comparing tissue-specific data in tractable cellular models as opposed to relatively challenging primary cell settings.

DATA AVAILABILITY

Raw and processed next-generation sequencing data for EndoC-BH1, HepG2, SGBS_undiff and SGBS_diff cells are deposited in GEO under the Superseries accession GSE262484. Promoter-focused Capture-C data are deposited under accession GSE262496. Hi-C data are deposited under accession GSE262481. Bulk ATAC-seq data are deposited under accession GSE262479. Bulk RNA-seq data are deposited under accession GSE262480.

A genomics perspective of personalized prevention and management of obesity

This review discusses the landscape of personalized prevention and management of obesity from a nutrigenetics perspective. Focusing on macronutrient tailoring, we discuss the impact of genetic variation on responses to carbohydrate, lipid, protein, and fiber consumption. Our bioinformatic analysis of genomic variants guiding macronutrient intake revealed enrichment of pathways associated with circadian rhythm, melatonin metabolism, cholesterol and lipoprotein remodeling and PPAR signaling as potential targets of macronutrients for the management of obesity in relevant genetic backgrounds. Notably, our data-based in silico predictions suggest the potential of repurposing the SYK inhibitor fostamatinib for obesity treatment in relevant genetic profiles. In addition to dietary considerations, we address genetic variations guiding lifestyle changes in weight management, including exercise and chrononutrition. Finally, we emphasize the need for a refined understanding and expanded research into the complex genetic landscape underlying obesity and its management.

Future cardiometabolic implications of insulin hypersecretion in response to oral glucose: a prospective cohort study

Background

The cardiometabolic implications of postprandial hyperinsulinemia are unclear with recent studies suggesting both adverse and beneficial associations. We aimed to evaluate the longitudinal cardiometabolic implications of the post-challenge insulin secretory response over 4-years follow-up.

Methods

In this prospective cohort study, conducted in Toronto (Ontario, Canada), women comprising the full range of antepartum glucose tolerance were recruited in pregnancy (at the time of glucose tolerance screening, late in the second trimester) to undergo cardiometabolic testing in the years thereafter. Participants underwent oral glucose tolerance tests (OGTT) at 1-year, 3-years, and 5-years postpartum, enabling serial assessment of cardiovascular risk factors, glucose tolerance, insulin sensitivity or resistance (Matsuda index, HOMA-IR), and beta-cell function-via Insulin Secretion-Sensitivity Index-2 (ISSI-2) and insulinogenic index/HOMA-IR (IGI/HOMA-IR). Baseline post-challenge insulinemia was assessed with the corrected insulin response (CIR) at 1-year. Cardiometabolic factors were compared between baseline CIR tertiles.

Findings

Between Oct 23, 2003 and March 31, 2014, 306 women were enrolled. In this study population, there was progressive worsening of waist circumference (p = 0.016), HDL (p = 0.018), CRP (p = 0.006), and insulin sensitivity (p < 0.001) from the lowest to middle to highest tertile of CIR at 1-year. However, these adverse features were accompanied by progressively better beta-cell function (both p < 0.001), coupled with lower fasting and 2-h glucose on the OGTT (both p < 0.001). On adjusted longitudinal analyses, higher CIR tertile at 1-year was independently associated with (i) higher ISSI-2 and IGI/HOMA-IR and (ii) lower fasting and 2-h glucose at both 3-years and 5-years (all p < 0.001), but was not associated with BMI, waist, lipids, CRP or insulin sensitivity/resistance. The highest CIR tertile at 1-year predicted lower risk of pre-diabetes or diabetes at both 3-years (adjusted OR = 0.19; 95% CI 0.08-0.45) and 5-years (aOR = 0.18; 0.08-0.39), relative to the lowest tertile.

Interpretation

A robust post-challenge insulin secretory response does not indicate adverse cardiometabolic health but, rather, portends favourable metabolic function in the years to come. Future long-term study of the implications of the post-challenge insulinemic response is warranted.

Funding

Canadian Institutes of Health Research.

Insulin and aging - a disappointing relationship

Experimental studies in animal models of aging such as nematodes, fruit flies or mice have observed that decreased levels of insulin or insulin signaling promotes longevity. In humans, hyperinsulinemia and concomitant insulin resistance are associated with an elevated risk of age-related diseases suggestive of a shortened healthspan. Age-related disorders include neurodegenerative diseases, hypertension, cardiovascular disease, and type 2 diabetes. High ambient insulin concentrations promote increased lipogenesis and fat storage, heightened protein synthesis and accumulation of non-functional polypeptides due to limited turnover capacity. Moreover, there is impaired autophagy activity, and less endothelial NO synthase activity. These changes are associated with mitochondrial dysfunction and oxidative stress. The cellular stress induced by anabolic activity of insulin initiates an adaptive response aiming at maintaining homeostasis, characterized by activation of the transcription factor Nrf2, of AMP activated kinase, and an unfolded protein response. This protective response is more potent in the long-lived human species than in short-lived models of aging research resulting in a stronger pro-aging impact of insulin in nematodes and fruit flies. In humans, resistance to insulin-induced cell stress decreases with age, because of an increase of insulin and insulin resistance levels but less Nrf2 activation. These detrimental changes might be contained by adopting a lifestyle that promotes low insulin/insulin resistance levels and enhances an adaptive response to cellular stress, as observed with dietary restriction or exercise.

Metformin Can Attenuate Beta-Cell Hypersecretion-Implications for Treatment of Children with Obesity

In children with obesity, insulin hypersecretion is proposed to precede insulin resistance. We investigated if metformin could be used to attenuate insulin secretion from palmitate-treated isolated islets and its implication for children with obesity. Human islets were exposed to palmitate for 0.5 or 1 day, when metformin was introduced. After culture, glucose-stimulated insulin secretion (GSIS) was measured. Children with obesity, who had received metformin for over six months (n = 21, age 13.9 ± 1.8), were retrospectively evaluated. Children were classified as either "reducing" or "increasing" based on the difference between AUC0-120 of insulin during OGTT before and after metformin treatment. In human islets, GSIS increased after culture in palmitate for up to 1 day but declined with continued palmitate exposure. Whereas adding metformin after 1 day of palmitate exposure increased GSIS, adding metformin after 0.5 days reduced GSIS. In children with "reducing" insulin AUC0-120 (n = 9), 2 h glucose and triglycerides decreased after metformin treatment, which was not observed in patients with "increasing" insulin AUC0-120 (n = 12). In isolated islets, metformin attenuated insulin hypersecretion if introduced when islet secretory capacity was maintained. In children with obesity, improved glycemic and lipid levels were accompanied by reduced insulin levels during OGTT after metformin treatment.

Body Fat Distribution, Fasting Insulin Levels, and Insulin Secretion: A Bidirectional Mendelian Randomization Study

CONTEXT

Hyperinsulinemia and adiposity are associated with one another, but the directionality of this relation is debated.

OBJECTIVE

Here, we tested the direction of the causal effects of fasting insulin (FI) levels and body fat accumulation/distribution using 2-sample bidirectional Mendelian randomization (MR).

METHODS

We included summary statistics from large-scale genome-wide association studies for body mass index (BMI, n = 806 834), waist to hip ratio adjusted for BMI (WHRadjBMI, n = 694 649), abdominal subcutaneous, visceral and gluteofemoral adipose tissue (n = 38 965), FI levels (n = 98 210), pancreatic islets gene expression (n = 420), and hypothalamus gene expression (n = 155). We used inverse variance-weighted and robust MR methods that relied on statistically and biologically driven genetic instruments.

RESULTS

Both BMI and WHRadjBMI were positively associated with FI. Results were consistent across all robust MR methods and when variants mapped to the hypothalamus (presumably associated with food behavior) were included. In multivariable MR analyses, when waist circumference and BMI were mutually adjusted, the direct effect of waist circumference on FI was 2.43 times larger than the effect of BMI on FI. FI was not associated with adiposity. By contrast, using genetic instruments mapped to gene expression in pancreatic islets (presumably more specific to insulin secretion), insulin was positively associated with BMI and abdominal subcutaneous and gluteofemoral adipose tissue, but not with visceral adipose tissue.

CONCLUSION

Although these results will need to be supported by experimental investigations, results of this MR study suggest that abdominal adiposity may be a key determinant of circulating insulin levels. Alternatively, insulin secretion may promote peripheral adipose tissue accumulation.

Moderating "the great debate": The carbohydrate-insulin vs. the energy balance models of obesity

The increased prevalence of obesity in recent decades is a topic of great scientific and medical interest, but despite many advances, the causes of this increase have not been adequately identified. In this context, two conflicting models for obesity-the carbohydrate-insulin model (CIM) and the energy balance model (EBM)-are being vigorously debated by distinct cohorts of experts in the field. The goal of this perspective is to assess this "conflict of models" from a neutral perspective. I conclude that although both models have produced useful insights, they differ fundamentally in what they seek to explain, and neither has yet provided a validated mechanistic account for the rising obesity prevalence in some but not all members of the population. Rather than engaging in such debates over competing models, the field should be more focused on establishing specific mechanistic insights in identified patient groups and, eventually, actionable interventions based on them.

Long-Term High-Fat Diet Decreases Renal Insulin-Degrading Enzyme Expression and Function by Inhibiting the PPARγ Pathway

SCOPE

Long-term high-fat diet (HFD) causes insulin resistance, which is a primary etiological factor in the development of obesity and type 2 diabetes mellitus. Impaired insulin clearance is not only a consequence but also a cause of insulin resistance. The kidney is a major site of insulin clearance, where the insulin-degrading enzyme (IDE) plays a vital role in the proximal tubule. Thus, the study investigates the role of renal IDE in the regulation of insulin resistance in HFD-induced obese mice.

METHODS AND RESULTS

Twenty four-weeks of HFD in C57BL/6 mice causes insulin resistance and impaires insulin clearance, accompanied by a decrease in renal IDE expression and activity. Palmitic acid decreases IDE mRNA and protein expressions in HK-2 cells. RNA-Seq analysis found that the PPAR pathway is involved. 24-weeks of HFD decreases renal PPARγ, but not PPARα or PPARβ/δ mRNA expression. The inhibition of IDE expression by palmitic acid is prevented by the PPARγ agonist rosiglitazone. The amount of PPARγ bound to the promoters of IDE is decreased in palmitic acid-treated cells. Rosiglitazone improves insulin clearance and insulin resistance and increases renal IDE expression in HFD fed-mice.

CONCLUSION

Long-term HFD decreases renal IDE expression and activity, and causes insulin resistance, which involves PPARγ.

Protein-Balanced Dietary Habits Benefit Cognitive Function in Japanese Older Adults

Since daily dietary habits can affect cognitive function, dietary patterns such as the Mediterranean-DASH Intervention for Neurodegenerative Delay diet have been proposed as interventions to slow cognitive decline. However, because dietary habits vary widely among different food cultures, it is necessary to establish dietary pattern intervention methods that are appropriate for each population. Therefore, in this study, the dietary patterns of elderly Japanese individuals were classified using cluster analysis, and their relationship with cognitive function was investigated. We then modeled the dietary patterns and applied them to another cohort of elderly Japanese individuals to determine whether differences in dietary patterns could predict cognitive decline. One hundred and fifty older adults ≥ 65 years of age in the community were recruited. Their daily food intake and cognitive function were measured using the brief-type self-administered diet history questionnaire and Montreal Cognitive Assessment, respectively. K-means cluster analysis identified a high-carbohydrate (HC) dietary pattern with high cereal intake and a protein-balanced (PB) dietary pattern with high intake of legumes, vegetables, seafood, meat, and eggs. Cognitive function was significantly higher in the PB group than in the HC group. Furthermore, to classify the new data into HC and PB patterns, a classification model was created by discriminant analysis using food groups with significantly different intakes among dietary patterns. Next, we recruited 267 new older adults ≥ 65 years of age and measured food intake and cognitive function assessed using the memory performance index score. Individuals with cognitive decline were identified and their detailed cognitive functions were assessed using the neurocognitive index score. Cognitive function was significantly impaired in the HC pattern in both the general elderly and cognitively impaired cohorts. These findings suggest that a dietary pattern of low carbohydrate and high protein intake is associated with good cognitive function in elderly Japanese individuals. Classification by these dietary patterns can predict cognitive reservation in community-dwelling older adults.

Insulin Response to Oral Glucose and Cardiometabolic Disease: A Mendelian Randomization Study to Assess Potential Causality

Mendelian randomization (MR) suggests that postprandial hyperinsulinemia (unadjusted for plasma glucose) increases BMI, but its impact on cardiometabolic disease, a leading cause for mortality and morbidity in people with obesity, is not established. Fat distribution i.e., increased centripetal and/or reduced femoro-gluteal adiposity, is causally associated with and better predicts cardiometabolic disease than BMI. We therefore undertook bidirectional MR to assess the effect of corrected insulin response (CIR) (insulin 30 min after a glucose challenge adjusted for plasma glucose) on BMI, waist-to-hip ratio (WHR), leg fat, type 2 diabetes (T2D), triglyceride (TG), HDL, liver fat, hypertension (HTN), and coronary artery disease (CAD) in people of European descent. Inverse variance-weighted MR suggests a potential causal association between increased CIR and increased BMI (b = 0.048 ± 0.02, P = 0.03), increased leg fat (b = 0.029 ± 0.012, P = 0.01), reduced T2D (b = -0.73 ± 0.15, P = 6 × 10-7, odds ratio [OR] 0.48 [95% CI 0.36-0.64]), reduced TG (b = -0.07 ± 0.02, P = 0.003), and increased HDL (b = 0.04 ± 0.01, P = 0.006) with some evidence of horizontal pleiotropy. CIR had neutral effects on WHR (b = 0.009 ± 0.02, P = 0.69), liver fat (b = -0.08 ± 0.04, P = 0.06), HTN (b = -0.001 ± 0.004, P = 0.7, OR 1.00 [95% CI 0.99-1.01]), and CAD (b = -0.002 ± 0.002, P = 0.48, OR 0.99 [95% CI 0.81-1.21]). T2D decreased CIR (b -0.22 ± 0.04, P = 1.3 × 10-7), with no evidence that BMI, TG, HDL, liver fat, HTN, and CAD modulate CIR. In conclusion, we did not find evidence that increased CIR increases cardiometabolic disease. It might increase BMI with favorable fat distribution, reduce T2D, and improve lipids.

Competing paradigms of obesity pathogenesis: energy balance versus carbohydrate-insulin models

The obesity pandemic continues unabated despite a persistent public health campaign to decrease energy intake (“eat less”) and increase energy expenditure (“move more”). One explanation for this failure is that the current approach, based on the notion of energy balance, has not been adequately embraced by the public. Another possibility is that this approach rests on an erroneous paradigm. A new formulation of the energy balance model (EBM), like prior versions, considers overeating (energy intake > expenditure) the primary cause of obesity, incorporating an emphasis on “complex endocrine, metabolic, and nervous system signals” that control food intake below conscious level. This model attributes rising obesity prevalence to inexpensive, convenient, energy-dense, “ultra-processed” foods high in fat and sugar. An alternative view, the carbohydrate-insulin model (CIM), proposes that hormonal responses to highly processed carbohydrates shift energy partitioning toward deposition in adipose tissue, leaving fewer calories available for the body’s metabolic needs. Thus, increasing adiposity causes overeating to compensate for the sequestered calories. Here, we highlight robust contrasts in how the EBM and CIM view obesity pathophysiology and consider deficiencies in the EBM that impede paradigm testing and refinement. Rectifying these deficiencies should assume priority, as a constructive paradigm clash is needed to resolve long-standing scientific controversies and inform the design of new models to guide prevention and treatment. Nevertheless, public health action need not await resolution of this debate, as both models target processed carbohydrates as major drivers of obesity.

Extreme Variations in Muscle Fiber Composition Enable Detection of Insulin Resistance and Excessive Insulin Secretion

CONTEXT

Muscle fiber composition is associated with peripheral insulin action.

OBJECTIVE

We investigated whether extreme differences in muscle fiber composition are associated with alterations in peripheral insulin action and secretion in young, healthy subjects who exhibit normal fasting glycemia and insulinemia.

METHODS

Relaxation time following a tetanic contraction was used to identify subjects with a high or low expression of type I muscle fibers: group 1 (n = 11), area occupied by type I muscle fibers = 61.0 ± 11.8%, and group 2 (n = 8), type I area = 36.0 ± 4.9% (P < 0.001). Biopsies were obtained from the vastus lateralis muscle and analyzed for mitochondrial respiration on permeabilized fibers, muscle fiber composition, and capillary density. An intravenous glucose tolerance test was performed and indices of glucose tolerance, insulin sensitivity, and secretion were determined.

RESULTS

Glucose tolerance was similar between groups, whereas whole-body insulin sensitivity was decreased by ~50% in group 2 vs group 1 (P = 0.019). First-phase insulin release (area under the insulin curve during 10 minutes after glucose infusion) was increased by almost 4-fold in group 2 vs group 1 (P = 0.01). Whole-body insulin sensitivity was correlated with percentage area occupied by type I fibers (r = 0.54; P = 0.018) and capillary density in muscle (r = 0.61; P = 0.005) but not with mitochondrial respiration. Insulin release was strongly related to percentage area occupied by type II fibers (r = 0.93; P < 0.001).

CONCLUSIONS

Assessment of muscle contractile function in young healthy subjects may prove useful in identifying individuals with insulin resistance and enhanced glucose-stimulated insulin secretion prior to onset of clinical manifestations.

Lack of Evidence for a Causal Role of Hyperinsulinemia in the Progression of Obesity in Children and Adolescents: A Longitudinal Study

OBJECTIVE

The carbohydrate-insulin model (CIM) claims that chronic exposure to hyperinsulinemia induced by dietary carbohydrates explains development of obesity via direct effects of insulin and/or low postprandial metabolic fuel levels. We aimed at testing whether indices of hyperinsulinemia and postprandial glucose levels can predict increases in the degree of obesity over time.

RESEARCH DESIGN AND METHODS

Children and adolescents with obesity attending a pediatric obesity clinic performed oral glucose tolerance tests (OGTTs) and received standard obesity management. Indices of hyperinsulinemia and insulin secretion were derived from the OGTT and evaluated in the face of changes in the degree of obesity over time.

RESULTS

A total of 591 children (217 males and 374 females) participated, and the mean follow-up was 1.86 ± 1.29 years. OGTT-derived area under the curve of insulin, peak insulin, fasting insulin, the insulinogenic index, or insulin at 30 min were not associated with greater changes in the degree of obesity in univariate or multivariate analyses (adjusted for baseline age, BMI z score, sex, and ethnicity). Low postprandial glucose <75 mg/dL was not associated with greater changes in the degree of obesity in univariate or multivariate analyses. In a subsample of 104 participants with a follow-up >4 years, none of these parameters was associated with greater increases in the degree of obesity.

CONCLUSIONS

In children and adolescents with obesity, exposure to hyperinsulinemia, greater insulin secretion, or low postprandial glucose is not associated with greater increases in the degree of obesity over 2-4 years. The CIM should be evaluated in children with lower BMI and for longer follow-up periods.

[Two models of insulin resistance development and the strategy to combat age-related diseases: literature review]

BACKGROUND

Insulin resistance (IR) is the root cause of most age-related diseases (ARD), the major challenge for today's health systems. Therefore, adequate understanding of the mechanisms underlying IR is essential to build effective ARD prevention.

OBJECTIVE

Analyze the existing models of IR causation and progression in order to justify the most effective ARD prevention strategy.

METHODS

Search and analysis of publications on IR and hyperinsulinemia (HI) from databases elibrary.ru, PubMed, and Google Scholar.

RESULTS

Two models of IR development are analyzed along with the relationship between IR, HI, and obesity. The prevailing model considers obesity (imbalance of caloric intake and energy expenditure) as the main factor in the development of IR; HI is seen as a consequence of IR, mostly insignificant for the outcomes of IR. The model contradicts many experimental and clinical findings. The strategy to combat ARDs that follows from the model (hypocaloric diet and pharmacotherapy of IR) has proven mostly ineffective.The alternative model (IR as a consequence of HI, and obesity as one of IR manifestations) is more consistent with the pool of experimental and clinical data. It more precisely predicts ARD development and allows more adequate correction of adverse lifestyle factors. It corresponds to a different strategy for combating ARD: emphasis on low-carb diet and longer fasting window combined with consideration of other factors of IR.

CONCLUSION

If the prevailing model of IR development is revised, this should open up opportunities for more effective early prevention of a wide range of chronic diseases in which the role of IR is significant.

Stimulated Insulin Secretion Predicts Changes in Body Composition Following Weight Loss in Adults with High BMI

BACKGROUND

The aim of obesity treatment is to promote loss of fat relative to lean mass. However, body composition changes with calorie restriction differ among individuals.

OBJECTIVES

The goal of this study was to test the hypothesis that insulin secretion predicts body composition changes among young and middle-age adults with high BMI (in kg/m2) following major weight loss.

METHODS

Exploratory analyses were conducted with pre-randomization data from 2 large feeding trials: the Framingham, Boston, Bloomington, Birmingham, and Baylor study (FB4; n = 82, 43.9% women, BMI ≥27) and the Framingham State Food Study [(FS)2; n = 161, 69.6% women, BMI ≥25]. Participants in the 2 trials consumed calorie-restricted moderate-carbohydrate or very-low-carbohydrate diets to produce 12-18% weight loss in ∼14 wk or 10-14% in ∼10 wk, respectively. We determined insulin concentration 30 min after a 75-g oral glucose load (insulin-30) as a measure of insulin secretion and HOMA-IR as a measure of insulin resistance at baseline. Body composition was determined by DXA at baseline and post-weight loss. Associations were analyzed using general linear models with adjustment for covariates.

RESULTS

In FB4, higher insulin-30 was associated with a smaller decrease in fat mass (0.441 kg per 100 μIU/mL increment in baseline insulin-30; P = 0.005; -1.20-kg mean difference between the first compared with the fifth group of insulin-30) and a larger decrease in lean mass (-0.465 kg per 100 μIU/mL; P = 0.004; 1.27-kg difference). Participants with higher insulin-30 lost a smaller proportion of weight loss as fat (-3.37% per 100 μIU/mL; P = 0.003; 9.20% difference). Greater HOMA-IR was also significantly associated with adverse body composition changes. Results from (FS)2 were qualitatively similar but of a smaller magnitude.

CONCLUSIONS

Baseline insulin dynamics predict substantial individual differences in body composition following weight loss. These findings may inform understanding of the pathophysiological basis for weight regain and the design of more effective obesity treatment. Registered at clinicaltrials.gov as NCT03394664 and NCT02068885.

High Insulin in Early Childhood Is Associated with Subsequent Asthma Risk Independent of Body Mass Index

BACKGROUND

Asthma and obesity are major, interconnected public health challenges that usually have their origins in childhood, and for which the relationship is strengthened among those with insulin resistance.

OBJECTIVE

To determine whether high insulin in early life confers increased longitudinal risk for asthma independent of body mass index.

METHODS

The study used data from the Tucson Children's Respiratory Study (TCRS) and the Avon Longitudinal Study of Parents and Children (ALSPAC). Nonfasting insulin was measured in TCRS participants at age 6 years and fasting insulin in ALSPAC participants at age 8 years. Physician-diagnosed active asthma was determined at baseline and at subsequent assessments up to age 36 years in TCRS and 17 years in ALSPAC.

RESULTS

In TCRS, high insulin (upper quartile) at age 6 years was associated with increased odds of having active asthma from ages 8 to 36 years compared with low insulin (odds ratio,1.98; 95% CI, 1.28-3.05; P = .002). Similarly, in ALSPAC, high insulin was associated with a significantly higher risk of active asthma from ages 11 to 17 years compared with low insulin (odds ratio, 1.59; 95% CI, 1.12-2.27; P = .009). These findings were independent of baseline body mass index in both cohorts, and were not related to other demographic and asthma risk factors nor other tested markers of systemic inflammation and metabolic syndrome.

CONCLUSIONS

In 2 separate birth cohorts, higher blood insulin level in early childhood was associated with increased risk of active asthma through adolescence and adulthood, independent of body mass index. High insulin indicates a novel mechanism for asthma development, which may be a target for intervention.

A high-carbohydrate diet lowers the rate of adipose tissue mitochondrial respiration

Adipocyte mitochondrial respiration may influence metabolic fuel partitioning into oxidation versus storage, with implications for whole-body energy expenditure. Although insulin has been shown to influence mitochondrial respiration, the effects of dietary macronutrient composition have not been well characterized. The aim of this exploratory study was to test the hypothesis that a high-carbohydrate diet lowers the oxygen flux of adipocyte mitochondria ex vivo. Among participants in a randomized-controlled weight-loss maintenance feeding trial, those consuming a high-carbohydrate diet (60% carbohydrate as a proportion of total energy, n = 10) had lower rates of maximal adipose tissue mitochondrial respiration than those consuming a moderate-carbohydrate diet (40%, n = 8, p = 0.039) or a low-carbohydrate diet (20%, n = 9, p = 0.005) after 10 to 15 weeks. This preliminary finding may provide a mechanism for postulated calorie-independent effects of dietary composition on energy expenditure and fat deposition, potentially through the actions of insulin on fuel partitioning.

Effects of bisphenol A on pancreas and thyroid gland of young and adult female Sprague Dawlеy rats

Bisphenol A (BPA), a chemical involved in formation of plastic vessels, is one of the most widespread endocrine disrupting chemicals. The study was designed to investigate the effect of BPA on pancreas and thyroid gland of young and adult female Sprague Dawley rats. The rats were exposed to 330 mg/kg BPA orally every other day for 12 weeks; control rats were exposed orally to ethyl alcohol and corn oil. Samples were collected at 4, 8 and 12 weeks for hormonal, biochemical assays and histopathological examination. The insulin hormone in exposed young rats was decreased, but its level in adult ones was increased; the biochemical assay for blood sugar level showed a significant increase in young rats and decrease in adult ones. T3 hormone was increased in treated young and adult rats; T4 hormone was increased in treated adults, while calcium level was decreased in treated adult rats. The histopathological findings of pancreas revealed vacuolation in its endocrine parts in young rats, while in adult ones there was intralobular fatty infiltration - a typical picture of diabetes. The thyroid gland in treated young female rats showed increased cellularity of parafollicular cells; moreover there was parafollicular haemorrhage, and in adult ones - desquamation in lining epithelium of follicular cells. In conclusion, exposure of young and adult female rats to BPA resulted in changes in the pancreatic and thyroid gland cells manifested by morphological, hormonal and biochemical parameters.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

On the causal relationships between hyperinsulinaemia, insulin resistance, obesity and dysglycaemia in type 2 diabetes

Hundreds of millions of people are affected by hyperinsulinaemia, insulin resistance, obesity and the dysglycaemia that mark a common progression from metabolic health to type 2 diabetes. Although the relative contribution of these features and the order in which they appear may differ between individuals, the common clustering and seemingly progressive nature of type 2 diabetes aetiology has guided research and clinical practice in this area for decades. At the same time, lively debate around the causal relationships between these features has continued, as new data from human trials and highly controlled animal studies are presented. This 'For debate' article was prompted by the review in Diabetologia by Esser, Utzschneider and Kahn ( https://doi.org/10.1007/s00125-020-05245-x ), with the purpose of reviewing established and emerging data that provide insight into the relative contributions of hyperinsulinaemia and impaired glucose-stimulated insulin secretion in progressive stages between health, obesity and diabetes. It is concluded that these beta cell defects are not mutually exclusive and that they are both important, but at different stages.

Diet and exercise in NAFLD/NASH: Beyond the obvious

Lifestyle represents the most relevant factor for non-alcoholic fatty liver disease (NAFLD) as the hepatic manifestation of the metabolic syndrome. Although a tremendous body of clinical and preclinical data on the effectiveness of dietary and lifestyle interventions exist, the complexity of this topic makes firm and evidence-based clinical recommendations for nutrition and exercise in NAFLD difficult. The aim of this review is to guide readers through the labyrinth of recent scientific findings on diet and exercise in NAFLD and non-alcoholic steatohepatitis (NASH), summarizing "obvious" findings in a holistic manner and simultaneously highlighting stimulating aspects of clinical and translational research "beyond the obvious". Specifically, the importance of calorie restriction regardless of dietary composition and evidence from low-carbohydrate diets to target the incidence and severity of NAFLD are discussed. The aspect of ketogenesis-potentially achieved via intermittent calorie restriction-seems to be a central aspect of these diets warranting further investigation. Interactions of diet and exercise with the gut microbiota and the individual genetic background need to be comprehensively understood in order to develop personalized dietary concepts and exercise strategies for patients with NAFLD/NASH.

Hyperinsulinemia and Its Pivotal Role in Aging, Obesity, Type 2 Diabetes, Cardiovascular Disease and Cancer

For many years, the dogma has been that insulin resistance precedes the development of hyperinsulinemia. However, recent data suggest a reverse order and place hyperinsulinemia mechanistically upstream of insulin resistance. Genetic background, consumption of the “modern” Western diet and over-nutrition may increase insulin secretion, decrease insulin pulses and/or reduce hepatic insulin clearance, thereby causing hyperinsulinemia. Hyperinsulinemia disturbs the balance of the insulin–GH–IGF axis and shifts the insulin : GH ratio towards insulin and away from GH. This insulin–GH shift promotes energy storage and lipid synthesis and hinders lipid breakdown, resulting in obesity due to higher fat accumulation and lower energy expenditure. Hyperinsulinemia is an important etiological factor in the development of metabolic syndrome, type 2 diabetes, cardiovascular disease, cancer and premature mortality. It has been further hypothesized that nutritionally driven insulin exposure controls the rate of mammalian aging. Interventions that normalize/reduce plasma insulin concentrations might play a key role in the prevention and treatment of age-related decline, obesity, type 2 diabetes, cardiovascular disease and cancer. Caloric restriction, increasing hepatic insulin clearance and maximizing insulin sensitivity are at present the three main strategies available for managing hyperinsulinemia. This may slow down age-related physiological decline and prevent age-related diseases. Drugs that reduce insulin (hyper) secretion, normalize pulsatile insulin secretion and/or increase hepatic insulin clearance may also have the potential to prevent or delay the progression of hyperinsulinemia-mediated diseases. Future research should focus on new strategies to minimize hyperinsulinemia at an early stage, aiming at successfully preventing and treating hyperinsulinemia-mediated diseases.

Metabolic Characterization of Meat, Fish, and Soda Intake in Males: Secondary Results from a Randomized Inpatient Pilot Study

OBJECTIVE

This study aimed to evaluate whether a 12-week, weight-maintaining, macronutrient-stable dietary intervention that varies only by meat, fish, or soda consumption alters 24-hour energy expenditure (24hrEE) and substrate oxidation.

METHODS

Healthy males were recruited to participate in a 12-week inpatient study and were randomized to a weight-maintaining dietary intervention that contained varying combinations of meat (0% or 19%), fish (0% or 6%), or soda (0% or 14%) in a factorial design. Macronutrient composition across dietary intervention groups was as follows: 50% of energy from carbohydrates, 30% of energy from fat, and 20% of energy from protein. Whole-room indirect calorimetry at baseline and week 12 were used to measure 24hrEE and substrate oxidation.

RESULTS

Twenty-six males (mean [SEM], age: 46.6 [10.4] years; BMI: 26.9 [4.1] kg/m2 ) completed all measurements. Fish consumption resulted in higher 24hrEE by 126 (55) kcal/d compared with no fish consumption (P = 0.03), whereas 24hrEE for soda consumption was 132 (56) kcal/d (P = 0.03) lower. Approximately 80% of the decrease in 24hrEE with soda consumption was due to lower awake-inactive energy expenditure (EE; P = 0.001). No specific EE component accounted for the differences observed with fish consumption.

CONCLUSIONS

The data indicate that dietary sources of protein and carbohydrates appear to influence 24hrEE and inactive EE.

Hyperinsulinemia in Obesity, Inflammation, and Cancer

The relative insufficiency of insulin secretion and/or insulin action causes diabetes. However, obesity and type 2 diabetes mellitus can be associated with an absolute increase in circulating insulin, a state known as hyperinsulinemia. Studies are beginning to elucidate the cause-effect relationships between hyperinsulinemia and numerous consequences of metabolic dysfunctions. Here, we review recent evidence demonstrating that hyperinsulinemia may play a role in inflammation, aging and development of cancers. In this review, we will focus on the consequences and mechanisms of excess insulin production and action, placing recent findings that have challenged dogma in the context of the existing body of literature. Where relevant, we elaborate on the role of specific signal transduction components in the actions of insulin and consequences of chronic hyperinsulinemia. By discussing the involvement of hyperinsulinemia in various metabolic and other chronic diseases, we may identify more effective therapeutics or lifestyle interventions for preventing or treating obesity, diabetes and cancer. We also seek to identify pertinent questions that are ripe for future investigation.

Investigation of glycaemic traits in psychiatric disorders using Mendelian randomisation revealed a causal relationship with anorexia nervosa

Data from observational studies have suggested an involvement of abnormal glycaemic regulation in the pathophysiology of psychiatric illness. This may be an attractive target for clinical intervention as glycaemia can be modulated by both lifestyle factors and pharmacological agents. However, observational studies are inherently confounded, and therefore, causal relationships cannot be reliably established. We employed genetic variants rigorously associated with three glycaemic traits (fasting glucose, fasting insulin, and glycated haemoglobin) as instrumental variables in a two-sample Mendelian randomisation analysis to investigate the causal effect of these measures on the risk for eight psychiatric disorders. A significant protective effect of a natural log transformed pmol/L increase in fasting insulin levels was observed for anorexia nervosa after the application of multiple testing correction (OR = 0.48 [95% CI: 0.33-0.71]-inverse-variance weighted estimate). There was no consistently strong evidence for a causal effect of glycaemic factors on the other seven psychiatric disorders considered. The relationship between fasting insulin and anorexia nervosa was supported by a suite of sensitivity analyses, with no statistical evidence of instrument heterogeneity or horizontal pleiotropy. Further investigation is required to explore the relationship between insulin levels and anorexia.

Low Carb and Ketogenic Diets Increase Quality of Life, Physical Performance, Body Composition, and Metabolic Health of Women with Breast Cancer

Breast cancer (BC) patients often ask for a healthy diet. Here, we investigated a healthy standard diet (SD), a low carb diet (LCD), and a ketogenic diet (KD) for BC patients during the rehabilitation phase. KOLIBRI was an open-label non-randomized one-site nutritional intervention trial, combining inpatient and outpatient phases for 20 weeks. Female BC patients (n = 152; mean age 51.7 years) could select their diet. Data collected were: Quality of life (QoL), spiroergometry, body composition, and blood parameters. In total 30, 92, and 30 patients started the KD, LCD, and SD, respectively. Of those, 20, 76, and 25 completed the final examination. Patients rated all diets as feasible in daily life. All groups enhanced QoL, body composition, and physical performance. LCD participants showed the most impressive improvement in QoL aspects. KD participants finished with a very good physical performance and muscle/fat ratio. Despite increased cholesterol levels, KD patients had the best triglyceride/high-density lipoprotein (HDL) ratio and homeostatic model assessment of insulin resistance index (HOMA-IR). Most metabolic parameters significantly improved in the LCD group. SD participants ended with remarkably low cholesterol levels but did not improve triglyceride/HDL or HOMA-IR. In conclusion, both well-defined KDs and LCDs are safe and beneficial for BC patients and can be recommended during the rehabilitation phase.

Bidirectional temporal relationship between obesity and hyperinsulinemia: longitudinal observation from a Chinese cohort

INTRODUCTION

Although obesity and hyperinsulinemia are closely intercorrelated, their temporal sequence is still uncertain. This study aims to investigate the temporal relationship patterns between obesity measures and hyperinsulinemia in Chinese adults.

RESEARCH DESIGN AND METHODS

The longitudinal cohort consisted of 2493 participants (860 males and 1633 female, mean age 56.71 years at follow-up) for whom measurements of obesity and hyperinsulinemia measures were collected twice between 2011 and 2014, with an average follow-up time of 3 years. Cross-lagged panel analysis was used to examine the temporal relationship between obesity measures (body mass index (BMI); waist circumference (WC); hip circumference (HC); waist-to-hip ratio (WHR)) and hyperinsulinemia (insulin, homeostasis model assessment of insulin resistance (HOMA-IR), or homeostasis model assessment of beta cell function (HOMA-%β)).

RESULTS

After the adjustment of age, sex, smoking, drinking and follow-up years, in the BMI-insulin model, the path coefficient (β₂=0.229; p<0.001) of baseline BMI to follow-up insulin was significantly greater than the path coefficient (β₁=0.073; p<0.001) of baseline insulin to follow-up BMI (p<0.001 for β₂>β₁). In the WHR-insulin model, the path coefficient (β₁=0.152; p<0.001) of baseline insulin to follow-up WHR was significantly greater than the path coefficient (β₂=0.077; p<0.001) of baseline WHR to follow-up insulin (p=0.007 for β₁>β₂). In the WC/HC-insulin model, the path coefficients of baseline insulin to follow-up WC or HC (β_1s) were also greater than the path coefficients of baseline WC or HC to follow-up insulin (β_2s), but the difference between β_1s and β_2s were not significant. The similar temporal patterns were founded between obesity measures with HOMA-IR or HOMA-%β.

CONCLUSIONS

These findings indicate that there is a bidirectional relationship between obesity and hyperinsulinemia, and abdominal obesity measures are more sensitive to hyperinsulinemia measures than BMI.

Effects of Anthocyanins in Composite Meals on Cardiometabolic Outcomes-A Systematic Review of Randomized Controlled Feeding Trials

Accumulating epidemiological evidence suggests that anthocyanin intake is associated with reduced risks of cardiometabolic disorders, highlighting the importance of incorporating the phytochemical in our diets. Numerous food-based intervention studies have examined, in controlled meal settings, the role of anthocyanin on cardiometabolic health; but their effects have not been systematically summarized. This study aims to systematically review and summarize the effects of anthocyanin consumption with composite meals on cardiometabolic health from randomized controlled feeding trials. A systematic literature search for relevant human nutritional intervention studies was performed using PubMed, Embase, Cochrane Library, CINAHL Plus with Full Text, and Scopus databases. The Cochrane Risk of Bias tool was used to assess the study quality. Eighteen articles involving 371 participants were included in this review. Consistent improvements from anthocyanin intake were found in glycemic, gastric inhibitory peptide (GIP), interleukin-6 (IL-6), and oxygen radical absorbance capacity (ORAC) responses. Anthocyanin intake did not significantly affect other markers of energy metabolism, vascular functions, oxidative stress and antioxidant status, as well as inflammatory responses. Inconsistencies in successful outcomes between epidemiological studies and included interventions were largely attributed to matrix effects, which may impede the bioaccessibility of anthocyanins and consequently, limiting its health benefits when co-delivered with some foods.

Comparative transcriptome analysis identifies CARM1 and DNMT3A as genes associated with osteoporosis

To identify new candidate genes in osteoporosis, mainly involved in epigenetic mechanisms, we compared whole gene-expression in osteoblasts (OBs) obtained from women undergoing hip replacement surgery due to fragility fracture and severe osteoarthritis. Then, we analyzed the association of several SNPs with BMD in 1028 women. Microarray analysis yielded 2542 differentially expressed transcripts belonging to 1798 annotated genes, of which 45.6% (819) were overexpressed, and 54.4% (979) underexpressed (fold-change between - 7.45 and 4.0). Among the most represented pathways indicated by transcriptome analysis were chondrocyte development, positive regulation of bone mineralization, BMP signaling pathway, skeletal system development and Wnt signaling pathway. In the translational stage we genotyped 4 SNPs in DOT1L, HEY2, CARM1 and DNMT3A genes. Raw data analyzed against inheritance patterns showed a statistically significant association between a SNP of DNMT3A and femoral neck-(FN) sBMD and primarily a SNP of CARM1 was correlated with both FN and lumbar spine-(LS) sBMD. Most of these associations remained statistically significant after adjusting for confounders. In analysis with anthropometric and clinical variables, the SNP of CARM1 unexpectedly revealed a close association with BMI (p = 0.000082), insulin (p = 0.000085), and HOMA-IR (p = 0.000078). In conclusion, SNPs of the DNMT3A and CARM1 genes are associated with BMD, in the latter case probably owing to a strong correlation with obesity and fasting insulin levels.

Low carbohydrate ketogenic therapy as a metabolic treatment for binge eating and ultraprocessed food addiction

PURPOSE OF REVIEW

The aim of this study was to highlight the recent advancements and future directions for potential use of a low carbohydrate ketogenic dietary approach to treat binge eating and ultraprocessed food addiction. Herein, we explore proposed mechanisms of why a diet low in refined carbohydrates, processed sugar and higher fat content may be helpful in alleviating symptoms.

RECENT FINDINGS

Emerging evidence suggests there may be a metabolic role in development of maladaptive eating. These findings broaden our understanding of eating psychopathology causes. Ultraprocessed, refined or high glycemic index carbohydrates are a possible trigger mediating neurochemical responses similar to addiction. The carbohydrate-insulin model of obesity supports observations of these foods triggering abnormal blood sugar and insulin spikes subsequently leading to changes in metabolic and neurobiological signaling. This results in overeating symptoms and hunger exacerbation, which differs from observed effects of healthy fat consumption and lack of similar insulin spikes. As supported in recent case series, significantly reducing or abstaining from these addictive-like ultraprocessed foods and highly refined carbohydrates could be considered a treatment approach.

SUMMARY

The current review highlights recent and pertinent evidence with respect to theoretical and practical application of low carbohydrate ketogenic therapeutic approaches for ultraprocessed food addiction and binge eating symptoms. VIDEO ABSTRACT:.

The Western diet: a blind spot of eating disorder research?-a narrative review and recommendations for treatment and research

Over the last 50 years, in parallel with the obesity epidemic, the prevalence of eating disorders has increased and presentations have changed. In this narrative review, we consider recent research exploring the implications of changing patterns of food consumption on metabolic and neurobiological pathways, a hitherto neglected area in eating disorder research. One of the major changes over this time has been the introduction of ultra-processed (NOVA-4) foods, which are gradually replacing unprocessed and minimally processed foods. This has resulted in the increased intake of various sugars and food additives worldwide, which has important metabolic consequences: triggering insulin and glucose response, stimulating appetite, and affecting multiple endocrine and neurobiological pathways, as well as the microbiome. A paradigm shift is needed in the conceptual framework by which the vulnerability to, and maintenance of, different eating disorders may be understood, by integrating recent knowledge of the individual metabolic responses to modern highly processed foods into existing psychological models. This could stimulate research and improve treatment outcomes.

Insulin: too much of a good thing is bad

BACKGROUND

Insulin shares a limited physiological concentration range with other endocrine hormones. Not only too low, but also too high systemic insulin levels are detrimental for body functions.

MAIN BODY

The physiological function and clinical relevance of insulin are usually seen in association with its role in maintaining glucose homeostasis. However, insulin is an anabolic hormone which stimulates a large number of cellular responses. Not only too low, but also excess insulin concentrations are detrimental to the physiological balance. Although the glucoregulatory activity of insulin is mitigated during hyperinsulinemia by dampening the efficiency of insulin signaling ("insulin resistance"), this is not the case for most other hormonal actions of insulin, including the promotion of protein synthesis, de novo lipogenesis, and cell proliferation; the inhibition of lipolysis, of autophagy-dependent cellular turnover, and of nuclear factor E2-related factor-2 (Nrf2)-dependent antioxidative; and other defense mechanisms. Hence, there is no general insulin resistance but selective impairment of insulin signaling which causes less glucose uptake from the blood and reduced activation of endothelial NO synthase (eNOS). Because of the largely unrestricted insulin signaling, hyperinsulinemia increases the risk of obesity, type 2 diabetes, and cardiovascular disease and decreases health span and life expectancy. In epidemiological studies, high-dose insulin therapy is associated with an increased risk of cardiovascular disease. Randomized controlled trials of insulin treatment did not observe any effect on disease risk, but these trials only studied low insulin doses up to 40 IU/day. Proof for a causal link between elevated insulin levels and cardiovascular disease risk comes from Mendelian randomization studies comparing individuals with genetically controlled low or high insulin production.

CONCLUSIONS

The detrimental actions of prolonged high insulin concentrations, seen also in cell culture, argue in favor of a lifestyle that limits circadian insulin levels. The health risks associated with hyperinsulinemia may have implications for treatment regimens used in type 2 diabetes.

Insulin-related dietary indices predict 24-h urinary C-peptide in adult men

The dietary insulin index directly estimates the postprandial insulin secretion potential of foods, whereas the empirical dietary index for hyperinsulinaemia (EDIH) assesses the insulinaemic potential of usual diets based on fasting plasma C-peptide, and is primarily reflective of insulin resistance. It is unknown whether these insulin-related indices are predictive of an integrated measure of insulin secretion. We conducted a cross-sectional analysis that included 293 non-diabetic men with 24-h urinary C-peptide data from the Men's Lifestyle Validation Study. EDIH, dietary insulin index and dietary insulin load were calculated using validated FFQ. We conducted multivariable-adjusted linear regression to estimate relative and absolute concentrations of 24-h urinary C-peptide. In multivariable-adjusted models, we found a significant positive association between all three insulin-related dietary indices and 24-h urinary C-peptide (P < 0·05). Relative concentrations of 24-h urinary C-peptide per 1-sd increase in insulin-related dietary indices were 1·12 (95 % CI 1·02, 1·23) for EDIH, 1·18 (95 % CI 1·07, 1·29) for dietary insulin index and 1·16 (95 % CI 1·06, 1·27) for dietary insulin load. When we further adjusted for BMI, the association was attenuated for EDIH, to 1·07 (95 % CI 0·98, 1·16), and remained unchanged for dietary insulin index and dietary insulin load. In conclusion, EDIH, dietary insulin index and dietary insulin load were predictive of integrated insulin secretion assessed by 24-h urinary C-peptide. Findings after adjustment for BMI appear to confirm the relation of EDIH to insulin resistance and dietary insulin index/load to insulin secretion; the respective constructs of the two dietary indices.

Human postprandial responses to food and potential for precision nutrition

Metabolic responses to food influence risk of cardiometabolic disease, but large-scale high-resolution studies are lacking. We recruited n = 1,002 twins and unrelated healthy adults in the United Kingdom to the PREDICT 1 study and assessed postprandial metabolic responses in a clinical setting and at home. We observed large inter-individual variability (as measured by the population coefficient of variation (s.d./mean, %)) in postprandial responses of blood triglyceride (103%), glucose (68%) and insulin (59%) following identical meals. Person-specific factors, such as gut microbiome, had a greater influence (7.1% of variance) than did meal macronutrients (3.6%) for postprandial lipemia, but not for postprandial glycemia (6.0% and 15.4%, respectively); genetic variants had a modest impact on predictions (9.5% for glucose, 0.8% for triglyceride, 0.2% for C-peptide). Findings were independently validated in a US cohort (n = 100 people). We developed a machine-learning model that predicted both triglyceride (r = 0.47) and glycemic (r = 0.77) responses to food intake. These findings may be informative for developing personalized diet strategies. The ClinicalTrials.gov registration identifier is NCT03479866.

Development of Obesity: The Driver and the Passenger

Obesity has reached epidemic proportions and is one of the greatest challenges for public health in the twenty-first century. The macronutrient composition of diets, in particular the amount and ratio of carbohydrates, fat and protein, have received considerable attention in recent decades due to its potential relevance to the development of obesity and weight loss. The effects of various macronutrients on body weight regulation are still under debate. High-carbohydrate diets, and particularly high-fat diets, have been blamed for the increase in the prevalence of obesity. This paper shows that neither fat nor carbohydrates are fattening per se. Mixed diets with substantial amounts of fat and high-glycemic carbohydrates, like current WDs, are required to promote weight gain and obesity. High-glycemic carbohydrates are the active partner (the "driver"), which promotes fat storage through its insulinogenic effect, while fat is the passive partner (the "passenger") on the way to obesity. Elevated insulin levels (postprandial, but more importantly due to hypersecretion and hyperinsulinemia) promote fat storage and play a key role in obesogenesis and the obesity epidemic. Furthermore, mixed diets high in high-glycemic carbohydrates and fat promote fetal programming, with long-term adverse impacts on the offspring, including insulin hypersecretion, (childhood) obesity and metabolic diseases. Maternal obesity and high weight gain during pregnancy have also been linked to deleterious effects on fetal programming. As the global obesity epidemic increasingly affects women of reproductive age, a significant percentage of fetuses will experience fetal programming with a tendency towards obesity - a self-reinforcing process that further fuels the epidemic. A change in lifestyle and diet composition is needed to prevent or limit the development of obesity and related diseases.

Nonalcoholic Fatty Liver Disease: A Challenge from Mechanisms to Therapy

Focusing on previously published mechanisms of non-alcoholic fatty liver disease (NAFLD), their uncertainty does not always permit a clear elucidation of the grassroot alterations that are at the basis of the wide-spread illness, and thus curing it is still a challenge. There is somehow exceptional progress, but many controversies persist in NAFLD research and clinical investigation. It is likely that hidden mechanisms will be brought to light in the near future. Hereby, the authors present, with some criticism, classical mechanisms that stand at the basis of NAFLD, and consider contextually different emerging processes. Without ascertaining these complex interactions, investigators have a long way left ahead before finding an effective therapy for NAFLD beyond diet and exercise.

Insulin Resistance in Healthy U.S. Adults: Findings from the National Health and Nutrition Examination Survey (NHANES)

BACKGROUND

Insulin is fundamental in two conditions that are epidemic in the United States and globally: obesity and type II diabetes. Given insulin's established mechanistic involvement in energy balance and glucose tolerance, we examined its relationship to common health-related endpoints in a large population-based sample.

METHODS

The National Health and Nutrition Examination Survey is a cross-sectional study that uses a complex multistage probability design to obtain a representative sample of the United States population. Adult participants were included from 8 successive 2-year data waves (1999-2014), including 9,224 normal individuals, 7,699 prediabetic, and 3,413 diabetic subjects. The homeostatic model for insulin resistance (HOMA-IR) was available for 20,336 participants and its relationship with demographic, anthropometric, and clinical data was analyzed. We examined the relationship of HOMA-IR to 8 groups of outcome variables: general health, anthropometric/metabolic [waist size, body mass index (BMI)], cardiovascular (blood pressure), lipid [triglycerides, high-density lipoprotein (HDL)], hepatic [alanine aminotransferase (ALT), gamma-glutamyl transferase (GGT)], hematologic [white blood cells (WBC), hemoglobin (Hgb), platelets], inflammatory (C-reactive protein), and nutritional (vitamins D and C, serum folate, and pyridoxine) variables.

RESULTS

HOMA-IR was generally strongly, monotonically, and highly significantly associated with adjusted outcomes in normal subjects, although clinical laboratory values were generally within normal bounds across insulin quartiles. In the normal subset, the odds ratio and 95% confidence interval for a quartile change in HOMA-IR for obesity (BMI > 30) was 3.62 (3.30-3.97), and for the highest quintile for the triglyceride/HDL the ratio was 2.00 (1.77-2.26), for GGT it was 1.40 (1.24-1.58), and for WBC it was 1.28 (1.16-1.40). The relationship of HOMA-IR to the various outcomes was broadly similar to that observed in prediabetics and diabetics with a few exceptions.

CONCLUSIONS

HOMA-IR levels in a large sample of normal individuals are associated with poorer general health and adverse changes across a wide range of markers. A similar pattern of alterations is observed in prediabetic and diabetic samples.

IMPACT

Clinically, checking insulin levels may be helpful to identify patients that merit further observation and are candidates for early interventions.

Using metabolite profiling to construct and validate a metabolite risk score for predicting future weight gain

Background

Excess weight gain throughout adulthood can lead to adverse clinical outcomes and are influenced by complex factors that are difficult to measure in free-living individuals. Metabolite profiling offers an opportunity to systematically discover new predictors for weight gain that are relatively easy to measure compared to traditional approaches.

Methods and results

Using baseline metabolite profiling data of middle-aged individuals from the Framingham Heart Study (FHS; n = 1,508), we identified 42 metabolites associated (p < 0.05) with longitudinal change in body mass index (BMI). We performed stepwise linear regression to select 8 of these metabolites to build a metabolite risk score (MRS) for predicting future weight gain. We replicated the MRS using data from the Mexico City Diabetes Study (MCDS; n = 768), in which one standard deviation increase in the MRS corresponded to ~0.03 increase in BMI (kg/m²) per year (i.e. ~0.09 kg/year for a 1.7 m adult). We observed that none of the available anthropometric, lifestyle, and glycemic variables fully account for the MRS prediction of weight gain. Surprisingly, we found the MRS to be strongly correlated with baseline insulin sensitivity in both cohorts and to be negatively predictive of T2D in MCDS. Genome-wide association study of the MRS identified 2 genome-wide (p < 5 × 10⁻⁸) and 5 suggestively (p < 1 × 10⁻⁶) significant loci, several of which have been previously linked to obesity-related phenotypes.

Conclusions

We have constructed and validated a generalizable MRS for future weight gain that is an independent predictor distinct from several other known risk factors. The MRS captures a composite biological picture of weight gain, perhaps hinting at the anabolic effects of preserved insulin sensitivity. Future investigation is required to assess the relationships between MRS-predicted weight gain and other obesity-related diseases.

Sex-specific Mendelian randomization study of genetically predicted insulin and cardiovascular events in the UK Biobank

Insulin drives growth and reproduction which trade-off against longevity. Genetically predicted insulin, i.e., insulin proxied by genetic variants, is positively associated with ischemic heart disease, but sex differences are unclear, despite different disease rates and reproductive strategies by sex. We used Mendelian randomization in 392,010 white British from the UK Biobank to assess the sex-specific role of genetically predicted insulin in myocardial infarction (MI) (14,442 cases, 77% men), angina (21,939 cases, 65% men) and heart failure (5537 cases, 71% men). Genetically predicted insulin was associated with MI (odds ratio (OR) 4.27 per pmol/L higher insulin, 95% confidence interval (CI) 1.60 to 11.3) and angina (OR 2.93, 1.27 to 6.73) in men, but not women (MI OR 0.80, 95% CI 0.23 to 2.84, angina OR 1.10, 95% CI 0.38 to 3.18). Patterns were similar for insulin resistance and heart failure. Mitigating the effects of insulin might address sexual disparities in health.

Hyperinsulinemia: An Early Indicator of Metabolic Dysfunction

Hyperinsulinemia is strongly associated with type 2 diabetes. Racial and ethnic minority populations are disproportionately affected by diabetes and obesity-related complications. This mini-review provides an overview of the genetic and environmental factors associated with hyperinsulinemia with a focus on racial and ethnic differences and its metabolic consequences. The data used in this narrative review were collected through research in PubMed and reference review of relevant retrieved articles. Insulin secretion and clearance are regulated processes that influence the development and progression of hyperinsulinemia. Environmental, genetic, and dietary factors are associated with hyperinsulinemia. Certain pharmacotherapies for obesity and bariatric surgery are effective at mitigating hyperinsulinemia and are associated with improved metabolic health. Hyperinsulinemia is associated with many environmental and genetic factors that interact with a wide network of hormones. Recent studies have advanced our understanding of the factors affecting insulin secretion and clearance. Further basic and translational work on hyperinsulinemia may allow for earlier and more personalized treatments for obesity and metabolic diseases.

Long-Term Change in both Dietary Insulinemic and Inflammatory Potential Is Associated with Weight Gain in Adult Women and Men

BACKGROUND

The influence of long-term dietary patterns on weight gain and the underlying potential biological mechanisms are not fully understood.

OBJECTIVE

We prospectively examined the association of changes in 2 empirical hypothesis-oriented dietary patterns (insulinemic and inflammatory) and weight gain over 24 y at 4-y intervals.

METHODS

We followed 54,397 women in the Nurses' Health Study and 33,043 men in the Health Professionals Follow-Up Study (1986-2010), and computed the empirical dietary index for hyperinsulinemia (EDIH) and empirical dietary inflammatory pattern (EDIP) scores from food frequency questionnaires administered every 4 y. Both scores are weighted sums of 18 food groups, which characterize dietary insulinemic or inflammatory potential based on plasma levels of insulin response or inflammatory biomarkers. We used multivariable-adjusted linear regression to examine 4-y changes in the dietary scores and weight change within the same period.

RESULTS

The mean baseline body mass index (BMI, in kg/m2) was 25.4. Compared with participants who made minimal dietary changes (quintile 3) over 6 4-y periods; participants who changed their diets toward lower insulinemic or inflammatory potential (quintile 1) gained significantly less weight (in kilograms per 4 y) independent of total energy intake, BMI, physical activity, and smoking status: EDIH: -0.65 (95% CI: -0.73, -0.57), EDIP: -0.29 (-0.37, -0.21) among women; and EDIH: -0.60 (-0.71, -0.49), EDIP: -0.19 (-0.27, -0.07) among men. In contrast, those who changed their diets toward higher insulinemic or inflammatory potential (quintile 5) gained significantly more weight: EDIH: 0.43 (0.36, 0.51), EDIP: 0.15 (0.07, 0.23) among women; and EDIH: 0.49 (0.38, 0.59), EDIP: 0.22 (0.11, 0.33) among men (P-trend < 0.0001 for all comparisons). Associations were stronger among individuals who were overweight or obese, younger, less physically active, and had never smoked.

CONCLUSIONS

High dietary insulinemic and inflammatory potential is associated with substantial long-term weight gain in adult men and women independent of total energy intake. Dietary patterns with low insulinemic and inflammatory potential may aid in weight gain prevention.

Developmental exposure to a very low dose of bisphenol A induces persistent islet insulin hypersecretion in Fischer 344 rat offspring

BACKGROUND

In children with obesity, accentuated insulin secretion has been coupled with development of type 2 diabetes mellitus (T2DM). Bisphenol A (BPA) is a chemical with endocrine- and metabolism-disrupting properties which can be measured in a majority of the population. Exposure to BPA has been associated with the development of metabolic diseases including T2DM.

OBJECTIVE

The aim of this study was to investigate if exposure early in life to an environmentally relevant low dose of BPA causes insulin hypersecretion in rat offspring.

METHODS

Pregnant Fischer 344 rats were exposed to 0.5 (BPA0.5) or 50 (BPA50) µg BPA/kg BW/day via drinking water from gestational day 3.5 until postnatal day 22. Pancreata from dams and 5- and 52-week-old offspring were procured and islets were isolated by collagenase digestion. Glucose-stimulated insulin secretion and insulin content in the islets were determined by ELISA.

RESULTS

Basal (5.5 mM glucose) islet insulin secretion was not affected by BPA exposure. However, stimulated (11 mM glucose) insulin secretion was enhanced by about 50% in islets isolated from BPA0.5-exposed 5- and 52-week-old female and male offspring and by 80% in islets from dams, compared with control. In contrast, the higher dose, BPA50, reduced stimulated insulin secretion by 40% in both 5- and 52-week-old female and male offspring and dams, compared with control.

CONCLUSION

A BPA intake 8 times lower than the European Food Safety Authority's (EFSA's) current tolerable daily intake (TDI) of 4 µg/kg BW/day of BPA delivered via drinking water during gestation and early development causes islet insulin hypersecretion in rat offspring up to one year after exposure. The effects of BPA exposure on the endocrine pancreas may promote the development of metabolic disease including T2DM.