High whole-body fat percentage is independently associated with increased mortality. We aimed to identify a simple anthropometric linear equation that is more accurate than the body mass index (BMI) ...to estimate whole-body fat percentage among adult individuals. National Health and Nutrition Examination Survey (NHANES) 1999-2004 data (n = 12,581) were used for model development and NHANES 2005-2006 data (n = 3,456) were used for model validation. From the 365 anthropometric indices generated, the final selected equation was as follows: 64 - (20 × height/waist circumference) + (12 × sex), named as the relative fat mass (RFM); sex = 0 for men and 1 for women. In the validation dataset, compared with BMI, RFM better predicted whole-body fat percentage, measured by dual energy X-ray absorptiometry (DXA), among women and men. RFM showed better accuracy than the BMI and had fewer false negative cases of body fat-defined obesity among women and men. RFM reduced total obesity misclassification among all women and all men and, overall, among Mexican-Americans, European-Americans and African-Americans. In the population studied, the suggested RFM was more accurate than BMI to estimate whole-body fat percentage among women and men and improved body fat-defined obesity misclassification among American adult individuals of Mexican, European or African ethnicity.
Insulin clearance has recently been highlighted as a fundamental aspect of glucose metabolism, as it has been hypothesized that its impairment could be related to an increased risk of developing type ...2 diabetes. This review focuses on methods used to calculate insulin clearance: from the early surrogate indices employing C-peptide:insulin molar ratio, to direct measurement methods used in animal models, to modeling-based techniques to estimate the components of insulin clearance (hepatic versus extrahepatic). The methods are explored and interpreted by critically highlighting advantages and limitations.
It has long been hoped that our understanding of the pathogenesis of diabetes would be helped by the use of mathematical modeling. In 1979 Richard Bergman and Claudio Cobelli worked together to find ...a "minimal model" based upon experimental data from Bergman's laboratory. Model was chosen as the simplest representation based upon physiology known at the time. The model itself is two quasi-linear differential equations; one representing insulin kinetics in plasma, and a second representing the effects of insulin and glucose itself on restoration of the glucose after perturbation by intravenous injection. Model would only be sufficient if it included a delay in insulin action; that is, insulin had to enter a remote compartment, which was interstitial fluid (ISF). Insulin suppressed endogenous glucose output (by liver) slowly. Delay proved to be due to initial suppression of lipolysis; resultant lowering of free fatty acids reduced liver glucose output. Modeling also demanded that normalization of glucose after injection included an effect of glucose itself on glucose disposal and endogenous glucose production - these effects were termed "glucose effectiveness." Insulin sensitivity was calculated from fitting the model to intravenous glucose tolerance test data; the resulting insulin sensitivity index, SI, was validated with the glucose clamp method in human subjects. Model allowed us to examine the relationship between insulin sensitivity and insulin secretion. Relationship was described by a rectangular hyperbola, such that Insulin Secretion x Insulin Sensitivity = Disposition Index (DI). Latter term represents ability of the pancreatic beta-cells to compensate for insulin resistance due to factors such as obesity, pregnancy, or puberty. DI has a genetic basis, and predicts the onset of Type 2 diabetes. An additional factor was clearance of insulin by the liver. Clearance varies significantly among animal or human populations; using the model, clearance was shown to be lower in African Americans than Whites (adults and children), and may be a factor accounting for greater diabetes prevalence in African Americans. The research outlined in the manuscript emphasizes the powerful approach by which hypothesis testing, experimental studies, and mathematical modeling can work together to explain the pathogenesis of metabolic disease.
Experiences as Editor of Obesity Bergman, Richard N.
Obesity (Silver Spring, Md.),
November 2022, 2022-11-00, 20221101, Volume:
30, Issue:
11
Journal Article
A Better Index of Body Adiposity Bergman, Richard N.; Stefanovski, Darko; Buchanan, Thomas A. ...
Obesity (Silver Spring, Md.),
20/May , Volume:
19, Issue:
5
Journal Article
Peer reviewed
Open access
Obesity is a growing problem in the United States and throughout the world. It is a risk factor for many chronic diseases. The BMI has been used to assess body fat for almost 200 years. BMI is known ...to be of limited accuracy, and is different for males and females with similar %body adiposity. Here, we define an alternative parameter, the body adiposity index (BAI = ((hip circumference)/((height)1.5)–18)). The BAI can be used to reflect %body fat for adult men and women of differing ethnicities without numerical correction. We used a population study, the “BetaGene” study, to develop the new index of body adiposity. %Body fat, as measured by the dual‐energy X‐ray absorptiometry (DXA), was used as a “gold standard” for validation. Hip circumference (R = 0.602) and height (R = −0.524) are strongly correlated with %body fat and therefore chosen as principal anthropometric measures on which we base BAI. The BAI measure was validated in the “Triglyceride and Cardiovascular Risk in African‐Americans (TARA)” study of African Americans. Correlation between DXA‐derived %adiposity and the BAI was R = 0.85 for TARA with a concordance of C_b = 0.95. BAI can be measured without weighing, which may render it useful in settings where measuring accurate body weight is problematic. In summary, we have defined a new parameter, the BAI, which can be calculated from hip circumference and height only. It can be used in the clinical setting even in remote locations with very limited access to reliable scales. The BAI estimates %adiposity directly.
There is wide variance among individuals in the fraction of insulin cleared by the liver (20% to 80%). Hepatic insulin clearance is 67% lower in African Americans than European Americans. Clearance ...is also lower in African American children 7-13 years of age. Lower hepatic insulin clearance will result in peripheral hyperinsulinemia: this exacerbates insulin resistance, which stresses the β-cells, possibly resulting in their ultimate failure and onset of type 2 diabetes. We hypothesize that lower insulin clearance can be a primary cause of type 2 diabetes in at-risk individuals.
Most of the literature related to high altitude medicine is devoted to the short-term effects of high-altitude exposure on human physiology. However, long-term effects of living at high altitudes may ...be more important in relation to human disease because more than 400 million people worldwide reside above 1500 m. Interestingly, individuals living at higher altitudes have a lower fasting glycemia and better glucose tolerance compared with those who live near sea level. There is also emerging evidence of the lower prevalence of both obesity and diabetes at higher altitudes. The mechanisms underlying improved glucose control at higher altitudes remain unclear. In this review, we present the most current evidence about glucose homeostasis in residents living above 1500 m and discuss possible mechanisms that could explain the lower fasting glycemia and lower prevalence of obesity and diabetes in this population. Understanding the mechanisms that regulate and maintain the lower fasting glycemia in individuals who live at higher altitudes could lead to new therapeutics for impaired glucose homeostasis.
BACKGROUNDMirabegron is a β3-adrenergic receptor (β3-AR) agonist approved only for the treatment of overactive bladder. Encouraging preclinical results suggest that β3-AR agonists could also improve ...obesity-related metabolic disease by increasing brown adipose tissue (BAT) thermogenesis, white adipose tissue (WAT) lipolysis, and insulin sensitivity.METHODSWe treated 14 healthy women of diverse ethnicities (27.5 ± 1.1 years of age, BMI of 25.4 ± 1.2 kg/m2) with 100 mg mirabegron (Myrbetriq extended-release tablet, Astellas Pharma) for 4 weeks in an open-label study. The primary endpoint was the change in BAT metabolic activity as measured by 18F-2-fluoro-d-2-deoxy-d-glucose (18F-FDG) PET/CT. Secondary endpoints included resting energy expenditure (REE), plasma metabolites, and glucose and insulin metabolism as assessed by a frequently sampled intravenous glucose tolerance test.RESULTSChronic mirabegron therapy increased BAT metabolic activity. Whole-body REE was higher, without changes in body weight or composition. Additionally, there were elevations in plasma levels of the beneficial lipoprotein biomarkers HDL and ApoA1, as well as total bile acids. Adiponectin, a WAT-derived hormone that has antidiabetic and antiinflammatory capabilities, increased with acute treatment and was 35% higher upon completion of the study. Finally, an intravenous glucose tolerance test revealed higher insulin sensitivity, glucose effectiveness, and insulin secretion.CONCLUSIONThese findings indicate that human BAT metabolic activity can be increased after chronic pharmacological stimulation with mirabegron and support the investigation of β3-AR agonists as a treatment for metabolic disease.TRIAL REGISTRATIONClinicaltrials.gov NCT03049462.FUNDINGThis work was supported by grants from the Intramural Research Program of the NIDDK, NIH (DK075112, DK075116, DK071013, and DK071014).
Glucokinase (GCK) mediates hepatic glucose uptake during hyperglycemia and is crucial for the regulation of glucose-responsive glycolysis genes. Mutations in GCK are responsible for maturity-onset ...diabetes of the young, and glucokinase regulatory protein (GKRP) , the regulator of hepatic GCK, is also a diabetes susceptibility locus. Recently in in vivo experiments, we used hepatic lactate export as a surrogate for GCK activity, which was a measure of “glucose effectiveness.” We hypothesized that in vitro GCK and GKRP suppression in hepatocytes promotes a reduction in lactate and pyruvate export from the liver. We used cryopreserved canine hepatocytes and knocked down GCK and GKRP via lipid delivery of siRNA. A control group did not receive siRNA. We measured lactate dehydrogenase D (LDHD) and pyruvate kinase (PK) gene expression and lactate and pyruvate release into the medium 24 and 48 h after siRNA delivery. Selective blocking of GCK and GKRP did not change cell proliferation but reduced the expression of these genes by 90% and 85%, respectively (P<0.0vs. controls; n=4) . GCK and GKRP knockdown reduced LDHD by 71% and 74%, respectively (P<0.001) ; similarly, PK was reduced by 84% and 82%, respectively (P<0.001) . Lactate exported into the medium was reduced by 36% (P<0.001) and 26% (P<0.05) by GCK and GKRP siRNA, respectively, after 48 h of hepatocyte culture. However, pyruvate was reduced by 17% only after 48 h culture of GCK siRNA (P<0.05) . Thus, we showed that direct suppression of GCK and GKRP genes by siRNA in vitro affects glucose-responsive glycolysis genes, consequently reducing lactate export which can be used as a surrogate for reduced glucokinase activity in hepatocytes. The use of antisense oligonucleotides or CRISPR gene-editing methods in animals will be useful methods to study the glucose-lactate relationship in vivo and will evaluate the role of glucose effectiveness in the pathogenesis of type 2 diabetes.
Disclosure
M.Kabir: None. M.Ader: None. R.N.Bergman: Consultant; Fractyl Health, Inc., Novo Nordisk, Research Support; AstraZeneca, Janssen Research & Development, LLC.
Funding
National Institutes of Health R01- DK027619-28
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