Is metabolically healthy obesity a useful concept?

Metabolic health status and fecundability in a Singapore preconception cohort study

BACKGROUND

Obesity compromises metabolic health and female fertility, yet not all obese women are similar in metabolic status. The extent to which fecundability is influenced by the metabolic health status of women who are overweight or obese before conception is unknown.

OBJECTIVE

This study aimed to: (1) determine the metabolic health status, and (2) examine the association between metabolic health status and fecundability of overweight and obese women trying to conceive in the Singapore PREconception Study of long-Term maternal and child Outcomes cohort study.

STUDY DESIGN

We conducted a prospective preconception cohort study of Asian women (Chinese, Malay, and Indian) aged 18 to 45 years trying to conceive who were treated from 2015 to 2017 in KK Women's and Children's Hospital in Singapore (n=834). We defined women to have metabolically unhealthy status if they: (1) met 3 or more modified Joint Interim Statement metabolic syndrome criteria; or (2) had homeostasis model assessment-insulin resistance index ≥2.5. Body mass index was categorized as normal (18.5-22.9 kg/m2), overweight (23-27.4 kg/m2), or obese (≥27.5 kg/m2) on the basis of cutoff points for Asian populations. Fecundability was measured by time to pregnancy in menstrual cycles within a year of enrolment. Discrete-time proportional hazards models were used to estimate fecundability odds ratios, with adjustment for confounders and accounting for left truncation and right censoring.

RESULTS

Of 232 overweight women, 28 (12.1%) and 25 (10.8%) were metabolically unhealthy by metabolic syndrome ≥3 criteria and homeostasis model assessment-insulin resistance ≥2.5, respectively. Of 175 obese women, 54 (30.9%) and 93 (53.1%) were metabolically unhealthy by metabolic syndrome ≥3 criteria and homeostasis model assessment-insulin resistance ≥2.5, respectively. Compared with metabolically healthy normal-weight women, lower fecundability was observed in metabolically unhealthy overweight women on the basis of metabolic syndrome criteria (fecundability odds ratios, 0.38 [95% confidence interval, 0.15-0.92]) and homeostasis model assessment-insulin resistance (fecundability odds ratios, 0.68 [95% confidence interval, 0.33-1.39]), with metabolic syndrome criteria showing a stronger association. Metabolically unhealthy obese women showed lower fecundability than the healthy normal-weight reference group by both metabolic syndrome (fecundability odds ratios, 0.35; 95% confidence interval, 0.17-0.72) and homeostasis model assessment-insulin resistance criteria (fecundability odds ratios, 0.43; 95% confidence interval, 0.26-0.71). Reduced fecundability was not observed in overweight or obese women who showed healthy metabolic profiles by either definition.

CONCLUSION

Overweight or obesity was not synonymous with having metabolic syndrome or insulin resistance. In our preconception cohort, metabolically unhealthy overweight and obese women showed reduced fecundability, unlike their counterparts who were metabolically healthy. These findings suggest that metabolic health status, rather than simply being overweight and obese per se, plays an important role in fecundability.

Effects of Body Weight Change on Development of Chronic Kidney Disease in Obese Metabolic Phenotypes

Introduction

Obesity is a risk factor for chronic kidney disease (CKD), but whether the reduction of body mass index (BMI) helps prevent CKD is controversial. Recently, obese metabolic phenotypes have raised considerable interest. We thus investigated the effect of BMI change on CKD development.

Methods

We analyzed the data of 6,959 subjects who underwent annual health checkups in both 2013 and 2018. The subjects were categorized into five groups according to their BMI percentage change (ΔBMI) and classified into four obese metabolic phenotypes. By a multivariate logistic regression analysis, we investigated the association between BMI change and CKD development within the 5 years.

Results

In total subjects, compared with the maintained BMI group (ΔBMI ≥0% but <2.5%), the odd ratios (ORs) and 95% confidence intervals (CIs) of CKD development were 0.70 (95% CI 0.54–0.91) for the severe BMI decrease group (ΔBMI <−2.5%), and 1.40 (95% CI 1.08–1.81) for the severe BMI increase group (ΔBMI ≥5%). In the metabolically healthy obese (MHO) phenotype, the risks of CKD development were significantly higher in the moderate BMI increase group (ΔBMI ≥2.5% but <5%) (OR 3.04, 95% CI 1.19–7.78) and a severe BMI increase group (OR 2.88, 95% CI 1.13–7.35). Regarding the metabolically unhealthy nonobese (MUNO) phenotype, the risks of CKD development were significantly lower in the severe BMI decrease group (OR 0.43, 95% CI 0.25–0.74) and the moderate BMI decrease group (ΔBMI ≥−2.5% but <0%) (OR 0.58, 95% CI 0.35–0.98).

Conclusions

In the MHO phenotype, an increased BMI deteriorated CKD development, and a decreased BMI ameliorated CKD development in the MUNO phenotype.

Distinct whole-blood transcriptome profile of children with metabolic healthy overweight/obesity compared to metabolic unhealthy overweight/obesity

BACKGROUND

Youth populations with overweight/obesity (OW/OB) exhibit heterogeneity in cardiometabolic health phenotypes. The underlying mechanisms for those differences are still unclear. This study aimed to analyze the whole-blood transcriptome profile (RNA-seq) of children with metabolic healthy overweight/obesity (MHO) and metabolic unhealthy overweight/obesity (MUO) phenotypes.

METHODS

Twenty-seven children with OW/OB (10.1 ± 1.3 years, 59% boys) from the ActiveBrains project were included. MHO was defined as having none of the following criteria for metabolic syndrome: elevated fasting glucose, high serum triglycerides, low high-density lipoprotein-cholesterol, and high systolic or diastolic blood pressure, while MUO was defined as presenting one or more of these criteria. Inflammatory markers were additionally determined. Total blood RNA was analyzed by 5'-end RNA-sequencing.

RESULTS

Whole-blood transcriptome analysis revealed a distinct pattern of gene expression in children with MHO compared to MUO children. Thirty-two genes differentially expressed were linked to metabolism, mitochondrial, and immune functions.

CONCLUSIONS

The identified gene expression patterns related to metabolism, mitochondrial, and immune functions contribute to a better understanding of why a subset of the population remains metabolically healthy despite having overweight/obesity.

IMPACT

A distinct pattern of whole-blood transcriptome profile (RNA-seq) was identified in children with metabolic healthy overweight/obesity (MHO) compared to metabolic unhealthy overweight/obesity (MUO) phenotype. The most relevant genes in understanding the molecular basis underlying the MHO/MUO phenotypes in children could be: RREB1, FAM83E, SLC44A1, NRG1, TMC5, CYP3A5, TRIM11, and ADAMTSL2. The identified whole-blood transcriptome profile related to metabolism, mitochondrial, and immune functions contribute to a better understanding of why a subset of the population remains metabolically healthy despite having overweight/obesity.

Effectiveness of Bariatric Surgery in Patients with the Metabolically Healthy Obese Phenotype

BACKGROUND

To evaluate the effectiveness and safety of bariatric surgery in metabolically healthy obese (MHO) patients.

METHODS

In this retrospective, observational study, we reviewed the medical records of patients who underwent bariatric surgery at a tertiary care hospital between January 2007 and March 2015. Patients who underwent revisional surgery and patients with type 1 diabetes were excluded from the analysis. MHO patients were defined as those without a previous diagnosis of diabetes or atherogenic dyslipidemia and absence of hypoglycemic treatment or treatment with fibrates.

RESULTS

A total of 188 patients were included (mean age 48.97 ± 10.32 years, 68.6% of women). Sleeve gastrectomy was performed in 121 patients (64%) and a gastric bypass in 67 patients (36%). Prior to surgery, 36 patients (19%) were MHO. In the second- and third-year post-surgery, MHO patients presented a higher percentage of total weight loss (%TWL) (35.16% vs. 30.34%; p = 0.02 and 33.97% vs. 27.78%; p = 0.013 respectively). Multiple regression analysis showed that MHO was associated with a higher weight loss irrespective of age, sex, baseline BMI, and type of surgery. We did not detect any differences in acute complications between patients with and without MHO after bariatric surgery.

CONCLUSIONS

Bariatric surgery in MHO patients in our study was associated with higher weight loss than that in MUHO patients. There were no differences between the two groups in respect to acute complications following surgery.

Effect of Metabolic Health and Obesity Phenotype on Risk of Diabetes Mellitus: A Population-Based Longitudinal Study

BACKGROUND

Epidemiologic evidence on body mass index (BMI)-metabolic status phenotypes and diabetes risk remains controversial, especially for metabolically healthy obesity (MHO). We aimed to examine the effect of metabolic health and obesity phenotype on diabetes risk in the Chinese population.

METHODS

A population-based cohort study was carried out. The baseline survey was conducted in 2017, with two follow-up visits in 2018 and 2020. Diabetes was defined based on the criteria of the World Health Organization. Robust generalized estimating equation models with a binary distribution using a log link and exchange structure were applied for the pooled analysis sample.

RESULTS

A total sample of 9623 observations was pooled for the longitudinal data analysis. The average follow-up time was 1.64 years per person and the overall incidence density of diabetes was 6.94% person-years. Decreased diabetes risk was found in metabolically healthy overweight phenotype (RR = 0.65; 95% CI = 0.47-0.90) and no significant associations were detected for the MHO individuals (RR = 0.99; 95% CI = 0.63-1.53) compared with those of metabolically healthy normal weight, in contrast to metabolically unhealthy normal weight (MU-NW) (RR = 1.81; 95% CI = 1.28-2.55), metabolically unhealthy overweight (MU-OW) (RR = 2.02; 95% CI = 1.57-2.61) and metabolically unhealthy obesity (MUO) (RR = 2.48; 95% CI = 1.89-3.26) phenotypes. Significant associations between BMI-metabolic status phenotypes and diabetes were found in both males and females.

CONCLUSION

The MUO phenotype needs to be accorded much more importance. MU-NW and MU-OW are also important component for targeted prevention. Our findings can be targeted for optimizing preventive strategies to mitigate the obviously increased prevalence of diabetes.

Increased AHR Transcripts Correlate With Pro-inflammatory T-Helper Lymphocytes Polarization in Both Metabolically Healthy Obesity and Type 2 Diabetic Patients

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor whose transcription activity is regulated by small compounds provided by diet, xenobiotics, and metabolism. It has been proven to be involved in energy homeostasis and inflammation in most recent years. Epidemiologically, exposure to xenobiotic AHR ligands contributes to obesity and type 2 diabetes (T2D). AHR is also the critical transcription factor determining the lineage commitment of pro-inflammatory Th17 and Th22 cells from naïve CD4+ T lymphocytes. It has been well-illustrated in animal models that IL-22, the major effector cytokine of Th17 and Th22 cells, played a major role in the interaction of metabolism and gut microbiota. But there were still missing links between gut microbiota, IL-22, and metabolism in humans. Our previous findings indicated that elevated circulating levels of IL-22 and frequencies of Th22 cells were associated with insulin resistance in both patients with obesity and T2D. Additionally, the hyperactive Th17 and Th22 cells phenotype also correlate with islets β-cell dysfunction in T2D. In this study, we made efforts to determine AHR expressions in peripheral blood mononuclear cells (PBMCs) from patients with T2D and metabolically healthy obesity (MHO). Correlation analyses were conducted to assess the possible link between AHR and the metabolic and inflammatory context. We revealed that mRNA expression of AHR was up-regulated and correlated with the percentage of Th17, Th22 as well as Th1 cells. Elevated plasma levels of IL-22 and IL-17 also correlated with increased AHR transcripts in PBMCs from both MHO and T2D patients. The transcription factor AHR may thus have a plausible role in the interaction between metabolism and pro-inflammatory status of patients in the development of obesity and T2D.

MicroRNA profiles in plasma samples from young metabolically healthy obese patients and miRNA-21 are associated with diastolic dysfunction via TGF-β1/Smad pathway

Background

Metabolically healthy obese patients accounts for a large part of obese population, but its clinical significance and cardiac dysfunction are often underestimated. The microRNA profiles of metabolically healthy obese patients were investigated in the study, and the selected microRNA (miRNA) based on our microarray assay will be further verified in a relatively large metabolically healthy obese population.

Methods

microRNA microarray was performed from six metabolically healthy obese and 6 health control blood samples. Based on the bioinformatics analysis, we further measured RT‐PCR, fibrosis markers, echocardiograms, and TGF‐β1/Smad signaling pathway in 600 metabolically healthy obese population.

Results

We found that miRNAs expression characteristics in metabolically healthy obese groups were markedly different from healthy control group. MiRNA‐21 was significantly increased in the samples of metabolically healthy obese patients. Besides, miRNA‐21 levels were associated with cardiac fibrosis marker. Meanwhile, higher miRNA‐21 levels were related to elevated E/E′. Besides, patients with the highest miRNA‐21 quartile showed the lowest ratio of E/A. These associations between miRNA‐21 and diastolic function parameters were independent of obesity and other confounding variables. Of note, TGF‐β1and Smad 3 were significantly upregulated while Smad 7 was downregulated according to the miRNA‐21 quartiles in metabolically healthy obese group.

Conclusions

We demonstrated the profiles of circulating microRNAs in metabolically healthy obese patients. Increased plasma miRNA‐21 levels were related to impaired diastolic function independent of other relevant confounding variables. MiRNA‐21 could be one of the mechanistic links between obesity and diastolic dysfunction through regulating cardiac fibrosis via TGF‐β1/Smad signaling pathway in obese hearts, which may serve as a novel target of disease intervention.

Metabolically Healthy Obesity-Heterogeneity in Definitions and Unconventional Factors

The concept of heterogeneity among obese individuals in their risk for developing metabolic dysfunction and associated complications has been recognized for decades. At the origin of the heterogeneity idea is the acknowledgement that individuals with central obesity are more prone to developing type 2 diabetes and cardiovascular disease than those with peripheral obesity. There have been attempts to categorize subjects according to their metabolic health and degree of obesity giving rise to different obese and non-obese phenotypes that include metabolically unhealthy normal-weight (MUHNW), metabolically healthy obese (MHO), and metabolically unhealthy obese (MUO). Individuals belonging to the MHO phenotype are obese according to their body mass index although exhibiting fewer or none metabolic anomalies such as type 2 diabetes, dyslipidemia, hypertension, and/or unfavorable inflammatory and fribinolytic profiles. However, some authors claim that MHO is only transient in nature. Additionally, the phenotype categorization is controversial as it lacks standardized definitions possibly blurring the distinction between obesity phenotypes and confounding the associations with health outcomes. To add to the discussion, the factors underlying the origin or protection from metabolic deterioration and cardiometabolic risk for these subclasses are being intensely investigated and several hypotheses have been put forward. In the present review, we compare the different definitions of obesity phenotypes and present several possible factors underlying them (adipose tissue distribution and cellularity, contaminant accumulation on the adipose tissue, dysbiosis and metabolic endotoxemia imposing on to the endocannabinoid tone and inflammasome, and nutrient intake and dietary patterns) having inflammatory activation at the center.

Association of Metabolically Healthy Overweight Phenotype With Abnormalities of Glucose Levels and Blood Pressure Among Chinese Adults

IMPORTANCE

Whether the metabolically healthy overweight (MHO) phenotype is resistant to metabolic abnormalities remains unknown.

OBJECTIVE

To evaluate the association of MHO with glucose level abnormalities and high blood pressure (BP) in Chinese adults.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study was conducted from January 1, 2013, to October 31, 2018, in the Health Management Center at Ren Ji Hospital, Shanghai, China, using data from 55 155 recruited Chinese adults. Body weight, fasting blood glucose (FBG) level, hemoglobin A1c (HbA1c) level, and BP were measured annually.

EXPOSURES

Metabolically healthy overweight was defined as a body mass index (calculated as weight in kilograms divided by height in meters squared) of 24.0 in 2013 (baseline) and 2014, no history of metabolic diseases, and normal FBG level, HbA1c level, BP, lipid profile, serum uric acid level, and liver ultrasonographic findings at baseline; the remaining participants were defined as being metabolically healthy normal.

MAIN OUTCOMES AND MEASURES

Glucose level abnormality was confirmed if the FBG level was 101 mg/dL or greater or the HbA1c level was 5.7%, and high BP was confirmed if the systolic BP was 130 mm Hg or higher or the diastolic BP was 80 mm Hg or higher at least twice during the subsequent 4 years of follow-up.

RESULTS

A total of 3204 metabolically healthy Chinese adults (mean [SD] age, 39.8 [10.9] years; 1940 women [60.5%]) were included in the study. The prevalence of MHO was 7.0%. A total of 146 incident cases of glucose level abnormality and 220 cases of high BP during 4 years of follow-up were identified. Compared with the metabolically healthy normal group, the MHO group had a higher risk of glucose level abnormality (adjusted hazard ratio, 2.36; 95% CI, 1.52-3.64) and high BP (adjusted hazard ratio, 1.73; 95% CI, 1.18-2.53) after adjusting for several potential confounders.

CONCLUSIONS AND RELEVANCE

Metabolically healthy overweight may be associated with a high future risk of glucose abnormality and high BP in Chinese adults. If the individuals are confirmed with MHO, early interventions, including diet and exercise, should be recommended to decrease the risk of developing abnormalities of glucose and BP.