Association between fat free mass and glucose homeostasis: Common knowledge revisited

Comparative lipidomic profiling in adolescents with obesity and adolescents with type 1 diabetes

OBJECTIVE

Both adolescents with obesity and those with type 1 diabetes (T1D) exhibit alterations in lipid profiles, but direct comparisons are limited. Comparing lipidomic profiles between obese individuals and those with T1D is crucial for identifying specific metabolic markers, informing tailored interventions, and advancing precision medicine strategies for these distinct populations. The aim of the study was to compare lipidomic profiles between adolescents with obesity and those with T1D, and to analyze associations between metabolites and clinical parameters.

METHODS

We included 156 adolescents aged 11-18 years (59.6% girls) from the HEPAFIT (n=114, obesity) and Diactive-1 Cohort (n=42, T1D) studies. Clinical measures included anthropometrics, body composition, lipids, liver enzymes, glucose, and HbA1c. Lipidomic analysis of 277 serum/plasma metabolites used UHPLC-MS.

RESULTS

Distinct lipid profiles were seen, with higher diglycerides, triglycerides, and certain phosphatidylinositols in the obesity group, while phosphatidylcholines, phosphatidylethanolamines, cholesterol esters, sphingomyelins, and ceramides were elevated in T1D. Triglycerides acyl chain lengths and saturation levels also varied. Multivariate analysis identified seven metabolites -PC(O-18:1/18:1), PC(O-18:1/22:4), PE(O-16:0/18:1), PE(18:2e/22:6), PC(40:1), PC(O-22:1/20:4), and PE(P-18:0/18:1)- significantly associated with clinical parameters.

CONCLUSIONS

Distinct lipid profiles were observed among adolescents with obesity and T1D in the study, emphasizing the importance of understanding specific metabolite associations with clinical parameters for more precise health management.

Relationship Between Body Composition and Insulin Resistance Evaluated by the TyG Index: A Retrospective Study Among Chinese Population

OBJECTIVE

The triglyceride glucose (TyG) index, a novel and easily obtained marker of insulin resistance (IR), has been shown to predict metabolic diseases. Monitoring body composition is crucial in assessing disease states. This study aimed to investigate the relationship between body composition and IR as assessed by the TyG index.

METHODS

Between January 2018 and December 2021, 12,186 individuals were initially enroled, with 4061 adults were ultimately included. Body composition, including fat mass (FM), fat mass index (FMI), fat-free mass (FFM), fat-free mass index (FFMI), and percent body fat (PBF), was measured using bioelectrical impedance analysis. Spearman analysis assessed correlations between body composition indices and the TyG index. Binary logistic regression identified independent predictors of IR.

RESULTS

Older women (≥ 50 years old) showed significantly higher BMI, PBF, FM, FMI, FFMI, HOMA-IR, and the TyG index, but lower FFM compared to younger women; Older men exhibited significantly lower BMI, FM, FFM, FFMI, HOMA-IR, and the TyG index than the younger men. FM, FMI, FFM, FFMI, and PBF were positively correlated with the TyG index. FFMI and PBF significantly predicted IR in both genders. Combined FFMI and PBF yielded an area under the ROC curves of 0.718 in women and 0.661 in men for IR diagnosis.

CONCLUSION

The TyG index correlates with body composition parameters of FFMI and PBF as well as HOMA-IR potentially making it a convenient marker of metabolic risk.

Fat-Free Mass: Friend or Foe to Metabolic Health?

BACKGROUND

Fat mass (FM) and fat-free mass (FFM) are body composition estimates commonly reported in research studies and clinical settings. Recently, fat-free mass indexed to height (fat-free mass index; FFMI) has been shown to be positively associated with impaired insulin sensitivity or insulin resistance. Consequently, hypertrophic resistance training which can increase FFM was also questioned. This paper sets out to evaluate these propositions.

METHODS

In this narrative review, we discuss possible reasons that link FFMI to adverse metabolic health outcomes including the limitations of the body composition model that utilizes FFM. The safety of resistance training is also briefly discussed.

RESULTS

Approximately 50% of FFM is comprised of skeletal muscle (SM), with the other 50% being viscera, skin, and bone; FFM and SM cannot be conflated. FFM and fat mass (FM) can both rise with increasing body weight and adiposity, indicating a positive correlation between the two compartments. Risk assessment models not adequately adjusting for this correlation may cause erroneous conclusions, however which way FM and FFM are indexed. Adipose tissue accumulation with weight gain, measured by dual-energy X-ray absorptiometry or bioelectrical impedance, can inflate FFM estimates owing to increased connective tissue. Increased adiposity can also result in fat deposition within skeletal muscle disrupting metabolic health. Importantly, non-skeletal muscle components of the FFM, i.e., the liver and pancreas, both critical in metabolic health, can also be negatively affected by the same lifestyle factors that impact SM. The most frequently used body composition techniques used to estimate FM and FFM cannot detect muscle, liver or pancreas fat infiltration. Prospective evidence demonstrates that resistance training is a safe and effective exercise modality across all ages, especially in older adults experiencing age- or disease-related declines in muscle health.

CONCLUSIONS

The association between FFM and insulin resistance is largely an artefact driven by inadequate assessment of skeletal muscle. If FM and FFM are used, at the minimum, they need to be evaluated in context with one another. Body composition methods, such as magnetic resonance imaging, which measures skeletal muscle rather than fat-free mass, and adipose tissue as well as muscle ectopic fat, are preferred methods. Resistance training is important in achieving and maintaining good health across the lifespan. While strength and power are critical components of resistance training, the reduction of skeletal mass through ageing or disease may require hypertrophic training to mitigate and slow down the progression of this often-inevitable process.

Body Composition and Its Interaction with Bone Mineral Density and Biochemical and Nutritional Parameters in Chilean Adults with Overweight/Obesity and Normal Weight

This study aimed to compare and relate the body composition (obtained through anthropometry with the pentacompartmental model and the tricompartmental model by DXA) with bone mineral density and biochemical and nutritional parameters in Chilean adults with overweight/obesity and normal weight from La Araucanía region, Chile. A case-control study was conducted with 116 adults and volunteers from the PURE cohort, collecting sociodemographic data, BMI assessment, waist-to-hip ratio (WHR), and body composition using the pentacompartmental model (5CM) and tricompartmental model (3CM) by DXA, as well as bone mineral density (BMD). Blood biochemical parameters (fasting glucose and lipid profile), physical activity (PA) measured by GPAQ, and average dietary habits (R24h) were measured. In the overweight/obesity group, the 5CM and 3CM adipose mass were indirectly and moderately correlated with PA (p < 0.05), except in the male 5CM group. In the overweight/obesity group, muscle and fat-free mass (FFM) of the 5CM and 3CM correlated directly and moderately with blood fasting glucose (BFG) and BMD (p < 0.05), except in females, where FFM was not related to BMD but was related to residual mass (p < 0.01). Independent of gender and BMI, bone mineral content was positively and highly correlated with BMD (p < 0.0000). In the male overweight/obesity group, bone, skin, and residual mass were correlated with BFG (p < 0.05). In conclusion, for the assessment of non-athletic adult populations, more routine use of the 5CM in clinical practice is recommended.

Fat-free mass index is a feasible predictor of insulin resistance in women with polycystic ovary syndrome: Evidence from a cross-sectional study

BACKGROUND

Insulin resistance (IR) and adipose tissue amplify the metabolic and reproductive outcomes in women with polycystic ovary syndrome (PCOS). It has been widely discussed that body composition influences metabolic health. Still, limited studies were focused on the role of the fat-free mass index (FFMI) in assessing IR in PCOS women.

AIMS

We aimed to explore the associations between FFMI/fat mass index (FMI) and IR in women with PCOS and assess the role of FFMI in predicting IR in women with PCOS.

METHODS

In the current cross-sectional study, women with PCOS aged between 18 and 40 years were enrolled from October 2018 to July 2022. Baseline demographic information was obtained using standardized self-administered questionnaires. Anthropometric, biochemical, and hormonal information was measured and recorded by investigators. Pearson's correlation and multivariable logistical regression were used to analyze the associations of FFMI/FMI and IR. In addition, receiver operating characteristic (ROC) curves were implied to measure the predictive role of FFMI/FMI for IR in women with PCOS.

RESULTS

A total of 371 women with PCOS, reproductive age (27.58 ± 4.89) were enrolled. PCOS women with IR have higher levels of triglyceride (TG), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), homeostatic model assessment of insulin resistance (HOMA-IR), FMI, and FFMI than that without IR. FMI (r = 0.492, p < 0.001) and FFMI (r = 0.527, p < 0.001) were positively associated with IR. After adjusting for potential confounders, FMI and FFMI were significantly associated with IR in PCOS women, and the OR was 1.385 (95%CI: 1.212-1.583) and 2.306 (95%CI: 1.675-3.174), respectively. Additionally, the FFMI (0.847, 95%CI: 0.784-0.888) has a larger area of ROC (AUC) than the FMI (0.836, 95%CI: 0.799-0.896), while there is no difference in predicting IR (95%CI: -0.18-0.41, p = 0.456).

CONCLUSION

These results indicated that FFMI and FMI could significantly increase the risk of IR, both of which could be feasible predictors of IR in PCOS women.

Sex-specific associations between skeletal muscle mass and incident diabetes: A population-based cohort study

AIMS

To investigate the sex-specific associations between predicted skeletal muscle mass index (pSMI) and incident type 2 diabetes in a retrospective longitudinal cohort of Chinese men and women.

MATERIALS AND METHODS

We enrolled Chinese adults without diabetes at baseline from WATCH (West chinA adulT health CoHort), a large health check-up-based database. We calculated pSMI to estimate skeletal muscular mass, and measured blood glucose variables and assessed self-reported history to identify new-onset diabetes. The nonlinear association between pSMI and incident type 2 diabetes was modelled using the penalized spline method. The piecewise association was estimated using segmented linear splines in weighted Cox proportional hazards regression models.

RESULTS

Of 47 885 adults (53.2% women) with a median age of 40 years, 1836 developed type 2 diabetes after a 5-year median follow-up. In women, higher pSMI was associated with a lower risk of incident type 2 diabetes (Pnonlinearity  = 0.09, hazard ratio [HR] per standard deviation increment in pSMI: 0.79 [95% confidence interval {CI} 0.68, 0.91]). A nonlinear association of pSMI with incident type 2 diabetes was detected in men (Pnonlinearity  < 0.001). In men with pSMI lower than 8.1, higher pSMI was associated with a lower risk of incident type 2 diabetes (HR 0.58 [95% CI 0.40, 0.84]), whereas pSMI was not significantly associated with incident diabetes in men with pSMI equal to or greater than 8.1 (HR 1.08 [95% CI 0.93, 1.25]).

CONCLUSIONS

In females, a larger muscular mass is associated with a lower risk of type 2 diabetes. For males, this association is significant only among those with diminished muscle mass.

Conflicting Associations among Bioelectrical Impedance and Cardiometabolic Health Parameters in Young White and Black Adults

PURPOSE

The purpose of this cross-sectional evaluation was to determine the associations between raw bioelectrical impedance and cardiometabolic health parameters in a sample of young non-Hispanic White and African American adults.

METHODS

A total of 96 (female: 52, male: 44) non-Hispanic White ( n = 45) and African American adults ( n = 51) between the ages of 19 and 37 yr (22.7 ± 3.83 yr) completed several fasted assessments including resting systolic blood pressure (rSBP), blood glucose (FBG), blood lipids, and bioelectrical impedance spectroscopy. Bioelectrical impedance spectroscopy-derived measurements included phase angle, bioimpedance index (BI), impedance ratio (IR), reactance index (XCi), fat-free mass (FFM), FFM index (FFMi), and absolute (a) and relative (%) total body water (TBW) and extracellular (ECF) and intracellular fluid (ICF). All bioelectric variables were collected at 50 kHz other than IR (250 kHz/5 kHz). Multiple regressions were conducted and adjusted for sex, age, and body mass index.

RESULTS

rSBP was positively, and HDL was inversely, associated with all bioelectrical impedance and absolute hydration variables (all P ≤ 0.050) other than XCi for rSBP and XCi and FFMi for HDL. rSBP ( P < 0.001) was inversely, and HDL ( P = 0.034) was positively, associated with IR. FBG was positively associated with BI, XCi, FFM, TBWa, and ECFa (all P < 0.050). Metabolic syndrome severity was positively associated with BI, FFM, TBWa, and ECFa for women (all P ≤ 0.050) and with ICFa for African American women ( P = 0.016).

CONCLUSIONS

Given the rapid increase in the prevalence of cardiometabolic health risks among young adults and the broad use of bioelectrical impedance in practice, the conflicting associations we observed in this age group suggest that bioelectrical impedance parameters should be used with caution in the context of cardiometabolic health risks and age.

Anticipated correlation between lean body mass to visceral fat mass ratio and insulin resistance: NHANES 2011-2018

Objective

The relationship between body composition and insulin resistance (IR) is controversial. This study aimed to thoroughly examine the correlation between adipose tissue, lean body mass, and IR as evaluated by the Homeostatic Model Assessment (HOMA-IR).

Methods

In this cross-sectional study, we utilized data from the National Health and Nutrition Examination Survey (NHANES) conducted between 2011 and 2018. Our study included 4981 subjects, and we employed multiple linear regression, smoothed curve fitting, threshold, and saturation effect analysis to investigate the relationship between lean body mass, visceral fat mass, and IR. Also, we used the lean body mass to visceral fat ratio (Log LM/VFM) as a proxy variable to analyze its association with IR alone.

Results

The study discovered a negative link between lean body mass and IR, but the visceral fat mass was positively correlated after correcting for covariates. A negative correlation was observed when the alternative variable Log LM/VFM was analyzed separately for its association with IR. This association was present regardless of whether the exposure variables were analyzed as continuous or categorical. The data analysis revealed a nonlinear relationship between Log LM/VFM and IR, as evidenced by the generalized additive model. In addition, a threshold effect with a critical value of 1.80 and a saturation effect with a critical point of 2.5 were also observed. Further subgroup analysis for sex, age, BMI, active levels, hypertension, and diabetes showed considerable robustness between the relationship of Log LM/VFM and IR.

Conclusion

Maintaining a proper ratio of lean body mass and visceral fat is beneficial for decreasing IR.

The protective effect of rs373863828 on type 2 diabetes does not operate through a body composition pathway in adult Samoans

OBJECTIVE

The aim of this study was to understand whether the paradoxical association of missense variant rs373863828 in CREB3 regulatory factor (CREBRF) with higher BMI but lower odds of diabetes is explained by either metabolically favorable body fat distribution or greater fat-free mass.

METHODS

This study explored the association of the minor allele with dual-energy x-ray absorptiometry-derived body composition in n = 421 Samoans and used path analysis to examine the mediating role of fat and fat-free mass on the relationship between rs373863828 and fasting glucose.

RESULTS

Among females, the rs373863828 minor A allele was associated with greater BMI. There was no association of genotype with percent body fat, visceral adiposity, or fat distribution in either sex. In both females and males, lean mass was greater with each A allele: 2.16 kg/copy (p = 0.0001) and 1.73 kg/copy (p = 0.02), respectively. Path analysis showed a direct negative effect of rs373863828 genotype on fasting glucose (p = 0.004) consistent with previous findings, but also an indirect positive effect on fasting glucose operating through fat-free mass (p = 0.027).

CONCLUSIONS

The protective effect of rs373863828 in CREBRF, common among Pacific Islanders, on type 2 diabetes does not operate through body composition. Rather, the variant's effects on body size/composition and fasting glucose likely operate via different, tissue-specific mechanisms.

Beyond the Calorie Paradigm: Taking into Account in Practice the Balance of Fat and Carbohydrate Oxidation during Exercise?

Recent literature shows that exercise is not simply a way to generate a calorie deficit as an add-on to restrictive diets but exerts powerful additional biological effects via its impact on mitochondrial function, the release of chemical messengers induced by muscular activity, and its ability to reverse epigenetic alterations. This review aims to summarize the current literature dealing with the hypothesis that some of these effects of exercise unexplained by an energy deficit are related to the balance of substrates used as fuel by the exercising muscle. This balance of substrates can be measured with reliable techniques, which provide information about metabolic disturbances associated with sedentarity and obesity, as well as adaptations of fuel metabolism in trained individuals. The exercise intensity that elicits maximal oxidation of lipids, termed LIPOXmax, FATOXmax, or FATmax, provides a marker of the mitochondrial ability to oxidize fatty acids and predicts how much fat will be oxidized over 45–60 min of low- to moderate-intensity training performed at the corresponding intensity. LIPOXmax is a reproducible parameter that can be modified by many physiological and lifestyle influences (exercise, diet, gender, age, hormones such as catecholamines, and the growth hormone-Insulin-like growth factor I axis). Individuals told to select an exercise intensity to maintain for 45 min or more spontaneously select a level close to this intensity. There is increasing evidence that training targeted at this level is efficient for reducing fat mass, sparing muscle mass, increasing the ability to oxidize lipids during exercise, lowering blood pressure and low-grade inflammation, improving insulin secretion and insulin sensitivity, reducing blood glucose and HbA_1c in type 2 diabetes, and decreasing the circulating cholesterol level. Training protocols based on this concept are easy to implement and accept in very sedentary patients and have shown an unexpected efficacy over the long term. They also represent a useful add-on to bariatric surgery in order to maintain and improve its weight-lowering effect. Additional studies are required to confirm and more precisely analyze the determinants of LIPOXmax and the long-term effects of training at this level on body composition, metabolism, and health.

Body composition, physical fitness and cardiovascular risk factors in 9-year-old children

The independent associations of body composition and physical fitness components with cardiovascular disease (CVD) risk factors in childhood are not fully understood. Thus, this cross-sectional study examined the independent associations of body composition and physical fitness with CVD risk factors in Swedish 9-year-old children (n = 411). Unadjusted linear regression analyses showed that body mass index (BMI), % fat mass and fat mass index were all positively associated with systolic and diastolic blood pressure, Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and Metabolic Syndrome (MetS) score (all β ≥ 0.229, P ≤ 0.001). These associations were virtually unaffected by adjustments for basic covariates (child's age and sex, maternal educational level and maternal BMI), fat-free mass and physical fitness. Fat-free mass index had generally weak associations with CVD risk factors and no associations were statistically significant after adjustments (all P > 0.27). Greater cardiorespiratory fitness and motor fitness were associated with lower HOMA-IR and MetS score in unadjusted models (all β ≤ - 0.158, P ≤ 0.039) but not after adjustments for basic covariates and body composition. These findings indicate that cardiovascular health promotion in childhood may focus on the maintenance of a healthy fat mass.

Increased odds of having the metabolic syndrome with greater fat-free mass: counterintuitive results from the National Health and Nutrition Examination Survey database

BACKGROUND

It is well established that body composition influences metabolic health, but emerging data are conflicting with the largely purported idea that a large fat-free mass (FFM) has a protective effect on health. A potential explanation for these discrepancies is the way FFM is represented. The first objective is to determine the association between the metabolic syndrome (MetS) and FFM when the latter was represented in three different ways: 1-absolute FFM; 2-relative to squared height (FFMi); and 3-relative to body weight (FFM%). The second objective is to assess the impact of FFM on the relative risk of having the MetS after taking fat mass, physical activity, and sociodemographic variables into account.

METHODS

A total of 5274 individuals from the National Health and Nutrition Examination Survey database were studied. Age-specific and sex-specific quartiles of the three representations of FFM were defined, and the prevalence of MetS was determined in each of them. Quartiles of FFMi (kg/m² ) were used to calculate the odds ratios of having the MetS independently of FM, physical activity levels, and sociodemographic variables.

RESULTS

The prevalence of MetS decreased with increasing quartiles of whole-body FFM% (Q1: 40%; Q4: 10%) but grew with increasing quartiles of absolute FFM (Q1: 13%; Q4: 40%) and FFMi (Q1: 10%; Q4: 44%). Similar results were observed for appendicular and truncal FFM. The odds ratios of having the MetS, independently of fat mass, physical activity, and sociodemographic variables, were significantly greater in the fourth quartile of FFMi when compared with the first quartiles of each specific subgroup [Q4 vs. Q1: younger men: 4.16 (1.99-8.68); younger women: 5.74 (2.46-13.39); older men: 1.98 (1.22-3.22); older women: 2.88 (1.69-4.90); all P ≤ 0.01].

CONCLUSIONS

These results support the notion that the representation of FFM significantly influences its association with MetS and that a larger FFM, whether absolute or relative to height, is associated with alterations in cardiometabolic health.

Fat-free/lean body mass in children with insulin resistance or metabolic syndrome: a systematic review and meta-analysis

BACKGROUND

Lean / Fat Free Body Mass (LBM) is metabolically involved in active processes such as resting energy expenditure, glucose uptake, and myokine secretion. Nonetheless, its association with insulin sensitivity / resistance / glucose tolerance and metabolic syndrome remains unclear in childhood.

METHODS

The current investigation aimed to examine the differences in fat-free mass /lean body mass according to the presence of insulin sensitivity/insulin resistance/glucose tolerance/metabolic syndrome in children. A systematic search was carried out in Medline/PubMed, Embase, Scopus, Web of Science, and SciELO, covering the period from each database's respective start to 21 June 2021. Two researchers evaluated 7111 studies according to the inclusion criteria: original human studies, written in English or Spanish, evaluating fat-free mass/lean body mass in children and adolescents including both with and without insulin sensitivity/insulin resistance /glucose tolerance and metabolic syndrome and reported the differences between them in terms of fat free mass/lean body mass. The results of the studies were combined with insulin sensitivity, insulin, resistance, glucose tolerance and metabolic syndrome. The standardized mean difference (SMD) in each study was calculated and combined using the random-effects model. Heterogeneity between studies was tested using the index of heterogeneity (I2), leave-one-out sensitivity analyses were performed, and publication bias was assessed using the Egger and Begg tests.

RESULTS

Finally, 15 studies which compared groups defined according to different glucose homeostasis criteria or metabolic syndrome out of 103 eligible studies were included in this systematic review and 12 studies in the meta-analysis. Meta-analysis showed lower fat-free mass/lean body mass percentage in participants with insulin resistance/glucose tolerance/metabolic syndrome (SMD -0.47; 95% CI, - 0.62 to - 0.32) while in mass units (kg), higher values were found in the same group (SMD, 1.01; 95% CI, 0.43 to 1.60).

CONCLUSIONS

Our results identified lower values of fat-free mass/lean body mass (%) in children and adolescents with insulin resistance/glucose tolerance/metabolic syndrome and higher values of fat-free mass/lean body mass when these are expressed in kg. The evidence of the impact of lean mass on children's glucose homeostasis or metabolic syndrome is limited, so future studies research should focus on explaining the effect of fat-free mass/lean body mass on different metabolic outcomes. Moreover, it may be interesting to evaluate the quality (muscle density) or functional (muscle strength) outcomes in addition to both absolute (kg) and relative (%) values in future studies. The systematic review was prospectively registered at PROSPERO (registration number CRD42019124734; available at: http://www.crd.york.ac.uk/prospero [accessed: 05 April 2019]).

Associations between skeletal muscle echo intensity and thickness in relation to glucose homeostasis in healthy and glucose impaired older males

BACKGROUND

Aging-related changes in muscle composition and mass may predispose older adults to developing insulin resistance. Ultrasound echo intensity and thickness are surrogates of muscle composition and mass, however, their associations with glucose homeostasis are not well established. We examined how muscle echo intensity and thickness correlate with markers of glucose homeostasis in older (≥65 years) males with normal (n = 22) or impaired (n = 10) glucose control.

METHODS

Echo intensity was measured for the biceps brachii, rectus abdominis, and rectus femoris. Muscle thickness was evaluated for the biceps brachii + brachioradialis, rectus abdominis, and rectus femoris + vastus intermedius. Glucose homeostasis was evaluated using a 2-h oral glucose tolerance test.

RESULTS

In older males with normal glucose homeostasis, higher echo intensity of the rectus abdominis and rectus femoris was moderately (r = 0.36 to 0.59) associated with 2-h glucose. On the contrary, higher muscle echo intensity of the rectus abdominis, biceps brachii, and rectus femoris was moderately-to-strongly (r = -0.36 to -0.79) associated with indices of better glucose homeostasis in the impaired group. Rectus abdominis muscle thickness was moderately associated (r = 0.36) with better glucose tolerance in the normal glucose homeostasis; however, in the glucose impaired group, muscle thickness was associated with (r = 0.37 to 0.73) with poorer glucose homeostasis.

CONCLUSIONS

Muscle echo intensity displays divergent associations with glucose homeostasis in older males with normal compared to impaired glucose control. Larger muscle thickness was associated with poorer glucose homeostasis in the glucose impaired group, but rectus abdominis muscle thickness was correlated with better homeostasis in healthy older males.

Associations of body composition and physical fitness with gestational diabetes and cardiovascular health in pregnancy: Results from the HealthyMoms trial

The aim of this study was to examine associations of body composition (fat mass index, % fat mass, fat-free mass index, body mass index) and physical fitness (cardiorespiratory fitness and handgrip strength) with gestational diabetes and cardiovascular health in early pregnancy. This cross-sectional study utilized baseline data (n = 303) collected in early pregnancy from the HealthyMoms trial. Body composition was measured using air-displacement plethysmography, cardiorespiratory fitness was assessed by means of the 6-min walk test and handgrip strength using a dynamometer. Logistic regression was used to estimate odds ratios (ORs) for gestational diabetes as well as high (defined as 1 SD above the mean) blood pressure, homeostatic model assessment for insulin resistance (HOMA-IR), and metabolic syndrome score (MetS score) per 1 SD increase in body composition and fitness variables. Fat mass index, % fat mass and body mass index were all strongly associated with gestational diabetes (ORs: 1.72–2.14, P ≤ 0.003), HOMA-IR (ORs: 3.01–3.80, P < 0.001), blood pressure (ORs: 1.81–2.05, P < 0.001) and MetS score (ORs: 3.29–3.71, P < 0.001). Associations with fat-free mass index were considerably weaker (ORs: 1.26–1.82, P = 0.001–0.15) and were strongly attenuated after adjustments for fat mass index (ORs: 0.88–1.54, P = 0.039–0.68). Finally, greater cardiorespiratory fitness was associated with lower risk of high HOMA-IR and MetS score (ORs: 0.57–0.63, P  ≤ 0.004) although these associations were attenuated when accounting for fat mass index (ORs: 1.08-1.11, P ≥ 0.61). In conclusion, accurately measured fat mass index or % fat mass were strongly associated with gestational diabetes risk and markers of cardiovascular health although associations were not stronger than the corresponding ones for body mass index. Fat-free mass index had only weak associations with gestational diabetes and cardiovascular health which support that the focus during clinical care would be on excess fat mass and not fat-free mass.

Exercising for Insulin Sensitivity - Is There a Mechanistic Relationship With Quantitative Changes in Skeletal Muscle Mass?

Skeletal muscle (SM) tissue has been repetitively shown to play a major role in whole-body glucose homeostasis and overall metabolic health. Hence, SM hypertrophy through resistance training (RT) has been suggested to be favorable to glucose homeostasis in different populations, from young healthy to type 2 diabetic (T2D) individuals. While RT has been shown to contribute to improved metabolic health, including insulin sensitivity surrogates, in multiple studies, a universal understanding of a mechanistic explanation is currently lacking. Furthermore, exercised-improved glucose homeostasis and quantitative changes of SM mass have been hypothesized to be concurrent but not necessarily causally associated. With a straightforward focus on exercise interventions, this narrative review aims to highlight the current level of evidence of the impact of SM hypertrophy on glucose homeostasis, as well various mechanisms that are likely to explain those effects. These mechanistic insights could provide a strengthened rationale for future research assessing alternative RT strategies to the current classical modalities, such as low-load, high repetition RT or high-volume circuit-style RT, in metabolically impaired populations.

Insulin resistance may be misdiagnosed by HOMA-IR in adults with greater fat-free mass: the ELSA-Brasil Study

AIMS

Conflicting results have been reported on the association of fat-free mass (FFM) and insulin resistance (IR). This study sought to test the association of FFM and IR by indexing FFM to avoid collinearity with fat mass.

METHODS

This cross-sectional study comprised 11,284 volunteers, aged 38-79 years. Body composition was assessed by multi-frequency bioelectrical impedance. FFM indexed to body surface area (FFMbsa) was calculated. IR and impaired glucose tolerance (IGT) were estimated with homeostatic model assessment of insulin resistance index (HOMA-IR) and 2-h oral glucose tolerance test (2h-OGTT), respectively.

RESULTS

Percent body fat decreased from the 1st to the 5th quintile of FFMbsa in both women (Eta² = 0.166) and men (Eta² = 0.133). In women, fasting insulin (Eta² = 0.002), glucose (Eta² = 0.006), and HOMA-IR (Eta² = 0.007) increased slightly, but 2-h plasma glucose (2-h PG) was similar across the quintiles of FFMbsa. In men, fasting insulin and HOMA-IR were similar across the quintiles of FFMbsa, whereas fasting glucose increased slightly (Eta² = 0.002) and 2-h PG decreased (Eta² = 0.005) toward the highest quintile of FFMbsa. The higher the odds ratio for IR, the greater the FFMbsa in both sexes. Differently, FFMbsa did not affect the odds of IGT in women, while in men the odds ratio for IGT was lower in the 5th quintile compared with the 1st quintile of FFMbsa.

CONCLUSIONS

Higher odds of IR associated with greater FFMbsa contrasted with lower odds of IGT associated with greater FFMbsa. IR may be misdiagnosed by HOMA-IR in adults with greater fat-free mass.

Ethnic Differences in Body Fat Deposition and Liver Fat Content in Two UK-Based Cohorts

OBJECTIVE

Differences in the content and distribution of body fat and ectopic lipids may be responsible for ethnic variations in metabolic disease susceptibility. The aim of this study was to examine the ethnic distribution of body fat in two separate UK-based populations.

METHODS

Anthropometry and body composition were assessed in two separate UK cohorts: the Hammersmith cohort and the UK Biobank, both comprising individuals of South Asian descent (SA), individuals of Afro-Caribbean descent (AC), and individuals of European descent (EUR). Regional adipose tissue stores and liver fat were measured by magnetic resonance techniques.

RESULTS

The Hammersmith cohort (n = 747) had a mean (SD) age of 41.1 (14.5) years (EUR: 374 men, 240 women; SA: 68 men, 22 women; AC: 14 men, 29 women), and the UK Biobank (n = 9,533) had a mean (SD) age of 55.5 (7.5) years (EUR: 4,483 men, 4,873 women; SA: 80 men, 43 women, AC: 31 men, 25 women). Following adjustment for age and BMI, no significant differences in visceral adipose tissue or liver fat were observed between SA and EUR individuals in the either cohort.

CONCLUSIONS

Our data, consistent across two independent UK-based cohorts, present a limited number of ethnic differences in the distribution of body fat depots associated with metabolic disease. These results suggest that the ethnic variation in susceptibility to features of the metabolic syndrome may not arise from differences in body fat.

Physical activity energy expenditure and fat-free mass: relationship with metabolic syndrome in overweight or obese postmenopausal women

Menopause transition is associated with detrimental changes in physical activity, body composition, and metabolic profile. Although physical activity energy expenditure (PAEE) is inversely associated with metabolic syndrome (MetS) in individuals at higher risk of cardiovascular disease, the association is unknown in low-risk individuals. The aim of the study was to investigate the association between PAEE and MetS (prevalence and severity) in inactive overweight or obese postmenopausal women with a low Framingham Risk Score (<10%). Cross-sectional data of 126 participants were divided into quartiles based on PAEE (Quartile (Q)1 = lowest PAEE) while fat-free mass (FFM) and fat mass were measured by dual-energy X-ray absorptiometry. MetS prevalence was significantly different between Q1 and Q4 (37.9% vs 13.3%, p = 0.03). After controlling for potential confounders, MetS severity was negatively associated with PAEE (B = -0.057, p < 0.01) and positively with FFM (B = 0.038, p < 0.001). Moderation analyses indicated that a greater FFM exacerbated the association between PAEE and MetS severity in Q1 and Q2 (PAEE × FFM; B = -0.004; p = 0.1). Our results suggest that displaying a low FRS and lower PAEE increase MetS prevalence and severity. In addition, greater FFM interacts with lower PAEE to worsens MetS severity, while higher PAEE lessened this effect. Novelty: Inactive individuals displaying higher daily PAEE also have a lower MetS prevalence. Greater FFM is associated with a worse MetS severity where a higher PAEE mitigated this deleterious effect in our cohort.

A counterintuitive perspective for the role of fat-free mass in metabolic health

Fat-free mass (FFM) has long been recognized to play a role in metabolic homeostasis. Over the years, it has become widely accepted by the scientific and general community alike that having a greater FFM can be protective for metabolic health. Hence, in the context of an aging population concurrently facing sarcopenia and an elevated incidence of metabolic diseases, substantial efforts are being made to study and develop interventions aiming to maintain or increase FFM. However, accumulating evidence now suggests that a large FFM may be deleterious to metabolic health, at least in some populations. The objective of this article is thus to raise awareness surrounding these results and to explore possible explanations and mechanisms underlying this counterintuitive association.

Leucine Supplementation Does Not Alter Insulin Sensitivity in Prefrail and Frail Older Women following a Resistance Training Protocol

BACKGROUND

Frailty is a clinical condition associated with loss of muscle mass and strength (sarcopenia). Although sarcopenia has multifactorial causes, it might be partly attributed to a blunted response to anabolic stimuli. Leucine acutely increases muscle protein synthesis, and resistance training (RT) is the strongest stimuli to counteract sarcopenia and was recently shown to improve insulin sensitivity (IS) in frail older women. Discrepancies exist regarding whether chronic supplementation of leucine in conjunction with RT can improve muscle mass and IS.

OBJECTIVE

The aim of this double-blinded placebo-controlled study was to determine the effects of leucine supplementation and RT on IS in prefrail and frail older women.

METHODS

Using the Fried criteria, 19 nondiabetic prefrail (1-2 criteria) and frail (≥3 criteria) older women (77.5 ± 1.3 y; body mass index (kg/m2): 25.1 ± 0.9) underwent a 3-mo intervention of RT 3 times/wk with protein-optimized diet of 1.2 g·kg-1·d-1 and 7.5 g·d-1 of l-leucine supplementation compared with placebo l-alanine. Pre-/postintervention primary outcomes were fasting plasma glucose, serum insulin, and 4-h responses to a standard meal of complete liquid formula. Secondary outcomes of resting energy expenditure using indirect calorimetry and body composition using dual-energy X-ray absorptiometry were obtained. Paired t tests analyzed pooled data, and 2-factor repeated-measures ANOVA determined supplementation, training, and interaction effects.

RESULTS

No significant time, group, or interaction effects were observed for postprandial areas under the curve of serum insulin or plasma glucose or for resting energy expenditure in l-leucine compared with l-alanine. Total lean body mass increased and percentage body fat decreased significantly for both groups postintervention (0.76 ± 0.13 and -0.92 ± 0.33 kg, respectively; time effect: P < 0.01).

CONCLUSIONS

IS was not affected by RT and leucine supplementation in nondiabetic prefrail and frail older women. Therefore, leucine supplementation does not appear to influence IS under these conditions. This trial was registered at clinicaltrials.gov as NCT01922167.

Prepregnancy Fat Free Mass and Associations to Glucose Metabolism Before and During Pregnancy

OBJECTIVE

Our aim was to quantify the individual contribution of prepregnancy (PP) fat-free mass (FFM), expressed as [PP-FFM index (PP-FFMI) = FFM (kg)/height (m2)], on markers of glucose homeostasis before and during pregnancy.

METHODS

Body composition was assessed in 43 women before pregnancy using air-displacement plethysmography. Blood was drawn at PP and gestational weeks ∼8 and 30. Relationships between body composition (independent) variables and glucose homeostasis (dependent) variables were assessed using adjusted correlations and simple and multiple linear regression analyses.

RESULTS

PP-FFMI was the strongest predictor of plasma insulin concentration [squared partial correlation (Pr2) = 17, P = 0.007] and homeostasis model assessment of insulin resistance (HOMA2-IR) (Pr2 = 16, P = 0.010). At gestation week 30, PP-FFMI and gestational weight gain (GWG) were the strongest predictors of insulin concentration (PP-FFMI: Pr2 = 20, P = 0.010; GWG: Pr2 = 12, P = 0.052) and HOMA2-IR (PP-FFMI: Pr2 = 19, P = 0.012; GWG: Pr2 = 13, P = 0.045). After accounting for PP fat mass index (PP-FMI), PP-FFMI and GWG were independently associated with first-phase insulin response (PP-FFMI: Pr2 = 20, P = 0.009; GWG: Pr2 = 15, P = 0.025) and second-phase insulin response (PP-FFMI: Pr2 = 19, P = 0.011; GWG: Pr2 = 17, P = 0.016). PP-FMI was the strongest predictor of an oral glucose tolerance test‒derived estimated metabolic clearance rate of glucose (PP-FMI: Pr2 = 14, P = 0.037) and estimated insulin sensitivity index (PP-FMI: Pr2 = 13, P = 0.047).

CONCLUSIONS

PP-FFMI was a predictor of markers of glucose homeostasis before and during pregnancy. Studies assessing the effect of skeletal muscle quality on metabolic regulation during pregnancy are warranted.

Fat-free mass and glucose homeostasis: is greater fat-free mass an independent predictor of insulin resistance?

BACKGROUND

A greater fat-free mass (FFM) is purported to be associated with protective effects on insulin resistance (IR). However, recent studies suggested negative associations between FFM and IR.

OBJECTIVES

(1) To explore the direction of the association between FFM and IR in a large heterogeneous sample after controlling for confounding factors. (2) To determine cut off values of FFM associated with an increased risk of IR.

METHODS

Outcome variables were measured in 7044 individuals (48.6% women, 20-79 years; NHANES, 1999-2006): body composition [fat mass (FM), FFM and appendicular FFM (aFFM); DXA], FFM index [FFMI: FFM/height (kg/m²)], appendicular FFMI [aFFM/height (kg/m²)] and insulin resistance (HOMA-IR). Multivariate regression analyses were performed to determine the independent predictors of HOMA-IR in younger (20-49 years) and older (50-79 years) men and women. ROC analyses were used to determine FFM cut-offs to identify a higher risk of insulin resistance (HOMA-IR > 75th percentile).

RESULTS

aFFMI was an independent predictor of IR in younger (men: β = 0.21; women: β = 0.31; all p ≤ 0.001) and older (men: β = 0.11; women: β = 0.37; all p ≤ 0.001) individuals. Thresholds for aFFMI at which the risk of IR was significantly increased were 8.96 and 8.39 kg/m² in younger and older men, and 7.22 and 6.64 kg/m² in younger and older women, respectively.

CONCLUSION

Independently of age, a greater aFFMI was an independent predictor of IR. These results suggest revisiting how we envision the link between FFM and IR and explore potential mechanisms.