Effect of high cardiorespiratory fitness and high body fat on insulin resistance

The association of fitness and fatness with intermediate hyperglycemia incidence in women: A cohort study

The purpose of this study was to examine the associations of cardiorespiratory fitness, general adiposity, and central adiposity with incident intermediate hyperglycemia (IH) in women. We conducted a prospective cohort study of 1534 women aged 20-79 years old who had an annual health check-up with no history of major chronic diseases. At baseline, fitness was assessed by a Balke graded exercise test, and the estimated metabolic equivalents were used to create quartile groups. Women were also grouped based on their body mass index (<25 kg/m², 25-29.9 kg/m², and ≥ 30 kg/m²) and waist-to-height ratio (≥0.50 or < 0.50). Cox proportional hazards models were conducted to assess the association of fitness and fatness variables with incident IH defined as fasting glucose of 5.6-6.9 mmol/L. Overall, 18.1% (n = 277) of the women developed IH during an average follow-up of 5.06 years. Fitness, body mass index, and waist-to-height ratio at baseline were the independent predictors of the IH incidence in separate age-adjusted models; yet when all three variables were included in the same model along with confounding variables, only fitness remained significant and demonstrated a clear inverse association with incident IH (P-for-trend <0.001). Health promotion efforts should focus on improving fitness for the prevention of IH in women.

Ectopic fat and aerobic fitness are key determinants of glucose homeostasis in nonobese Asians

BACKGROUND

The importance of ectopic fat deposition and physical fitness in the pathogenesis of insulin resistance and beta cell dysfunction in subjects from the nonobese Asians is not known.

MATERIALS AND METHODS

We conducted a cross-sectional study and measured insulin sensitivity (M value; 4-hour hyperinsulinaemic-euglycaemic clamp), insulin secretion rate (3-hour mixed meal tolerance test with oral minimal modelling), percent body fat, visceral adipose tissue, intramyocellular and intrahepatic lipid contents (magnetic resonance imaging and spectroscopy), cardiorespiratory fitness (VO₂ max; graded exercise test) and habitual physical activity (short International Physical Activity Questionnaire) in 60 healthy nonobese Asian subjects (BMI = 21.9 ± 1.7 kg/m² , age = 41.8 ± 13.4 years).

RESULTS

M was inversely associated with percent body fat (r = -0.460, P < 0.001), visceral fat (r = -0.623, P < 0.001) and liver fat (r = -0.601, P < 0.001), whereas insulin secretion correlated positively with these adiposity indices (percent body fat: r = 0.303, P = 0.018; visceral fat: r = 0.409, P = 0.010; hepatic fat: r = 0.393, P = 0.002). VO₂ max correlated negatively with insulin secretion rate (r = -0.420, P < 0.001) and positively with M (r = 0.658, P < 0.001). The amount of vigorous physical activity was positively associated with VO₂ max (r = 0.682, P < 0.001). Multiple stepwise linear regression analyses indicated that VO₂ max, age, and IHTG or VAT were independent determinants of insulin sensitivity and secretion (adjusted R²  = 69% and 33%, respectively, P < 0.001).

CONCLUSIONS

Increased ectopic fat deposition is associated with reduced insulin sensitivity and increased insulin secretion in healthy nonobese Asians. Poor cardiorespiratory fitness, likely due to inadequate participation in vigorous exercise, is strongly related to suboptimal metabolic function. Interventions to encourage engagement in physical activity may thus be important for improving metabolic health in nonobese Asians.

Association of low muscle mass and combined low muscle mass and visceral obesity with low cardiorespiratory fitness

Objective

Previous studies have shown that low cardiorespiratory fitness (CRF), visceral obesity and low muscle mass may share pathophysiological mechanisms, such as insulin resistance and chronic inflammation. In this study, we investigated whether low CRF is associated with low muscle mass, visceral obesity, and visceral obesity combined with low muscle mass.

Research Design and Methods

The associations between CRF and low muscle mass and combined low muscle mass and visceral obesity were examined in 298 apparently healthy adults aged 20–70 years. Low muscle mass was defined using a skeletal muscle mass index (SMI) that was calculated using dual energy X-ray absorptiometry. Visceral obesity was defined as a visceral fat area (VFA) exceeding 100 cm² in women and 130 cm² in men. We classified the participants into 4 low muscle mass/visceral obesity groups according to SMI and VFA. CRF was measured using a cycle ergometer test.

Results

CRF level correlated positively with SMI and negatively with VFA. Individuals with low muscle mass had lower CRF values than those without low muscle mass. After adjustment for age, sex, lifestyle factors, and markers for insulin resistance and inflammation, participants in the lowest quartile of CRF had an odds ratio (OR) for low muscle mass of 4.98 compared with those in the highest quartile (95% confidence interval (CI) = 1.19–12.99; P for trend = 0.001) and an OR for combined low muscle mass and visceral obesity of 31.46 (95% CI = 4.31–229.68; P for trend = 0.001).

Conclusions

Individuals with lower CRF exhibited increased risk of low muscle mass and combined low muscle mass and visceral obesity. These results suggest that low CRF may be a potential indicator for low muscle mass and combined low muscle mass and visceral obesity in Korean adults.

Waist circumference and cardiorespiratory fitness are independently associated with glucose tolerance and insulin resistance in obese women

The purpose of this study was to determine the independent associations between physical activity (PA), cardiorespiratory fitness (CRF), abdominal obesity and insulin action in obese women. We studied 141 abdominally obese women (waist circumference (WC): 106.4 ± 10.2 cm). PA duration (min/day) and intensity (counts/min) were obtained by accelerometry. CRF was measured using a treadmill. WC was measured at the iliac crest; abdominal adiposity was measured by magnetic resonance imaging. Glucose and insulin measures were obtained during a 75-g, 2-h glucose tolerance test. The homeostasis model of assessment iHOMA2-IS was used to estimate insulin sensitivity. PA duration and intensity were not associated with glucose or insulin metabolism (p > 0.05). However, moderate-to-vigorous PA (MVPA) duration was associated with fasting insulin and iHOMA2-IS (p < 0.01). CRF was associated with fasting insulin and iHOMA2-IS (r = 0.27, p ≤ 0.01), whereas WC was associated with fasting insulin (r = 0.50, p < 0.01) and iHOMA2-IS (r = -0.52, p ≤ 0.01). Following adjustment for CRF, MVPA, and age, WC remained associated with fasting glucose, insulin, 2-h glucose and iHOMA2-IS (r = -0.44, p ≤ 0.01). CRF was associated with fasting glucose as well as 1- and 2-h glucose (r = 0.24, p < 0.01) after adjusting for WC, MVPA, and age. MVPA was not associated with glucose or insulin measures after control for CRF and WC (p > 0.05). Mediation analysis revealed that CRF and WC combined mediated the relationship between MVPA and both glucose tolerance and insulin resistance (p < 0.05). In conclusion, among abdominally obese women, WC and CRF are independently associated with measures of glucose tolerance and insulin resistance and mediate the association between MVPA and insulin resistance.

The relationship between insulin sensitivity and maximal oxygen uptake is confounded by method of adjustment for body composition

BACKGROUND

The use of ratios for analyzing physiologic variables often creates spurious associations.

METHODS

Results of a euglycaemic clamp, a graded exercise test to measure maximal oxygen uptake (VO2max) and underwater weighing in 358 nondiabetic adults (166 women and 192 men) were used to compare the effects of weight standardization by division or by partial Spearman correlations on the association between VO2max and insulin sensitivity.

RESULTS

VO2max and insulin sensitivity were negatively correlated when VO2max was divided by weight. When partial Spearman correlations were used to adjust VO2max for body composition, the correlation between VO2max and insulin sensitivity was greatly diminished.

CONCLUSIONS

Division of VO2max by weight does not adjust for weight, but it creates spurious associations between VO2max and insulin sensitivity.

An overview of the contribution of fatness and fitness factors, and the role of exercise, in the formation of health status for individuals who are overweight

Over the last half century there has been an epidemic of diminished health status induced by what seems as a concurrent rise in a population of individuals that are overfat. During the past few decades, the use of exercise has become a staple in the prevention and treatment options for the retarding the development of health issues pertaining to individuals who are overweight, overfatness or experience obesity. However, there are few studies and reviews look at the global issues surrounding the metabolic and hormone consequences of overfatness and the interaction of exercise with adiposity in humans developing the health status for the individual. This review offers an insight into our current understanding of health issues pertaining to metabolic and hormonal disruption related to overfatness and the treatment effect that exercise, especially resistance exercise, can have on impacting the health status, and overall well-being, for individuals who are overfat, regardless of body compositional changes leading toward a lessening of diseased state, and eventually a return to a normal health status for the individual.

Cardiorespiratory fitness and insulin sensitivity in overweight or obese subjects may be linked through intrahepatic lipid content

OBJECTIVE

Low cardiorespiratory fitness (CRF) predisposes one to cardiovascular disease and type 2 diabetes in part independently of body weight. Given the close relationship between intrahepatic lipid content (IHL) and insulin sensitivity, we hypothesized that the direct relationship between fitness and insulin sensitivity may be explained by IHL.

RESEARCH DESIGN AND METHODS

We included 138 overweight to obese, otherwise healthy subjects (aged 43.6 +/- 8.9 years, BMI 33.8 +/- 4 kg/m(2)). Body composition was estimated by bioimpedance analyses. Abdominal fat distribution, intramyocellular, and IHL were assessed by magnetic resonance spectroscopy and tomography. Incremental exercise testing was performed to estimate an individual's CRF. Insulin sensitivity was determined during an oral glucose tolerance test.

RESULTS

For all subjects, CRF was related to insulin sensitivity (r = 0.32, P < 0.05), IHL (r = -0.27, P < 0.05), and visceral (r = -0.25, P < 0.05) and total fat mass (r = -0.32, P < 0.05), but not to intramyocellular lipids (r = -0.08, NS). Insulin sensitivity correlated significantly with all fat depots. In multivariate regression analyses, independent predictors of insulin sensitivity were IHL, visceral fat, and fitness (r(2) = -0.43, P < 0.01, r(2) = -0.34, and r(2) = 0.29, P < 0.05, respectively). However, the positive correlation between fitness and insulin sensitivity was abolished after adjustment for IHL (r = 0.16, NS), whereas it remained significant when adjusted for visceral or total body fat. Further, when subjects were grouped into high versus low IHL, insulin sensitivity was higher in those subjects with low IHL, irrespective of fitness levels.

CONCLUSIONS

Our study suggests that the positive effect of increased CRF on insulin sensitivity in overweight to obese subjects may be mediated indirectly through IHL reduction.

Association of cardiorespiratory fitness with insulin sensitivity in overweight and obese postmenopausal women: a Montreal Ottawa New Emerging Team study

The purpose of this study was to examine the relation between insulin sensitivity and cardiorespiratory fitness in overweight and obese postmenopausal women. The study population consisted of 127 overweight and obese postmenopausal women (age, 57.7 +/- 4.8 years; body mass index, 32.7 +/- 4.7 kg/m(2)). Subjects were classified by dividing the entire cohort into tertiles (T) based on insulin sensitivity expressed per kilograms of lean body mass (LBM) (T1, <10.9; T2, 10.9-12.9, T3, >12.9 mg/min per kilogram of LBM, respectively). Outcome measures were body composition (dual-energy x-ray absorptiometry), visceral adipose tissue (computed tomography), insulin sensitivity (hyperinsulinemic-euglycemic clamp), cardiorespiratory fitness (indirect calorimetry), lower-body muscle strength (1 maximal repetition), physical activity energy expenditure (doubly labeled water), fasting lipids, and inflammatory profile. We found a significant positive relationship between insulin sensitivity and cardiorespiratory fitness (r = 0.25, P = .005). Moreover, cardiorespiratory fitness was higher in the T3 group compared to the T1 group (36.2 +/- 6.1 vs 33.1 +/- 5.0 mL/kg LBM per minute, respectively; P = .028). However, the difference was no longer significant after controlling for visceral adipose tissue or muscle strength. Finally, cardiorespiratory fitness was an independent predictor of insulin sensitivity. High levels of cardiorespiratory fitness are associated with higher levels of insulin sensitivity in overweight and obese postmenopausal women. Moreover, visceral adipose tissue accumulation or muscle strength may be potential mediators of this relationship.