Metabolic and cardiovascular assessment in moderate obesity: effect of weight loss

Modelling and assessment of glucose-lactate kinetics in youth with overweight, obesity and metabolic dysfunction-associated steatotic liver disease: A pilot study

AIM

In this study, we investigated glucose and lactate kinetics during a 75 g oral glucose tolerance test (OGTT) in 23 overweight and obese adolescents and assessed putative differences among participants with and without metabolic dysfunction-associated steatotic liver disease (MASLD).

METHODS

We enrolled 23 young people (six girls) with obesity [body mass index 33 (29-37)]. Glucose-lactate kinetics parameters (disposal glucose insulin sensitivity, SID; fraction of glucose converted into lactate, fr; fractional lactate clearance rate, kL) and lactate production rate (LPR) were estimated using the oral glucose-lactate minimal model. MASLD presence was assessed using the proton density fat fraction. We analysed glucose, lactate and LPR time to peak, peak values and area under the curve and evaluated differences using the Wilcoxon test. MASLD and no-MASLD participants were compared using the Mann-Whitney test. Correlations between parameters were assessed using the Spearman correlation coefficient (ρ). We also tested the performance of two (4 or 3 h OGTT) protocols in estimating oral glucose-lactate minimal model and LPR parameters.

RESULTS

Glucose peaks 30 min earlier than lactate (p = .0019). This pattern was present in the no-MASLD group (p < .001). LPR peaks 30 min later in the MASLD group (p = .02). LPR and kL were higher in MASLD, suggesting higher glycolysis and lactate utilization. SID and fr correlate significantly (ρ = -0.55, p = .008). SID and fr were also correlated with the body mass index, (ρ = -0.45, p = .04; and ρ = 0.45; p = .03). The protocol duration did not influence the estimates of the parameters.

DISCUSSION

Youth with MASLD showed a delayed glucose metabolism, possibly because of greater utilization of the underlying substrates. A 3-h OGTT may be used to assess lactate metabolism effectively.

Gender Differences in the Context of Obstructive Sleep Apnea and Metabolic Diseases

The relationship between obstructive sleep apnea (OSA) and endocrine and metabolic disease is unequivocal. OSA, which is characterized by intermittent hypoxia and sleep fragmentation, leads to and exacerbates obesity, metabolic syndrome, and type 2 diabetes (T2D) as well as endocrine disturbances, such as hypothyroidism and Cushing syndrome, among others. However, this relationship is bidirectional with endocrine and metabolic diseases being considered major risk factors for the development of OSA. For example, polycystic ovary syndrome (PCOS), one of the most common endocrine disorders in women of reproductive age, is significantly associated with OSA in adult patients. Several factors have been postulated to contribute to or be critical in the genesis of dysmetabolic states in OSA including the increase in sympathetic activation, the deregulation of the hypothalamus-pituitary axis, the generation of reactive oxygen species (ROS), insulin resistance, alteration in adipokines levels, and inflammation of the adipose tissue. However, probably the alterations in the hypothalamus-pituitary axis and the altered secretion of hormones from the peripheral endocrine glands could play a major role in the gender differences in the link between OSA-dysmetabolism. In fact, normal sleep is also different between men and women due to the physiologic differences between genders, with sex hormones such as progesterone, androgens, and estrogens, being also connected with breathing pathologies. Moreover, it is very well known that OSA is more prevalent among men than women, however the prevalence in women increases after menopause. At the same time, the step-rise in obesity and its comorbidities goes along with mounting evidence of clinically important sex and gender differences. Metabolic and cardiovascular diseases, seen as a men's illness for decades, presently are more common in women than in men and obesity has a higher association with insulin-resistance-related risk factors in women than in men. In this way, in the present manuscript, we will review the major findings on the overall mechanisms that connect OSA and dysmetabolism giving special attention to the specific regulation of this relationship in each gender. We will also detail the gender-specific effects of hormone replacement therapies on metabolic control and sleep apnea.

Exercise reduces body fat and improves insulin sensitivity and pancreatic β-cell function in overweight and obese male Taiwanese adolescents

BACKGROUND

Improvements in insulin resistance and pancreatic β-cell function have been shown following exercise in adults with obesity; however, few adolescent-based studies have been conducted. This study examined the impact of exercise training on body fat and insulin sensitivity and secretion in overweight and obese adolescents.

METHODS

The effects of a 12-week exercise program on the parameters of adiposity and glucose homeostasis were investigated in 47 overweight and obese male adolescents.

RESULTS

After the exercise training program, body weight, body mass index, waist circumference, and body fat were significantly decreased (P < 0.001). Improvements in insulin sensitivity (HOMA-IR: 1.40 vs. 0.86, P < 0.001) and the disposition index (5.84 vs. 12.77, P < 0.001) were also observed. Compared to baseline, oral glucose tolerance tests showed reduced glucose and insulin levels at all time points following the exercise training (all P < 0.001). Subgroup analysis of overweight and obese adolescents with abnormal glucose tolerance revealed that there was no difference in plasma glucose levels as compared to the lean group.

CONCLUSIONS

A 12-week exercise training is effective in reducing body fat and improving insulin sensitivity and secretion. In addition, the benefits of the exercise intervention were even experienced by those with impaired glucose tolerance.

Text messaging (SMS) as a tool to facilitate weight loss and prevent metabolic deterioration in clinically healthy overweight and obese subjects: a randomised controlled trial

OBJECTIVE

To examine whether SMS text messaging facilitates a reduction of weight and waist circumference (WC) and favourable changes in lipid profile and insulin levels in clinically healthy overweight and obese subjects.

DESIGN

A randomised controlled trial.

SETTING AND INTERVENTION

Primary care health centre in Riga, Latvia. Text messaging once in two weeks.

SUBJECTS

A total of 123 overweight and obese men and women aged 30-45 years with no cardiovascular diseases (CVDs) or diabetes.

MAIN OUTCOME MEASURES

changes in anthropometric parameters (weight, WC, body mass index (BMI)) and biochemical parameters (lipids, fasting glucose and insulin).

RESULTS

We found a statistically significant decrease in weight (2.4%), BMI and WC (4.8%) in the intervention group, while the control group showed a statistically non-significant increase in weight and BMI and decrease in WC. Between group results obtained over the course of a year showed statistically significant mean differences between weight (-3.4 kg (95% CI -5.5, -1.3)), BMI kg/m² (-1.14 (95% CI -1.9, -0.41)), WC (-4.6 cm (95% CI -6.8, -2.3)), hip circumference (-4.0 cm (95% CI -5.9, -2.0)) and fasting insulin (2.43 μU/ml (95% CI 0.6, 4.3)). Mean differences of changes in glucose and lipid levels were statistically non significant: fasting glucose (-0.01 mmol/l (95% CI -0.19, 0.17)), TC mmol/l (-0.04 mmol/l (95% CI -0.29, 0.21)), HDL-C (0.14 mmol/l (95% CI -0.65, 0.09)), LDL-C (-0.02 mmol/l (95% CI -0.22, 0.18)) and TG (0.23 mmol/l (95% CI -0.06, 0.52)).

CONCLUSIONS

SMS messaging in clinically healthy overweight and obese subjects facilitates a slight decrease in weight, BMI and WC. It is anticipated that the implications of this strategy might facilitate the design of preventive and promotive strategies among high risk groups in Latvia.

Impact of short term consumption of diets high in either non-starch polysaccharides or resistant starch in comparison with moderate weight loss on indices of insulin sensitivity in subjects with metabolic syndrome

This study investigated if additional non-starch polysaccharide (NSP) or resistant starch (RS), above that currently recommended, leads to better improvement in insulin sensitivity (IS) than observed with modest weight loss (WL). Obese male volunteers (n = 14) were given an energy-maintenance (M) diet containing 27 g NSP and 5 g RS daily for one week. They then received, in a cross-over design, energy-maintenance intakes of either an NSP-enriched diet (42 g NSP, 2.5 g RS) or an RS-enriched diet (16 g NSP, 25 g RS), each for three weeks. Finally, a high protein (30% calories) WL diet was provided at 8 MJ/day for three weeks. During each dietary intervention, endogenous glucose production (EGP) and IS were assessed. Fasting glycaemia was unaltered by diet, but plasma insulin and C-peptide both decreased with the WL diet (p < 0.001), as did EGP (-11%, p = 0.006). Homeostatis model assessment of insulin resistance improved following both WL (p < 0.001) and RS (p < 0.05) diets. Peripheral tissue IS improved only with WL (57%-83%, p < 0.005). Inclusion of additional RS or NSP above amounts currently recommended resulted in little or no improvement in glycaemic control, whereas moderate WL (approximately 3 kg fat) improved IS.

Supplementation with n3 fatty acid ethyl esters increases large and small artery elasticity in obese adults on a weight loss diet

Increased arterial stiffness is associated with enhanced risk of cardiovascular disease in obese individuals. Whether n3 fatty acid ethyl ester (FAEE) supplementation improves arterial stiffness in obese participants on a weight loss diet has not yet been investigated. The objective of the study was to carry out a 12-wk randomized, single-blind trial to test the effect of a 25% energy deficit weight loss diet alone (WL) (n = 12) or WL plus 4 g/d Omacor (46% EPA and 38% DHA) supplementation (WL+FAEE) (n = 13) on arterial elasticity in obese adults. Large (C1) and small artery elasticity (C2) were measured by pulse contour analysis of the radial artery. WL alone reduced (P < 0.05 in all) body weight (-3%), waist circumference (-4%), systolic (-3%) and diastolic (-3%) blood pressures, cardiac output (-4%), plasma TG concentration (-25%), and the homeostasis model assessment (HOMA) score (-12%) and increased plasma HDL cholesterol (+9%) and adiponectin (+18%) concentrations. However, WL alone did not alter C1 and C2. The WL+FAEE intervention significantly reduced body weight (-4%), waist circumference (-4%), systolic (-8%) and diastolic (-5%) blood pressures, pulse pressure (-5%), heart rate (-8%), plasma TG concentration (-36%), and HOMA score (-12%) and increased stroke volume (+3%), plasma HDL cholesterol (+6%) and adiponectin concentrations (+28%), and C1 (+20%) and C2 (+22%) artery elasticity. The changes in systolic blood pressure, heart rate, plasma TGs, C1, and C2 were significantly greater in the WL+FAEE group than in the WL group. Supplementation with n3 FAEEs improves C1 and C2 independently of weight loss in obese adults.

Improvement of Insulin Resistance and Early Atherosclerosis in Patients after Gastric Banding

OBJECTIVE

To evaluate the effect of massive weight loss on insulin sensitivity, soluble adhesion molecules, and markers of the insulin resistance syndrome (IRS).

RESEARCH METHODS AND PROCEDURES

Eighteen morbidly obese patients underwent gastric banding and were evaluated before and 6 and 12 months after surgery. Total insulin secretion, hepatic insulin extraction, and insulin sensitivity were analyzed by oral glucose-tolerance test model analysis. In addition, soluble intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, leptin, high-sensitivity C-reactive protein, plasminogen activating factor-1 (PAI-1), and tissue plasminogen activator were measured.

RESULTS

BMI dropped from 45.22 +/- 5.62 to 36.99 +/- 4.34 kg/m(2) after 6 months and 33.72 +/- 5.55 kg/m(2) after 12 months (both p < 0.0001). This intervention resulted in a significant reduction of blood pressure (p < 0.00001), triglycerides (p < 0.01), fasting blood glucose (p = 0.03), basal insulin (p < 0.001), and basal C-peptide (p = 0.008) levels. Total insulin secretion decreased (p < 0.05), whereas hepatic insulin extraction (p < 0.05) and oral glucose insulin sensitivity index (p < 0.0001) increased compared with baseline. Leptin (p < 0.0001) and E-selectin levels decreased significantly after 6 and 12 months (p = 0.05), whereas significantly lower levels of intercellular adhesion molecule-1 and PAI-1 were only seen after 6 months. Subclinical inflammation, measured by high-sensitivity C-reactive protein, was lowered to normal ranges. No changes were observed in vascular cell adhesion molecule-1 and tissue plasminogen activator levels.

DISCUSSION

Although gastric banding ameliorates several features of the IRS, including 29.05% improvement in insulin sensitivity and blood pressure and reduction of soluble adhesion molecules and PAI-1, considerable weight loss did not normalize all components of the IRS in morbidly obese patients.

Bypassing the duodenum does not improve insulin resistance associated with diet-induced obesity in rodents

Roux-en-y gastric bypass (RYGB) surgery rapidly improves glucose tolerance and reverses insulin resistance in obese patients. It has been hypothesized that this effect is mediated by the diversion of nutrients from the proximal small intestine. We utilized duodenal-jejunal bypass (DJB) as a modification of gastric bypass to determine the effect of nutrient diversion from the foregut without gastric restriction on insulin resistance in obese rats. The effects of DJB or Sham surgery on glucose homeostasis were determined in both high-fat-fed Long-Evans and Wistar rats. Body weight and food intake were measured weekly postoperatively, and body composition was monitored before and after surgery. Glucose tolerance was tested before and as early as 1 month postoperation; additionally, in Wistar rats, insulin sensitivity was determined by a hyperinsulinemic-euglycemic clamp (HIEC). DJB did not affect body weight, body composition, glucose tolerance, or insulin concentrations over the period of the study. The average glucose infusion rate (GIR) during the HIEC was 6.2 ± 1.16 mg/kg/min for Sham rats compared to 7.2 ± 1.71 mg/kg/min for DJB rats (P = 0.62), and neither endogenous glucose production (EGP; P = 0.81) nor glucose utilization (glucose disappearance (R(d)), P = 0.59) differed between DJB and Sham rats. DJB does not affect insulin resistance induced by a high-fat diet in Long-Evans and Wistar rats. These data suggest that duodenal bypass alone is an insufficient mechanism to alter insulin sensitivity independent of weight loss in obese, nondiabetic rodents.

Characterizing the profile of obese patients who are metabolically healthy

The presence of obesity-related metabolic disturbances varies widely among obese individuals. Accordingly, a unique subset of obese individuals has been described in the medical literature, which seems to be protected or more resistant to the development of metabolic abnormalities associated with obesity. These individuals, now known as 'metabolically healthy but obese' (MHO), despite having excessive body fatness, display a favorable metabolic profile characterized by high levels of insulin sensitivity, no hypertension as well as a favorable lipid, inflammation, hormonal, liver enzyme and immune profile. However, recent studies have indicated that this healthier metabolic profile may not translate into a lower risk for mortality. Mechanisms that could explain the favorable metabolic profile of MHO individuals are poorly understood. However, preliminary evidence suggests that differences in visceral fat accumulation, birth weight, adipose cell size and gene expression-encoding markers of adipose cell differentiation may favor the development of the MHO phenotype. Despite the uncertainty regarding the exact degree of protection related to the MHO status, identification of underlying factors and mechanisms associated with this phenotype will eventually be invaluable in helping us understand factors that predispose, delay or protect obese individuals from metabolic disturbances. Collectively, a greater understanding of the MHO individual has important implications for therapeutic decision making, the characterization of subjects in research protocols and medical education.

Effect of loss of regional fat assessed by DXA on insulin resistance and dyslipidaemia in obese men

OBJECTIVE

To investigate the impact of reduction in total fat mass (FM) and regional FMs on indices of insulin resistance and dyslipidaemia in obese men (BMI > 30 kg/m²) after a 1-year weight loss (WL), and secondly, to examine the potential predictive effect of baseline insulin resistance on reduction in total and regional FMs.

MATERIAL AND METHODS

In nine men with WL > 4 kg, body composition by DXA (dual X-ray absorptiometry) and indices of insulin resistance were assessed: fasting insulin, C-Peptide and HOMA-IR. Insulin sensitivity (QUICKI) and serum lipids were also assessed.

RESULTS

Mean WL was 10.8%; Δ trunk and Δ leg FM were reduced by 30.1% and 21.3%, respectively, increasing leg/trunk FM ratio by 13.2%. Improvement in HOMA-IR was 63.1%, insulin 59.1%, and in QUICKI 17.4%. Loss of total FM, trunk FM, and increase in leg/trunk FM ratio were correlated with improvement in HOMA-IR (p < 0.001-0.05). Linear regression analysis of ln-transformed improvements in HOMA-IR was non-significantly related with losses of trunk FM and increases in leg/trunk FM ratio (p = 0.06). Multivariate analysis suggested improvements in fasting insulin and C-Peptide could be explained by leg/trunk FM ratio (R² = 0.60, p = 0.013, R² = 0.37, p = 0.012, respectively) and in HOMA-IR by trunk FM (R² = 0.42, p = 0.06). The loss of FM and change in FM distribution had no effect on serum lipids.

CONCLUSION

Both loss of trunk FM and increase in leg/trunk FM ratio assessed by DXA contribute to the improvement in insulin resistance.

Preoperative weight gain might increase risk of gastric bypass surgery

BACKGROUND

Weight loss improves the cardiovascular and metabolic risk associated with obesity. However, insufficient data are available about the health effects of weight gain, separate from the obesity itself. We sought to determine whether the changes in body weight before open gastric bypass surgery (OGB) would have a significant effect on the immediate perioperative hospital course.

METHODS

A retrospective chart review of 100 consecutive patients was performed to examine the effects of co-morbidities and body weight changes in the immediate preoperative period on the hospital length of stay and the rate of admission to the surgical intensive care unit (SICU).

RESULTS

Of our class III obese patients undergoing OGB, 95% had ≥1 co-morbid condition and an overall SICU admission rate of 18%. Compared with the patients with no perioperative SICU admission, the patients admitted to the SICU had a greater degree of insulin resistance (homeostatic model analysis-insulin resistance 10.8 ± 1.3 versus 5.9 ± 0.5, P = .001), greater serum triglyceride levels (225 ± 47 versus 143 ± 8 mg/dL, P = .003), and had gained more weight preoperatively (.52 ± .13 versus .06 ± .06 lb/wk, P = .003). The multivariate analyses showed that preoperative weight gain was a risk factor for a longer length of stay and more SICU admissions lasting ≥3 days, as were a diagnosis of sleep apnea and an elevated serum triglyceride concentration.

CONCLUSION

The results of the present retrospective study suggest that weight gain increases the risk of perioperative SICU admission associated with OGB, independent of the body mass index. Sleep apnea and elevated serum triglyceride levels were also important determinants of perioperative morbidity. In view of the increasing epidemic of obesity and the popularity of bariatric surgical procedures, we propose that additional clinical and metabolic research focusing on the understanding of the complex relationship among obesity, positive energy balance, weight gain, and perioperative morbidity is needed.

Effect of regional fat loss assessed by DXA on insulin resistance and dyslipidaemia in obese women

OBJECTIVE

To investigate the impact of reduction in total fat mass (FM) and regional FMs on indices of insulin resistance and dyslipidaemia in obese women (BMI > 30 kg/m(2)) after a 1-year weight loss (WL) program; and, secondly, to investigate the potential predictive effect of baseline insulin resistance on reduction in total and regional FMs.

MATERIAL AND METHODS

In 35 women with > 4 kg weight loss, body composition by DXA (dual X-ray absorptiometry), fasting insulin, C-Peptide, insulin resistance (HOMA-IR), insulin sensitivity (QUICKI), metabolic clearance rate (MCRestOGTT) and serum lipids were assessed.

RESULTS

Mean WL was 9.6%; trunk and leg FM were reduced proportionally (14.9-14.7%). Improvement in HOMA-IR was 34.7%, insulin 30.7%, QUICKI 8.6% and MCRest OGTT 74%. The reduction in total, trunk and leg FM were similarly correlated with improvement in indices of insulin resistance (p < 0.001-0.05) and also with initial HOMA-IR (p = 0.000-0.02). In linear regressions improvement in HOMA-IR was similarly related with these FMs (p = 0.008), and initial HOMA predicted loss of trunk FM (p = 0.01). In multivariate analysis improvement in HOMA-IR was explained by loss of total FM (R(2) = 0.20, p = 0.004); improvement of QUICKI by loss of leg FM (R(2) = 0.33, p < 0.001).

CONCLUSION

Loss of leg FM and trunk FM had similar importance for the improvement in insulin resistance. Baseline HOMA-IR predicted the potential for reduction in trunk FM.

Development of hyperinsulinemia and insulin resistance during the early stage of weight gain

Obesity is associated with insulin resistance and hyperinsulinemia, which is considered to be a core component in the pathophysiology of obesity-related comorbidities. As yet it is unknown whether insulin resistance and hyperinsulinemia already develop during weight gain within the normal range. In 10 healthy male subjects the effect of intentional weight gain by 2 BMI points was examined on insulin. C-peptide and glucose levels following a meal, 75 g of glucose, and a two-step hyperglycemic clamp increased plasma glucose by 1.38 and 2.75 mmol/l, respectively. Baseline insulin, C-peptide, and glucose concentrations were significantly higher after weight gain from 21.8 to 23.8 kg/m(2) BMI within 4(1/2) mo. Calculations of insulin secretion and clearance indicate that reduced insulin clearance contributes more to post-weight gain basal hyperinsulinemia than insulin secretion. Following oral or intravenous stimulation insulin concentrations were significantly higher post-weight gain during all three test conditions, whereas C-peptide and glucose levels did not differ. Calculations of insulin secretion and clearance demonstrated that higher stimulated insulin concentrations are entirely due to clearance but not secretion. Despite significantly higher insulin levels, the rate of intravenous glucose required to maintain the defined elevation of glucose levels was either identical (1.38 mmol/l) or even significantly lower (2.75 mmol/l) following weight gain. The present study demonstrates for the first time that insulin resistance already develops during weight gain within the normal range of body weight. The associated basal and stimulated hyperinsulinemia is the result of differentiated changes of insulin secretion and clearance, respectively.

beta-cell function in morbidly obese subjects during free living: long-term effects of weight loss

Insulin hypersecretion and insulin resistance are physiologically linked features of obesity. We tested whether extreme hypersecretion impairs beta-cell function under free-living conditions and whether major weight loss modifies insulin hypersecretion, insulin sensitivity, and beta-cell function. Plasma glucose, C-peptide, and free fatty acid concentrations were measured at hourly intervals during 24 h of normal life (including calorie-standardized meals) in 20 morbidly obese nondiabetic patients (BMI 48.4 +/- 1.7 kg/m2) and 7 nonobese age- and sex-matched control subjects; 8 of the obese patients were restudied 6 months and 2 years following biliopancreatic diversion. Insulin secretion was reconstructed from C-peptide levels by deconvolution and related to concurrent glucose levels through a mathematical model incorporating key features of beta-cell function: rate sensitivity, beta-cell glucose sensitivity, and potentiation. Insulin sensitivity (by the euglycemic insulin clamp technique) was reduced by 50% in obese subjects (23.1 +/- 2.5 of obese subjects vs. 52.9 +/- 4.9 micromol.min(-1) . kg(FFM)(-1) of control subjects, means +/- SE, P = 0.0004) as was mean 24-h insulin clearance (median 809 [interquartile range 451] vs. 1,553 [520] ml.min(-1) . m(-2), P < 0.001) due to a 50% reduction in hepatic insulin extraction (P < 0.01). Over 24 h, insulin secretion was doubled in obese subjects (468 nmol [202] in obese subjects vs. 235 [85] of control subjects, P=0.0002). Despite the hypersecretion, beta-cell glucose sensitivity, rate sensitivity, and potentiation were similar in obese and control subjects. Six months postoperatively (weight loss = 33 +/- 3 kg), both insulin hypersecretion (282 nmol [213]) and insulin sensitivity (51.6 +/- 3.7 micromol.min(-1).kg(FFM)(-1)) were normalized. At 2 years (weight loss = 50 +/- 8 kg), insulin sensitivity was supernormal (68.7 +/- 3.3 micromol.min(-1).kg(FFM)(-1)) and insulin secretion was lower than normal (167 nmol [37]) (both P < 0.05 vs. control subjects). In conclusion, severe uncomplicated obesity is characterized by gross insulin hypersecretion and insulin resistance, but the dynamic aspects of beta-cell function are intact. Malabsorptive bariatric surgery corrects both the insulin hypersecretion and the insulin resistance at a time when BMI is still high. With continued weight loss over a 2-year period, moderately obese subjects become supersensitive to insulin and, correspondingly, insulin hyposecretors.

The effect of insulin on cardiac autonomic balance predicts weight reduction after gastric bypass

AIMS/HYPOTHESIS

The aim of this study was to assess the predictive role of autonomic reactivity in body weight loss induced by gastric bypass.

METHODS

A group of 22 morbidly obese subjects, who were due to undergo a gastric bypass, were submitted, before surgery, to a euglycaemic-hyperinsulinaemic clamp, during which a continuous recording of the ECG was performed. The effect of insulin on cardiac autonomic balance was evaluated by performing power spectral analysis of heart rate variability. The low-to-high frequency ratio was calculated before and during the clamp and its modifications were expressed as % delta low-to-high frequency ratio (%Delta L: H).

RESULTS

Preoperative %Delta L: H showed a significant (p=0.0009, r2=0.43), positive relationship to the reduction of body weight, measured 1 year after surgery and expressed as % excess weight loss (% EWL). Preoperative BMI was also significantly (p=0.0009, r2=0.43) negatively related to the 12-month % EWL. In a multiple regression analysis, %Delta L: H remained a significant (p=0.003), independent predictor of body weight loss, even when preoperative BMI or age, % fat mass, insulinaemia and glucose disposal were taken into account.

CONCLUSIONS/INTERPRETATION

The best correction of excess body weight was achieved by those obese subjects who had a preserved capacity to shift their cardiac autonomic balance towards a sympathetic prevalence in response to an euglycaemic-hyperinsulinaemic clamp. Further studies are needed to elucidate the mechanisms through which the autonomic nervous system influences weight reduction.

Differential effect of weight loss on insulin resistance in surgically treated obese patients

PURPOSE

To compare the effects of equivalent weight loss induced by two bariatric surgical techniques on insulin action in severely obese patients.

METHODS

Eighteen nondiabetic patients with severe obesity (mean [+/- SD] body mass index: 53.5 +/- 9.0 kg/m(2)) and 20 sex- and age-matched lean subjects (body mass index: 23.8 +/- 3.0 kg/m(2)) underwent metabolic studies, including measurement of insulin sensitivity by the insulin clamp technique. Patients then underwent either vertical banded gastroplasty with Roux-en-Y gastric bypass, or biliopancreatic diversion, and were restudied at 5 to 6 months and again at 16 to 24 months postsurgery.

RESULTS

At baseline, patients were hyperinsulinemic (194 +/- 47 pmol/L vs. 55 +/- 25 pmol/L, P < 0.0001), hypertriglyceridemic (1.56 +/- 0.30 mmol/L vs. 0.78 +/- 0.32 mmol/L, P < 0.0001), and profoundly insulin resistant (insulin-mediated glucose disposal: 20.8 +/- 4.4 micromol/min/kg fat-free mass vs. 52.0 +/- 10.1 micromol/min/kg, P < 0.0001) as compared with controls. Weight loss by the two procedures was equivalent in both amount (averaging -53 kg) and time course. In the gastric bypass group, insulin sensitivity improved (23.8 +/- 6.0 micromol/min/kg at 5 months and 33.7 +/- 11.3 micromol/min/kg at 16 months, P < 0.01 vs. baseline and controls). In contrast, in the biliopancreatic diversion group, insulin sensitivity was normalized already at 6 months (52.5 +/- 12.4 micromol/min/kg, P = 0.72 vs. controls) and increased further at 24 months (68.7 +/- 9.5 micromol/min/kg, P < 0.01 vs. controls) despite a persistent obese phenotype (body mass index: 33.2 +/- 8.0 kg/m(2)).

CONCLUSION

In surgically treated obese patients, insulin sensitivity improves in proportion to weight loss with use of predominantly restrictive procedures (gastric bypass), but is reversed completely by predominantly malabsorptive approaches (biliopancreatic diversion) long before normalization of body weight. Selective nutrient absorption and gut hormones may interact with one another in the genesis of the metabolic abnormalities of obesity.

beta-cell function in obesity: effects of weight loss

In nondiabetic subjects, obesity is associated with a modest expansion of beta-cell mass, possibly amounting-according to the best available estimates-to 10-30% for each 10 kg of weight excess. Whether age of onset and duration of obesity, recent changes in body weight, and body fat distribution have any effect on beta-cell mass in humans is unknown. Both fasting insulin secretion and the total insulin response to oral glucose have the following characteristics: 1) they increase with BMI in an approximately linear fashion, 2) both fat-free and fat mass are significant positive correlates, and 3) BMI exerts a positive effect separate from that of insulin resistance (i.e., obesity may be a state of primary insulin hypersecretion). The mechanisms are currently unknown, though chronic small increments in plasma glucose may play a role. In contrast, dynamic properties of beta-cell function, such as glucose sensitivity (i.e., dose-response function), rate sensitivity, and potentiation, do not appear to be substantially altered by the presence of obesity, body fat distribution, or insulin resistance as long as glucose tolerance is maintained. Weight loss, by diet or restrictive bariatric surgery, is associated with consensual decrements in insulin resistance and insulin hypersecretion. The latter, however, seems to be more persistent, suggesting that the postobese state may reproduce the primary insulin hypersecretion of the obese state. Malabsorptive bariatric surgery, in contrast, normalizes insulin sensitivity and abolishes insulin hypersecretion even before achievement of ideal body weight. Lipid-triggered messages from the gastrointestinal tract to the insulin target tissues and endocrine pancreas are the subject of intense investigation.

Effects of different hypocaloric diets on protein secretion from adipose tissue of obese women

Little is known about common factors (e.g., macronutrients and energy supply) regulating the protein secretory function of adipose tissue. We therefore compared the effects of randomly assigned 10-week hypoenergetic (-600 kcal/day) diets with moderate-fat/moderate-carbohydrate or low-fat/high-carbohydrate content on circulating levels and production of proteins (using radioimmunoassays and enzyme-linked immunosorbent assays) from subcutaneous adipose tissue in 40 obese but otherwise healthy women. Similar results were obtained by the two diets. Body weight decreased by approximately 7.5%. The secretion rate of leptin decreased by approximately 40%, as did that of tumor necrosis factor-alpha (TNF-alpha), and interleukin (IL)-6 and -8 decreased by 25-30%, whereas the secretion of plasminogen activator inhibitor 1 (PAI-1) and adiponectin did not show any changes. Regarding mRNA expression (by real-time PCR), only that of leptin and IL-6 decreased significantly. Circulating levels of leptin and PAI-1 decreased by 30 and 40%, respectively, but there were only minor changes in circulating TNF-alpha, IL-6, or adiponectin. In conclusion, moderate caloric restriction but not macronutrient composition influences the production and secretion of adipose tissue-derived proteins during weight reduction, leptin being the most sensitive and adiponectin and PAI-1 the least sensitive.

Normal insulin sensitivity in lean offspring of obese parents

OBJECTIVE

Offspring of diabetic or hypertensive patients are insulin resistant at a prediabetic/prehypertensive stage. We tested the hypothesis that insulin action may be impaired in the offspring of obese nondiabetic parents.

RESEARCH METHODS AND PROCEDURES

Twenty-one lean offspring of nonobese subjects [(OL) 22 +/- 3 years of age] were matched to 23 lean offspring of obese subjects (OOb) by gender distribution, age, BMI, and waist circumference. Anthropometry, oral glucose tolerance, in vivo insulin sensitivity [by a euglycemic insulin clamp (6 pmol/min per kilogram(FFM); where FFM represents fat-free mass)], and thermogenesis (by indirect calorimetry) were measured in each subject. The study subjects were from a population of 267 nuclear families (one offspring and both his/her parents) in which there was statistically significant (chi2 = 30.2, p = 0.001) concordance of BMI between parents and offspring.

RESULTS

In comparing OOb with OL, no statistically significant difference or trend toward a difference was detected in fasting plasma glucose and insulin concentrations, glucose and insulin responses to oral glucose, insulin sensitivity [metabolism value = 45 +/- 12 (OOb) vs. 47 +/- 17 micro mol/min per kilogram(FFM) (OL)], insulin-induced inhibition of protein and lipid oxidation, stimulation of glucose oxidation and nonoxidative glucose disposal, respiratory quotient, resting energy expenditure, and glucose-induced thermogenesis.

DISCUSSION

The metabolic similarity between lean offspring of obese parents and those of nonobese parents suggests that insulin resistance and its correlates are not co-inherited with the predisposition to develop obesity.

Insulin resistance in nondiabetic morbidly obese patients: effect of bariatric surgery

OBJECTIVE

To evaluate insulin action on substrate use and insulinemia in nondiabetic class III obese patients before and after weight loss induced by bariatric surgery.

RESEARCH METHODS AND PROCEDURES

Thirteen obese patients (four men/nine women; BMI = 56.3 +/- 2.7 kg/m2) and 13 lean subjects (five men/eight women; BMI = 22.4 +/- 0.5 kg/m2) underwent euglycemic clamp, oral glucose tolerance test, and indirect calorimetry. The study was carried out before (Study I) and after ( approximately 40% relative to initial body weight; Study II) weight loss induced by Roux-en-Y Gastric bypass with silastic ring surgery.

RESULTS

The obese patients were insulin resistant (whole-body glucose use = 19.7 +/- 1.5 vs. 51.5 +/- 2.4 micromol/min per kilogram fat-free mass, p < 0.0001) and hyperinsulinemic in the fasting state (332 +/- 86 vs. 85 +/- 5 pM, p < 0.0001) and during the oral glucose tolerance test compared with the lean subjects. Fasting plasma insulin normalized after weight loss, whereas whole-body glucose use increased (35.5 +/- 3.7 micromol/min per kilogram fat-free mass, p < 0.05 vs. Study I). The higher insulin clearance of obese did not change during the follow-up period. Insulin-induced glucose oxidation and nonoxidative glucose disposal were lower in the obese compared with the lean group (all p < 0.05). In Study II, the former increased slightly, whereas nonoxidative glucose disposal reached values similar to those of the control group. Fasting lipid oxidation was higher in the obese than in the control group and did not change significantly in Study II. The insulin effect on lipid oxidation was slightly improved (p = 0.01 vs. Study I).

DISCUSSION

The rapid weight loss after surgery in obese class III patients normalized insulinemia and improved insulin sensitivity almost entirely due to glucose storage, whereas fasting lipid oxidation remained high.

Weight loss reduces tissue factor in morbidly obese patients

OBJECTIVE

To investigate the tissue factor (TF) pathway in clinical obesity and associated metabolic syndrome.

RESEARCH METHODS AND PROCEDURES

Thirty-seven morbidly obese patients (4 men; BMI, 48 +/- 7 kg/m(2); range, 42 to 53 kg/m(2)), undergoing elective gastroplasty for the induction of weight loss, were examined for hemostatic, metabolic, and inflammatory parameters at baseline and 14 +/- 5 months postoperatively.

RESULTS

Weight loss significantly reduced circulating plasma TF (314 +/- 181 vs. 235 +/- 113 pg/mL, p = 0.04), coagulation factor VII (130 +/- 22% vs. 113 +/- 19%, p = 0.023), and prothrombin fragment F1.2 (2.4 +/- 3.4 vs. 1.14 +/- 1.1 nM, p = 0.04) and normalized glucose metabolism in 50% of obese patients preoperatively classified as diabetic or of impaired glucose tolerance. The postoperative decrease in plasma TF correlated with the decrease of F1.2 (r = 0.56; p = 0.005), a marker of in vivo thrombin formation. In subgroup analysis stratified by preoperative glucose tolerance, baseline circulating TF (402.6 +/- 141.6 vs. 176.2 +/- 58.2, p < 0.001) and TF decrease after gastroplasty (DeltaTF: 164.7 +/- 51.4 vs. -81 +/- 31 pg/mL, p = 0.02) were significantly higher in obese patients with impaired glucose tolerance than in patients with normal glucose tolerance.

DISCUSSION

Procoagulant TF is significantly reduced with weight loss and may contribute to a reduction in cardiovascular risk associated with obesity.

Testosterone levels in obese male patients with obstructive sleep apnea syndrome: relation to oxygen desaturation, body weight, fat distribution and the metabolic parameters

To investigate the impact of obstructive sleep apnea syndrome (OSAS) on testosterone levels and on the main parameters of the metabolic syndrome in abdominally obese men, 15 male subjects with abdominal obesity phenotype and polysomnographic diagnosis of OSAS (OB-OSAS) and 15 controls matched for age and anthropometric parameters (OB) were investigated. Anthropometry, SHBG, sex hormones and several parameters of the metabolic syndrome were measured. Only subjects with an Epworth Sleepiness Score greater than 10 underwent a polysomnographic study with calculation of the number of desaturation rates per sleeping hour (ODI), the minimal oxygen saturation during each desaturation episode (minSaO2) and the mean minimal arterial oxygen saturation for the whole night period (MminSaO2). Both total and free testosterone levels were lower in OB-OSAS than in OB patients. A negative correlation between polysomnographic parameters (ODI, minSaO2 and MminSaO2) and testosterone levels was found. The relationship between total and free testosterone and ODI persisted after adjusting for body mass index (BMI) and waist (W) values. Triglyceride and uric acid levels were significantly higher in OB-OSAS than in OB patients. A negative correlation between testosterone and acid uric level and a positive correlation between testosterone and HDL-cholesterol level was found, regardless of BMI and W circumference, particularly in the OB-OSAS group. Our study suggests that, in patients with obesity and OSAS, the severity of hypoxia during sleeping hours may be an additional factor in reducing testosterone levels, regardless of BMI and abdominal fatness. This may contribute in worsening metabolic abnormalities which, in men with OSAS, exceed those expected on the basis of degree of obesity and pattern of fat distribution.

Restored insulin inhibition on insulin secretion in nondiabetic severely obese patients after weight loss induced by bariatric surgery

OBJECTIVE

To examine the impact of important weight loss on insulin inhibition of its own secretion during experimentally induced hyperinsulinemia under euglycemic conditions.

DESIGN

Longitudinal, clinical intervention study--bariatric surgery (vertical banded gastroplasty--gastric bypass--Capella technique), re-evaluation after 4 and 14 months.

SUBJECTS

Nine obese patients class III (BMI=54.6+/-2.6 kg/m2) and nine lean subjects (BMI=22.7+/-0.7 kg/m2).

MEASUREMENTS

Euglycemic hyperinsulinemic clamp (insulin infusion: 40 mU/min m2), C-peptide plasma levels, electrical bioimpedance methodology, and oral glucose tolerance test (OGTT).

RESULTS

BMI was reduced in the follow-up: 44.5+/-2.2 and 33.9+/-1.5 kg/m2 at 4 and 14 months. Insulin-induced glucose uptake was markedly reduced in obese patients (19.5+/-1.9 micromol/min kg FFM) and improved with weight loss, but in the third study, it was still lower than that observed in controls (35.9+/-4.0 vs 52.9+/-2.2 micromol/min kg FFM). Insulin-induced inhibition of its own secretion was blunted in obese patients (19.9+/-5.7%, relative to fasting values), and completely reversed to values similar to that of lean ones in the second and third studies (-60.8+/-4.2 and -54.0+/-6.1%, respectively).

CONCLUSION

Weight loss in severe obesity improved insulin-induced glucose uptake, and completely normalized the insulin inhibition on its own secretion.

Effect of weight loss on VLDL-triglyceride and apoB-100 kinetics in women with abdominal obesity

The effects of obesity and weight loss on lipoprotein kinetics were evaluated in six lean women [body mass index (BMI): 21 +/- 1 kg/m(2)] and seven women with abdominal obesity (BMI: 36 +/- 1 kg/m(2)). Stable isotope tracer techniques, in conjunction with compartmental modeling, were used to determine VLDL-triglyceride (TG) and apolipoprotein B-100 (apoB-100) secretion rates in lean women and in obese women before and after 10% weight loss. VLDL-TG and VLDL-apoB-100 secretion rates were similar in lean and obese women. Weight loss decreased the rate of VLDL-TG secretion by approximately 40% (from 0.41 +/- 0.05 to 0.23 +/- 0.03 micromol x kg fat-free mass(-1) x min(-1); P < 0.05). The relative decline in VLDL-TG produced from nonsystemic fatty acids, derived from intraperitoneal and intrahepatic TG, was greater (61 +/- 7%) than the decline in VLDL-TG produced from systemic fatty acids, predominantly derived from subcutaneous TG (25 +/- 8%; P < 0.05). Weight loss did not affect VLDL-apoB-100 secretion rate. We conclude that weight loss decreases the rate of VLDL-TG secretion in women with abdominal obesity, primarily by decreasing the availability of nonsystemic fatty acids. There is a dissociation in the effect of weight loss on VLDL-TG and apoB-100 metabolic pathways that may affect VLDL particle size.

Relationship of clinic, ambulatory, and laboratory stress blood pressure to left ventricular mass in overweight men and women with high blood pressure

OBJECTIVE

This study was designed to evaluate the relationship between left ventricular (LV) mass and blood pressure (BP) recorded in the following contexts: in the clinic, using standard auscultatory procedures, during a typical day using ambulatory BP monitoring, and in the laboratory environment during behavioral stress testing.

METHODS

Ninety-seven men and women with clinic systolic blood pressure (SBP) of 130 to 180 mm Hg and/or diastolic blood pressure (DBP) of 85 to 110 mm Hg and mild to moderate obesity were included in the study. Laboratory stressors included the following tasks: Public Speaking; Anger Interview; Mirror Trace; and Cold Pressor. LV mass was measured using echocardiography and adjusted for body size by dividing by height(2.7) to yield LV mass index (LVMI).

RESULTS

LVMI was positively correlated with clinic SBP (r = 0.24, p <.05), ambulatory SBP (r = 0.34, p <.01), and aggregated laboratory stress SBP (r = 0.28, p <.01). Of the individual stressors, only SBP responses to the Mirror Trace and Cold Pressor tasks were independently correlated with LVMI (r = 0.35 and 0.34, respectively, p values <.01). Hierarchical regression analyses revealed that laboratory stress SBP remained a significant predictor of LVMI, after controlling for BMI and clinic pressure.

CONCLUSIONS

These findings suggest that cardiovascular responses to behavioral stress are associated with individual differences in LVMI in men and women with high blood pressure who are overweight. Laboratory studies of behavioral stress may help promote our understanding of the pathophysiology of LVH.

Dimensions and wall force development capacity of human pial arteries from normotensives is not altered in obesity

OBJECTIVE

The dimensions and maximum wall tension capacity of segments of human pial arteries from normotensive obese and non-obese patients were compared.

DESIGN

Segment size was assessed by quantitative morphometry of fixed sections and wall force by in vitro myography.

SUBJECTS

Twenty normotensive non-obese and 13 normotensive obese humans body mass index (BMI) 22.4+/-0.5 and 33.9+/-1.7 kg/m(2), respectively) were studied.

RESULTS

There was no significant difference in the perimeter of the outer medial border, the smoothed out length of the internal elastic lamina, the ratios of media thickness to area and lumen diameter and the maximum wall force development between the two groups.

CONCLUSION

Obesity per se is not associated with initial dimensional changes nor capacity to develop wall tension that might lead to the emergence of hypertension.

Short-term moderate weight loss and resistance training do not affect insulin-stimulated glucose disposal in postmenopausal women

OBJECTIVES

Moderate weight loss and exercise have been proposed as important tools in the treatment and prevention of type 2 diabetes. Therefore, we tested the hypothesis that short-term (4 weeks) moderate energy restriction (-750 kcal/day) would result in a significant increase in insulin-stimulated glucose disposal (40 mU x m(-2) x min(-1) hyperinsulinemic-euglycemic clamp) in moderately overweight postmenopausal women and that when combined with resistance training (RT) an even greater effect would be seen.

RESEARCH DESIGN AND METHODS

Older women were randomly assigned to energy restriction (WLoss group; n = 9) or energy restriction plus RT (RT + WLoss group; n = 10).

RESULTS

For the WLoss versus the RT + WLoss groups, changes in body weight (-3.0 +/- 0.2 kg vs. -3.2 +/- 0.3 kg), fat mass (FM) (-3.0 +/- 0.3 kg vs. -3.2 +/- 0.3 kg), and percent body fat (BF) (-2.1 +/- 0.4 vs. -2.4 +/- 0.3%) were not different between groups. Muscle mass (group-by-time interaction, P = 0.04) was preserved in RT + WLoss (0.40 +/- 0.40 kg) and reduced in WLoss (-0.64 +/- 0.18 kg). There were no changes in fat-free mass (FFM) and waist-to-hip ratio in either group. Whole body glucose disposal (WLoss 6.14 +/- 0.57 vs. 6.03 +/- 0.53, RT + WLoss 5.85 +/- 0.60 vs. 6.09 +/- 0.56 mg/kg of FFM/min) did not change in either group.

CONCLUSIONS

The results of this study demonstrate that short-term energy restriction resulting in moderate decreases in body weight (4.0 +/- 0.3%) and FM (8.2 +/- 0.7%) did not improve insulin-stimulated glucose disposal. The addition of RT to the hypoenergetic diet preserved muscle mass but provided no synergistic effect on insulin action. These results suggest that a greater change in body weight or FM may be necessary to observe a significant improvement in insulin action.

Do different dimensions of the metabolic syndrome change together over time? Evidence supporting obesity as the central feature

OBJECTIVE

The metabolic syndrome is a loosely defined cluster of cardiovascular risk factors including low HDL cholesterol, hypertriglyceridemia, glucose intolerance, and hypertension. Evidence for inclusion of these features in the syndrome has mostly come from cross-sectional studies, and a few studies have examined how the various factors change together over time.

RESEARCH DESIGN AND METHODS

We conducted a prospective population-based cohort study of 937 individuals aged 40-65 years who underwent oral glucose tolerance testing on two occasions at 4.5-year intervals. Changes in the components of the metabolic syndrome were analyzed by principal component analysis in the entire population and in a subgroup of 471 individuals who did not receive pharmaceutical therapy for hypertension and dyslipidemia.

RESULTS

Principal component analysis identified three independent factors in men: a blood pressure factor (systolic and diastolic blood pressure and BMI), a glucose factor (fasting and 120-min postload glucose, BMI, waist-to-hip ratio [WHR], and fasting insulin level), and a lipid factor (triglycerides and HDL cholesterol, BMI, WHR, and fasting insulin level). In women, an additional factor was identified, which included BMI, WHR, fasting insulin, and triglycerides. Analysis of the contribution of these variables to the different subdimensions indicated that BMI was the central feature of the syndrome in both sexes.

CONCLUSIONS

This analysis of change in the features of the metabolic syndrome over time provides evidence of the fundamental importance of obesity in the origin of this disorder.

Human obesity: an evolutionary approach to understanding our bulging waistline

The unique worldwide spread of the human species and the remarkably long post-reproductive survival show that our genome permits excellent adaptation to vastly different environments. Moreover, the main scourges of later age, namely malignant growths and atherosclerosis, appear in humans later than in shorter-living animals. In recent years, excess weight and obesity have become mass phenomena with a pronounced upward trend in all developed countries. However, despite the detrimental effects of being overweight, these populations live longer than ever, which in part may be explained by the availability of better medical treatment. The prevalence and predicted further spread of obesity can be understood in the light of evolution. In all animal species energy metabolism is asymmetric with energy accumulation ('thrifty genotype') being the necessary condition of survival during hard times. For humans, which are no different to other animals in this respect, this genetic programming was necessary for survival because during the course of history, including the recorded history in the more developed Middle East, Europe or China, there was never a long period of uninterrupted food abundance, whereas famines were regular and frequent. Therefore fat accumulation, when food was available, meant survival at times of shortage, while the possible detrimental effects of overindulgence in food and being overweight expressed in unrealistically old age were irrelevant. It is the central, mostly intra-abdominal fat (in both humans and animals) that is more medically important than the subcutaneous truncal fat, and the accumulation of both types of fat is conditioned by high food consumption; therefore it is a historic novelty for human populations. In contrast, lower-body fat in human females is unique in the animal kingdom: it is much less metabolically active, it is of much lower pathologic significance than central fat, and it is programmed to be mobilized mostly during pregnancy and lactation. In view of all this, norms of desired weight should be based on hard mortality and morbidity statistics and not on theoretical, esthetic or fashion considerations. By this criterion, the upper limit of desirable weight is likely to be body mass index (BMI) 27 or 28, but specified for different populations (sex, race, ethnic origin); moreover, with aging, the detrimental effects of obesity diminish and finally disappear. Risks of other pathologies related to obesity (e.g. diabetes, hypertension and coronary disease) are also population-specific. However, total fatness, measured by BMI, is insufficiently sensitive as a risk factor, and fat distribution (upper-body versus low-body type, as reflected by waist circumference and waist:hip ratio) plays at least as prominent a role. Therefore the detailed norms, not yet available, should take into account both general obesity and fat distribution and be specific for different populations. Since long-term weight loss in adults is rarely achievable, public health measures should be aggressively directed at the prevention of obesity from childhood.

Lack of insulin inhibition on insulin secretion in non-diabetic morbidly obese patients

OBJECTIVE

Insulin inhibition of insulin secretion has been described in normal lean subjects. In this study, we examined whether this phenomenon also occurs in the morbidly obese who often have severe peripheral insulin resistance.

SUBJECTS

Twelve obese patients, normotolerant to glucose (8 F/4 M, body mass index (BMI)=54.8+/-2.5 kg/m(2), 39 y) and 16 lean control subjects (10 F/6 M, BMI=22.0+/-0.5 kg/m(2), 31 y).

DESIGN AND MEASUREMENTS

An experimental study using various parameters, including an euglycemic hyperinsulinemic clamp (280 pmol/min/m(2) of body surface), an oral glucose tolerance test (OGTT), electrical bioimpedance and indirect calorimetry.

RESULTS

The obese subjects were insulin resistant (M=19.8+/-1.6 vs 48.7+/-2.6 micromol/min kg FFM, P<0.0001) and hyperinsulinemic in the fasted state and after glucose ingestion. Fasting plasma C-peptide levels (obese 1425+/-131 pmol/l vs lean 550+/-63 pmol/l; P<0.0001) decreased less during the clamp in the obese groups (-16.9+/-6.9% vs -43.0+/-5.6% relative to fasting values; P=0.007). In the lean group, the C-peptide decrease during the clamp (percentage variation) was related to insulin sensitivity, M/FFM (r=0.56, P=0.03), even after adjustment for the clamp glucose variation.

CONCLUSION

We conclude that, in lean subjects, insulin inhibits its own secretion, and this may be related to insulin sensibility. This response is blunted in morbidly obese patients and may have a role in the pathogenesis of fasting hyperinsulinemia in these patients.

Relationship between impaired glucose tolerance, non-insulin-dependent diabetes mellitus and obesity

Plasma glucose concentration is the best predictor for the development of non-insulin-dependent diabetes mellitus (NIDDM). However, obesity is also a recognized risk factor for development of the disease, and is easier to track over time. Thus obesity could be of considerable clinical importance as a predictor of diabetes. Studies have shown that the degree of overweight, the change in weight and the duration of overweight are all separate predictors of diabetes. The British Regional Heart Study showed that an increasing body mass index (BMI) was associated with increased risk of developing diabetes, even at BMI values not considered obese. A separate study showed that weight gain increased the risk of diabetes independently of BMI, while weight loss decreased the risk. The duration of obesity was also an important factor in developing NIDDM. A long duration increased the risk of diabetes, irrespective of the final BMI value. The effects of obesity on insulin action have also been investigated. Studies have shown that insulin sensitivity is inversely related to insulin secretion, with a disproportionate increase in insulin secretion seen with decreasing sensitivity. A recent European study showed that the prevalence of both insulin hypersecretion and insulin resistance increased with increasing BMI. Thus, in obesity, higher insulin levels are necessary to maintain glucose tolerance, leading to increased stress on the beta-cells. In obese individuals, weight loss improved insulin sensitivity in proportion to the degree of weight loss, leading to decreased insulin secretion. Weight loss can therefore, at least in the short term, act to decrease the risk of developing diabetes by reducing insulin resistance, and thus relieving beta-cell stress, the factor ultimately responsible for hyperglycaemia in predisposed individuals.