Abdominal fat and insulin resistance in normal and overweight women: Direct measurements reveal a strong relationship in subjects at both low and high risk of NIDDM

Insulin sensitivity and serum triglyceride level in obese white and black women: relationship to visceral and truncal subcutaneous fat

Although independent associations of visceral fat with the insulin resistance syndrome were previously reported in obese women, the importance of truncal subcutaneous fat with regard to insulin sensitivity is still controversial. We measured the insulin sensitivity index (S(I)), serum triglyceride (TG) level, and regional fat by two methods: (1) the sum of five truncal and four peripheral skinfolds (TrSUM and PerSUM) in 38 white and black obese nondiabetic premenopausal women, and (2) abdominal visceral (VFM) and subcutaneous fat mass (AbdSCFM) by a combination of magnetic resonance imaging (MRI) and dual x-ray absorptiometry (DXA) in a subset of 26 of these women. After adjusting for the total body fat mass, TrSUM and VFM were independently and negatively related to S(I) (n = 38, P < .012 and n = 26, P < .035, respectively), whereas PerSUM and AbdSCFM were not related (P > .50). Based on multiple regression modeling, TrSUM significantly predicted S(I) independently of the VFM (n = 26, P < .001). Black women had lower S(I) at all levels of TrSUM (n = 38, P = .061 for the slope and P = .03 for the intercept of the regression lines). After adjusting for the total body fat mass, only VFM showed an independent positive relation to serum TG, and race did not affect this relationship (n = 26, P < .001). In conclusion, (1) we confirmed the independent association of the VFM with insulin resistance and elevated TG in obese women; (2) the AbdSCFM measured by a combination of MRI and DXA did not show an independent association with S(I) in obese women; and (3) the independent association of TrSUM with S(I) suggests that truncal subcutaneous fat depots contribute to insulin resistance in obese women independently of the degree of visceral fat.

Nutrition in early life: somatic growth and serum lipids

This paper addresses the questions of whether early nutritional experience affects later somatic growth, the growth of the adipose tissue, or the levels of scrum lipids among well-nourished children. The analyses are based on data from three prospective studies. Postnatal nutrition and growth: there were differences in growth between breast-fed and formula-fed children. There was no association between linear growth and differences in food energy or macronutrient intake. Birth size and postnatal growth: there was no association between ponderal index (PI) at birth and body mass index (BMI) in the second year. For boys, the PI at 3 and 6 months of age was significantly positively correlated with BMI at the ages of 8 and 15 years, but not for girls. Childhood growth and lipids: there was no association between lipids at the age of 8 years and either birth weight or length, but children who had had a low PI at birth had higher lipid levels at the age 8 years. A positive association was found between serum lipids and abdominal fat and BMI. We conclude that, although early diet may influence growth rate beyond infancy, the evidence for fat patterning resulting from differences in fetal or early postnatal nutrition is still open to question.

Lower intensity physical activity is advantageous for fat distribution and blood glucose among viscerally obese older adults

OBJECTIVE

The influence of daily accumulated physical activity on blood glucose among older adults with varying obesity patterns is unknown. The purpose of this investigation was to determine if the blood glucose lowering effect of daily movement is modulated by distribution of adiposity in a community-based sample of older persons.

METHODS

The study sample (N = 743) was mostly women (79.4%) with an average age of 74.5+/-0.3 yr. A question from the Yale Physical Activity Survey was the indicator of lower intensity physical activity. The response, answered in h x d(-1) spent in motion, was divided into tertiles (<3, 3 to <5, and > or = 5 h x d(-1)). Random blood glucose and total blood cholesterol were assessed via finger stick. The body mass index (BMI) and waist circumference (WC) delineated the categories of adiposity patterning as follows: nonobese (N = 354), BMI = 23.8+/-0.1 kg x m(-2) and WC = 80.3+/-0.4 cm; noncentral obese (N = 79), BMI = 30.8+/-0.1 kg x m(-2) and WC = 87.5+/-0.4 cm; and central obese (N = 310), BMI = 32.7+/-0.3 kg x m(-2) and WC = 103.3+/-0.5 cm.

RESULTS

After adjusting for age, gender, race, medication use, and postprandial state, blood glucose levels were lower with greater amounts of reported daily movement in the centrally obese, 8.6+/-0.4 mmol x L(-1), 6.6+/-0.4 mmol x L(-1), and 6.3+/-0.4 mmol x L(-1) for <3 h x d(-1), 3 to <5 h x d(-1), and > or = 5 h x d(-1), respectively (P < 0.001). As the centrally obese increased their hours of moving about, their WC was observed to be less, 105.7+/-0.8 cm, 103.4+/-0.8 cm, and 102.9+/-1.0 cm, respectively, independent of age, gender, race, and medication use (P < 0.05). Neither blood glucose nor WC differed between categories of daily movement in the noncentral obese or nonobese.

CONCLUSIONS

Our findings suggest that daily accumulated, lower intensity physical activity is advantageous for abdominal fat distribution and blood glucose among viscerally obese older adults.

The genetic basis of type 2 diabetes mellitus: impaired insulin secretion versus impaired insulin sensitivity

Despite the fact that it is the prevalent view that insulin resistance is the main genetic factor predisposing to development of type 2 diabetes, review of several lines of evidence in the literature indicates a lack of overwhelming support for this concept. In fact, the literature better supports the case of impaired insulin secretion being the initial and main genetic factor predisposing to type 2 diabetes, especially 1) the studies in people at high risk to subsequently develop type 2 diabetes (discordant monozygotic twins and women with previous gestational diabetes), 2) the studies demonstrating compete alleviation of insulin resistance with weight loss, and 3) the studies finding that people with type 2 diabetes or IGT can have impaired insulin secretion and no insulin resistance compared with well matched NGT subjects. The fact that insulin resistance may be largely an acquired problem in no way lessens its importance in the pathogenesis of type 2 diabetes. Life style changes (exercise, weight reduction) and pharmacological agents (e.g., biguanides and thiazolidendiones) that reduce insulin resistance or increase insulin sensitivity clearly have major beneficial effects (122, 144-146, 153-155).

Plasma leptin in relation to regional body fat in older New Zealand women

BACKGROUND

Leptin is the protein product of the obesity (ob) gene and is produced in adipose tissue. Plasma leptin values are highly correlated with total body fat mass but less is known concerning relationships of leptin with regional adiposity.

AIM

To investigate associations between leptin and dual energy X-ray absorptiometry (DEXA) measures of regional body fat deposition in older New Zealand women.

METHODS

Body composition was measured in 80 women aged 40 to 79 years (20 in each decade) using DEXA. Height and weight were measured by conventional anthropometry. Plasma leptin concentrations were assayed by radioimmunoassay.

RESULTS

Leptin was strongly correlated (p < 0.001) with weight (r = 0.751), body mass index (r = 0.782), total fat mass (r = 0.854) and % fat mass (r = 0.813). A statistical model with trunk fat (kg) and leg fat (kg) as the independent variables showed that trunk fat accounted for 72.1% of the variance in plasma leptin with leg fat explaining only a further 1.6% of the variance. No relationships were found between leptin and age, height, lean tissue mass or menopausal status (p > 0.05).

CONCLUSIONS

We conclude that trunk fat explains more of the variance in circulating leptin concentrations than leg fat, suggesting that the propensity to leptin resistance may be increased in women with higher central adiposity.

Diabetes in urban African Americans. XII. Anthropometry for assessing municipal hospital outpatients recently diagnosed with type 2 diabetes

OBJECTIVE

Abdominal obesity is associated with insulin resistance and cardiovascular risk factors, but there has been little information published to advance the use of abdominal anthropometry in the care of diabetic patients.

RESEARCH METHODS AND PROCEDURES

A cross-sectional survey of municipal hospital outpatients recently diagnosed with type 2 diabetes (73 men and 142 women of whom 89% were African Americans). Age-adjusted linear regression was used to compare the supine sagittal abdominal diameter (SAD), supine waist circumference, four anthropometric ratios, and the body mass index (kg/m2) for their ability to predict serum fasting C-peptide and lipid levels.

RESULTS

The best predictor of log-transformed C-peptide was SAD/height (p<0.0001 for men; p=0.0003 for women). SAD/thigh circumference was the best predictor of log-transformed triglycerides for men (p=0.002) and of total cholesterol/HDL cholesterol for women (p=0.043). The body mass index was less able to predict C-peptide, HDL cholesterol and total cholesterol/HDL cholesterol than was SAD/height or SAD/thigh circumference or waist circumference/height.

DISCUSSION

Anthropometric indices of abdominal obesity appear to be correlated with insulin production and lipid risk factors among municipal-hospital, type 2 diabetic patients much as they are in other studied populations. Since anthropometric data are inexpensively obtained and immediately available to the practitioner, their utility for preliminary clinical assessment deserves to be tested in prospective outcome studies.

Caloric restriction reverses hepatic insulin resistance in aging rats by decreasing visceral fat

Hyperinsulinemia and increased visceral/abdominal fat (VF) are common features of human aging. To examine the relationships among VF, peripheral, and hepatic insulin sensitivity, we studied 4- and 18-mo-old male Sprague-Dawley rats (n = 42) fed ad libitum (4 AL and 18 AL) or moderately calorie restricted (18 CR) up to 18 mo of age. Total fat mass (FM) and VF were decreased in 18 CR to approximately one-third of that of 18 AL (P < 0.001), while lean body mass (LBM) was unchanged. Most important, 18 CR had more FM (65+/-6 vs. 45+/-6 g) but less VF (7.8+/-0.6 vs. 12.3+/-3.3 g) compared with 4 AL (P < 0.01 for both). Thus, the effects of variable VF on HIS could be assessed, independent of FM and age. Marked hepatic insulin resistance ensued with aging (18 AL) and CR restored hepatic insulin sensitivity to the levels of young rats, while peripheral insulin sensitivity remained unchanged (by insulin clamp of 18 mU/kg/min). In fact, the rates of insulin infusion required to maintain basal hepatic glucose production in the presence of pancreatic clamp were 0.75+/-0.10, 1.41+/-0.13, and 0.51+/-0.12 mU/kg . min, in 4 AL, 18 AL, and 18 CR, respectively (P < 0.01 between all groups), and in 18 CR rats infused with insulin at similar rates as in the 18 AL (1.4 mU/kg/min) hepatic glucose production was decreased by 32% (P < 0. 005). Furthermore, when 18 CR rats were fed AL for 14 d, VF rapidly and selectively increased and severe hepatic insulin resistance was induced. We propose that in this animal model the age-associated decrease in hepatic (rather than peripheral) insulin action is the major determinant of fasting hyperinsulinemia and that increased visceral adiposity plays the major role in inducing hepatic insulin resistance. Thus, interventions designed to prevent the accumulation of VF are likely to represent an effective mean to improve carbohydrate metabolism in aging.

Cardiovascular disease insulin risk in Mexican-American and Anglo-American children and mothers

OBJECTIVE

To evaluate the relationship between insulin levels and cardiovascular risk factors in children and determine whether it varies among ethnic groups.

METHODS

Cardiovascular risk factors and insulin levels were compared in 144 Mexican-American and Anglo-American mother-child pairs, when the children were 11 years of age.

RESULTS

Although mean age did not differ between ethnicities, Mexican-American mothers and children both had a greater body mass index (mothers: 29.2 +/- 6.2 vs 27.2 +/- 7.9; children: 21.7 +/- 4.7 vs 19.7 +/- 4.6) and sum of skinfolds than did Anglo-Americans. Triglycerides, very low-density lipoprotein cholesterol, fasting insulin, and cholesterol/high-density lipoprotein ratio were higher, while high-density lipoprotein cholesterol was lower in both Mexican-American adults and children compared with Anglo-Americans. After adjusting for measures of obesity, only high-density lipoprotein cholesterol levels remained significantly lower in Mexican-Americans. For both adults and children, higher quartiles of insulin levels were associated with significantly higher triglycerides, blood pressure and lower high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol/apolipoprotein B levels (estimate of dense low-density lipoprotein size). A summary variable representing cardiovascular risk factors present in adult syndrome X patients was higher in both Mexican-American adults and children than in Anglo-Americans.

CONCLUSION

Mexican-American children and adults have higher levels of many cardiovascular risk factors, and this appears related to higher insulin levels and overweight. Appropriate nutrition, weight control, and exercise at early ages could be important in slowing the development of atherosclerosis.

Response of insulin, glucagon, lactate, and nonesterified fatty acids to glucose in visceral obesity with and without NIDDM: relationship to hypertension

Insulin, glucagon, glucose, nonesterified fatty acids (NEFA), and lactate response to oral glucose tolerance test (OGTT, 75 g glucose) and their correlation with mean blood pressure (BP), were studied in 10 normal subjects (N), 25 subjects with abdominal obesity (O), and 9 subjects with abdominal obesity and IGT or non-insulin-dependent diabetes (OD). O and OD patients, as compared to N subjects, showed increased fasting NEFA, lactate, insulin, and glucagon. NEFA area and insulin total and incremental areas were increased in O and OD (P < 0.001 in all instances). Glucagon total areas were increased only in OD (P < 0.01). Lactate total areas were increased in O (P < 0.001) and in OD (P < 0.01), while lactate incremental area was diminished in O and, even more, in OD subjects (P < 0.001 in both instances) and was inversely correlated with the basal level (P < 0.001). In all subjects as a whole, increase in NEFA area was weakly correlated with total and incremental insulinemic areas (P < 0.05) and more strongly correlated with glucagon and lactate areas (P < 0.01). Conversely, the incremental areas of lactate were negatively correlated with total insulin (P < 0.05), NEFA (P < 0.05), and glucagon (P < 0.001) areas. BP was increased in O (103.62 +/- 2.37) and, even more, in OD (109.41 +/- 5.22) compared to that seen in N (92.55 +/- 0.94 mm Hg), with P < 0.01, and was correlated with fasting insulin (P < 0.01) and glucose (P < 0.05) and, even more, with total (P < 0.001) and incremental (P < 0.01) insulin areas and NEFA areas (P < 0.001). Conversely, BP also was negatively correlated with incremental lactate area (P < 0.01) (similarly to insulin and NEFA area). Our data would suggest that in O and OD patients, insulin resistance is associated with elevated NEFA, insulin and glucagon as well as with high BP. since NEFA are inhibitors of Na,K-ATPase, they could contribute to elevate BP through the repression of this enzyme (which we have shown previously to be reduced in adipose tissue of obese subjects and correlated negatively with BP.

Abdominal obesity

The application of magnetic resonance imaging and computed tomography to obesity research has changed the focus from body mass and skinfold thickness to abdominal fat mass and visceral adiposity. Intra-abdominal fat constitutes less than 20% of total body fat but is a major determinant of fasting and postprandial lipid availability because of its physiological (lipolytic rate and insulin resistance) and anatomical (portal drainage) properties. High levels of serum free fatty acids, as a result of abdominal obesity, cause excessive tissue lipid accumulation and contribute to dyslipidaemia, beta cell dysfunction, and hepatic and peripheral insulin resistance. An individual's risk of non-insulin dependent diabetes mellitus and cardiovascular disease relates closely to the inheritance of central obesity and susceptibility to tissue lipotoxicity.

Glucose intolerance in familial combined hyperlipidaemia. EUFAM study group

BACKGROUND

Familial combined hyperlipidaemia (FCHL) is a common hereditary disorder. Hypertriglyceridaemia is associated with glucose intolerance and insulin resistance.

METHODS

To study glucose tolerance in FCHL patients with different lipid phenotypes [hypercholesterolaemia (IIA), mixed hyperlipidaemia (IIB), hypertriglyceridaemia (IV)], we investigated 253 family members and 92 spouses arising from 33 well-defined Finnish FCHL pedigrees.

RESULTS

In oral glucose tolerance tests the affected family members had higher values for glucose area under the curve than did non-affected family members [673+/-127 min mmolL(-1), 754+/-145 min mmol L(-1), 846+/-180 min mmol L(-1) and 838+/-183 min mmol L(-1) for phenotypes normal, IIA, IIB and IV respectively; P < 0.001 after adjustment for body mass index, waist circumference and age]. Impaired glucose tolerance and diabetes were more common among affected than non-affected family members (prevalences of normal glucose tolerance 94.0%, 80.0%, 54.3% and 58.5% for phenotypes normal, IIA, IIB and IV).

CONCLUSION

Affected FCHL family members were more glucose intolerant than non-affected family members. In men, this disturbance was not related to lipid phenotype nor was it explained by obesity.

Relationship of a novel polymorphic marker near the human obese (OB) gene to fat mass in healthy women

The cloning of the murine obese (ob) gene and its human homologue has recently been reported. Mutations in the mouse ob gene result in hereditary obesity; however, the role of variations of OB in the regulation of bodyweight in humans has yet to be determined. The contribution of putative genetic variations in the human OB gene to total and regional fat mass in a normal twin population has been analyzed through linkage and association with a novel polymorphic marker, located in proximity to this gene. The polymorphic dinucleotide repeat, isolated from a P1 clone containing the human OB gene, was physically localized by long-range restriction mapping to within 30 kilobases of the OB locus. The marker was genotyped in a population of 47 healthy female/female dizygotic (DZ) twin pairs for which direct measures of central abdominal and whole body fat had been obtained by dual X-ray absorbtiometry. Possible linkage between the microsatellite marker and whole-body (p = 0.008), but not central abdominal (p = 0.09), fat deposits was indicated. No association between fat depot phenotype and marker genotype was detected. These results suggest that genetic variation in or close to the human OB gene may play a role in the size of body fat stores in healthy women.

Regional lipolytic responses to isoproterenol in women

We previously found that epinephrine, a mixed beta- and alpha-adrenoreceptor agonist, stimulates systemic and nonsplanchnic upper body free fatty acid (FFA) release but not lower body FFA release in healthy nonobese women. To evaluate the role of beta-adrenergic-mediated effects on this regional difference in lipolysis, we measured systemic, leg, and splanchnic FFA kinetics ([3H]palmitate) in seven healthy nonobese women before and during an intravenous isoproterenol infusion. Isoproterenol increased systemic palmitate flux (87 +/- 12 vs. 100 +/- 10 mumol/min, P < 0.05) but failed to affect leg [10.8 +/- 1.2 vs. 11.4 +/- 2.3 mumol/min, P = not significant (NS)] or splanchnic (10.8 +/- 3.2 vs. 10.0 +/- 1.8 mumol/min, P = NS) palmitate release. Upper body nonsplanchnic palmitate release increased from 56 +/- 14 to 71 +/- 10 mumol/min. Systemic O2 consumption increased (227 +/- 11 to 241 +/- 10 ml/min, P = 0.006) during isoproterenol infusion, as did leg (318 +/- 42 vs. 404 +/- 53 ml/min, P < 0.01) and splanchnic (827 +/- 104 vs. 970 +/- 108 ml/min, P < 0.05) plasma flow. These results suggest that lower body adipose tissue lipolysis in women is less sensitive or responsive than nonsplanchnic upper body adipose tissue to beta-adrenergic stimulation and that regional differences in alpha 2-adrenergic-receptor responses were not responsible for the similar regional differences we observed previously with epinephrine.

Independent genetic factors determine the amount and distribution of fat in women after the menopause

Central adiposity is a strong predictor of cardiovascular disease in women. We studied postmenopausal twins to explore the strength and the relationship between genetic influences on body fat and its distribution in a group where cardiovascular disease is the major cause of mortality. Healthy twin women were recruited from a national media campaign. One hundred nineteen monozygotic (MZ) and 97 dizygotic twin pairs were studied (mean +/- SE age 60 +/- 0.3 yr; 10 +/- 0.4 yr post menopausal). Total and central body fat were measured by dual-energy x-ray absorptiometry. Intrapair resemblance was significantly greater in MZ pairs for total fat (MZ vs. dizygotic, r = 0.70 +/- 0.05 vs. r = 0.46 +/- 0.08, P = 0.005) and central fat (r = 0.62 +/- 0.06 vs. r = 0.35 +/- 0.09, P = 0.005), suggesting a strong genetic influence on these traits. Model-fitting analysis indicated that genetic factors contribute up to 60% of total population variance in both total and central body fat. The heritability of central fat remained, after adjustment for the heritability of total fat, suggesting an independent genetic influence on fat distribution. These results were unchanged after adjusting for the effects of estrogen replacement and smoking. In conclusion, total adiposity and central abdominal fat mass in normal postmenopausal women are under strong genetic influence. The data suggest that some of the genes responsible for central adiposity and its metabolic sequelae will be different from those responsible for total adiposity.