Liver-fat accumulation and insulin resistance in obese women with previous gestational diabetes

Age-related changes in total and regional fat distribution

Aging is associated with progressive changes in total and regional fat distribution that have negative health consequences. Indeed, a preferential increase in abdominal fat, in particular visceral fat, combined with a decrease in lower body subcutaneous fat are commonly cited in the literature. These age-related changes in body composition can occur independent of changes in total adiposity, body weight or waist circumference, and represent a phenotype closely associated with increased morbidity and mortality risk. Tissues such as the heart, liver and skeletal muscle in the elderly have increased fat deposition, which increases risk for insulin resistance and cardiovascular disease. Furthermore, aging is associated with increased fat content within bone marrow, which exposes the elderly to fracture risk beyond that associated with low bone mineral density alone. Many of the age-associated body compositional changes cannot be detected by simple anthropometric measures alone, and the influence of gender, race or ethnicity, and physical activity patterns on these changes is unclear. This review will explore some of these age-related changes in total and regional fat distribution. Consideration will also be given to the strengths and limitations associated with some of the anthropometric methodologies employed for assessing these changes.

Prediction of non-alcoholic fatty liver disease and liver fat using metabolic and genetic factors

BACKGROUND & AIMS

Our aims were to develop a method to accurately predict non-alcoholic fatty liver disease (NAFLD) and liver fat content based on routinely available clinical and laboratory data and to test whether knowledge of the recently discovered genetic variant in the PNPLA3 gene (rs738409) increases accuracy of the prediction.

METHODS

Liver fat content was measured using proton magnetic resonance spectroscopy in 470 subjects, who were randomly divided into estimation (two thirds of the subjects, n = 313) and validation (one third of the subjects, n = 157) groups. Multivariate logistic and linear regression analyses were used to create an NAFLD liver fat score to diagnose NAFLD and liver fat equation to estimate liver fat percentage in each individual.

RESULTS

The presence of the metabolic syndrome and type 2 diabetes, fasting serum (fS) insulin, fS-aspartate aminotransferase (AST), and the AST/alanine aminotransferase ratio were independent predictors of NAFLD. The score had an area under the receiver operating characteristic curve of 0.87 in the estimation and 0.86 in the validation group. The optimal cut-off point of -0.640 predicted increased liver fat content with sensitivity of 86% and specificity of 71%. Addition of the genetic information to the score improved the accuracy of the prediction by only <1%. Using the same variables, we developed a liver fat equation from which liver fat percentage of each individual could be estimated.

CONCLUSIONS

The NAFLD liver fat score and liver fat equation provide simple and noninvasive tools to predict NAFLD and liver fat content.

gamma-Glutamyltransferase, obesity, physical activity, and the metabolic syndrome in indigenous Australian adults

The aim of this study is to examine the association between obesity, metabolic syndrome, physical activity, and elevated gamma-glutamyltransferase (GGT) among Indigenous Australian adults who did not drink alcohol. A cross-sectional study of 791 Indigenous adults in rural North Queensland communities was conducted between 1999 and 2001. Measures included serum GGT, fasting glucose, cholesterol, and triglycerides; resting blood pressure, BMI, and waist circumference; and self-reported physical activity, alcohol intake, and tobacco smoking. Central obesity measured by waist circumference in this population was significantly associated with elevated GGT independently of lifestyle behaviors (Adjusted odds ratio (OR) = 2.7, 95% confidence interval (CI): 1.2-6.0). Metabolic syndrome (International Diabetes Federation definition) was also strongly associated with increased GGT (OR = 2.6, 95% CI: 1.5-4.6). Habitual physical activity may be slightly protective (OR = 0.9, 95% CI: 0.5-1.6) in this group, but this was not clearly demonstrated in this study. Prevention of type 2 diabetes and cardiovascular disease in this population should emphasize "waist loss" and metabolic health through dietary and other interventions.

Quantification of liver fat content: comparison of triple-echo chemical shift gradient-echo imaging and in vivo proton MR spectroscopy

PURPOSE

To validate a triple-echo gradient-echo sequence for measuring the fat content of the liver, by using hydrogen 1((1)H) magnetic resonance (MR) spectroscopy as the reference standard.

MATERIALS AND METHODS

This prospective study was approved by the appropriate ethics committee, and written informed consent was obtained from all patients. In 37 patients with type 2 diabetes (31 men, six women; mean age, 56 years), 3.0-T single-voxel point-resolved (1)H MR spectroscopy of the liver (Couinaud segment VII) was performed to calculate the liver fat fraction from the water (4.7 ppm) and methylene (1.3 ppm) peaks, corrected for T1 and T2 decay. Liver fat fraction was also computed from triple-echo (consecutive in-phase, opposed-phase, and in-phase echo times) breath-hold spoiled gradient-echo sequence (flip angle, 20 degrees), by estimating T2* and relative signal intensity loss between in- and opposed-phase values, corrected for T2* decay. Pearson correlation coefficient, Bland-Altman 95% limit of agreement, and Lin concordance coefficient were calculated.

RESULTS

Mean fat fractions calculated from the triple-echo sequence and (1)H MR spectroscopy were 10% (range, 0.7%-35.6%) and 9.7% (range, 0.2%-34.1%), respectively. Mean T2* time was 14.7 msec (range, 5.4-25.4 msec). Pearson correlation coefficient was 0.989 (P < .0001) and Lin concordance coefficient was 0.988 (P < .0001). With the Bland-Altman method, all data points were within the limits of agreement.

CONCLUSION

A breath-hold triple-echo gradient-echo sequence with a low flip angle and correction for T2* decay is accurate for quantifying fat in segment VII of the liver. Given its excellent correlation and concordance with (1)H MR spectroscopy, this triple-echo sequence could replace (1)H MR spectroscopy in longitudinal studies.

Exercise and the fatty liver

Fatty liver is an increasingly prevalent condition that is associated with several metabolic derangements, thus necessitating the development of effective therapeutic interventions. Growing evidence from cross-sectional studies suggest that physical activity may be a promising therapy for fatty liver. Unfortunately, longitudinal evidence supporting this observation in humans is sparse, as the majority of intervention studies have examined the relationship between liver fat and physical activity in conjunction with caloric and dietary fat restriction. Studies in rats demonstrate a beneficial effect of exercise on liver fat, mainly in situations of high fat feeding or obesity. Thus, the independent contribution of physical activity on variations in liver fat is unknown, but remains a promising intervention that requires further investigation. There is some evidence to suggest that both physical activity and liver fat are independent correlates of cardiovascular and type 2 diabetes risk. The relative contribution of each remains unclear, but implies that both should be considered when developing therapeutic interventions for chronic metabolic disease.

Causes and metabolic consequences of Fatty liver

Type 2 diabetes and cardiovascular disease represent a serious threat to the health of the population worldwide. Although overall adiposity and particularly visceral adiposity are established risk factors for these diseases, in the recent years fatty liver emerged as an additional and independent factor. However, the pathophysiology of fat accumulation in the liver and the cross-talk of fatty liver with other tissues involved in metabolism in humans are not fully understood. Here we discuss the mechanisms involved in the pathogenesis of hepatic fat accumulation, particularly the roles of body fat distribution, nutrition, exercise, genetics, and gene-environment interaction. Furthermore, the effects of fatty liver on glucose and lipid metabolism, specifically via induction of subclinical inflammation and secretion of humoral factors, are highlighted. Finally, new aspects regarding the dissociation of fatty liver and insulin resistance are addressed.

Insulin resistance and obesity in childhood

Childhood obesity is a significant health problem that has reached epidemic proportions around the world and is associated with several metabolic and cardiovascular complications. Insulin resistance is a common feature of childhood obesity and is considered to be an important link between adiposity and the associated risk of type 2 diabetes and cardiovascular disease. Insulin resistance is also a key component of the metabolic syndrome, and its prevalence in the paediatric population is increasing, particularly among obese children and adolescents. Several factors are implicated in the pathogenesis of obesity-related insulin resistance, such as increased free fatty acids and many hormones and cytokines released by adipose tissue. Valid and reliable methods are essential to assess the presence and the extent of insulin resistance, the associated risk factors and the effect of pharmacological and lifestyle interventions. The two most common tests to assess insulin resistance are the hyperinsulinemic euglycemic clamp and the frequently sampled i.v. glucose tolerance test utilizing the minimal model. However, both these tests are not easily accomplished, are time consuming, expensive and invasive. Simpler methods to assess insulin resistance based on surrogate markers derived from an oral glucose tolerance test or from fasting insulin and glucose levels have been validated in children and adolescents and widely used. Given the strong association between obesity, insulin resistance and the development of metabolic syndrome and cardiovascular disease, prevention and treatment of childhood obesity appear to be essential to prevent the development of insulin resistance and the associated complications.

Effects of pioglitazone and metformin on NEFA-induced insulin resistance in type 2 diabetes

AIMS/HYPOTHESIS

We sought to determine whether pioglitazone and metformin alter NEFA-induced insulin resistance in type 2 diabetes and, if so, the mechanism whereby this is effected.

METHODS

Euglycaemic-hyperinsulinaemic clamps (glucose approximately 5.3 mmol/l, insulin approximately 200 pmol/l) were performed in the presence of Intralipid-heparin (IL/H) or glycerol before and after 4 months of treatment with pioglitazone (n = 11) or metformin (n = 9) in diabetic participants. Hormone secretion was inhibited with somatostatin in all participants.

RESULTS

Pioglitazone increased insulin-stimulated glucose disappearance (p < 0.01) and increased insulin-induced suppression of glucose production (p < 0.01), gluconeogenesis (p < 0.05) and glycogenolysis (p < 0.05) during IL/H. However, glucose disappearance remained lower (p < 0.05) whereas glucose production (p < 0.01), gluconeogenesis (p < 0.05) and glycogenolysis (p < 0.05) were higher on the IL/H study day than on the glycerol study day, indicating persistence of NEFA-induced insulin resistance. Metformin increased (p < 0.001) glucose disappearance during IL/H to rates present during glycerol treatment, indicating protection against NEFA-induced insulin resistance in extrahepatic tissues. However, glucose production and gluconeogenesis (but not glycogenolysis) were higher (p < 0.01) during IL/H than during glycerol treatment with metformin, indicating persistence of NEFA-induced hepatic insulin resistance.

CONCLUSIONS/INTERPRETATION

We conclude that pioglitazone improves both the hepatic and the extrahepatic action of insulin but does not prevent NEFA-induced insulin resistance. In contrast, whereas metformin prevents NEFA-induced extrahepatic insulin resistance, it does not protect against NEFA-induced hepatic insulin resistance.

Cardiovascular risk factors and the metabolic syndrome in pediatric nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD), the most common cause of liver disease in children, is associated with obesity and insulin resistance. However, the relationship between NAFLD and cardiovascular risk factors in children is not fully understood. The objective of this study was to determine the association between NAFLD and the presence of metabolic syndrome in overweight and obese children.

METHODS AND RESULTS

This case-control study of 150 overweight children with biopsy-proven NAFLD and 150 overweight children without NAFLD compared rates of metabolic syndrome using Adult Treatment Panel III criteria. Cases and controls were well matched in age, sex, and severity of obesity. Children with NAFLD had significantly higher fasting glucose, insulin, total cholesterol, low-density lipoprotein cholesterol, triglycerides, systolic blood pressure, and diastolic blood pressure than overweight and obese children without NAFLD. Subjects with NAFLD also had significantly lower high-density lipoprotein cholesterol than controls. After adjustment for age, sex, race, ethnicity, body mass index, and hyperinsulinemia, children with metabolic syndrome had 5.0 (95% confidence interval, 2.6 to 9.7) times the odds of having NAFLD as overweight and obese children without metabolic syndrome.

CONCLUSIONS

NAFLD in overweight and obese children is strongly associated with multiple cardiovascular risk factors. The identification of NAFLD in a child should prompt global counseling to address nutrition, physical activity, and avoidance of smoking to prevent the development of cardiovascular disease and type 2 diabetes.

Effect of 6-month calorie restriction and exercise on serum and liver lipids and markers of liver function

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) and its association with insulin resistance are increasingly recognized as major health burdens. The main objectives of this study were to assess the relation between liver lipid content and serum lipids, markers of liver function and inflammation in healthy overweight subjects, and to determine whether caloric restriction (CR) (which improves insulin resistance) reduces liver lipids in association with these same measures.

METHODS AND PROCEDURES

Forty-six white and black overweight men and women (BMI = 24.7-31.3 kg/m(2)) were randomized to "control (CO)" = 100% energy requirements; "CR" = 25%; "caloric restriction and increased structured exercise (CR+EX)"= 12.5% CR + 12.5% increase in energy expenditure through exercise; or "low-calorie diet (LCD)" = 15% weight loss by liquid diet followed by weight-maintenance, for 6 months. Liver lipid content was assessed by magnetic resonance spectroscopy (MRS) and computed tomography (CT). Lipid concentrations, markers of liver function (alanine aminotransferase (ALT), alkaline phosphatase (ALK)), and whole-body inflammation (tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), high-sensitivity C-reactive protein (hsCRP)) were measured in fasting blood.

RESULTS

At baseline, increased liver lipid content (by MRS) correlated (P < 0.05) with elevated fasting triglyceride (r = 0.52), ALT (r = 0.42), and hsCRP (r = 0.33) concentrations after adjusting for sex, race, and alcohol consumption. With CR, liver lipid content was significantly lowered by CR, CR+EX, and LCD (detected by MRS only). The reduction in liver lipid content, however, was not significantly correlated with the reduction in triglycerides (r = 0.26; P = 0.11) or with the changes in ALT, high-density lipoprotein (HDL)-cholesterol, or markers of whole-body inflammation.

DISCUSSION

CR may be beneficial for reducing liver lipid and lowering triglycerides in overweight subjects without known NAFLD.

Ectopic fat and insulin resistance

Ectopic fat is defined by the deposition of triglycerides within cells of non-adipose tissue that normally contain only small amounts of fat. Over the past decade, magnetic resonance spectroscopy has been used extensively for noninvasive quantification of intramyocellular, intrahepatocellular, and more recently myocardial and pancreatic lipids. In liver and muscle, triglyceride content usually correlates with whole-body and tissue-specific insulin sensitivity. However, fat mass and oxidative capacity influence this relationship, indicating that ectopic lipid content is not the only factor that explains insulin resistance. Ectopic lipids may rather serve as biomarkers of the balance between metabolic supply and demand in different states of insulin sensitivity. Consequently, ectopic lipid concentrations, particularly in the liver, decrease with lifestyle- or drug-induced improvement of insulin sensitivity.

(1)H MR spectroscopy of skeletal muscle, liver and bone marrow

Proton magnetic resonance spectroscopy ((1)H MRS) offers interesting metabolic information even from organs outside the brain. In the first part, applications in skeletal muscle for determination of intramyocellular lipids (IMCL), which are involved in the pathogenesis of insulin resistance, are described. Peculiarities of spectral pattern are discussed and studies for short-term regulation of IMCL, as dietary intervention, exercise and fasting are presented. The second part deals with quantification of small amounts of lipids in the liver (hepatic lipids, HL), which is also of increasing interest in the field of diabetes research. Recommendations for correct assessment of spectra in this "moving organ" are given and the importance of HL is described by examples of a cohort at increased risk for type 2 diabetes. Regulation of HL is described on the basis of a few studies. The third part concentrates on spectral characterization of bone marrow. Peripheral bone marrow of adults consists mainly of fat, while central marrow regions in the pelvis, spinal column and breast bone (and the peripheral bone marrow of children as well) contribute to blood formation and show a variable composition of adipocytes (fat cells), interstitial fluid and water containing precursor cells for erythrocytes, leucocytes and thrombocytes. Adapted (1)H spectroscopic techniques allow a semi-quantitative analysis of bone marrow composition.

Association between dietary fat intake, liver fat, and insulin sensitivity in sedentary, abdominally obese, older men

Whether dietary fat influences the interaction between liver fat, visceral adipose tissue (VAT), and metabolic risk is unclear. Thus, we sought to determine the independent associations between 1 and 10 d dietary fat intake, liver fat, and VAT on insulin sensitivity using a cross-sectional design. Liver fat score (LFS) was assessed by computed tomography and VAT by magnetic resonance imaging in 42 abdominally obese older men. Insulin sensitivity was measured by the hyperinsulinemic–euglycemic clamp technique. Diet composition was determined from self-recorded diet records for 1 and 10 d preceding the assessment of LFS. LFS was positively associated with the 10 d average fat and alcohol intake, but not with any 1 d average dietary variables. VAT (r = –0.36) and LFS (r = –0.32) were both negatively correlated with insulin sensitivity (p < 0.05). When LFS and VAT were entered in the same model, only VAT was an independent predictor of insulin sensitivity (p < 0.05). Control for the average 10 d alcohol consumption and fat intake improved the association between insulin sensitivity and LFS (from r = –0.32, p > 0.10 to r = –0.49, p < 0.05), but not VAT. In fact, after control for the 10 d dietary variables, both LFS and VAT were independent predictors of insulin sensitivity (p < 0.05). This was not true for any of the 1 d dietary intake variables. In conclusion, liver fat is associated with dietary fat intake and alcohol consumption over 10 d, but not 1 d. Furthermore, dietary habits may influence the relationship between liver fat and insulin sensitivity.

Abdominal obesity and the risk of all-cause, cardiovascular, and cancer mortality: sixteen years of follow-up in US women

BACKGROUND

Accumulating evidence indicates that abdominal adiposity is positively related to cardiovascular disease (CVD) risk and some other diseases independently of overall adiposity. However, the association of premature death resulting from these diseases with abdominal adiposity has not been widely studied, and findings are inconsistent.

METHODS AND RESULTS

In a prospective cohort study of 44,636 women in the Nurses' Health Study, associations of abdominal adiposity with all-cause and cause-specific mortality were examined. During 16 years of follow-up, 3507 deaths were identified, including 751 cardiovascular deaths and 1748 cancer deaths. After adjustment for body mass index and potential confounders, the relative risks across the lowest to the highest waist circumference quintiles were 1.00, 1.11, 1.17, 1.31, and 1.79 (95% confidence interval [CI], 1.47 to 1.98) for all-cause mortality; 1.00, 1.04, 1.04, 1.28, and 1.99 (95% CI, 1.44 to 2.73) for CVD mortality; and 1.00, 1.18, 1.20, 1.34, and 1.63 (95% CI, 1.32 to 2.01) for cancer mortality (all P<0.001 for trend). Among normal-weight women (body mass index, 18.5 to < 25 kg/m(2)), abdominal obesity was significantly associated with elevated CVD mortality: Relative risk associated with waist circumference > or = 88 cm was 3.02 (95% CI, 1.31 to 6.99) and for waist-to-hip ratio > 0.88 was 3.45 (95% CI, 2.02 to 6.92). After adjustment for waist circumference, hip circumference was significantly and inversely associated with CVD mortality.

CONCLUSIONS

Anthropometric measures of abdominal adiposity were strongly and positively associated with all-cause, CVD, and cancer mortality independently of body mass index. Elevated waist circumference was associated with significantly increased CVD mortality even among normal-weight women.

The Relationship between Renal Injury and Change in Vitamin D Metabolism in Aged Rats with Insulin Resistance or Type 2 Diabetes Mellitus

Insulin resistance (IR), IR treated with vitamin D, IR treated with 1α-hydroxyvitamin D (1α-(OH)D), type 2 diabetes mellitus (T2DM), T2DM treated with vitamin D and T2DM treated with 1a-(OH)D were studied in animal models using aged Wistar rats. Glucose infusion rates and levels of urinary albumin (UA), serum 25-hydroxyvitamin D (25-(OH)D) and 1, 25-dihydroxyvitamin D (1, 25-(OH)2D) were measured. T2DM rats had higher UA than IR or normal rats, and levels of 25-(OH)D in all models were similar. IR rats had higher 1, 25-(OH)2D levels than T2DM rats, and had lower 1, 25-(OH)2D levels than normal rats. Treating IR or T2DM rats with vitamin D had no effect on 25-(OH)D or 1, 25-(OH)2D. Administration of 1α-(OH)D significantly increased 1, 25-(OH)2D in IR rats to above-normal levels, and significantly increased 1, 25-(OH)2D in T2DM rats to normal levels. In IR or T2DM, abnormal vitamin D metabolism is characterized by 1, 25-(OH)2D deficiency and is related to renal injury.

Fructose consumption: potential mechanisms for its effects to increase visceral adiposity and induce dyslipidemia and insulin resistance

PURPOSE OF REVIEW

Based on interim results from an ongoing study, we have reported that consumption of a high-fructose diet, but not a high-glucose diet, promotes the development of three of the pathological characteristics associated with metabolic syndrome: visceral adiposity, dyslipidemia, and insulin resistance. From these results and a review of the current literature, we present two potential sequences of events by which fructose consumption may contribute to metabolic syndrome.

RECENT FINDINGS

The earliest metabolic perturbation resulting from fructose consumption is postprandial hypertriglyceridemia, which may increase visceral adipose deposition. Visceral adiposity contributes to hepatic triglyceride accumulation, novel protein kinase C activation, and hepatic insulin resistance by increasing the portal delivery of free fatty acids to the liver. With insulin resistance, VLDL production is upregulated and this, along with systemic free fatty acids, increase lipid delivery to muscle. It is also possible that fructose initiates hepatic insulin resistance independently of visceral adiposity and free fatty acid delivery. By providing substrate for hepatic lipogenesis, fructose may result in a direct lipid overload that leads to triglyceride accumulation, novel protein kinase C activation, and hepatic insulin resistance.

SUMMARY

Our investigation and future studies of the effects of fructose consumption may help to clarify the sequence of events leading to development of metabolic syndrome.

Liver fat in the metabolic syndrome

BACKGROUND

The liver, once fatty, overproduces components of the metabolic syndrome, such as glucose and lipids. The amount of liver fat in subjects with and without the metabolic syndrome has not been determined. It is unknown which clinically available markers best reflect liver fat content.

MEASUREMENTS

Components of the metabolic syndrome as defined by the International Diabetes Federation and liver fat content by proton magnetic resonance spectroscopy were measured in 271 nondiabetic subjects (162 women, 109 men). In addition, other features of insulin resistance (serum insulin, C-peptide), intraabdominal and sc fat by magnetic resonance imaging, and liver enzymes (serum alanine aminotransferase and serum aspartate aminotransferase) were measured.

RESULTS

Liver fat was 4-fold higher in subjects with [n = 116; median 8.2% (interquartile range 3.2-18.7%)] than without [n = 155; 2.0% (1.0-5.0%); P < 0.0001] the metabolic syndrome. This increase in liver fat remained significant after adjusting for age, gender, and body mass index. All components of the metabolic syndrome correlated with liver fat content. The best correlate was waist in both women (r = 0.59, P < 0.0001) and men (r = 0.56, P < 0.0001). Liver fat correlated significantly with serum alanine aminotransferase (r = 0.39, P < 0.0001 for women; r = 0.44, P < 0.0001 for men) and aspartate aminotransferase (r = 0.27, P = 0.0005 for women; r = 0.31, P = 0.0012 for men) concentrations. The best correlates of liver fat were fasting serum insulin (r = 0.61; P < 0.0001 for both women and men) and C-peptide (r = 0.62; P < 0.0001 for both women and men).

CONCLUSIONS

Liver fat content is significantly increased in subjects with the metabolic syndrome as compared with those without the syndrome, independently of age, gender, and body mass index. Of other markers, serum C-peptide is the strongest correlate of liver fat.

Ultrasound evaluation of visceral fat and metabolic risk factors during early pregnancy

OBJECTIVE

The objective was to study the relationships between ultrasound estimated visceral fat and metabolic risk factors during early pregnancy.

RESEARCH METHODS AND PROCEDURES

Thirty consecutive healthy pregnant women at 11 to 14 weeks of gestation were studied. Maximum subcutaneous fat thickness (SFT) and visceral fat thickness (VFT) were successfully measured by ultrasound. Fasting plasma glucose, insulin, triglycerides, total cholesterol, high-density lipoprotein cholesterol (HDL-C), and blood pressure were measured. Insulin resistance was calculated by using the homeostasis model assessment (HOMA).

RESULTS

VFT significantly correlated with diastolic blood pressure (r = 0.37, p = 0.04), glycemia (r = 0.37, p = 0.04), insulinemia (r = 0.59, p = 0.001) insulin sensitivity (HOMA; r = 0.59, p = 0.001), triglycerides (r = 0.58, p = 0.03), HDL-C (r = -0.39, p = 0.03), and total cholesterol/HDL-C ratio (p = 0.002), whereas SFT was significantly correlated with only diastolic blood pressure (p = 0.03). VFT better significantly correlated with the metabolic risk factors than pre-gestational BMI [r = 0.39, p = 0.03 for insulinemia, r = 0.42, p = 0.02 for insulin sensitivity (HOMA), and r = 0.49, p = 0.01 for triglycerides and not significant for the rest].

DISCUSSION

Visceral fat thickness can be easily measured by ultrasound at early pregnancy and correlates better than BMI with metabolic risk factors.

Physical activity in the treatment of obesity: beyond body weight reduction

The prevalence of obesity is high and continues to increase. Obesity is a leading risk factor for premature mortality and numerous chronic health conditions. The role of physical activity as a treatment and (or) preventive strategy for combating obesity has been the subject of substantial research. Most of this research has focused solely on reductions in total body weight and (or) fat mass as the indicator of treatment success. Because the deposition of fat in the abdomen and nonadipose tissues of the liver and muscle plays a major role in the development of obesity-related health risk, these depots have emerged as alternative targets for obesity treatment. Absent from previous reviews is a detailed consideration of the influence of physical activity on these treatment outcomes. The purpose of this review is to evaluate the independent role of physical activity in the treatment of obesity in a broader context; that is, through its effects on abdominal obesity and liver and muscle fat, in addition to its established effects on body weight and (or) total fat mass. Consideration is also given to the utility of physical activity with minimal or no weight loss in the treatment of obesity.

Relationships between estimates of adiposity, insulin resistance, and nonalcoholic fatty liver disease in a large group of nondiabetic Korean adults

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is emerging as a major health problem in parallel with an increasing prevalence of obesity. Insulin resistance and abdominal and overall adiposity are closely associated with NAFLD; however, the interplay between them in the relationship with NAFLD is unclear, especially in nondiabetic individuals.

RESEARCH DESIGN AND METHODS

Abdominal ultrasound, hepatitis serology, and measurements of fasting plasma insulin (FPI), lipid concentrations, overall obesity (BMI), and abdominal obesity (waist circumference) were performed in 56,249 Korean subjects.

RESULTS

After rigorous exclusion criteria, 36,654 nondiabetic subjects (54% male) were enrolled. Subjects were divided into control (no fatty liver on ultrasound, serum alanine aminotransferase [ALT] <30 units/l [men] or <19 units/l [women]), fatty liver with normal ALT (FL-NALT), and fatty liver with a high ALT (FL-HALT) groups. After adjusting for age, BMI, and waist circumference, FPI and ratio of triglycerides to HDL cholesterol (TG/HDL-C ratio) were significantly higher in the FL-NALT than in the control group and even higher in the FL-HALT group. Odds ratios for the presence of FL-HALT with increasing quartiles of FPI and TG/HDL-C ratio were increased five- to sevenfold over those of the control group, independent of age, BMI, and waist circumference.

CONCLUSIONS

In this large population of individuals of Korean ancestry, results indicate that while overall (BMI) and abdominal (waist circumference) overweight/obesity are associated with features of NAFLD, surrogate estimates of insulin resistance, FPI concentration, and TG/HDL-C ratio predict NAFLD independently of age, BMI, and waist circumference.

Adipose tissue inflammation and increased ceramide content characterize subjects with high liver fat content independent of obesity

OBJECTIVE

We sought to determine whether adipose tissue is inflamed in individuals with increased liver fat (LFAT) independently of obesity.

RESEARCH DESIGN AND METHODS

A total of 20 nondiabetic, healthy, obese women were divided into normal and high LFAT groups based on their median LFAT level (2.3 +/- 0.3 vs. 14.4 +/- 2.9%). Surgical subcutaneous adipose tissue biopsies were studied using quantitative PCR, immunohistochemistry, and a lipidomics approach to search for putative mediators of insulin resistance and inflammation. The groups were matched for age and BMI. The high LFAT group had increased insulin (P = 0.0025) and lower HDL cholesterol (P = 0.02) concentrations.

RESULTS

Expression levels of the macrophage marker CD68, the chemokines monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha, and plasminogen activator inhibitor-1 were significantly increased, and those of peroxisome proliferator-activated receptor-gamma and adiponectin decreased in the high LFAT group. CD68 expression correlated with the number of macrophages and crown-like structures (multiple macrophages fused around dead adipocytes). Concentrations of 154 lipid species in adipose tissue revealed several differences between the groups, with the most striking being increased concentrations of triacylglycerols, particularly long chain, and ceramides, specifically Cer(d18:1/24:1) (P = 0.01), in the high LFAT group. Expression of sphingomyelinases SMPD1 and SMPD3 were also significantly increased in the high compared with normal LFAT group.

CONCLUSIONS

Adipose tissue is infiltrated with macrophages, and its content of long-chain triacylglycerols and ceramides is increased in subjects with increased LFAT compared with equally obese subjects with normal LFAT content. Ceramides or their metabolites could contribute to adverse effects of long-chain fatty acids on insulin resistance and inflammation.

Postprandial lipemia associates with liver fat content

CONTEXT/OBJECTIVE

Postprandial lipemia and low adiponectin represent novel risk factors for vascular disease. This study aimed to determine whether liver fat content and adiponectin are predictors of postprandial triglyceride (TG)-rich lipoproteins (TRL).

PATIENTS/INTERVENTIONS

Twenty-nine men were allocated into subgroups with either low (< or =5%) or high (>5%) liver fat measured with magnetic resonance proton spectroscopy. Subjects underwent an oral fat tolerance test with measurements of postprandial TG, cholesterol, apolipoprotein B-48 (apoB-48), and apoB-100 in TRL fractions, a euglycemic hyperinsulinemic clamp, and determination of abdominal fat volumes by magnetic resonance imaging.

RESULTS

Subjects with high liver fat displayed increased response of postprandial lipids in plasma, chylomicron, and very-low-density lipoprotein 1 (VLDL1) (Svedberg flotation rate 60-400) fractions. Liver fat correlated positively with postprandial responses (area under the curve) of TG (r = 0.597; P = 0.001), cholesterol (r = 0.546; P = 0.002), apoB-48 (r = 0.556; P = 0.002), and apoB-100 (r = 0.42; P = 0.023) in the VLDL1 fraction. Respective incremental areas under the curve correlated significantly with liver fat. Fasting adiponectin levels were inversely correlated with both postprandial lipids and liver fat content. Liver fat remained the only independent correlate in a multiple linear regression analysis for chylomicron and VLDL1 responses.

CONCLUSIONS

Liver fat content is a close correlate of postprandial lipids predicting the responses of TRL in chylomicrons and VLDL1 better than measures of glucose metabolism or body adiposity. Low adiponectin concentration is closely linked to high liver fat content and impaired TRL metabolism. High liver fat content associated with postprandial lipemia represents potential risk factors for cardiovascular disease.

Lifestyle intervention in individuals with normal versus impaired glucose tolerance

BACKGROUND

Lifestyle intervention is effective in the prevention of type 2 diabetes in individuals with impaired glucose tolerance (IGT). It is currently unknown whether it has beneficial effects on metabolism to a similar extent, in individuals with normal glucose tolerance (NGT) compared to individuals with IGT.

MATERIALS AND METHODS

Data from 181 subjects (133 with NGT and at risk for type 2 diabetes and 48 with IGT) who participated in the Tuebingen Lifestyle Intervention Program with increase in physical activity and decrease in caloric intake were included into this study. Body fat distribution was quantified by whole-body magnetic resonance (MR) tomography and liver fat and intramyocellular fat by (1)H-MR spectroscopy. Insulin sensitivity was estimated from an oral glucose tolerance test (OGTT).

RESULTS

After 9 +/- 2 months of follow-up, the diagnosis of IGT was reversed in 24 out of 48 individuals. Only 14 out of 133 participants with NGT developed IGT. Body weight decreased in both groups by 3% (both P < 0.0001). Two-hour glucose concentrations during an OGTT decreased in individuals with IGT (-14%, P < 0.0001) but not with NGT (+2%, P = 0.66). Insulin sensitivity increased both in individuals with IGT (+9%, P = 0.04) and NGT (+17%, P < 0.0001). Visceral fat (-8%, P = 0.006), liver fat (-28%, P < 0.0001) and intramyocellular fat (-15%, P = 0.006) decreased in participants with IGT. In participants with NGT these changes were significant for visceral fat (-16%, P < 0.0001) and liver fat (-35%, P < 0.0001).

CONCLUSIONS

Moderate weight loss under a lifestyle intervention with reduction in total, visceral and ectopic fat and increase in insulin sensitivity improves glucose tolerance in individuals with IGT but not with NGT. In individuals with NGT, the beneficial effects of a lifestyle intervention on fat distribution and insulin sensitivity possibly prevent future deterioration in glucose tolerance.

Independent associations between liver fat, visceral adipose tissue, and metabolic risk factors in men

The independent associations between liver fat, visceral adipose tissue (AT), and metabolic risk factors are unclear. Although it has been reported that visceral AT is the strongest predictor of metabolic risk, liver fat has also been reported as a strong independent associate of a deleterious metabolic profile. We examined the independent associations between liver fat, visceral AT, and metabolic risk factors in a sample of 293 men varying widely in adiposity. Liver fat and abdominal AT were measured by computed tomography (CT). Univariate analysis revealed that liver fat was associated (p < 0.05) with triglycerides (TG), systolic blood pressure (SBP), and total cholesterol (TC), but not with glucose or high-density lipoprotein cholesterol (HDLC). Liver fat remained a significant correlate (p < 0.05) of TG and TC after control for age and subcutaneous AT or cardiorespiratory fitness (CRF), but not after adjustment for visceral AT alone. Conversely, visceral AT remained significantly associated with TG, SBP, glucose, HDLC (p < 0.01), and TC (p = 0.05) independent of liver fat, subcutaneous AT, CRF, and age. Both liver fat and visceral AT were associated with metabolic risk in men. However, when controlled for each other, visceral AT was the only independent associate of metabolic risk.

Body mass index and hip and thigh circumferences are negatively associated with visceral adipose tissue after control for waist circumference

BACKGROUND

Waist circumference (WC) is positively associated with morbidity and mortality with or without control for hip circumference (HC) or body mass index (BMI; in kg/m(2)). This association is thought to be explained by an expanded visceral adipose tissue (VAT) depot. Conversely, HC and BMI are negatively associated with morbidity and mortality after control for WC. Whether this inverse association is explained in part by the ability of HC and BMI to identify subjects with increased subcutaneous adipose tissue (SAT), increased skeletal muscle (SM) mass, or decreased VAT after control for WC is unclear.

OBJECTIVE

We examined the independent associations between WC, HC, thigh circumference (ThC), and BMI with VAT and total, lower-body, and abdominal SAT and SM.

DESIGN

Total and regional body composition were measured in 256 white men and women with magnetic resonance imaging.

RESULTS

WC, HC, ThC, and BMI were all positively correlated with total, lower-body, and abdominal SAT and SM and with VAT. After statistical control for WC, HC, ThC, and BMI remained positively associated with total, lower-body, and abdominal SAT and SM (men only) but were negatively associated with VAT (P < 0.05). HC (P < 0.05) but not BMI (P > 0.10) or ThC (P = 0.06) remained negatively associated with VAT after further control for age.

CONCLUSIONS

HC, ThC, and BMI are positively associated with total, lower-body, and abdominal SAT and SM but negatively associated with VAT after control for WC. However, only HC remained negatively associated with VAT after control for age and WC.

Serum alanine aminotransferase levels decrease further with carbohydrate than fat restriction in insulin-resistant adults

OBJECTIVE

Although weight loss interventions have been shown to reduce steatosis in nonalcoholic fatty liver disease (NAFLD), the impact of dietary macronutrient composition is unknown. We assessed the effect on serum alanine aminotransferase (ALT) concentrations of two hypocaloric diets varying in amounts of carbohydrate and fat in obese insulin-resistant individuals, a population at high risk for NAFLD.

RESEARCH DESIGN AND METHODS

Post hoc analysis of ALT concentrations was performed in 52 obese subjects with normal baseline values and insulin resistance, as quantified by the steady-state plasma glucose (SSPG) test, who were randomized to hypocaloric diets containing either 60% carbohydrate/25% fat or 40% carbohydrate/45% fat (15% protein) for 16 weeks. The primary end point was change in ALT, which was evaluated according to diet, weight loss, SSPG, and daylong insulin concentrations.

RESULTS

Although both diets resulted in significant decreases in weight and SSPG, daylong insulin, and serum ALT concentrations, the 40% carbohydrate diet resulted in greater decreases in SSPG (P < 0.04), circulating insulin (P < 0.01), and ALT (9.5 +/- 9.4 vs. 4.2 +/- 8.3 units/l; P < 0.04) concentrations. ALT changes correlated with improvement in insulin sensitivity (P = 0.04) and daylong insulin (P < 0.01). Individuals with ALT concentrations above the proposed upper limits experienced significant declines in ALT, unlike those with lower ALT levels.

CONCLUSIONS

In a population at high risk for NAFLD, a hypocaloric diet moderately lower in carbohydrate decreased serum ALT concentrations to a greater degree than a higher-carbohydrate/low-fat diet, despite equal weight loss. This may result from a relatively greater decline in daylong insulin concentrations. Further research with histological end points is needed to further explore this finding.

Review: The role of insulin resistance in nonalcoholic fatty liver disease

CONTEXT

Insulin resistance is an almost universal finding in nonalcoholic fatty liver disease (NAFLD). This review outlines the evidence linking insulin resistance and NAFLD, explores whether liver fat is a cause or consequence of insulin resistance, and reviews the current evidence for treatment of NAFLD.

EVIDENCE ACQUISITION

Evidence from epidemiological, experimental, and clinical research studies investigating NAFLD and insulin resistance was reviewed.

EVIDENCE SYNTHESIS

Insulin resistance in NAFLD is characterized by reductions in whole-body, hepatic, and adipose tissue insulin sensitivity. The mechanisms underlying the accumulation of fat in the liver may include excess dietary fat, increased delivery of free fatty acids to the liver, inadequate fatty acid oxidation, and increased de novo lipogenesis. Insulin resistance may enhance hepatic fat accumulation by increasing free fatty acid delivery and by the effect of hyperinsulinemia to stimulate anabolic processes. The impact of weight loss, metformin, and thiazolidinediones, all treatments aimed at improving insulin sensitivity, as well as other agents such as vitamin E, have been evaluated in patients with NAFLD and have shown some benefit. However, most intervention studies have been small and uncontrolled.

CONCLUSION

Insulin resistance is a major feature of NAFLD that, in some patients, can progress to steatohepatitis. Treatments aimed at reducing insulin resistance have had some success, but larger placebo-controlled studies are needed to fully establish the efficacy of these interventions and possibly others in reducing the deleterious effects of fat accumulation in the liver.

Mechanisms of Disease: hepatic steatosis in type 2 diabetes--pathogenesis and clinical relevance

Hepatic steatosis is defined by an increased content of hepatocellular lipids (HCLs) and is frequently observed in insulin-resistant states including type 2 diabetes mellitus. A dietary excess of saturated fat contributes significantly to HCL accumulation. Elevated HCL levels mainly account for hepatic insulin resistance, which is probably mediated by partitioning of free fatty acids to the liver (fat overflow) and by an imbalance of adipocytokines (decreased adiponectin and/or increased proinflammatory cytokines). Both free fatty acids and adipocytokines activate inflammatory pathways that include protein kinase C, the transcription factor nuclear factor kappaB, and c-Jun N-terminal kinase 1 and can thereby accelerate the progression of hepatic steatosis to nonalcoholic steatohepatitis and cirrhosis. Proton magnetic resonance spectroscopy has made it possible to quantify HCL concentrations and to detect even small changes in these concentrations in clinical settings. Moderately hypocaloric, fat-reduced diets can decrease HCL levels by approximately 40-80% in parallel with loss of up to 8% of body weight. Treatment with thiazolidinediones (e.g. pioglitazone and rosiglitazone) reduces HCL levels by 30-50% by modulating insulin sensitivity and endocrine function of adipose tissue in type 2 diabetes. Metformin improves hepatic insulin action without affecting HCL levels, whereas insulin infusion for 67 h increases HCL levels by approximately 18%; furthermore, HCL levels positively correlate with the insulin dosage in insulin-treated type 2 diabetes. In conclusion, liver fat is a critical determinant of metabolic fluxes and inflammatory processes, thereby representing an important therapeutic target in insulin resistance and type 2 diabetes mellitus.

Effect of calorie restriction with or without exercise on insulin sensitivity, beta-cell function, fat cell size, and ectopic lipid in overweight subjects

OBJECTIVE

The purpose of this article was to determine the relationships among total body fat, visceral adipose tissue (VAT), fat cell size (FCS), ectopic fat deposition in liver (intrahepatic lipid [IHL]) and muscle (intramyocellular lipid [IMCL]), and insulin sensitivity index (S(i)) in healthy overweight, glucose-tolerant subjects and the effects of calorie restriction by diet alone or in conjunction with exercise on these variables.

RESEARCH DESIGN AND METHODS

Forty-eight overweight volunteers were randomly assigned to four groups: control (100% of energy requirements), 25% calorie restriction (CR), 12.5% calorie restriction +12.5% energy expenditure through structured exercise (CREX), or 15% weight loss by a low-calorie diet followed by weight maintenance for 6 months (LCD). Weight, percent body fat, VAT, IMCL, IHL, FCS, and S(i) were assessed at baseline and month 6.

RESULTS

At baseline, FCS was related to VAT and IHL (P < 0.05) but not to IMCL. FCS was also the strongest determinant of S(i) (P < 0.01). Weight loss at month 6 was 1 +/- 1% (control, mean +/- SE), 10 +/- 1% (CR), 10 +/- 1% (CREX), and 14 +/- 1% (LCD). VAT, FCS, percent body fat, and IHL were reduced in the three intervention groups (P < 0.01), but IMCL was unchanged. S(i) was increased at month 6 (P = 0.05) in the CREX (37 +/- 18%) and LCD (70 +/- 34%) groups (P < 0.05) and tended to increase in the CR group (40 +/- 20%, P = 0.08). Together the improvements in S(i) were related to loss in weight, fat mass, and VAT, but not IHL, IMCL, or FCS.

CONCLUSIONS

Large adipocytes lead to lipid deposition in visceral and hepatic tissues, promoting insulin resistance. Calorie restriction by diet alone or with exercise reverses this trend.

Visceral fat is an independent predictor of all-cause mortality in men

OBJECTIVE

To examine the independent associations of abdominal fat (visceral and subcutaneous) and liver fat with all-cause mortality.

RESEARCH METHODS AND PROCEDURES

Participants included 291 men [97 decedents and 194 controls; mean age, 56.4 +/- 12.0 (SD) years] who received a computed tomography (CT) examination at the preventive medicine clinic in Dallas, TX, between 1995 and 1999, with a mean mortality follow-up of 2.2 +/- 1.3 years. Abdominal fat was determined using contiguous CT images from the L3-L4 to L4-L5 intervertebral space. Liver fat was assessed using the CT-determined liver attenuation value, which is inversely related to liver fat. Logistic regression was used to determine the independent association between the fat depots and all-cause mortality.

RESULTS

During the study, there were 97 deaths. Visceral fat [odds ratio (OR) per SD: 1.83; 95% CI: 1.23 to 2.73], abdominal subcutaneous fat (1.44; 1.02 to 2.03), liver fat (0.64; 0.46 to 0.87), and waist circumference (1.41; 1.01 to 1.98) were significant individual predictors of mortality after controlling for age and length of follow-up. In a model including all three fat measures (subcutaneous, visceral, and liver fat), age, and length of follow-up, only visceral fat (1.93; 1.15 to 3.23) was a significant predictor of mortality.

DISCUSSION

Visceral fat is a strong, independent predictor of all-cause mortality in men.

New imaging techniques of fat, muscle and liver within the context of determining insulin sensitivity

Body fat distribution and ectopic fat deposition are important determinants of insulin sensitivity. Fat deposition in muscle and the liver, in particular, has been found to impair insulin signalling in these insulin-sensitive tissues. Thus, exact quantification of fat content may help to distinguish between different sites of insulin resistance. Increased fat deposition in the visceral compartment compared with the subcutaneous depot also represents an important factor leading to insulin resistance. Recent data clearly showed that visceral fat is a strong determinant of liver fat content. Exact quantification of fat distribution by magnetic resonance imaging and magnetic resonance spectroscopy may help to define distinct 'fat-distribution phenotypes'. This may allow a search for new candidate genes for type 2 diabetes mellitus and identify, at an early stage, individuals at risk for decline in insulin sensitivity.

Non-esterified fatty acid concentrations are independently associated with hepatic steatosis in obese subjects

AIMS/HYPOTHESIS

We tested the hypothesis that NEFA concentrations are higher in obese subjects with fatty liver than in obese subjects without fatty liver.

MATERIALS AND METHODS

We recruited 22 obese (BMI>30 kg/m(2)) men aged 42-64 years, in whom liver fat was assessed by ultrasound and classified into categories of no, mild to moderate and severe fatty liver by two independent radiologists. Regional and visceral abdominal fat were assessed by dual-energy X-ray absorptiometry and magnetic resonance imaging, and endogenous glucose production, whole-body glucose disposal during an insulin clamp, and NEFA concentrations were measured, along with NEFA suppression (percent (%) suppression and insulin sensitivity index for NEFA during an OGTT).

RESULTS

Seven subjects had no evidence of fatty liver, nine had mild or moderate fatty liver and six had severe fatty liver. The amount of visceral fat was not associated with the degree of fatty liver. Whole-body glucose disposal was inversely associated with fatty liver (38.4, 26.5 and 23.9 mumol kg(-1) min(-1) for the groups with no fatty liver, mild to moderate fatty liver and severe fatty liver, respectively, p=0.004). NEFA suppression during the OGTT was decreased (62.5, 50.8 and 41%, p=0.03, for no, mild to moderate, and severe fatty liver, respectively) and the insulin sensitivity index for NEFA was decreased (0.80, 0.40 and 0.34, p<0.0001). Regression modelling suggested that NEFA concentrations were associated with fatty liver independently of whole-body glucose production and disposal measurements.

CONCLUSIONS/INTERPRETATION

In obese men, NEFA concentrations during an OGTT are associated with fatty liver independently of classic measures of insulin sensitivity determined by the hyperinsulinaemic clamp. The contribution to this association by factors regulating NEFA concentrations requires further study.

Acute inhibition of lipolysis does not affect postprandial suppression of endogenous glucose production

To test the hypothesis that intrahepatic availability of fatty acid could modify the rate of suppression of endogenous glucose production (EGP), acipimox or placebo was administered before and during a test meal. We used a modified isotopic methodology to measure EGP in 11 healthy subjects, and (1)H magnetic resonance spectroscopic measurement of hepatic triglyceride stores was also undertaken. Acipimox suppressed plasma free fatty acids markedly before the meal (0.05 +/- 0.01 mmol/l at -10 min, P = 0) and throughout the postprandial period (0.03 +/- 0.01 mmol/l at 150 min). Mean peak plasma glucose was significantly lower after the meal on acipimox days (8.9 +/- 0.4 vs. 10.1 +/- 0.5 mmol/l, P < 0.01), as was mean peak serum insulin (653.1 +/- 99.9 vs. 909 +/- 118 pmol/l, P < 0.01). Fasting EGP was similar (11.15 +/- 0.58 micromol.kg(-1).min(-1) placebo vs. 11.17 +/- 0.89 mg.kg(-1).min(-1) acipimox). The rate of suppression of EGP after the meal was almost identical on the 2 test days (4.36 +/- 1.52 vs. 3.69 +/- 1.21 micromol.kg(-1).min(-1) at 40 min). There was a significant negative correlation between the acipimox-induced decrease in peak plasma glucose and liver triglyceride content (r = -0.827, P = 0.002), suggesting that, when levels of liver fat were low, inhibition of lipolysis was able to affect glucose homeostasis. Acute pharmacological sequestration of fatty acids in triglyceride stores improves postprandial glucose homeostasis without effect on the immediate postprandial suppression of EGP.

Fatty acids and insulin resistance in muscle and liver

Free fatty acids (FFAs) circulate round the body and represent important nutrients and the key oxidative fuel for the heart and resting skeletal muscle. In addition, FFAs are thought to be potent signalling molecules. Growing evidence indicates that FFAs may be involved in type 2 diabetes mellitus and obesity by mediating insulin resistance. In 1963, it was postulated that accumulated glucose-6-phosphate as a result of increased FFA oxidation leads to decreased glucose uptake. An alternative hypothesis is that increased concentrations of plasma FFA induce insulin resistance in humans through inhibition of glucose transport activity, which appears to be a consequence of decreased insulin receptor substrate-1-associated phosphatidyl inositol 3 kinase activity. Moreover, FFAs can arise locally, and increased intramyocellular and hepatocellular lipids have been shown to be associated with insulin resistance. This paper reviews the main aspects of FFA metabolism in the development of insulin resistance in skeletal muscle and liver, as well as the role of ectopic lipid deposits as a local source of FFAs. Finally, the role of thiazolidinediones as modulators of FFA-induced insulin resistance will be discussed.

Insulin resistance: a metabolic pathway to chronic liver disease

Insulin resistance (IR) is the pathophysiological hallmark of nonalcoholic fatty liver disease (NAFLD), one of the most common causes of chronic liver disease in Western countries. We review the definition of IR, the methods for the quantitative assessment of insulin action, the pathophysiology of IR, and the role of IR in the pathogenesis of chronic liver disease. Increased free fatty acid flux from adipose tissue to nonadipose organs, a result of abnormal fat metabolism, leads to hepatic triglyceride accumulation and contributes to impaired glucose metabolism and insulin sensitivity in muscle and in the liver. Several factors secreted or expressed in the adipocyte contribute to the onset of a proinflammatory state, which may be limited to the liver or more extensively expressed throughout the body. IR is the common characteristic of the metabolic syndrome and its related features. It is a systemic disease affecting the nervous system, muscles, pancreas, kidney, heart, and immune system, in addition to the liver. A complex interaction between genes and the environment favors or enhances IR and the phenotypic expression of NAFLD in individual patients. Advanced fibrotic liver disease is associated with multiple features of the metabolic syndrome, and the risk of progressive liver disease should not be underestimated in individuals with metabolic disorders. Finally, the ability of insulin-sensitizing, pharmacological agents to treat NAFLD by reducing IR in the liver (metformin) and in the periphery (thiazolidinediones) are discussed.

Polymorphisms in the gene encoding adiponectin receptor 1 are associated with insulin resistance and high liver fat

AIMS/HYPOTHESIS

The adipokine adiponectin has insulin-sensitising, anti-atherogenic and anti-inflammatory properties. Recently, the genes for mouse and human adiponectin receptor-1 (ADIPOR1) and -2 (ADIPOR2) have been cloned. The aim of this study was to investigate whether genetic variants of the genes encoding ADIPOR1 and ADIPOR2 play a role in human metabolism.

MATERIALS AND METHODS

We screened ADIPOR1 and ADIPOR2 for polymorphisms and determined their association with glucose metabolism, lipid metabolism, an atherogenic lipid profile and inflammatory markers in 502 non-diabetic subjects. A subgroup participated in a longitudinal study; these subjects received diet counselling and increased their physical activity.

RESULTS

We identified six variants of ADIPOR1 and seven variants of ADIPOR2. A single-nucleotide polymorphism (SNP) in the putative promoter region 8503 bp upstream of the translational start codon (-8503 G/A) of ADIPOR1 (frequency of allele A=0.31) was in almost complete linkage disequilibrium with another SNP (-1927 T/C) in intron 1. Subjects carrying the -8503 A and -1927 C alleles had lower insulin sensitivity, as estimated from a 75 g OGTT (p=0.04) and determined during a euglycaemic clamp (n=295, p=0.04); they also had higher HbA(1)c levels (p=0.02) and, although the difference was not statistically significant, higher liver fat (n=85, determined by proton magnetic resonance spectroscopy, p=0.056) (all p values are adjusted for age, sex and percentage of body fat). In the longitudinal study (n=45), the -8503 A and -1927 C alleles were associated with lower insulin sensitivity (p=0.03) and higher liver fat (p=0.02) at follow-up compared with the -8503 G and -1927 T alleles, independently of basal measurements, sex and baseline and follow-up percentage of body fat.

CONCLUSIONS/INTERPRETATION

The present findings suggest that the -8503 G/A SNP in the promoter or the -1927 T/C SNP in intron 1 of ADIPOR1 may affect insulin sensitivity and liver fat in humans.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

Acquired obesity is associated with increased liver fat, intra-abdominal fat, and insulin resistance in young adult monozygotic twins

We determined whether acquired obesity is associated with increases in liver or intra-abdominal fat or impaired insulin sensitivity by studying monozygotic (MZ) twin pairs discordant and concordant for obesity. We studied nineteen 24- to 27-yr-old MZ twin pairs, with intrapair differences in body weight ranging from 0.1 to 24.7 kg [body mass index (BMI) range 20.0-33.9 kg/m2], identified from a population-based FinnTwin16 sample. Fat distribution was determined by magnetic resonance imaging, percent body fat by dual-energy X-ray absorptiometry, liver fat by proton spectroscopy, insulin sensitivity by measuring the fasting insulin concentration, and whole body insulin sensitivity by the euglycemic insulin clamp technique. Intrapair differences in BMI were significantly correlated with those in intra-abdominal fat (r = 0.82, P < 0.001) and liver fat (r = 0.57, P = 0.010). Intrapair differences in fasting insulin correlated with those in subcutaneous abdominal (r = 0.60, P = 0.008), intra-abdominal (r = 0.75, P = 0.0001) and liver (r = 0.49, P = 0.048) fat. Intrapair differences in whole body insulin sensitivity correlated with those in subcutaneous abdominal (r = -0.72, P = 0.001) and intra-abdominal (r = -0.55, P = 0.015) but not liver (r = -0.20, P = 0.20) fat. We conclude that acquired obesity is associated with increases in intra-abdominal and liver fat and insulin resistance, independent of genetic factors.

Gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is defined as glucose intolerance of various degrees that is first detected during pregnancy. GDM is detected through the screening of pregnant women for clinical risk factors and, among at-risk women, testing for abnormal glucose tolerance that is usually, but not invariably, mild and asymptomatic. GDM appears to result from the same broad spectrum of physiological and genetic abnormalities that characterize diabetes outside of pregnancy. Indeed, women with GDM are at high risk for having or developing diabetes when they are not pregnant. Thus, GDM provides a unique opportunity to study the early pathogenesis of diabetes and to develop interventions to prevent the disease.

The role of glucocorticoid action in the pathophysiology of the Metabolic Syndrome

Glucocorticoids are stress hormones that modulate a large number of physiological actions involved in metabolic, inflammatory, cardiovascular and behavioral processes. The molecular mechanisms and the physiological effects of glucocorticoids have been extensively studied. However, the involvement of glucocorticoid action in the etiology of the Metabolic Syndrome has not been well appreciated. Recently, accumulating clinical evidence and animal genetics studies have attracted growing interest in the role of glucocorticoid action in obesity and insulin resistance. This review will discuss the metabolic effects in the context of glucocorticoid metabolism and establish the association of glucocorticoid action with the features of the Metabolic Syndrome, especially obesity and insulin resistance. Special discussions will be focused on corticosteroid-binding globulin and 11beta-hydroxysteroid dehydrogenase type 1, two proteins that mediate glucocorticoid action and have been implicated in the Metabolic Syndrome. Due to the complexities of the glucocorticoid biology and the Metabolic Syndrome and limited space, this review is only intended to provide a general link between the two areas with broad rather than in-depth discussions of clinical, pharmacological and genetic findings.

Low subcutaneous thigh fat is a risk factor for unfavourable glucose and lipid levels, independently of high abdominal fat. The Health ABC Study

AIMS

We investigated whether low subcutaneous thigh fat is an independent risk factor for unfavourable glucose and lipid levels, and whether these associations differ between sexes, and between white and black adults. Our secondary aim was to investigate which body composition characteristics (lean tissue, fat tissue) are reflected by anthropometric measures (waist and thigh circumference).

METHODS

Anthropometric measurements and computed tomography of the abdomen and of the thigh were performed for all participants of the Health, Aging and Body Composition Study, who were aged 70-79 years. Fasting glucose, triglycerides and HDL-cholesterol, and 2-h postload glucose were determined.

RESULTS

After excluding those already diagnosed with diabetes or dyslipidaemia, we analysed data from 2,106 participants. After adjustment for abdominal subcutaneous and visceral fat, and intermuscular thigh fat, larger thigh subcutaneous fat area was statistically significantly associated with lower ln-transformed triglycerides [standardised beta (95% CI) -0.12 (-0.20 to -0.04) in men and -0.13 (-0.21 to -0.05) in women] and higher ln-HDL-cholesterol [0.10 (0.02 to 0.19) and 0.09 (0.01 to 0.18), respectively]. The associations with lower glucose levels were strong in men [-0.11 (-0.20 to -0.02) for fasting and -0.14 (-0.23 to -0.05) for postload glucose], but not statistically significant in women [-0.02 (-0.10 to 0.07) and -0.04 (-0.13 to 0.05), respectively]. There were no differences in the associations between white and black persons. Waist circumference was more strongly associated with abdominal subcutaneous fat, and this association became stronger with increasing BMI, whereas the association with visceral fat became weaker. Thigh circumference was equally dependent on thigh fat and thigh muscle in men, whereas in women the fat component was the main contributor.

CONCLUSION

Larger subcutaneous thigh fat is independently associated with more favourable glucose (in men) and lipid levels (in both sexes) after accounting for abdominal fat depots, which are associated with unfavourable glucose and lipid levels. Anthropometric measures reflect different fat depots at different levels of BMI at the abdomen, and reflect both fat and lean tissue at the thigh. These results emphasise the importance of accurate measures of regional body composition when investigating potential health risks.

Magnetic resonance spectroscopy to measure hepatic triglyceride content: prevalence of hepatic steatosis in the general population

Despite the increasing prevalence of nonalcoholic fatty liver disease (NAFLD), the criteria used to diagnose the disorder remain poorly defined. Localized proton magnetic resonance spectroscopy (MRS) accurately measures hepatic triglyceride content (HTGC) but has been used only in small research studies. Here, MRS was used to analyze the distribution of HTGC in 2,349 participants from the Dallas Heart Study (DHS). The reproducibility of the procedure was validated by showing that duplicate HTGC measurements were high correlated (r = 0.99, P < 0.001) and that the coefficient of variation between measurements was low (8.5%). Intake of a high-fat meal did not significantly affect the measurements, and values were similar when measurements were made from the right and left hepatic lobes. To determine the "upper limit of normal" for HTGC, the distribution of HTGC was examined in the 345 subjects from the DHS who had no identifiable risk factors for hepatic steatosis (nonobese, nondiabetic subjects with minimal alcohol consumption, normal liver function tests, and no known liver disease). The 95th percentile of HTGC in these subjects was 5.56%, which corresponds to a hepatic triglyceride level of 55.6 mg/g. With this value as a cutoff, the prevalence of hepatic steatosis in Dallas County was estimated to be 33.6%. Thus MRS provides a sensitive, quantitative, noninvasive method to measure HTGC and, when applied to a large urban US population, revealed a strikingly high prevalence of hepatic steatosis.

Fat in the liver and insulin resistance

Insulin resistance in humans is not always accompanied by obesity, since severe insulin resistance also characterizes patients lacking subcutaneous fat such as those with HAART- (highly-active antiretroviral therapy)-associated lipodystrophy. Both obese and lipodystrophic patients, however, have an increase in the amount of fat hidden in the liver. Liver fat content can be accurately quantified non-invasively by proton magnetic resonance spectroscopy. It is closely correlated with fasting insulin concentrations and direct measures of hepatic insulin sensitivity while the amount of subcutaneous adipose tissue is not. An increase in liver fat content has been shown to predict type 2 diabetes, independently of other cardiovascular risk factors. This is easily explained by the fact that the liver, once fatty, overproduces most of the known cardiovascular risk factors such as very low density lipoprotein (VLDL), glucose, C-reactive protein (CRP), plasminogen activator inhibitor-1 (PAI-1), fibrinogen and coagulation factors. The causes of inter-individual variation in liver fat content, independent of obesity, are largely unknown but could involve differences in signals from adipose tissue such as in the amount of adiponectin produced and differences in fat intake. Adiponectin deficiency characterizes both lipodystrophic and obese insulin-resistant individuals, and serum levels correlate with liver fat content. Liver fat content can be decreased by weight loss and by a low as compared to a high fat diet. In addition, treatment of both lipodystrophic and type 2 diabetic patients with peroxisome proliferators activator receptor-gamma (PPARgamma) agonists, but not metformin, decreases liver fat and markedly increases adiponectin levels. The fatty liver may help to explain why some but not all obese individuals are insulin resistant and why even lean individuals may be insulin resistant, and thereby at risk of developing type 2 diabetes and cardiovascular disease.

Alterations in postprandial hepatic glycogen metabolism in type 2 diabetes

Decreased skeletal muscle glucose disposal and increased endogenous glucose production (EGP) contribute to postprandial hyperglycemia in type 2 diabetes, but the contribution of hepatic glycogen metabolism remains uncertain. Hepatic glycogen metabolism and EGP were monitored in type 2 diabetic patients and nondiabetic volunteer control subjects (CON) after mixed meal ingestion and during hyperglycemic-hyperinsulinemic-somatostatin clamps applying 13C nuclear magnetic resonance spectroscopy (NMRS) and variable infusion dual-tracer technique. Hepatocellular lipid (HCL) content was quantified by 1H NMRS. Before dinner, hepatic glycogen was lower in type 2 diabetic patients (227 +/- 6 vs. CON: 275 +/- 10 mmol/l liver, P < 0.001). After meal ingestion, net synthetic rates were 0.76 +/- 0.16 (type 2 diabetic patients) and 1.36 +/- 0.15 mg x kg(-1) x min(-1) (CON, P < 0.02), resulting in peak concentrations of 283 +/- 15 and 360 +/- 11 mmol/l liver. Postprandial rates of EGP were approximately 0.3 mg x kg(-1) x min(-1) (30-170 min; P < 0.05 vs. CON) higher in type 2 diabetic patients. Under clamp conditions, type 2 diabetic patients featured approximately 54% lower (P < 0.03) net hepatic glycogen synthesis and approximately 0.5 mg x kg(-1) x min(-1) higher (P < 0.02) EGP. Hepatic glucose storage negatively correlated with HCL content (R = -0.602, P < 0.05). Type 2 diabetic patients exhibit 1) reduction of postprandial hepatic glycogen synthesis, 2) temporarily impaired suppression of EGP, and 3) no normalization of these defects by controlled hyperglycemic hyperinsulinemia. Thus, impaired insulin sensitivity and/or chronic glucolipotoxicity in addition to the effects of an altered insulin-to-glucagon ratio or increased free fatty acids accounts for defective hepatic glycogen metabolism in type 2 diabetic patients.

Determination of Maternal Body Composition in Pregnancy and Its Relevance to Perinatal Outcomes

Three models and 10 specific methods for determining maternal body composition are discussed and their perinatal relevance reviewed. English language publications (1950 to January 2004) were searched electronically and by hand. Search terms included "body composition," "human," " pregnancy," "obesity," "adiposity," "regional," "2-, 3-, 4-component," "truncal," "peripheral," "central," "visceral" along with specific techniques and outcomes listed subsequently. Three models of body composition are described: 2-component being fat and fat-free mass; 3-component being fat, water, and protein; and 4-component being fat, water, protein, and osseous mineral. Ten techniques of body composition assessment are described: 1) anthropometric techniques including skinfold thicknesses and waist-hip ratio; 2) total body water (isotopically labeled); 3) hydrodensitometry (underwater weighing); 4) air-displacement plethysmography; 5) bio-impedance analysis (BIA); 6) total body potassium (TBK); 7) dual-energy x-ray absorptiometry (DEXA); 8) computed tomography (CT); 9) magnetic resonance imaging (MRI); and 10) ultrasound (USS). Most methods estimate total adiposity. Regional fat distribution-central (truncal) compared with peripheral (limb) or visceral compared with subcutaneous-is important because of regional variation in adipocyte metabolism. Skinfolds, DEXA, CT, MRI, or USS can distinguish central from peripheral fat. CT, MRI, or USS can further subdivide central fat into visceral and subcutaneous. Perinatal outcomes examined in relation to body composition include pregnancy duration, birth weight, congenital anomalies, gestational diabetes, gestational hypertension, and the fetal origins of adult disease. A few studies suggest that central compared with peripheral fat correlates better with birth weight, gestational carbohydrate intolerance, and hypertension. Means of accurately assessing maternal body composition remain cumbersome and impractical, but may more accurately predict perinatal outcomes than traditional assessments such as maternal weight.