Plasma leptin concentrations in Pima Indians living in drastically different environments

Rules for body fat interventions based on an operating point mechanism

Interventions to reduce fat are important for human health. However, they can have opposing effects such as exercise that decreases fat but increases food intake, or coherent effects such as leptin resistance which raises both. Furthermore, some interventions show an overshoot in food intake, such as recovery from a diet, whereas others do not. To explain these properties we present a graphical framework called the operating point model, based on leptin control of feeding behavior. Steady-state fat and food intake is given by the intersection of two experimental curves - steady-state fat at a given food intake and ad libitum food intake at a given fat level. Depending on which curve an intervention shifts, it has opposing or coherent effects with or without overshoot, in excellent agreement with rodent data. The model also explains the quadratic relation between leptin and fat in humans. These concepts may guide the understanding of fat regulation disorders.

Non-hematopoietic effects of endogenous erythropoietin on lean mass and body weight regulation

OBJECTIVE

To investigate the concurrent relationships between human plasma erythropoietin concentrations and energy expenditure (EE), body composition, plasma leptin concentrations, and associations with weight change.

METHODS

Plasma to measure erythropoietin and leptin; data for body composition; 24-h EE measured in a whole-room calorimeter; and 75 g oral glucose tolerance testing were available from 109 full-heritage Pima Indians (55% male) from a larger study designed to understand the causes of obesity. Seventy-nine subjects had data for weight at a later visit (mean follow-up = 4.3 ± 1.9 years) to calculate percent weight change per year.

RESULTS

Erythropoietin, adjusted for covariates, correlated with 24-h EE (r = 0.26, P = 0.007), sleeping EE (r = 0.29, P = 0.003), fat-free mass (r = 0.19, P = 0.05), and fat mass (r = 0.27, P = 0.005), but not insulin or glucose measures. The association of erythropoietin with 24-h EE was fully mediated by fat-free mass. Erythropoietin associated with leptin in women (ρ = 0.36, P = 0.01), but not in men (P = 0.9), independently from fat mass. The association of erythropoietin with percent weight change per year was in opposing directions (interaction: P = 0.002) in males (r = -0.35, P = 0.02) versus females (r = 0.37, P = 0.02).

CONCLUSIONS

Non-hematopoietic endogenous erythropoietin action may be involved in body weight regulation in opposing directions in men and women, i.e., weight loss in men and weight gain in women.

High-Risk Populations: The Pimas of Arizona and Mexico

The purpose of this review is first, to broadly summarize the long-term commitment that began in 1965 to studying type 2 diabetes and obesity through the cooperation of the Pima Indians of Arizona, and second, to discuss the investigations with the Pima Indians of Mexico that started in 1991. The later studies emphasize gene-environment interactions in the pathogenesis of these metabolic disorders. Through the participation of both groups of Pimas, the researchers made key findings with regard to the epidemiology, physiology, clinical assessment and genetics of type 2 diabetes and obesity.

Study design of the Maycoba Project: obesity and diabetes in Mexican Pimas

OBJECTIVE

To focus on the rationale and methods of the Maycoba Project.

METHODS

Study population included Mexican Pima Indians (MPI) and Blancos aged ≥20-years, living in the village of Maycoba and surrounding area. Surveys in 1995 and 2010 included a medical history, biochemical and anthropomet- ric measurements. Additionally, socio- economic, physical activity, and dietary interviews were conducted. The 2010 study incorporated investigations on type 2 diabetes (T2D) and obesity-associated genetic alleles and human-envi- ronment changes.

RESULTS

The study results are limited to demographic data and description of the eligible and ex- amined sample.

CONCLUSIONS

This study may yield important information on T2D and obesity etiology in a traditional population exposed to environmental changes.

Association of leptin genetic polymorphism -2548 G/A with gestational diabetes mellitus

The aim of this study was to investigate possible associations of -2548 G/A polymorphism in leptin gene promoter and pregnancy-associated diseases with abnormal fetal growth such as preeclampsia and gestational diabetes. The study was also focused on whether it is rather maternal or fetal variants that determines the pathological growth status. Peripheral or cord blood samples obtained from 49 preeclamptic women and their 39 newborns, 53 healthy controls and their 53 healthy newborns and 48 patients with gestational diabetes mellitus were evaluated for leptin gene (LEP) locus -2548 genotypes. The significantly higher risk for gestational diabetes mellitus was observed in the presence of an allele (AA and AG genotypes) against carriers of GGgenotype(OR=2.84, 95%CI1.14-7.07,p=0.02). Thereisa significant risk of diabetes mellitus associated to A allele (OR=1.79, 95%CI 1.02-3.14, p=0.03). Furthermore, evaluations of preeclamptic patients' data revealed a significant association of genotype distribution and delivery and spontaneous abortion rate, where the GG carriers performed the highest pregnancy rate while the AG carriers performed the lowest spontaneous abortion rate. Our results support the hypothesis for -2548 G/A leptin gene polymorphism involvement in ethiopathogenesis of pregnancy-associated diseases with abnormal fetal growth, especially gestational diabetes mellitus.

Physical activity is correlated with serum leptin independent of obesity: results of the national surveillance of risk factors of noncommunicable diseases in Iran (SuRFNCD-2007)

Reports on the relationship between leptin and physical activity (PA) at the population level are scarce. The present study examined the relationship between serum leptin concentrations and PA in a nationally representative sample of 3001 Iranian adults aged 25 to 64 years. Data of our third national surveillance of risk factors of noncommunicable diseases were analyzed. Using the Global Physical Activity Questionnaire, the duration and intensity of PA were evaluated in 3 domains: work, commuting, and recreation. Total PA was calculated using metabolic equivalents for PA intensity. Serum leptin was measured with an enzyme-linked immunosorbent assay. After adjustment for age, area of residence, smoking, body mass index, and waist circumference, total PA (r = -0.129, P = .038 in men and r = -0.226, P = .006 in women), the duration of vigorous-intensity activity (r = -0.120, P = .044 in men and r = -0.154, P = .019 in women), the duration of moderate-intensity activity (r = -0.114, P = .047 in men and r = -0.160, P = .018 in women), and time spent on sedentary behaviors (r = 0.194, P = .014 in men and r = -0.204, P = .007 in women) were significantly correlated with serum leptin. In both sexes, participants in higher categories of PA had significantly lower serum leptin levels. In conclusion, our results demonstrated an inverse association between leptin concentrations and PA independent of age, sex, smoking, and body adiposity. Our results point to the regulatory effects of PA on serum leptin.

Novel factors as therapeutic targets to treat diabetes. Focus on leptin and ghrelin

BACKGROUND

Obesity is the major cause of type 2 diabetes. In the mid 1990s interest in adipose tissue was revived by the discovery of leptin. The association of obesity and diabetes emphasizes their shared physiopathological features. At the end of the 1990s, ghrelin, a potent gastric orexigenic factor, was found to be involved in obesity. Leptin and ghrelin have opposite actions in several tissues including the regulation of feeding in the brain.

OBJECTIVE/METHODS

To survey the role of leptin and ghrelin in glucose metabolism. We summarize the current state of research and discuss the roles of ghrelin and leptin in glucose homeostases and the potential application of drugs targeting leptin and ghrelin signalling to prevent and treat diabetes.

RESULTS/CONCLUSIONS

A pressing challenge is to determine how leptin, ghrelin and other adipokines or gastric factors are involved in metabolic disorders. Answering these questions will require the development of new pharmacological tools that target specific adipokine systems. Hopefully, new therapeutic targets will be identified.

Health-promoting effects of bovine colostrum in Type 2 diabetic patients can reduce blood glucose, cholesterol, triglyceride and ketones

Bovine colostrum (BC) has been reported to enhance immune function, reduce fat accumulation and facilitate the movement of glucose to the muscle. However, very few attempts have been made to examine its anti-diabetic effects in diabetes patients. The aim of this study was to evaluate whether BC decreases blood glucose, as well as cholesterol, triglyceride (TG) and ketones levels, which can be elevated by obesity and stress in Type 2 diabetic patients. Sixteen patients (men=8, women=8) with Type 2 diabetes were randomized into the study. Each ingested 5 g of BC on an empty stomach every morning and night for 4 weeks. Blood glucose, ketones (beta-hydroxybutyric acid), total cholesterol and TGs were measured every week. In both the men and women, blood glucose levels at 2 and 8 h postprandial decreased continually during the experimental period. The rate of decrease in blood glucose at 8 h postprandial was not different between the men and women, but was higher in the women (14.25+/-2.66) than in the men (10.96+/-1.82%) at 2 h postprandial. Total cholesterol and TG levels decreased significantly in both the men and women after 4 weeks. Also, beta-hydroxybutyric acid level decreased with BC ingestion, but this was not significant. These results suggest that BC can decrease levels of blood glucose and ketones, as well as reduce cholesterol and TGs, all of which may cause complications in Type 2 diabetic patients.

The thyroid hormone mediated effects of insulin on serum leptin levels of diabetic rats

In this study, we aimed to evaluate the possible relations of serum leptin and thyroid hormones on insulin treatment of surgically thyroidectomized and streptozotosin induced diabetic group of rats and whether the thyroid hormones control the leptin levels or leptin levels affect the thyroid hormones in DM. The Sprague-Dawley rats were assigned to eight groups: group 1, control; group 2, diabetes (injected intraperitoneally (i.p.) with streptozotocin (stz) 55 mg/kg); group 3, diabetes + insulin (rats were treated with insulin, 7-10 U/kg/day, subcutaneously); group 4, surgically thyroidectomized control; group 5, thyroidectomized + diabetes (3 weeks after the surgical operation, injected i.p. with stz); group 6, thyroidectomized + diabetes + insulin; group 7, thyroidectomized + diabetes + insulin + thyroid hormone (after diabetes induction, rats were treated with insulin and thyroid hormone, levothyroxin sodium (T4; 2.5 microg/kg); group 8, thyroidectomized + diabetes + insulin + thyroid hormone (T4; 5 microg/kg). The free and total T3 and T4 levels were measured in serum samples by otoanalyzer, and leptin levels were determined by ELISA method. The main finding of our recent study is that the decreased levels of serum leptin during the diabetes, hypothyroidism, and hypothyroidism with diabetes can be regulated in different percentages with the treatment of insulin and various doses of thyroid hormone. The observations in our study suggest the idea that during diabetic hypothyroidism, without thyroid hormone treatment, insulin is not sufficient to balance the metabolic pathways so mediated effects of insulin in leptin regulation via thyroid hormones are an increased possibility.

Monounsaturated fat-rich diet prevents central body fat distribution and decreases postprandial adiponectin expression induced by a carbohydrate-rich diet in insulin-resistant subjects

OBJECTIVE

Central obesity is associated with insulin resistance through factors that are not fully understood. We studied the effects of three different isocaloric diets on body fat distribution, insulin sensitivity, and peripheral adiponectin gene expression.

RESEARCH DESIGN AND METHODS

Eleven volunteers, offspring of obese type 2 diabetic patients with abdominal fat deposition, were studied. These subjects were considered insulin resistant as indicated by Matsuda index values <4 after an oral glucose tolerance test, and they maintained A1C <6.5% without therapeutic intervention. All subjects underwent three dietary periods of 28 days each in a crossover design: 1) diet enriched in saturated fat (SAT), 2) diet rich in monounsaturated fat (MUFA) (Mediterranean diet), and 3) diet rich in carbohydrates (CHOs).

RESULTS

Weight, body composition, and resting energy expenditure remained unchanged during the three sequential dietary periods. Using dual-energy X-ray absorptiometry we observed that when patients were fed a CHO-enriched diet, their fat mass was redistributed toward the abdominal depot, whereas periphery fat accumulation decreased compared with isocaloric MUFA-rich and high-SAT diets (ANOVA P < 0.05). Changes in fat deposition were associated with decreased postprandial mRNA adiponectin levels in peripheral adipose tissue and lower insulin sensitivity index values from a frequently sampled insulin-assisted intravenous glucose tolerance test in patients fed a CHO-rich diet compared with a MUFA-rich diet (ANOVA P < 0.05).

CONCLUSIONS

An isocaloric MUFA-rich diet prevents central fat redistribution and the postprandial decrease in peripheral adiponectin gene expression and insulin resistance induced by a CHO-rich diet in insulin-resistant subjects.

Intake compensates for resting metabolic rate variation in female C57BL/6J mice fed high-fat diets

OBJECTIVE

The literature is divided over whether variation in resting metabolic rate (RMR) is related to subsequent obesity. We set out to see whether the effect of RMR on weight gain in mice could be revealed with high-fat feeding.

RESEARCH METHODS AND PROCEDURES

Female C57BL/6J mice received a low- (10 kcal%fat n = 47), medium- (45 kcal%fat n = 50), or high-fat diet (60 kcal%fat n = 50) for 12 weeks. Pre-treatment RMR was measured by indirect calorimetry. Body composition was estimated using DXA before and after treatment.

RESULTS

Mice on the high-fat diet gained 39% of body mass, whereas control animals gained 3.5%. There was no interaction between RMR and dietary type on weight gain, and there was no association between weight gain and RMR for any of the treatments. RMR accounted for 2.4% of the variation in pre-treatment food intake corrected for initial body mass; however, the gradient of this relationship indicated that variations in RMR were, on average, compensated for by adjustments in food intake.

DISCUSSION

Individual variations in RMR did not predispose mice to weight gain independent of the dietary treatment. Deviations from the relationship between RMR and food intake were not associated with weight gain. This suggests that variations in energy expenditure, caused by RMR and physical activity, are closely linked to dietary intake, and, therefore, well compensated. Individual variations in the strength of this association may underpin individual variability in the responses to diet.

Brain adipocytokine action and metabolic regulation

Adipose tissue secretes factors that control various physiological systems. The fall in leptin during fasting mediates hyperphagia and suppresses thermogenesis, thyroid and reproductive hormones, and immune system. On the other hand, rising leptin levels in the fed state stimulate fatty acid oxidation, decrease appetite, and limit weight gain. These divergent effects of leptin occur through neuronal circuits in the hypothalamus and other brain areas. Leptin also regulates the activities of enzymes involved in lipid metabolism, e.g., AMP-activated protein kinase and stearoyl-CoA desaturase-1, and also interacts with insulin signaling in the brain. Adiponectin enhances fatty acid oxidation and insulin sensitivity, in part by stimulating AMP-activated protein kinase phosphorylation and activity in liver and muscle. Moreover, adiponectin decreases body fat by increasing energy expenditure and lipid catabolism. These effects involve peripheral and possibly central mechanisms. Adipose tissue mediates interconversion of steroid hormones and secretes proinflammatory cytokines, vasoactive peptides, and coagulation and complement proteins. Understanding the actions of these "adipocytokines" will provide insight into the pathogenesis and treatment of obesity and related diseases.

Leptin and incident type 2 diabetes: risk or protection?

AIMS/HYPOTHESIS

The aim of this study was to investigate the association of leptin levels with incident diabetes in middle-aged adults, taking into account factors purportedly related to leptin resistance.

SUBJECTS AND METHODS

We conducted a case-cohort study (570 incident diabetes cases and 530 non-cases) representing the 9-year experience of 10,275 participants of the Atherosclerosis Risk in Communities Study. Plasma leptin was measured by direct sandwich ELISA.

RESULTS

In proportional hazards models adjusting for age, study centre, ethnicity and sex, high leptin levels (defined by sex-specific cut-off points) predicted an increased risk of diabetes, with a hazard ratio (HR) comparing the upper with the lower quartile of 3.9 (95% CI 2.6-5.6). However, after further adjusting additionally for obesity indices, fasting insulin, inflammation score, hypertension, triglycerides and adiponectin, high leptin predicted a lower diabetes risk (HR=0.40, 95% CI 0.23-0.67). Additional inclusion of fasting glucose attenuated this protective association (HR=0.59, 95% CI 0.32-1.08, p<0.03 for linear trend across quartiles). In similar models, protective associations were generally seen across subgroups of sex, race, nutritional status and smoking, though not among those with lower inflammation scores or impaired fasting glucose (interaction p=0.03 for both).

CONCLUSIONS/INTERPRETATION

High leptin levels, probably reflecting leptin resistance, predict an increased risk of diabetes. Adjusting for factors purportedly related to leptin resistance unveils a protective association, independent of adiponectin and consistent with some of leptin's described protective effects against diabetes.

Population variation and differences in serum leptin independent of adiposity: a comparison of Ache Amerindian men of Paraguay and lean American male distance runners

Background

Serum leptin variation is commonly associated with fat percentage (%), body mass index (BMI), and activity. In this investigation, we report population differences in mean leptin levels in healthy men as well as associations with fat % and BMI that are independent of these factors and reflect likely variation resulting from chronic environmental conditions.

Methods

Serum leptin levels, fat %, and BMI were compared between lean American distance runners and healthy Ache Native Americans of Paraguay. Mean levels were compared as were the regressions between fat %, BMI, and leptin. Comparisons were performed between male American distance runners (n = 13, mean age 32.2 ± 9.2 SD) and highly active male New World indigenous population (Ache of Paraguay, n = 20, mean age 32.8 ± 9.2) in order to determine whether significant population variation in leptin is evident in physically active populations living under different ecological circumstances independent of adiposity and BMI.

Results

While the Ache were hypothesized to exhibit higher leptin due to significantly greater adiposity (fat %, Ache 17.9 ± 1.8 SD; runners 9.7 ± 3.2, p < 0.0001), leptin levels were nonetheless significantly higher in American runners (Ache 1.13 ng/ml ± 0.38 SD; runners 2.19 ± 1.15; p < 0.007). Significant differences in the association between leptin and fat % was also evident between Ache and runner men. Although fat % was significantly related with leptin in runners (r = 0.90, p < 0.0001) fat % was negatively related in Ache men (r = -0.50, p < 0.03).

Conclusion

These results illustrate that chronic ecological conditions in addition to activity are likely factors that contribute to population variation in leptin levels and physiology. Population variation independent of adiposity should be considered to be an important source of variation, especially in light of ethnic and population differences in the incidence and etiology of obesity, diabetes, and other metabolic conditions.

Total energy expenditure, resting metabolic rate and physical activity level in free-living rural elderly men and women from Cuba, Chile and México

OBJECTIVE

The objective of this study was to assess total energy expenditure (TEE), resting metabolic rate (RMR) and physical activity level (PAL), and to estimate energy requirements (ERs) in free-living elderly subjects from Cuba, Chile and Mexico.

DESIGN

Cross-sectional study designed to estimate ERs.

SETTING

Rural regions of Cuba, Chile and Mexico.

SUBJECTS

Forty subjects >60 years old were selected to participate in this study.

INTERVENTIONS

A dose of doubly labeled water (DLW) was administered and urine samples were collected in the following 12-14 days. From the isotopic analysis, TEE was derived. RMR was measured by indirect calorimetry.

RESULTS

TEE in Chilean (8.8+/-1.6 MJ/day) and Cuban (8.3+/-1.3 MJ/day) elderly was not different, and was higher for the Mexican group (9.5+/-1.5 MJ/day) (P < 0.0001). RMR was not different between countries. PAL and activity energy expenditure (AEE) were only different between Chile and Mexico (P < 0.002). For the three regions, overall PALs were 1.70+/-0.16 for male and 1.62+/-0.13 for female subjects (P < 0.02), and AEE was 3.05+/-0.66 and 2.27+/-0.66 MJ/day for male and female subjects, respectively (P < 0.001). Predictive equations (MJ/day) were RMR = 1.6447 + 0.05714 x weight (kg) + 0.449 sex (male = 1; female = 0) (R2 = 0.75; SEE = 0.479) and TEE = 3.414 + 0.0795 x weight (kg) + 1.227 x sex (male = 1; female = 0) (R2 = 0.75; SEE = 0.668).

CONCLUSIONS

There were differences in TEE and PAL owing to sex and region. The average PAL in men was higher than the PAL reported either with factorial approach or with the DLW method in elderly. Predictive ER equations based on RMR and TEE gave very similar results to calculations from the 2004 FAO/WHO/UNU report.

Rethinking leptin and insulin action: Therapeutic opportunities for diabetes

Leptin is an adipocyte-derived hormone that primarily acts in the hypothalamus and plays a key role in the regulation of food intake, body weight, energy expenditure and neuroendocrine function. Leptin has direct peripheral effects on several tissues, and it may be independently involved in insulin secretion and action besides its effects on body weight regulation. Basal plasma leptin and insulin concentrations correlate with each other. Insulin and glucose appear to increase leptin secretion. In turn, leptin increases peripheral insulin sensitivity while decreasing insulin secretion from pancreatic beta cells. Leptin increases skeletal muscle glucose uptake and oxidation, and suppresses hepatic glucose output. Effects of leptin on lipid metabolism might reduce lipotoxicity and therefore contribute to the improvement of hepatic, skeletal and whole body insulin sensitivity. Leptin is the first adipokine used in the treatment of hypoleptinemic clinical disorders. Although leptin therapy has limited success in common obesity, it has impressive effects in congenital leptin deficiency, lipoatrophic diabetes and syndromes of severe insulin resistance. Leptin has been reported to ameliorate hyperinsulinemia and diabetes in the clinical setting of congenital leptin deficiency. It also improves hyperglycemia, insulin resistance, hyperinsulinemia, dyslipidemia and hepatic steatosis in lipoatrophic diabetes. These promising results warrant clinical trials to test the hypothesis that leptin alone or with classical antidiabetic agents may potentially be beneficial in the treatment of hypoleptinemic non-obese individuals with glucose intolerance and diabetes. This review summarizes the clinical applications of leptin, particularly emphasizing the effects of leptin on glucose homeostasis.

Anthropometry of 5-19-year-old Tongan children with special interest in the high prevalence of obesity among adolescent girls

BACKGROUND

Despite much concern about adult obesity among Pacific Islanders, childhood obesity has seldom been investigated.

AIM

Based on the anthropometry of Tongan children aged 5-19 years, this study aims to elucidate age and sex differences in obesity prevalence calculated from BMI and its relation to body fat estimated by skinfold thicknesses.

SUBJECTS AND METHODS

895 students, aged 5-19 years, in the most modernized island and a remote island, were measured for stature, body weight, circumferences at waist, hip and mid-upper arm, and skinfold thicknesses at biceps, triceps and subscapular. The prevalence of overweight and obesity was calculated using the reference data of the International Obesity Task Force (IOTF) and the Centers for Disease Control and Prevention (CDC).

RESULTS

The prevalence of obesity of Tongan adolescent girls defined by the IOTF and CDC references was 19.4% and 22.8%, respectively, being considerably higher than that of not only juvenile girls but also adolescent boys. Among adolescents, the girls' BMI was positively correlated with fat mass whereas in boys it was not. The sex difference in adolescents was parallel to that in adults, being attributable to gender differences in daily behavioural patterns.

CONCLUSIONS

Among Tongan adolescents, obesity prevalence in girls was much higher than in boys, in association with fat accumulation in the former.

Role of physical activity in preventing and treating obesity

There is an inverse relationship between physical activity and weight gain. However, additional research is needed to quantify the amount of physical activity required to prevent weight gain in different populations, improve the way we convey physical activity recommendations to the public, and help the individuals increase their physical activity. Although physical activity does not appear to contribute significantly to weight loss, it is critical for maintenance of weight loss. Available data are consistent in that 60-90 min/day of moderate-intensity physical activity is required to maintain a significant weight loss. Although there is agreement about the need for high levels of physical activity to maintain weight loss, there is a need for more research to understand why physical activity is critical for weight loss maintenance. Finally, additional research is needed to determine whether there is an optimal level of physical activity below which it is difficult for most people to achieve a balance between energy intake and expenditure at a healthy body weight. The increasing prevalence of obesity may reflect the fact that the majority of the population has fallen below such a level of physical activity.

No difference in serum leptin concentrations between urban-dwelling Austronesians and Non-Austronesians in Papua New Guinea

Pacific Islands populations can be broadly divided into Austronesians (AN) and Non-Austronesians (NAN); obesity and type 2 diabetes are prevalent in the former, although leptin levels in both groups have seldom been investigated. Thirty-seven (20 male and 17 female) adult pairs, matched by age and percent body fat, from AN-speaking Balopa and NAN-speaking Huli, all of whom migrated to settle in Port Moresby, the capital of Papua New Guinea, were selected for comparison of their serum leptin concentrations. The Balopa did not differ significantly from the Huli in age (30.5 +/- 9.7 and 30.0 +/- 8.7 years for males, 33.7 +/- 8.9 and 34.1 +/- 7.5 years for females, respectively) or percent body fat (19.4 +/- 5.6 and 18.8 +/- 4.6 for males, 34.1 +/- 6.2 and 33.3 +/- 5.0 for females), although the BMI of females was lower in the Balopa (26.4 +/- 4.9) than in the Huli (29.7 +/- 4.7) (P = 0.02). In both ethnic groups, females had markedly higher leptin concentrations than males, but there was no significant inter-group difference in males (3.5 +/- 2.6 and 3.1 +/- 4.7 ng/ml, P = 0.14) or females (22.7 +/- 12.9 and 19.7 +/- 11.9 ng/ml, P = 0.40), after controlling for lifestyle factors and serum lipids. Multiple regression analysis revealed that significant predictors of leptin concentration were % body fat (beta = 0.58), sex (male, 0; female, 1; beta = 0.27), and smoker status (non-smoker, 0; smoker, 1; beta = -0.15) (R(2) = 0.80), implying that the leptin concentration was primarily determined by lifestyle-derived body fatness. In conclusion, the NAN populations do not endogenously differ in leptin status from the AN populations, who have been recognized as a typical group with a "thrifty" genotype.

Serum leptin levels in Ache Amerindian females with normal adiposity are not significantly different from American anorexia nervosa patients

Serum leptin, a polypeptide hormone secreted primarily by adipocytes, is a reflection of somatic fat availability in humans and other vertebrates. Among Ache Amerindians, leptin levels are very low in contrast to other populations, despite comparable adiposity with individuals exhibiting much higher leptin levels. In order to gain a greater understanding of these differences, leptin levels were compared between Ache Amerindian females (n = 12, mean age = 32.2 +/- 14.0 SD), American females diagnosed with anorexia nervosa (n = 22, mean age = 23.0 +/- 4.0), and non-anorectic American controls (n = 23, mean age = 23.0 +/- 4.0). Ache leptin (5.6 +/- 3.2 ng/ml) was not significantly different from anorectic patients (5.6 +/- 3.7 ng/ml; P > 0.98) despite greater adiposity (Ache 33.3% +/- 4.4% vs. anorectic 7.0% +/- 2.0%; P < 0.0001). Ache adiposity was also higher than American controls (leptin 19.1 +/- 8.1 ng/ml; fat 28% +/- 5.0%; P < 0.004) underscoring the uniqueness of Ache leptin profiles. This suggests a greater range of population variation in leptin physiology than previously suspected and intimates the potential role of chronic environmental conditions.

The hypoglycemic effects of hesperidin and naringin are partly mediated by hepatic glucose-regulating enzymes in C57BL/KsJ-db/db mice

Dietary antioxidant compounds such as bioflavonoids may offer some protection against the early stage of diabetes mellitus and the development of complications. We investigated the effect of citrus bioflavonoids on blood glucose level, hepatic glucose-regulating enzymes activities, hepatic glycogen concentration, and plasma insulin levels, and assessed the relations between plasma leptin and body weight, blood glucose, and plasma insulin. Male C57BL/KsJ-db/db mice (db/db mice, 5 wk old), an animal model for type 2 diabetes, were fed a nonpurified diet for 2 wk and then were fed an AIN-76 control diet or the control diet supplemented with hesperidin (0.2 g/kg diet) or naringin (0.2 g/kg diet). Hesperidin and naringin supplementation significantly reduced blood glucose compared with the control group. Hepatic glucokinase activity and glycogen concentration were both significantly elevated in the hesperidin- and the naringin-supplemented groups compared with the control group. Naringin also markedly lowered the activity of hepatic glucose-6-phosphatase and phosphoenolpyruvate carboxykinase compared with the control group. Plasma insulin, C-peptide, and leptin levels in the db/db mice from the 2 bioflavonoid-supplemented groups were significantly higher than those of the control group. Furthermore, plasma leptin was positively correlated with plasma insulin level (r = 0.578, P < 0.01) and body weight (r = 0.541, P < 0.05), and was inversely correlated with the blood glucose level (r = -0.46, P < 0.05). The current results suggest that hesperidin and naringin both play important roles in preventing the progression of hyperglycemia, partly by increasing hepatic glycolysis and glycogen concentration and/or by lowering hepatic gluconeogenesis.

Does leptin link sleep loss and breathing disturbances with major public diseases?

Leptin is best known as a regulator of energy homeostasis, but it also interacts with sleep and breathing. Leptin secretion increases at night and decreases during the day. The circadian secretory profile of leptin is determined both by the hypothalamic circadian pacemaker and sleep-wake cycle. Leptin is also a powerful respiratory stimulant. Serum leptin levels are higher in obstructive sleep apnoea syndrome but lower during extended sleep deprivation in healthy subjects or in narcolepsy. Abnormalities in serum leptin concentrations have recently been linked with deleterious effects on weight control, cardiovascular health and glucose regulation. Since sleep curtailment and sleep-disordered breathing are epidemics of the modern society, better understanding of leptin pathophysiology could open new perspectives to pathophysiology of major public diseases, including obesity and metabolic syndrome.

Effects of oral zinc supplementation on serum leptin levels in Ache males of eastern Paraguay

Significant population variation has been demonstrated in serum leptin levels, independent of adiposity. Included within these populations, Ache males have significantly lower leptin levels compared to American subjects with comparable adiposity. The underlying causes of these differences are not understood but zinc has been shown to be an important regulator of leptin in humans and rodents. Zinc deficiency is associated with somatic wasting and significant declines in circulating leptin levels. Zinc deficiency is common in underdeveloped regions and may therefore contribute to low leptin levels among Ache men. To ascertain the potential role of zinc on Ache male leptin profiles, zinc supplementation was conducted to observe leptin responsiveness. Ache males were given daily oral zinc supplementation (50mg zinc gluconate) (n = 8) or placebo (n = 6) for 10 days. Serum leptin levels were measured on the first and last days of the treatment/placebo period. Despite supplementation exceeding triple the USDA recommended daily requirements, serum leptin levels did not change in the zinc-supplemented group (P = 0.61) and were not significantly different from males receiving placebo (P = 0.72). It is concluded that zinc is not likely to be a contributing factor in male Ache leptin profiles and that other sources of variation such as chronic energetic stresses affecting leptin production and perhaps receptor number or sensitivity should be considered.

Body composition by hydrometry (deuterium oxide dilution) and bioelectrical impedance in subjects aged >60 y from rural regions of Cuba, Chile and Mexico

BACKGROUND

In Latin American and Caribbean countries such as Chile, Mexico and Cuba, the population over 60 y has increased steadily. In this age group, there is scarce information about body composition, particularly for those living in rural areas.

OBJECTIVE

The purpose of this study was to determine body composition in free-living and healthy elderly subjects >60 y from rural areas of Chile, Cuba and Mexico using deuterium oxide dilution and bioelectrical impedance (BIA) and to develop and cross-validate a predictive equation for this group of subjects by BIA for future use as a field technique.

SUBJECTS

The study included 133 healthy subjects (73 males and 60 females) >60 y from rural regions of Cuba, Chile and Mexico.

MEASUREMENTS

Total body water, body weight, height and other anthropometric and BIA variables (resistance and reactance) were measured.

METHODS

Total body water was determined by deuterium oxide dilution, and fat-free mass (FFM)/fat mass were derived from this measurement. The total sample was used in a split-sample internal cross-validation. BIA and other anthropometric variables were integrated to multiple regression model to design the best predictive equation, which was validated in the other sample. ANOVA, multiple regression and Bland and Altman's procedure were used to analyze the data.

RESULTS

Body weight, percentage of fat and fat-free mass were lower in the Cuban men and women compared with Chilean and Mexican men and women. The best predictive equation of the FFM was: FFM kg=(-7.71+(H(2)/R x 0.49)+(country or ethnicity x 1.12)+(body weight x 0.27)+(sex x 3.49)+(Xc x 0.13)), where H(2) is height(2) (cm); R is resistance (Omega); country: Chile=1, Mexico=2 and Cuba=3; sex: women=0 and men=1; body weight (kg) and Xc is reactance (Omega). R(2) was 0.944 and the root mean square error (RMSE) was 2.08 kg. The mean+/-s.d. of FFM prediction was 44.2+/-9.2 vs 44.6+/-10.1. The results of cross-validation showed no significant difference with the line of identity, showing that the predicted equation was accurate. The intercept (=-0.32) was not significantly different from zero (P=0.89) and the slope (=1.02) not significantly different from 1.0 (P>0.9). The R(2) was 0.86, RMSE=3.86 kg of FFM and the pure error was 3.83.

CONCLUSION

The new BIA equation is accurate, precise and showed good agreement. The use of this equation could improve the estimates of body composition for the elderly population for these regions, as well as enhancing the opportunity to conduct studies in the elderly population from Latin America.

Leptin: obesity, diabetes and other peripheral effects--a review

There is an increasing epidemic of obesity in the Western and developing world that has not spared children and, hence, is of great concern. Obesity presents numerous physiological and psychosocial problems for the child. Childhood obesity not only increases the risk of obesity in adulthood, it is associated with type 2 diabetes mellitus; is the leading cause of pediatric hypertension; increases the risk of coronary heart disease; and increases stress on the weight-bearing joints. Social and psychological problems are also significant consequences of obesity in children, with lowering of self-esteem and its effects on relationships with peers. Obesity is clearly associated with increased levels of the recently discovered hormone, leptin. Leptin, secreted from adipocytes, is involved in the regulation of food intake, energy expenditure, and energy balance in humans. This review focuses on the hormone, leptin, in an effort to document some of its many local and systemic effects on the body and, specifically, its potential role in obesity-induced diabetes.

Leptin: metabolic control and regulation

Leptin, a protein released from adipose tissue, is being recognized to play an integral role in endocrine regulation of metabolism. While it is clearly evident that leptin is decreased during caloric restriction, the response of leptin to other types of stress has been plagued by conflicting data. With hypoglycemia stress, the literature may conflict because experimentally hypoglycemia is induced with infusion of insulin, an endocrine factor that can increase leptin levels. With exercise, leptin's response may depend on duration and intensity of exercise. While it has been clearly shown that the sympathetic nervous system (SNS) inhibits leptin secretion in a variety of experimental modes, the hypothalamic-pituitary-adrenal (HPA) axis may stimulate leptin secretion. This creates a paradox of leptin regulation during stress since both systems are activated with stress. If the SNS inhibition overrides the HPA axis' activation of leptin secretion, leptin's role during stress may be to allow a shifting of fuel consumption towards carbohydrate utilization. In type 1 diabetes mellitus, autonomic dysfunction may prevent the fall in leptin during stress. Although obesity is associated with type 2 diabetes mellitus, patients may have decreased leptin levels, especially when glucose is poorly controlled. This may contribute to further obesity and worsening of the disease. The purpose of this review to is critically analyze the literature regarding the impact of different types of stress on leptin secretion, the function of leptin during stress, and the role of leptin in the pathophysiology of diabetes.

Low prevalence of type 2 diabetes despite a high average body mass index in the Aymara natives from Chile

The aim of this study was to estimate the prevalence of type 2 diabetes mellitus (DM2), impaired glucose tolerance (IGT), and the frequency of dyslipidemia, obesity, and hypertension in the rural Aymara population from Northern Chile. In this cross-sectional study, 196 Aymara adult subjects were characterized with respect to their reported physical activity, fasting plasma glucose levels, insulin concentrations, blood pressures, body mass indexes, and plasma lipid profiles. The participants also underwent a 2-h oral glucose tolerance test. The diagnostic criteria for DM2 and IGT followed those of the World Health Organization. The overall prevalence of DM2 was estimated as 1.5% (95% confidence interval: 0.3--4.5). Overall prevalence of IGT was calculated as 3.6% (1.5--7.3). The occurrence of obesity and dyslipidemia was relatively high in the Aymara population, although the frequency of sedentary habits, and the prevalence of hypertension were low. In conclusion, the prevalence of DM2 in the rural Aymara population living at high altitudes in Northern Chile, was much lower than that of other Amerindian groups that adopted lifestyles from industrialized Western societies. Despite a relatively high prevalence of a body mass index of at least 30 kg/m(2), especially in women (23.5%), high physical activity levels and low plasma-insulin concentrations may have been responsible in part for the low prevalence of DM2 in the Aymara population.

Serum leptin levels and anthropometric correlates in Ache Amerindians of eastern Paraguay

Leptin is a recently discovered peptide hormone secreted primarily from adipocytes in humans and other mammals; it is a reflection of fat stores, and has been associated with reproductive function. However, few leptin measurements are available from nonindustrialized populations, including contemporary hunter/gatherer communities undergoing the transition to sedentary agriculture. This investigation reports single-sample serum leptin measurements in healthy Ache Amerindian males (n = 21; average age, 32.8 +/- 3.4 SE) and females (n = 12; average age, 31.3 +/- 4.3) in eastern Paraguay. Ache leptin concentrations were much lower than in industrialized populations, although significant sexual dimorphism was evident (female 5.64 ng/ml +/- 0.91 SE vs. male 1.13 ng/ml +/- 0.08; P < 0.0001). Indeed, female leptin levels were similar to those of anorexic women, despite apparently adequate adiposity. Controlling for fat percentage, no significant sex difference was evident, suggesting that adiposity was the primary source of leptin variation. Body fat percentage was highly correlated with leptin in females (r2 = 0.72; P < 0.0005) but not males, who exhibited a modest negative correlation (r2 = 0.25; P < 0.03). Weight (r2 = 0.45; P = 0.02) and BMI (kg/m2) (r2 = 0.81; P < 0.0001) were also significantly correlated in females but not males. These results suggest that: 1) clinical leptin norms based on industrialized populations may represent the highest range of human variation and may not be representative of most human populations; 2) hormonal priming may underlie population variation in leptin profiles; and 3) the relative importance of leptin as a proximate mechanism regulating reproductive effort during human evolution may have been modest.

Large differences in serum leptin levels between nonwesternized and westernized populations: the Kitava study

OBJECTIVES

To compare serum leptin between nonwesternized and westernized populations.

SETTING

(i) The tropical island of Kitava, Trobriand Islands, Papua New Guinea and (ii) the Northern Sweden MONICA study population. Design. Cross-sectional survey.

METHODS

Fasting levels of serum leptin were analysed in 163 randomly selected Kitavans aged 20-86 years and in 224 Swedes aged 25-74.

MAIN OUTCOME MEASURE

Mean and determinants of serum leptin.

RESULTS

Geometric mean of serum leptin in Kitavan males and females were 1.5 and 4.0 vs. 4.9 and 13.8 ng mL-1 in Swedish male and females (P < 0.0001 for both sexes). In Kitavans, observed geometric mean were close to predicted levels (1.8 ng mL(-1) for males and 4.5 ng mL-1 for females) based on multiple linear regression equations including body mass index (BMI), triceps skinfolds (TSF) and age from the Swedish population-based sample. In Kitavans serum leptin was positively related to TSF amongst both sexes and, amongst females, to BMI. In Kitavans leptin was not related to fasting serum insulin. TSF explained 55% of the variation of leptin amongst females. There was a slight age-related increase of leptin amongst males. In Kitava leptin was not related to fasting serum insulin which was substantially lower than in Sweden.

CONCLUSION

The low concentrations of serum leptin amongst Kitavans probably relates to the absence of overweight and hyperinsulinaemia. At a population level serum leptin can apparently be predicted from simple measures of adiposity.