Is there a relationship between leptin and insulin sensitivity independent of obesity? A population-based study in the Indian Ocean nation of Mauritius. Mauritius NCD Study Group

OBJECTIVE

It has been shown previously in smaller studies that fasting serum leptin and insulin concentrations are highly correlated, and insulin sensitive men have lower leptin levels than insulin resistant men matched for fat mass. We have examined the association between insulin resistance (assessed by fasting insulin) and leptin after controlling for overall and central adiposity in a population-based cohort.

DESIGN

Leptin levels were compared across insulin resistance quartiles within three categories of obesity (tertiles of body mass index (BMI)). Partial correlation coefficents and multiple linear regression models were used to assess the relationship between leptin and fasting insulin after adjusting for BMI and waist to hip ratio (WHR) or waist circumference.

SUBJECTS

Subjects were normoglycemic participants of a 1987 non-communicable diseases survey conducted in the multiethnic population of Mauritius. 1227 men and 1310 women of Asian Indian, Creole and Chinese ethnicity had normal glucose tolerance and fasting serum leptin measurements.

RESULTS

Mean serum leptin concentration increased across quartiles of fasting insulin in each BMI group and gender, after controlling for BMI, WHR and age. Furthermore, fasting insulin was a significant determinant of serum leptin concentration, independent of BMI and WHR, in both men and women. Similar results were found if waist circumference replaced BMI and WHR in the model.

CONCLUSION

These results suggest that insulin resistance/concentration may contribute to the relatively wide variation in leptin levels seen at similar levels of body mass or alternatively, leptin may play a role in the etiology of insulin resistance. Further studies will be important to determine whether the hyperleptinemia/insulin resistance relationship has a role in the natural history of obesity, Type 2 diabetes mellitus and the other metabolic abnormalities associated with insulin resistance.

Dysregulation of leptin in response to fasting in insulin-resistant Psammomys obesus (Israeli sand rats)

Leptin is thought to play a significant role in energy balance as an afferent signal to the hypothalamus that reflects body fat content. In addition, leptin may also act as an acute sensor of energy balance independent of body fat mass, since ob gene expression and plasma leptin concentrations are decreased in lean animals and humans in response to short-term caloric deprivation. However, in obese animals and humans, the acute response of leptin to fasting is less clear. We investigated the effects of a 24-hour fast on circulating plasma leptin concentrations in lean and obese Psammomys obesus (Israeli sand rats). In the lean, insulin-sensitive group (n = 25) a 24-hour fast caused a 44% decrease in plasma leptin, whereas in the obese, insulin-resistant group (n = 24) plasma leptin increased by 18% after fasting (P < .003). There was no difference between the two groups regarding the effect of a 24-hour fast on body weight, blood glucose, or plasma insulin. Within the insulin-resistant group, there was no difference in the response of leptin to fasting between hyperglycemic and normoglycemic animals. We conclude that there is a dysregulation of leptin in response to acute caloric deprivation in obese, insulin-resistant but not in lean, insulin-sensitive P obesus.

Relationship of serum leptin to total and truncal body fat

1. In this study we investigated the relationship between serum leptin levels and body fat distribution in a random sample of women of widely ranging age and body mass index. Anthropometry and dual energy X-ray absorptiometry were used to measure body fat and its distribution. 2. Leptin levels (log transformed) were not significantly correlated with age, but were significantly positively correlated (P < 0.001) with most anthropometric measures except waist-to-hip circumference ratio. The strongest correlations were with total grams of body fat and percentage body fat (r = 0.68 and 0.76 respectively, P < 0.001). When corrected for percentage body fat the partial correlation coefficients for all other measures became non-significant. The correlation with truncal body fat fell significantly from 0.66 to -0.05 after correction, but the partial correlation with total body fat remained significant (P < 0.005) when grams of truncal fat were controlled for (r = 0.21). 3. These results indicate that the relationship of serum leptin to percentage body fat is the strongest, and that truncal body fat, although the most metabolically active, does not appear to have an independent association with serum leptin.

Leptin inhibits insulin binding in isolated rat adipocytes

Leptin is secreted from adipose tissue, and is thought to act as a 'lipostat', signalling the body fat levels to the hypothalamus resulting in adjustments to food intake and energy expenditure to maintain body weight homeostasis. In addition, plasma leptin concentrations have been shown to be related to insulin sensitivity independent of body fat content, suggesting that the hyperleptinemia found in obesity could contribute to the insulin resistance. We investigated the effects of leptin on insulin binding by isolated adipocytes. Adipocytes isolated from Sprague-Dawley rats exhibited a dose-dependent reduction in the uptake of 125I-labelled insulin when incubated with various concentrations of exogenous leptin. For example, addition of 50 nM leptin reduced total insulin binding in isolated adipocytes by 19% (P < 0.05). Analysis of displacement curve binding data suggested that leptin reduced maximal insulin binding in a dose-dependent manner, but had no significant effect on the affinity of insulin for its binding site. We conclude that leptin directly inhibited insulin binding by adipocytes, and the role of leptin in the development of insulin resistance in obese individuals requires further investigation.

Ob (obese) gene expression and leptin levels in Psammomys obesus

In this study we investigated ob gene expression and plasma leptin levels in Psammomys obesus (the Israeli Sand Rat), a polygenic animal model of obesity and non-insulin-dependent diabetes mellitus. The ob gene was expressed exclusively in adipocytes of Psammomys obesus. DNA sequencing revealed a high degree of homology with other species (90% with mouse, 88% with rat and 79% with human). No ob gene sequence differences were found between lean and obese Psammomys obesus, and the codon 105 mutation found in ob/ob mice was not detected. Ob gene expression in Psammomys obesus correlated with body weight (r = 0.436, p < 0.001), percent body fat (r = 0.645, p < 0.001) and plasma insulin concentration (r = 0.651, p < 0.001). This is the first time that ob gene expression has been shown to increase steadily over a continuous wide range of body weight or plasma insulin in an animal model of obesity. Ob gene expression was significantly elevated in obese compared with lean Psammomys obesus (p < 0.05). No significant difference in ob gene expression was found between the four adipose tissue depots tested. Psammomys obesus plasma leptin levels correlated with body weight (r = 0.36, p < 0.05), percent body fat (r = 0.702, p < 0.01) and plasma insulin concentration (r = 0.735, p < 0.001). Plasma leptin concentrations were significantly increased in insulin-resistant animals independent of body weight. These results show that Psammomys obesus is an excellent animal model in which to study the ob gene and leptin, and confirm the importance of insulin as a significant factor in the regulation of leptin and ob gene expression.

Development of obesity and insulin resistance in the Israeli sand rat (Psammomys obesus). Does leptin play a role?

The Israeli Sand Rat (Psammomys obesus) is an excellent polygenic model for the study of obesity and diabetes. The metabolic characteristics and the heterogeneous development of these defects, including elevated leptin levels, mimic those found in susceptible human populations. Interestingly, only animals that develop metabolic abnormalities demonstrate hyperleptinemia and, in these animals, leptin administration at the same dose that is effective in ob/ob mice is ineffective in reducing food intake or body weight. Perhaps leptin resistance needs to develop in Israeli Sand Rats to allow the development of obesity and, in fact, leptin resistance may be the "thrifty gene" that predisposes individuals to the development of obesity and subsequent metabolic abnormalities. However, there remain many unanswered questions about the physiological actions of leptin. The widespread tissue location of receptors and the actions of leptin independent of food intake highlight the need for further research aimed at determining the major physiological action of this newly discovered and exciting hormone.

Leptin and the development of obesity and diabetes in Psammomys obesus

The recently discovered ob gene and its circulating product, leptin, may be critical factors in the control of energy balance. Recent studies in ob/ob mice, which lack circulating leptin, have shown dramatic reductions in food intake and bodyweight after leptin treatment. In addition, studies in both humans with obesity and animal models of obesity have demonstrated hyperleptinemia. Here, we report a longitudinal study examining changes in circulating leptin during the development of obesity and diabetes in Psammomys obesus. Over the 8 weeks of the study, lean animals increased their bodyweight by 154% and leptin levels remained essentially unchanged. In contrast, animals that developed obesity (223% increase in bodyweight), hyperglycemia, and hyperinsulinemia also developed hyperleptinemia between 4 weeks and 8 weeks of age. These results demonstrate that the development of hyperleptinemia is associated with the development of obesity and subsequent metabolic abnormalities.

Amino acid levels following beef protein and amino acid supplement in male subjects

In the present study the plasma amino acid response of six lean subjects to a protein meal and a commercial amino acid supplement were compared. The amino acid supplement studied was formulated and marketed to be taken after exercise and at other times with the aim of increasing protein synthesis and/or decreasing protein degradation and to lower the ratio of tryptophan to the other large neutral amino acids (LNAA); tyrosine, valine, leucine, isoleucine, phenylalanine and methionine (trp/LNAA), to reduce fatigue. The amino acid supplement administered at the dose recommended by the manufacturer (4 g) was able to bring about a rapid but short-lived (15-30 min) increase in plasma amino acid concentrations and to produce a similarly brief decrease in the trp/LNAA and tyr/LNAA ratios and therefore achieved these aims with respect to amino acid levels even if only briefly. The changes in trp/LNAA and tyr/LNAA ratios after the supplement were of the same order as those produced after the much larger (50 g) protein meal but of shorter duration. However the relatively small insulin response after the amino acid supplement points to a lower level of amino acid uptake by muscle and other tissues for protein synthesis compared to that produced by the beef meal.

The effect of dietary energy restriction on body weight gain and the development of noninsulin-dependent diabetes mellitus (NIDDM) in Psammomys obesus

Food intake was restricted to 75% of ad libitum levels in 37 male Psammomys obesus (Israeli Sand Rats) from the ages of 4 (weaning) to 10 weeks. Energy restriction reduced the mean bodyweight at 10 weeks by 29% compared with 44 ad libitum fed controls. Hyperglycemia was prevented completely in the food-restricted group, and mean blood glucose concentrations were significantly reduced (3.8 +/- 0.2 vs. 5.5 +/- 0.4 mumol/L; p < 0.05) compared with control animals. Plasma insulin concentrations were also decreased significantly compared with ad libitum fed controls (105 +/- 13 vs. 241 +/- 29 mU/L; p < 0.05). Although energy restriction prevented hyperglycemia from developing in 10-week-old P. obesus, 19% of the food restricted animals still developed hyperinsulinemia. We concluded that hyperphagia between the ages of 4 to 10 weeks may be essential for the development of noninsulin-dependent diabetes mellitus in P. obesus, but that hyperinsulinemia may still occur in the absence of hyperphagia and hyperglycemia, suggesting a significant genetic influence on the development of hyperinsulinemia in this animal model.

Non-insulin dependent diabetes mellitus in Psammomys obesus is independent of changes in tissue fatty acid composition

Recently it has been postulated that membrane fatty acid composition may be involved in the pathogenesis of insulin resistance and non-insulin dependent diabetes mellitus (NIDDM). The aim of this study was to determine whether alterations in tissue phospholipid (PL) fatty acids are present in hyperglycemic and hyperinsulinemic Psammomys obesus. On a native diet of salt bush, P. obesus (Israeli sand rat) remains lean and free of diabetes; however, when placed on a normal laboratory chow, a significant proportion of these animals develops a number of metabolic disorders associated with NIDDM, providing an ideal animal model of obesity and NIDDM. Four groups of mature P. obesus were studied: group A: normoglycemic and normoinsulinemic; group B: normoglycemic and hyperinsulinemic; group C: hyperglycemic and hyperinsulinemic; and group D: hyperglycemic and hypoinsulinemic. In liver and red gastrocnemius muscle, there were no significant differences between groups A, B, and C in fatty acid composition of PL. Minor differences in individual fatty acids were demonstrated in group D animals (increased liver 20:4n-6 and increased muscle 22:5n-3); however, the unsaturation indices in liver and muscle were not significantly different between any of the groups. In considering that the minor changes in group D animals were not demonstrated in hyperinsulinemic group B animals or hyperglycemic, hyperinsulinemic group C animals, it is likely that the differences in group D animals were secondary to the more severe disturbances in glucose homeostasis and hypoinsulinemia present in these animals. The results of this study suggest that in this rodent diabetic model significant disturbances in glucose homeostasis and hyperinsulinemia may develop independently of changes in tissue fatty acid composition.

Dietary guar gum improves insulin sensitivity in streptozotocin-induced diabetic rats

Although dietary recommendations for diabetics stress the need for increased carbohydrate and dietary fiber, the effectiveness of dietary fiber in improving insulin sensitivity remains controversial. The aim of this study was to compare the effects of a soluble fiber (guar gum) and an insoluble fiber (wheat bran) on insulin sensitivity in streptozotocin-induced (STZ) diabetic rats. Consequently, the rats were divided into two groups and one half were rendered diabetic with streptozotocin. The STZ diabetic and nondiabetic rats were further randomized and fed a diet containing dietary fiber (7 g/100 g diet) from either guar gum or wheat bran. The hyperinsulinemic clamp technique, combined with infusion of the glucose analog, 2-deoxyglucose (2DG), was utilized to examine insulin sensitivity. Bran-fed STZ diabetic rats were significantly (P < 0.001) hyperglycemic, which was ameliorated by guar gum. Insulin-mediated glucose disposal was increased by the guar diet compared with the bran diet in both the STZ diabetic rats [17.7 +/- 2.2 vs. 11.8 +/- 2.4 mL/(kg x min), P < 0.05] and the nondiabetic rats [20.5 +/- 2.8 vs. 15.5 +/- 1.5 mL/(kg x min), P < 0.05]. The accumulation of 2DG in peripheral muscles reflected the changes in insulin sensitivity with a trend for increased 2DG uptake in the majority of analyzed tissues in rats fed the guar diet, both nondiabetic and STZ diabetic, compared with the bran-fed rats. Accompanying these alterations in insulin sensitivity, guar gum suppressed food intake in the hyperphagic diabetic rats by 20% (P < 0.001). The present results demonstrate the effectiveness of guar gum in improving insulin sensitivity in STZ diabetic rats and suggest that reduced food intake may be an important mechanism of action of guar in hyperphagic diabetic rats.

Is leptin sensitivity the link between smoking cessation and weight gain?

The known association between smoking cessation and weight gain, and the suggested role of leptin in the control of body weight, led to the present study which examined the association between smoking and serum leptin concentrations. Mean serum leptin levels, independent of body mass index (BMI), were calculated in male smokers and non-smokers from Nauru, Western Samoa and Mauritius. Smokers were generally leaner than non-smokers, and of similar ages. Levels of physical activity and glucose tolerance status were similar for smokers and non-smokers in Nauru and Western Samoa, while in Mauritius smokers were more active and less likely to be diabetic. Leptin concentrations in smokers were significantly lower than in non-smokers, even after adjusting for BMI, waist/hip ratio (WHR) or waist girth (P < or = 0.04). This association was independent of diabetes status. Smoking, via nicotinic mechanisms, may modify the sensitivity of hypothalamic leptin receptors and consequently modulate leptin synthesis and reduce body weight.

Low-dose growth hormone replacement lowers plasma leptin and fat stores without affecting body mass index in adults with growth hormone deficiency

OBJECTIVE

The ob gene product, leptin, is considered to be a marker of adipose tissue mass and a possible homeostatic regulator of body mass. Our objective was to examine the effect of GH replacement on adipose tissue stores and leptin in adult hypopituitarism.

SUBJECTS

Twenty adults, mean age 47 years (range 20-69) with proven GH deficiency were randomly allocated to either GH (up to 0.25 U/kg/week in daily doses) or placebo for 3 months before cross-over to the opposite treatment.

MEASUREMENTS

Body composition was measured by dual-energy X-ray absorptiometry (DEXA) in the whole body, trunk and limbs. Plasma leptin was measured by radioimmunoassay at baseline and +2, +4, +8 and +12 weeks in each treatment arm.

RESULTS

Total body tissue fat (mean +/- SE) was 30.1 +/- 2.2% after GH compared with 31.9 +/- 2.2% after placebo, P < 0.001 (ANOVA). There were no significant changes in BMI (kg/m2), 29.1 +/- 1.3 after placebo vs 28.8 +/- 1.2 after GH; or waist to hip ratio (WHR), 0.91 +/- 0.01 after both placebo and GH. Baseline plasma leptin showed a significant correlation with baseline BMI, r = 0.67, P < 0.005 and baseline percentage total body fat, R = 0.89, P < 0.001. Plasma leptin (adjusted by using baseline percentage total body fat as a covariate) showed a significant linear decrease with time on GH compared with placebo (P = 0.03, ANOVA).

CONCLUSIONS

Plasma leptin and total body fat fall promptly in response to low-dose replacement of GH in GH-deficient subjects. Hormone-induced changes in leptin can occur in humans in the absence of change in body mass index.

Activities of liver pyruvate dehydrogenase complex and 3-hydroxyacyl-CoA dehydrogenase in sand rat (Psammomys obesus)

The sand rat (Psammomys obesus) is an animal model for non-insulin dependent diabetes mellitus, which is induced by a regular chow diet. The total activity of liver pyruvate dehydrogenase complex in the sand rats under normoglycemic and normoinsulinemic conditions was one half as high as that in the albino rats, but the activity of liver 3-hydroxyacyl-CoA dehydrogenase was more than 4 times greater in the former than in the latter, suggesting a low capacity for glucose oxidation and a high capacity for fatty acid oxidation in the sand rats. These metabolic conditions may be related to the predisposition of the animals towards diabetes. Diet-induced diabetes in the sand rats resulted in decreasing the active form of liver pyruvate dehydrogenase complex and in increasing the activity of liver 3-hydroxyacyl-CoA dehydrogenase, suggesting that the diabetic conditions further suppress glucose oxidation and promote fatty acid oxidation.

Muscle glycogen storage after prolonged exercise: effect of the frequency of carbohydrate feedings

We reported previously that intake of carbohydrate foods with a high glycemic index (GI) produced greater glycogen storage and greater postprandial glucose and insulin responses during 24 h of postexercise recovery than did intake of low-GI carbohydrate foods. In the present study we examined the importance of the greater incremental glucose and insulin concentrations on glycogen repletion by comparing intake of large carbohydrate meals ("gorging") with a pattern of frequent, small, carbohydrate snacks ("nibbling"), which simulates the flattened glucose and insulin responses after low-GI carbohydrate meals. Eight well-trained triathletes [x +/- SEM: 25.6 +/- 1.5 y of age, weighing 70.2 +/- 1.9 kg, and with a maximal oxygen uptake (VO2max) of 4.2 +/- 0.2 L/min] undertook an exercise trial (2 h at 75% VO2max followed by four 30-s sprints) to deplete muscle glycogen on two occasions, 1 wk apart For 24 h after each trial, subjects rested and consumed the same diet composed exclusively of high-GI carbohydrate foods, providing 10 g carbohydrate/kg body mass. The "gorging" trial provided the food as four large meals of equal carbohydrate content eaten at 0, 4, 8, and 20 h of recovery, whereas in the "nibbling" trial each of the meals was divided into four snacks and fed at hourly intervals (0-11, 20-23 h). However, there was no significant difference in muscle glycogen storage between the two groups over the 24 h (gorging: 74.1 +/- 8.0 mmol/kg wet wt; nibbling: 94.5 +/- 14.6 mmol/kg wet wt). The results of this study suggest that there is no difference in postexercise glycogen storage over 24 h when a high-carbohydrate diet is fed as small frequent snacks or as large meals, and that a mechanism other than lowered blood glucose and insulin concentrations needs to be sought to explain the reduced rate of glycogen storage after consumption of low-GI carbohydrate foods.

Assessment of the effect of increased dietary fibre intake on bowel function in patients with spinal cord injury

It is common for constipation to occur following severe spinal cord injury (SCI). Although a bowel management program including a high fibre diet is an integral part of rehabilitation, the effect of a high fibre diet on large bowel function in SCI has not been examined. The aims of this study were to assess the nutrient intake of SCI patients, to determine baseline transit time, stool weight and evacuation time and to assess the effect of addition of bran on large bowel function. Eleven subjects, aged 32 +/- 10.5 years participated in the study. The level of injury ranged from C4 to T12; only one patient had an incomplete injury. Baseline mean energy intake was 7823 +/- 1443 kJ/d, protein intake 93 +/- 21 g/d, carbohydrate intake 209 +/- 39 g/d and mean dietary fibre intake 25 +/- 8 g/d. Mean baseline stool weight was 128 +/- 55 g/d and bowel evacuation time was 13 +/- 7.4 min/d. Three subjects who consumed < 18 g dietary fibre/d had low stool weights of 60-70 g/d and two had very delayed transit times that were too slow to enable quantitation. Mean mouth to anus transit time was 51.3 +/- 31.2 h, mean colonic transit time 28.2 +/- 3.5 h, right colonic transit time 5.9 +/- 4.5 h, left colonic transit time 14.5 +/- 5.2 h and rectosigmoid colonic transit time 7.9 +/- 5.6 h. Following the addition of bran, dietary fibre intake significantly increased from 25 g/d to 31 g/d (P < 0.001). However, the mean colonic transit time increased from 28.2 h to 42.2 h (P < 0.05) and rectosigmoid colon transit time increased from 7.9 to 23.3 h (P < 0.02). Stool weight, mouth to anus, left and right colon transit time and evacuation time did not change significantly. Results of this study suggest that increasing dietary fibre in SCI patients does not have the same effect on bowel function as has been previously demonstrated in individuals with 'normally functioning' bowels. Indeed the effect may be the opposite to that desired. This preliminary study highlights the need for further research to examine the optimal level of dietary fibre intake in SCI patients.

The effect of inhibiting fatty acid oxidation on basal glucose metabolism in Psammomys obesus

We administered etomoxir (an inhibitor of fatty acid oxidation) for five days at a dose of 50 mg/kg/day to three groups of Psammomys obesus. Group A were normoglycemic and normoinsulinemic, group B were normoglycemic and hyperinsulinemic, and group C were hyperglycemic and hyperinsulinemic. When compared with group A, the hyperglycemic/hyperinsulinemic rats of group C had elevated hepatic glucose production (HPG) and elevated glucose uptake (Rg) in all tissues measured reaching statistical significance in white gastrocnemius, soleus and diaphragm. Five days of etomoxir treatment reduced the plasma glucose levels of group C. Etomoxir treatment reduced HGP and although the change was not significant, it was supported by significant reductions of Rg in several tissues including diaphragm, heart, small intestine, brain and white adipose tissue. Five days of etomoxir treatment also reduced the plasma insulin levels in group B and group C, when compared to the levels before treatment. These results demonstrate that inhibition of fatty acid oxidation significantly reduced hyperglycemia, hyperinsulinemia and Rg in some tissues in group C animals suggesting that elevated levels of fatty acid oxidation and increased glucose turnover may be associated with development of NIDDM in Psammomys obesus.

Basal glucose turnover in Psammomys obesus. An animal model of type 2 (non-insulin-dependent) diabetes mellitus

The aim of this study was to examine whole-body glucose turnover and glucose uptake into individual tissues in Psammomys obesus. The animals were classified according to the level of circulating glucose and insulin in the fed state: group A was normoglycaemic and normoinsulinaemic (glucose < 8.0 mmol/l), insulin < 150 mU/l), group B was normoglycaemic and hyperinsulinaemic (glucose < 8.0 mmol/l, insulin > or = 150 mU/l), and group C was hyperglycaemic and hyperinsulinaemic (glucose > or = 8.0 mmol/l, insulin 150 mU/l). The animals were deprived of food for 6 h, after which they were anaesthetized and cannulated, using the jugular vein for infusions and the carotid artery for blood sampling. Whole-body glucose turnover was measured using a primed-continuous infusion of 6-[3H]-glucose and saline to quantitatively assess hepatic glucose production (HGP), glucose disposal (Rd), and the metabolic clearance rate of glucose (MCR). Following the 2-h infusion period, the glucose metabolic index (Rg') of individual tissues was measured using a fixed-dose bolus of 2-deoxy-[14C] glucose. Under the steady-state conditions of the experiment, HGP was assumed to be equal to Rd, and both variables were found to be significantly correlated to the fasting glucose concentration (r=0.534, P<0.05, n=19). On the other hand, MCR was found to be inversely correlated to the fasting plasma glucose concentration (r=0.670 P < 0.01, n=19). When the animals were divided into three groups as described above, HGP in group C animals was significantly elevated compared with group A (20.8 +/- 2.6 vs 12.7 +/- 0.6 mg.kg-1.min-1; P < 0.05), and MCR showed a tendency to be lower in group C than group A, although the difference was not statistically significant. HGP and MCR were not significantly different between groups A and B. Measurement of the glucose metabolic index in individual tissues showed that group C animals had significantly higher Rg' values in muscles and adipose tissues compared with those in group A (P < 0.05). In addition, Rg' in group B white gastrocnemius and soleus were significantly higher than in group A despite similar rates of HGP and levels of glycaemia. These findings suggest that an early increase in skeletal muscle glucose uptake and hyperinsulinaemia can be demonstrated in group B Psammomysobesus before significant hyperglycaemia.

Effect of coingestion of fat and protein with carbohydrate feedings on muscle glycogen storage

Dietary guidelines for achieving optimal muscle glycogen storage after prolonged exercise have been given in terms of absolute carbohydrate (CHO) intake (8-10 g.kg-1.day-1). However, it is of further interest to determine whether the addition of fat and protein to carbohydrate feedings affects muscle glycogen storage. Eight well-trained triathletes [23.1 +/- 2.0 (SE) yr; 74.0 +/- 3.4 kg; peak O2 consumption = 4.7 +/- 0.4 l/min] undertook an exercise trial (2 h at 75% peak O2 consumption, followed by four 30-s sprints) on three occasions, each 1 wk apart. For 24 h after each trial, the subjects rested and were assigned to the following diets in randomized order: control (C) diet (high glycemic index CHO foods; CHO = 7 g.kg-1.day-1), added fat and protein (FP) diet (C diet + 1.6 g.kg-1.day-1 fat + 1.2 g.kg-1.day-1 protein), and matched-energy diet [C diet + 4.8 g.kg-1.day-1 additional CHO (Polycose) to match the additional energy in the FP diet]. Meals were eaten at t = 0, 4, 8, and 21 h of recovery. The total postprandial incremental plasma glucose area was significantly reduced after the FP diet (P < 0.05). Serum free fatty acid and plasma triglyceride responses were significantly elevated during the FP trial (P < 0.05). There were no differences between trials in muscle glycogen storage over 24 h (C, 85.8 +/- 2.7 mmol/kg wet wt; FP, 80.5 +/- 8.2 mmol/kg wet wt; matched-energy, 87.9 +/- 7.0 mmol/kg wet wt).(ABSTRACT TRUNCATED AT 250 WORDS)

Resistant starch in the diet increases breath hydrogen and serum acetate in human subjects

The colonic fermentation of two diets differing in amounts of resistant starch (RS) was studied. High- and low-RS diets were fed to eight healthy subjects in three meals for 1 d. Breath hydrogen and two blood samples were collected over a 28-h period. The high-RS diet provided 59.1 +/- 4.7 g (mean +/- SE) RS and the low-RS diet provided 5.2 +/- 0.4 g RS. Breath hydrogen and the average total serum acetate were significantly higher during the high-RS diet than during the low-RS diet: 34.1 +/- 4.7 and 23.9 +/- 3.9 ppm (P < 0.001) and 169.1 +/- 12.8 and 118 +/- 6.6 mumol/L (P < 0.01), respectively. Butyrate and propionate were also detected in serum samples. Although not statistically significant, there was a trend (P = 0.087) for butyrate to increase with the high-RS diet. Subjects reported greater gastrointestinal symptoms during the high-RS diet. These results suggest that RS may have effects comparable with those of some fermentable dietary fibers.

The effect of restricting energy intake on diabetes in Psammomys obesus

The aim of this paper was to determine whether restricting energy intake would reduce the elevated levels of glucose, insulin, cholesterol and triglyceride in diabetic Psammomys obesus (sand rat). Between 11 and 12 weeks of age Psammomys obesus were divided into three groups based on blood glucose and plasma insulin levels in the fed ad libitum state; group 1 was normoglycemic (4.4 +/- 0.3 mM) and normoinsulinemic (0.46 +/- 0.04 ng/ml), group 2 was normoglycemic (5.0 +/- 0.3 mM) and hyperinsulinemic (3.58 +/- 0.62 ng/ml) and group 3 was hyperglycemic (11.2 +/- 1.2 mM) and hyperinsulinemic (6.23 +/- 0.73 ng/ml). Energy intake was restricted to 67% of normal for 2 weeks before ad libitum feeding was resumed for a further 2 weeks. Animals in group 3 developed the most abnormalities when compared to group 1 including increased levels of food intake (16.3 +/- 0.5 vs 14.2 +/- 0.5 g/day, P < 0.05), body weight (192 +/- 5 vs 162 +/- 4 g, P < 0.05), triglycerides (1.5 +/- 0.2 vs 0.96 +/- 0.08 mM, P < 0.05), and cholesterol (2.8 +/- 0.2 vs 2.1 +/- 0.1 mM, P < 0.05). In group 3, food restriction was effective in reducing glucose levels (but not insulin) both during and following the restriction period respectively (11.2 +/- 1.2 vs 4.6 +/- 0.5, and 5.9 +/- 1.3, mM, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction in hyperglycemia by mild food restriction in streptozotocin induced diabetic rats improves insulin sensitivity

Hyperglycemia has been shown to contribute to the development and maintenance of insulin resistance in diabetic subjects and animal models of diabetes. Normalisation of circulating glucose levels is effective in restoring insulin action. The aim of the current study was to investigate the effects of mild food restriction on hyperglycemia in streptozotocin (STZ) treated (50 mg/kg) diabetic rats and to determine if the reductions in glycemia following food restriction were sufficient to alter insulin sensitivity. Food restriction was achieved in STZ diabetic and normal rats by limiting food access to two one-hourly meals daily and further in normal rats by restricting the feeding period to a single two-hour meal daily. Food intake was lowered by 39.7% (p < 0.01) in the food restricted STZ rats, without significant alteration in weight gain over 4 weeks. Similarly, in the normal rats once and twice daily meals lowered food intake by 37.6% and 21.6% when compared to the ad-libitum fed group, respectively. After 3 weeks food restriction in the STZ diabetic rats mean plasma glucose levels over a 12 hour period were reduced by 13.9%, glucose levels after a 6 hr fast were reduced by 33% (p < 0.05). Plasma insulin levels remained unaltered by food restriction. After 4 weeks food restriction in STZ diabetic rats basal glucose turnover was reduced (p < 0.05) and the metabolic clearance rate of glucose (MCR) increased (p < 0.05). During the hyperinsulinemic clamp hepatic glucose output (HGO) was suppressed and MCR elevated more effectively in the food restricted STZ than the ad-libitum STZ rats.(ABSTRACT TRUNCATED AT 250 WORDS)

A cross-sectional and short-term longitudinal characterisation of NIDDM in Psammomys obesus

The present study was undertaken to examine the cross-sectional and short-term longitudinal changes in glucose and insulin concentrations as well as measure the enzymatic activity of PEPCK and glycogen synthase in our Psammomys obesus colony. In the cross-sectional study, blood samples were taken from one group of animals at 19 weeks of age (n = 37) in the fed state and following a 4-h fast. In a separate group of 19-week-old animals (n = 69), samples were taken 1 h following an OGTT (1 g/kg body weight) in Psammomys subjected to a 16-h fast. In the longitudinal study, blood samples were taken from one group of animals in the fed state at 7, 11, 15 and 19 weeks of age. All of the cross-sectional data have described the classic inverted U-shaped curve (Starling's curve of the pancreas) in the relationship between glucose and insulin levels. This trend was also reflected by Psammomys subjected to the OGTT; a mild impairment in glucose tolerance was associated with an increase in the insulin response and a further impairment in glucose tolerance was associated with a reduction in the insulin response. Similar results were obtained following a 4-h fast. The short-term longitudinal glucose and insulin data revealed that of the 37 animals examined over the 12-week period, 16 progressed along the inverted U-shaped curve described by the cross-sectional data. Of the other animals, 8 remained unchanged, 7 were unclassifiable and 6 hyperglycaemic Psammomys developed normoglycaemia at the expense of elevated insulin levels.(ABSTRACT TRUNCATED AT 250 WORDS)