Modulation of leucine oxidation and turnover by graded amounts of carbohydrate intake in obese subjects

Our previous in vitro studies with rat tissues have suggested that ketone bodies may regulate the oxidation of branched-chain amino acids. To investigate the physiological and clinical significance of this observation, we determined the effect of starvation-induced ketosis on leucine metabolism in obese subjects. Rates of turnover, plasma clearance, and expiratory ¹⁴CO₂ production (indicator of oxidation) after intravenous infusion of a trace amount of [1-¹⁴C]-leucine were measured before and one week after starvation (80 cal/day). This dietary treatment caused a significant increase in the rate of ¹⁴CO₂ production, but significantly reduced the turnover (9.1 versus 7.0 mmole/hr) and plasma clearance (65 versus 34 L/hr) of leucine. When ketosis was prevented by a daily intake of 300 calories of carbohydrate, the rate of ¹⁴CO₂ production was significantly decreased. On the other hand, starvation-induced decreases in turnover and plasma clearance of leucine, increases in plasma concentrations of branched-chain amino acids (marker for heightened proteolysis), decreases in plasma concentrations of alanine (marker for stimulated hepatic gluconeogenesis), and decreases in plasma concentrations of glucose and insulin were not prevented until carbohydrate intake was increased to 500 or 800 calories per day. Increases in daily carbohydrate intake (up to 500 calories) were accompanied by decreases in urinary excretion of nitrogen, but not 3-methylhistidine (marker for muscle proteolysis). Our data suggest that: (1) ketosis directly or indirectly enhances oxidation of leucine, (2) starvation-induced ketosis, proteolysis, and gluconeogenesis can be prevented sequentially by carbohydrate diets providing fro 300–800 calories per day, (3) the reduced turnover of leucine in starvation is most likely the result of reduced protein synthesis, and (4) diminution of branched-chain amino acid catabolism is a component of the nitrogen-sparing effect of carbohydrate.     

Failure of glyburide and insulin treatment to decrease leucine flux in obese type II diabetic patients

Poorly-controlled type I diabetic patients have elevated rates of leucine appearance (indicating increased proteolysis), which are reduced with insulin therapy. It also has been suggested that obesity increases leucine appearance rate by reducing sensitivity to insulin. In the present study, we examined whether non-diabetic obese women or poorly-controlled obese type II diabetic patients have elevated leucine appearance rates, and whether diabetic patients have a reduction in leucine appearance with treatment of their hyperglycemia. Among non-diabetic women, postabsorptive leucine appearance rate was positively correlated with the percentage of body weight as fat (r = 0.92, P less than 0.01). Obese women with untreated type II diabetes did not have a higher mean (+/- s.e.m.) leucine appearance rate (2.13 +/- 0.18 mumols/min/kg fat-free mass, determined by infusion of 1-[1-13C] leucine as a tracer) than obese non-diabetic women with a similar fat-free mass (2.49 +/- 0.09 mumols/min/kg fat-free mass). After two weeks of glyburide therapy mean glucose concentrations decreased 24 percent and glucose production decreased 18 percent, but leucine appearance rate was not altered (2.08 +/- 0.18 mumols/min/kg fat-free mass). After 2 weeks of insulin therapy, mean fasting glucose concentration and glucose production rate were normal (55 per cent and 46 per cent below pre-treatment levels), but leucine appearance rates remained unchanged (2.17 +/- 0.18 mumols/min/kg fat-free mass). We conclude that type II diabetes in obese patients is not associated with elevated proteolysis, that treatments that significantly improve or normalize postabsorptive glucose metabolism in obese type II diabetic patients do not affect postabsorptive proteolysis, and that obesity per se (without diabetes) increases proteolysis.     

Estrogen supplementation reduces whole body leucine and carbohydrate oxidation and increases lipid oxidation in men during endurance exercise

Healthy active men exhibit higher rates of carbohydrate (CHO) and leucine oxidation and lower rates of lipid oxidation compared with their female counterparts both at rest and during moderate intensity endurance exercise. We postulated that this reduced dependence on amino acids as a fuel source in women was due to the female sex hormone estrogen. In a randomized, double-blind, placebo-controlled, cross-over design, we investigated the effect of supplementing 12 recreationally active men with estrogen on whole body substrate oxidation and leucine kinetics at rest and during moderate intensity endurance exercise. Subjects cycled for 90 min at an intensity of 65% maximum O(2) consumption after 8 d of either estrogen supplementation (2 mg 17beta-estradiol/d) or placebo (polycose). After a 2-wk washout period, they repeated the test after 8 d of the alternate treatment. On the test day, after a primed continuous infusion of l-[(13)C]leucine, O(2) consumption, CO(2) production, steady-state breath (13)CO(2), and plasma alpha-[(13)C]ketoisocaproate enrichments were measured at rest and at 60, 75, and 90 min during exercise in the postabsorptive state. Exercise increased energy expenditure more than 5-fold, CHO oxidation more than 6-fold, lipid oxidation more than 4-fold, and leucine oxidation 2.2-fold (all P < 0.0001), whereas it decreased the ratio of lipid to CHO oxidation by 50-70% (P = 0.003) compared with values at rest. Estrogen supplementation decreased respiratory exchange ratio during exercise (P = 0.03). Estrogen supplementation significantly decreased CHO oxidation by 5-16% (P = 0.04) and leucine oxidation by 16% (P = 0.01), whereas it significantly increased lipid oxidation by 22-44% (P = 0.024) at rest and during exercise. We conclude that estrogen influences fuel source selection at rest and during endurance exercise in recreationally active men, characterized by a reduced dependence on amino acids and CHO and an increased reliance on lipids as a fuel source.     

Nutrient oxidation patterns and protein metabolism in lean and obese subjects

The immediate metabolic response to eating has been compared in a group of grossly obese subjects (W/H2 = 45) with that in lean controls (W/H2 = 22). Dietary intake of energy for obese subjects was based on their estimated basal energy expenditure for ideal body weight (given at an hourly rate of 3 X BMR over a 4-h period). Lean subjects were measured twice: control 1 with the same intake of energy as the obese in terms of ideal body weight and control 2 with the same energy intake in relation to each subject's measured resting energy expenditure (2.2 X REE). The changes in energy expenditure and nutrient disposal with the onset of eating have been assessed by a method of combined respiratory gas analysis and intravenous infusion of 13C-labelled leucine. Leucine kinetics were used to quantitate rapid changes in protein oxidation and to assess protein synthesis and degradation. 1) Total energy expenditure was 20-30 per cent greater in obese subjects than lean subjects in fasting and feeding. Energy expenditure expressed per kg fat-free mass, from D2O dilution, was similar in obese and lean subjects in both fasting (5.8 v. 5.5 kJ/kg FFM/h) and feeding [6.7 v. 6.3 (Control 2) kJ/kg FFM/h]. 2) The onset of eating was associated with increased carbohydrate and protein oxidation with decreased fat oxidation in both lean and obese individuals. In obese subjects, however, both the decrease in fat oxidation and the increase in protein oxidation were significantly smaller (P less than 0.05) than the corresponding increments in lean subjects (Control 2). 3) The rate of protein synthesis was significantly (P less than 0.05) higher in obese subjects both in the fasting state (99 v. 84 mumols leucine/kg FFM/h) and in the fed state [94 v. 67 (Control 2) mumols leucine/kg FFM/h]. The rate of protein degradation was also higher in obese individuals in fasting (117 +/- 6 v. 106 +/- 4 mumol leucine/kg FFM/h) and feeding [65 +/- 4 v. 54 +/- 6 (Control 2) mumol leucine/kg FFM/h] though these differences are not statistically significant (P greater than 0.05). 4) The observed differences between obese and lean individuals in protein and energy metabolism in the fasted state and in the immediate response to eating do not support a hypothesis of greater metabolic efficiency in obesity.     

A three-day insulin-induced normoglycemia improves carbohydrate oxidation in type 2 diabetic subjects

Two months of a better glycemic control improve carbohydrate oxidation in type 2 diabetes. However, this benefit is uncertain for a shorter duration. We tested the effect of 3 days of normoglycemia induced by an insulin infusion. Ten type 2 diabetic subjects (body mass index [BMI], 30.0 +/- 1.1; glycosylated hemoglobin [HbA(1C)], 10.1 +/- 0.5) were studied twice, before and after normal glucose levels were maintained by a 72-hour intravenous insulin infusion. Indirect calorimetry was performed 1 hour before (basal) and during the 3 hours after (postprandial) the ingestion of a standard meal (carbohydrates, 72 g; fat, 21 g; protein, 32 g), at noon. Carbohydrate storage was calculated as ingested carbohydrate - (postprandial glycosuria + suprabasal postprandial carbohydrate oxidation). After normoglycemia, glucose and triglyceride levels were decreased (basal glucose, 13.8 +/- 1.1 mmol/L to 8.8 +/- 0.5; postprandial, 14.9 +/- 0.9 to 11.0 +/- 0.5; basal triglycerides, 2.2 +/- 0.1 mmol/L to 1.6 +/- 0.2; postprandial, 2.7 +/- 0.2 to 1.9 +/- 0.2; all P <.01), C peptides were unchanged. Glycosuria (before, 0.30 mg/kg/min) was abolished after normoglycemia. Basal carbohydrate, lipid, protein oxidation, and energy production rates were unchanged. Postprandial carbohydrate oxidation was increased after normoglycemia (before, 1.33 +/- 0.38 mg/kg/min; after, 1.77 +/- 0.42; P <.05). Lipid oxidation and plasma free fatty acids (FFA) tended to be more suppressed by the meal after normoglycemia (not significant [NS]). Carbohydrate storage (before, 67,5 +/- 4.6 g; after, 65.7 +/- 3.6; NS) and diet-induced thermogenesis did not change after normoglycemia. Short-term insulin-induced normoglycemia improves the postprandial oxidation of carbohydrates, but not their storage.     

High protein vs high carbohydrate hypoenergetic diet for the treatment of obese hyperinsulinemic subjects

OBJECTIVE: To test the hypothesis that hyperinsulinemic obese subjects would respond differently to changes in the composition of hypoenergetic diets. DESIGN: A 4-week randomized dietary intervention trial. SUBJECTS: Thirteen male obese hyperinsulinemic normoglycemic subjects were divided into two groups and fed hypoenergetic diets providing 80% of their resting energy expenditure (REE). One group received a high-protein diet (HP; 45% protein, 25% carbohydrates, and 30% fat as percent of dietary energy) and the other a high-carbohydrate diet (HC; 12% protein, 58% carbohydrates and 30% fat). MEASUREMENTS: Anthropometry, body composition, fasting serum insulin and lipids, and REE were performed before and after the feeding period. RESULTS: Weight loss was higher in the HP than HC group (8.3+/-0.7 vs 6.0+/-0.6 kg, P<0. 05). There was a decrease in body fat in both groups, whereas body water decreased significantly more in the HP group. REE decreased more in the HC than the HP group (-384.3+/-84.6 vs -132.3+/-51.0 kcal, P<0.05). Serum total cholesterol, triglycerides and LDL cholesterol decreased significantly to a similar extent in both diet groups, while HDL cholesterol was decreased significantly only in the HP group. Mean fasting insulin decreased significantly in both diet groups and reached the normal range only in the HP group. CONCLUSION: A low-carbohydrate (LC), HP hypoenergetic diet could be the diet composition of choice for a weight-reducing regimen in obese hyperinsulinemic subjects.     

极低碳水化合物饮食对肥胖症患者心血管危险因素的影响

 目的 观察极低碳水化合物饮食(VLCD)治疗对单纯性肥胖患者心血管危险因素的影响。 方法 观察35例肥胖患者经VLCD治疗8周后,体重、腰围及血压改善的同时,空腹血糖(FPG)、空腹胰岛素(FIns)、血脂谱、尿微量白蛋白/肌酐(UACR)、C反应蛋白(CRP)、TNFα、脂联素(adiponectin)等心血管危险因素的改变。另采集35例健康志愿者作为基线对照组。 结果 基线时肥胖组较正常对照组有更显著的心血管危险因素(P值均<0.05)。试验结束时肥胖患者的体重与腰围分别减少了(8.5±0.7)kg与(6.6±1.1)cm(P值均<0.01);收缩压、舒张压、FIns、TC、TG等指标均较前显著降低(P值均<0.05);FPG、LDL-C及HDL-C等的改变无统计学意义;UACR、CRP、TNFα分别减少了(1.86±0.86)μg/mg、(1.15±0.45)mg/L及(0.94±0.21)ng/L(P值均<0.05);脂联素水平增加了(2.12±0.59)mg/L(P<0.01)。结论 8周的VLCD治疗肥胖症可有效减重并显著改善多种心血管危险因素。     

Effect of orlistat therapy on carbohydrate, lipid, vitamin and hormone plasma levels in obese subjects

Orlistat is an inhibitor of lipase which splits triglycerides into free fatty acides and glycerol. This drug, by inhibiting hydrolysis of triglycerides, is the cause of significant loss of fat in the faeces. 13 obese and 15 nonobese subjects were examined. Obese subjects received orlistat (Xenical, F. Hoffmann La Roche Ltd, Switzerland) 3 x 120 mg/d. Treatment with orlistat for 16 weeks was followed by a significant fall of BMI and MAP, insulinemia, insulin/glucose ratio, leptinemia, serum total cholesterol, triglycerides, HDL-cholesterol and 25-OH-D concentration respectively. Orlistat did not influence significantly serum LDL-cholesterol concentration but unexpectedly increased plasma levels of folic acid, vitamin B12 and NPY. CONCLUSIONS: (1) Monitoring of plasma 25-OH-D levels in obese patients on orlistat therapy seems to be mandatory. (2) In spite of significant changes (in opposite direction) in leptinemia and serum NPY level observed in obese subjects treated with orlistat, presence of a functional relationship between these hormones could not be confirmed.     

Plasma growth hormone response to L-dopa in obese subjects

The growth hormone response to oral administration of 500 or 1000 mg of L-dopa was investigated in nine obese subjects, none of whom showed evidence of glucose intolerance. Growth hormone and cortisol responsiveness to insulin hypoglycemia was also tested in these subjects. A significant growth hormone response following L-dopa administration was seen in only two subjects. Five subjects displayed normal growth hormone responsiveness following insulin-induced hypoglycemia, and normal increments of plasma cortisol levels following induction of such hypoglycemia were seen in six of the eight subjects in whom this was studied. Only one of the subjects with a normal growth hormone response following L-dopa administration exhibited a normal response to hypoglycemia. Increasing the dose of L-dopa in a given subject did not enhance growth hormone responsiveness. No consistent cortisol response to either dose of L-dopa was noted. L-dopa therefore, is still another stimulus, which, while effective in normal subjects, is ineffective with regard to eliciting growth hormone release in obese subjects. It appears to be less effective than hypoglycemia in this regard. The lack of responsiveness to L-dopa in these obese subjects would imply that their decreased sensitivity to other stimuli capable of provoking growth hormone release in normal subjects is not secondary to decreased levels of the hypothalamic neuro transmitter agent(s) believed to be involved in growth hormone regulation.     

Diet-induced thermogenesis in man: thermic effects of single protein and carbohydrate test meals in lean and obese subjects

Postprandial thermogenesis of 8 healthy males of normal body weight and 17 healthy obese subjects with a body weight gain of more than 10 kg per year was measured continuously by means of a respiratory chamber over 10 h after test meals of 1 and 2 MJ protein (casein) and 2 MJ carbohydrate (hydrolized starch). The total thermic response to all test meals was reduced by about 50% in the obese subjects. The thermic response was related to body weight, energy intake, resting metabolic rate and weight loss during restricted energy intake. The necessity for a careful characterization of the obese subjects in studies of thermogenesis and of efficiency of energy utilization in obesity is pointed out. It is suggested that thermic response to food can be considered as a suitable indicator for the distinction between people of different metabolic efficiency.     

Reduced carbohydrate intake in citrin-deficient subjects

Summary  Citrin is the liver-type aspartate-glutamate carrier that resides within the inner mitochondrial membrane. Citrin deficiency (due to homozygous or compound heterozygous mutations in the gene SLC25A13) causes both adult-onset type II citrullinaemia (CTLN2) and neonatal intrahepatic cholestasis (NICCD). Clinically, CTLN2 is characterized by hyperammonaemia and citrullinaemia, whereas NICCD has a much more varied and transient presentation that can include multiple aminoacidaemias, hypoproteinaemia, galactosaemia, hypoglycaemia, and jaundice. Personal histories from CTLN2 patients have repeatedly described an aversion to carbohydrate-rich foods, and clinical observations of dietary and therapeutic outcomes have suggested that their unusual food preferences may be directly related to their pathophysiology. In the present study, we monitored the food intake of 18 Japanese citrin-deficient subjects whose ages ranged from 1 to 33 years, comparing them against published values for the general Japanese population. Our survey confirmed a marked decrease in carbohydrate intake, which accounts for a smaller proportion of carbohydrates contributing to the total energy intake (PFC ratio) as well as a shift towards a lower centile distribution for carbohydrate intake relative to age- and sex-matched controls. These results strongly support an avoidance of carbohydrate-rich foods by citrin-deficient patients that may lead to worsening of symptoms. Competing interests: None declared References to electronic databases: Citrullinaemia, type II, adult-onset (CTLN2): OMIM 603471. Citrullinaemia, type II, neonatal-onset (neonatal intrahepatic cholestasis caused by citrin deficiency, NICCD): OMIM 605814.     

Study on the effect of insulin on carbohydrate and lipid metabolism in obese subjects with normal glucose tolerance]

In altogether 32 test persons with normal weight and obese test persons glucose-insulin-tolerance-tests were carried out. In obese persons with normal carbohydrate tolerance -- characterized by 50 g oral glucose tolerance test -- by the decreased glucose assimilation coefficients and the significantly increased level of glycaemia after intravenous application of glucose a disturbance of the glucose-insulin-homoeostasis is already implied. Basal and glucose-stimulated concentrations of IRI in the peripheral venous blood were significantly increased in obese persons. The parameters of lipolysis glycerol and free fatty acids show after a glucose-stimulated insulin excretion and after exogenic insulin application a somewhat retarded decrease in obese persons compared with the control group. In connection with the significantly increased insulin levels in obese persons these findings might refer to a decreased antilipolytic effect of insulin. The two fundamental physiological effects of insulin in the carbohydrate and fat metabolism -- glucose utilization and inhibition of lipolysis -- seem to be distrubed in the same way in obesity.     

Randomized comparison of reduced fat and reduced carbohydrate hypocaloric diets on intrahepatic fat in overweight and obese human subjects

Obesity-related hepatic steatosis is a major risk factor for metabolic and cardiovascular disease. Fat reduced hypocaloric diets are able to relieve the liver from ectopically stored lipids. We hypothesized that the widely used low carbohydrate hypocaloric diets are similarly effective in this regard. A total of 170 overweight and obese, otherwise healthy subjects were randomized to either reduced carbohydrate (n = 84) or reduced fat (n = 86), total energy restricted diet (-30% of energy intake before diet) for 6 months. Body composition was estimated by bioimpedance analyses and abdominal fat distribution by magnetic resonance tomography. Subjects were also submitted to fat spectroscopy of liver and oral glucose tolerance testing. In all, 102 subjects completed the diet intervention with measurements of intrahepatic lipid content. Both hypocaloric diets decreased body weight, total body fat, visceral fat, and intrahepatic lipid content. Subjects with high baseline intrahepatic lipids (>5.56%) lost ≈7-fold more intrahepatic lipids compared with those with low baseline values (<5.56%) irrespective of diet composition. In contrast, changes in visceral fat mass and insulin sensitivity were similar between subgroups, with low and high baseline intrahepatic lipids. CONCLUSION: A prolonged hypocaloric diet low in carbohydrates and high in fat has the same beneficial effects on intrahepatic lipid accumulation as the traditional low-fat hypocaloric diet. The decrease in intrahepatic lipids appears to be independent of visceral fat loss and is not tightly coupled with changes in whole body insulin sensitivity during 6 months of an energy restricted diet.     

Mutations in the adiponectin gene in lean and obese subjects from the Swedish obese subjects cohort

Adiponectin (also called AdipoQ, gelatin-binding protein 28, Acrp30) DNA sequence variants were determined in 96 unrelated female subjects with severe obesity (mean body mass index [BMI], 42.3 kg/m2) and in 96 non-obese female controls (mean BMI, 23.0 kg/m2) from the Swedish Obese Subjects (SOS) cohort. A single base substitution (T45G) at codon 15 of exon 2 resulting in no change in amino acid (Gly15Gly) was found in equal frequencies among obese and control subjects. However, this polymorphism was associated with serum cholesterol and waist circumference (P=.023 and.043, respectively) in the obese group. A IVS2 + G62T sequence variation was also identified, but had similar prevalence rates in obese and control subjects. Blood glucose was highest in the obese female subjects who were homozygotes for the G allele (GG) of the IVS2 + G62T polymorphism (N=56; P=.033) and all the diabetics (n=6) in this sample were in this group. IVS2 + G62T polymorphism was also associated with BMI (P=.014), diastolic blood pressure (P=.009), and sagittal diameter (P=.032). A missense point mutation at codon 111 (Tyr111His) was not associated with any obesity-related phenotypes. In conclusion, adiponectin DNA sequence variations might play a role in the complications of morbid obesity and should be further investigated.