The comparative oxidation of glucose, fructose, sorbitol and xylitol in normal man

The aim of the study was to compare the effects of fructose, sorbitol and xylitol with those of glucose on blood glucose and insulin levels and carbohydrate utilization in man. The experiment was performed by means of continuous indirect calorimetry in five groups of five to six normal volunteers during infusion of either glucose, fructose, sorbitol, xylitol or a mixture of fructose, glucose and xylitol in the proportion of 2:1:1. Glucose and insulin did not present any important variations during the fructose, sorbitol and xylitol infusiosns. However, carbohydrate oxidation rose significantly during administration of these substrates. Carbohydrate oxidation rose 80 mg/min for fructose, 27 mg/min for sorbitol, 39 mg/min for xylitol and 75 mg/min for the carbohydrate mixture, in comparison to 101 mg/min for glucose. It is concluded that fructose, sorbitol and xylitol provoke an increase in carbohydrate utilization without a corresponding rise in glycemia and insulinemia.     

Comparison between a glucose-fructose-xylitol solution and a sole glucose solution for surgical patients with glucose tolerance impairment

The metabolic response to the postoperative delivery of a sole glucose solution or a glucose-fructose-xylitol solution, and their effects upon carbohydrate metabolism, in patients with glucose tolerance impairment, were evaluated. Twenty four patients who showed an abnormal 75g-OGTT or were noninsulin-dependent diabetics were divided in two groups. The GFX-B group (n = 11) received a 10.5% solution, containing glucose, fructose and xylitol at 4:2:1 ratio, and the PHY-3 group (n = 13) received a 10% glucose solution, both, continuously infused for 3 days postoperatively. The infusion of PHY-3 tended to produce a higher increase in blood glucose than the infusion of GFX-B, that was significantly different on the 3POD (P less than 0.05). The increase in IRI and CPR was also significantly greater in PHY-3 group than in GFX-B group on the 3POD (P less than 0.05). We concluded that it was not only the slight lower glucose load of the GFX-B solution, but also, the different infused carbohydrate substrate which had influenced the magnitude of insulin secretion and the blood glucose level. Then, its use in glucose intolerant patients may be of some benefit to partially minimize the postoperative hyperglycemic response.     

Comparative effects of fructose and glucose on the lipid and carbohydrate metabolism of perfused rat liver.

1. Livers from rats fed on a standard diet were perfused with whole blood, and infused continuously with glucose and fructose at equimolar rates. 2. Infusion of fructose increased both the secretion of very-low-density-lipoprotein (VLDL)-triglycerides and the incorporation of free fatty acids (FFA) from the perfusate into VLDL-lipids, but neither of these two processes was affected by infusion of glucose. 3. Infusion of fructose decreased the oxidation and increased the esterification of FFA, but glucose infusion had no effect on these processes. When fructose and glucose were infused together was a further decrease in oxidation. 4. When fructose was infused alone or together with glucose, blood concentrations rapidly became stabilized at those found in the hepatic portal vein in vivo, with similar rates of hepatic uptake to those found in the intact animal. Infusion of glucose alone resulted in continuously increasing perfusate glucose concentrations, and rates of uptake which were only 20% of those for fructose. Blood glucose concentrations were reduced, and lactate concentrations were increased by fructose infusion, and when glucose and fructose were infused together there was a greatly increased rate of glucose uptake. 5. Liver glycogen was not affected by the infusion of fructose or glucose alone; however, their combined addition significantly increased its concentration. 6. Uptake of perfusate FFA was not affected by either fructose or glucose infusions. 7. The results are discussed in terms of the differences in nutrition and metabolism between glucose and fructose, with particular reference to the development of hypertriglyceridaemia.     

Effect of excess xylitol on nitrogen and glucose metabolism in parenterally fed rats.

The objectives of this study were to investigate the effects of an excess of xylitol on nitrogen balance and glucose metabolism in parenterally fed rats. Female Sprague-Dawley rats (200-250 g, n = 17) were catheterized for total parenteral nutrition and then randomized into two groups based on subsequent diet. The two diets used were isonitrogenous (1.5 g of nitrogen per kilogram per day) and isocaloric, with half the calories (125 kcal/kg per day) being derived from lipid (125 kcal/kg per day) and the other half from either glucose or xylitol (125 kcal/kg per day). The rats were fed a half-strength total parenteral nutrition diet for the day after surgery and a full-strength total parenteral nutrition diet for the following 4 days. Urines were collected daily for the determination of nitrogen balance. On day 5, the rats were given a 7- to 8-hour infusion of 6.6-d2 glucose (6 mg/h and 2-d1 glucose (12 mg/h). At the conclusion of the isotope infusion period, the rats were killed and blood was collected. Urine output was increased by 22% per day in the xylitol-treated rats, and they excreted 46.5 mmol of xylitol per liter per kilogram per day (7.1 g/kg per day, approximately 22.7% of dose). The xylitol group lost weight, had poorer nitrogen balance (341 +/- 31 vs 83 +/- 29 mg/kg per day [mean +/- standard error of the mean], p < .05), and developed fatty livers. Analysis of the liver fat distribution pattern indicated that the source of the excess hepatic lipid was dietary fat.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermogenesis in men and women induced by fructose vs glucose added to a meal

Energy expenditure (EE) was measured by indirect calorimetry in 20 subjects (10 men and 10 women) for 30 min before and 6 h after the ingestion of a mixed meal containing 20% protein, 33% fat, and either 75 g glucose or 75 g fructose as carbohydrate source (47%). Diet-induced thermogenesis (DIT) and the rate of carbohydrate oxidation were significantly greater with fructose (12.4 +/- 0.6% and 54.8 +/- 2.1 g/6 h, respectively) than with glucose (10.7 +/- 0.7%, p less than 0.01, and 48.3 +/- 2.4 g/6 h, p less than 0.01, respectively). The DIT of male (12.1 +/- 1% and 13.9 +/- 0.8% with glucose and fructose, respectively) was greater than that of female subjects (9.2 +/- 0.7%, p less than 0.05, and 11.0 +/- 0.7%, p less than 0.05, respectively). In contrast to the glucose meal, negligible changes in plasma levels of glucose and insulin were observed with the fructose meal but plasma levels of lactate increased more with fructose than with glucose (peak values: 3.3 +/- 0.6 vs 1.5 +/- 0.1 mmol/L, respectively). When fructose provides the only carbohydrate source of a mixed meal, it induces a larger increase in carbohydrate oxidation and thermogenesis than when glucose is the carbohydrate source.     

Preoperative oral carbohydrate administration reduces postoperative insulin resistance

Infusions of carbohydrates before surgery reduce postoperative insulin resistance. We in-vestigated the effects of a carbohydrate drink, given shortly before surgery, on postoperative metabolism. METHOD: Insulin sensitivity, glucose turnover ([6,6, 2H2]-D-glucose) and substrate utilization were measured using hyperinsulinemic normoglycemic clamps and indirect calorimetry in two matched groups of patients before and after elective colorectal surgery. The drink group (n = 7) received 800 ml of an isoosmolar carbohydrate rich beverage the evening before the operation (100 g carbohydrates), as well as another 400 ml (50 g carbohydrates) 2 h before the initiation of anesthesia. The fasted group (n = 7) was operated after an overnight fast. RESULTS: After surgery, energy expenditure increased in both groups. Endogenous glucose production was higher after surgery and the difference was significant during low insulin infusion rates in both groups (P < 0.05). The supressibility of endogenous glucose production by the two step insulin infusion was similar pre-and postoperatively in both groups. At the high insulin infusion rate postoperatively, whole body glucose disposal was more reduced in the fasted group (-49 +/- 6% vs -26 +/- 8%, P < 0.05 vs drink). Furthermore, during high insulin infusion rates, glucose oxidation decreased postoperatively only in the fasted group (P < 0. 05) and postoperative levels of fat oxidation were greater in the fasted group (P < 0.05 vs drink). Only minor postoperative changes in cortisol and glucagon were found and no differences were found between the treatment groups. CONCLUSIONS: Patients given a carbohydrate drink shortly before elective colorectal surgery displayed less reduced insulin sensitivity after surgery as compared to patients who were operated after an overnight fast.     

Comparison of effects of dietary glucose versus fructose during pregnancy on fetal growth and development in rats

Dietary carbohydrate during pregnancy is essential. Whether this requirement is specific to glucose was investigated. We examined whether fructose at low, intermediate and high levels can substitute for an isoenergetic amount of glucose by feeding graded levels of both carbohydrates (0, 4, 12, 60%) in a triglyceride-based diet throughout pregnancy. It was concluded that the carbohydrate requirement for the rat during pregnancy is not specific to glucose and that the level, not the type, of carbohydrate was critical (experiment 1). A second aspect of the study (experiment 2) was the comparison of isoenergetic, low carbohydrate diets containing different sources of 4% glucose equivalents: glucose, fructose or lipid-glycerol. Fructose and lipid-glycerol were not equivalent substitutes for glucose in the pregnant rat dam at these very low intakes.     

Effects of glucagon in the control of endogenous glucose production in man.

Endogenous glucose production has been shown to increase during administration of glucagon + fructose, but not during administration of fructose alone. To determine the mechanisms by which glucagon exerts this action, endogenous glucose production (EGP) and gluconeogenesis from fructose (GNF) were measured in eight healthy subjects infused 1) with graded doses of glucagon (2 and 4 ng.kg-1.min-1 for 3 h each) during constant infusion of 13C-fructose (3 mg.kg-1.min-1), and 2) with graded doses of 13C-fructose (3 and 6 mg.kg-1.min-1) during constant glucagon infusion (2 ng.kg-1.min-1). GNF was estimated from 13C-glucose synthesis. In both protocols, infusion of 3 mg.kg-1.min-1 fructose + 2 ng.kg-1.min-1 glucagon increased EGP by 5-8% (P < 0.05), while GNF represented 43-49% of EGP. Thereafter, increasing the glucagon infusion rate further increased EGP to 118 +/- 3% of basal values (P < 0.01) without altering the proportion due to GNF. In contrast, increasing the fructose infusion rate at constant glucagonemia increased EGP similarly (by 19 +/- 4%, P < 0.05) but enhanced the contribution of GNF to 76 +/- 2% (P < 0.001). Graded infusion of glucagon or fructose alone failed to stimulate EGP. The present findings indicate that hyperglucagonemia stimulates endogenous glucose production during fructose infusion. This effect is not secondary to a stimulation of gluconeogenesis, but to a channelling of glucose-6-phosphate towards systemic release.     

Glucose kinetics in protein depletion--effect of glucose infusion in the fasted rat

A primed constant infusion of [6-3H]glucose was used to determine glucose turnover in rats fasted for 48 h that had previously been pair-fed isoenergetic 4% and 14.4% protein diets for 6 wk. The protein-depleted rats had a low body weight and lower plasma glucose and plasma insulin concentrations compared with the 14.4% protein pair-fed control animals. The rate of appearance of glucose in plasma in the protein-depleted rats was significantly less than that in the pair-fed controls. During an intravenous infusion of unlabeled glucose (38.8 mumol.kg-1.min-1) plasma glucose concentrations and glucose appearance increased in both groups. Plasma insulin concentration remained lower in the 4% protein-fed group though the percentage of increase above basal was similar in both groups during glucose infusion. The clearance of glucose from the blood and suppression of endogenous glucose production during the exogenous glucose infusion were similar in both control and protein-depleted rats. Rats fed a 14.4% protein diet ad libitum consumed more diet than the pair-fed groups and their body weights were greater. However, fasting plasma glucose and insulin, concentrations were similar to the 14.4% protein pair-fed animals. This indicates that the observed changes in glucose metabolism in the 4% protein-fed animals were due to a reduced dietary ratio of protein to carbohydrate rather than reduced energy intake.     

Tolerance to glucose polymers in malnourished infants with diarrhea and disaccharide intolerance

The response of infants with diarrhea and lactose intolerance to feedings containing soy protein and sucrose (Sobee), and/or to a carbohydrate free formula (RCF), to which glucose polymers (GP) were added, was assessed in twenty patients. They all were less than ten months of age and had varying degrees of malnutrition. Eleven had acute diarrhea and nine had chronic diarrhea. None of them had classical enteropathogenic strains and parasites in the stools. All had lactose intolerance when feedings were begun with cow's milk formula and some also had sucrose intolerance when fed sucrose containing soy formulas. They had persistent loose stools and excreted feces with an acid pH and with carbohydrates, thus they were given dietary treatment with RCF with GP. There were 9 patients with acute diarrhea and lactose intolerance (1 of them also had sucrose intolerance), who improved on RCF with GP feedings; but 2 patients (lactose and sucrose intolerant) failed to respond to this diet. There were six patients with chronic diarrhea and lactose intolerance (four of them also had sucrose intolerance), who improved on RCF with GP formula, but there were three patients who failed on this treatment. These data show that some infants with diarrhea, malnutrition, and lactose-sucrose intolerance may also develop intolerance to GP and require further dietary management with glucose as the source of carbohydrate in the diet.     

Blood insulin, glucose, fructose and gastric inhibitory polypeptide levels in carbohydrate-sensitive and normal men given a sucrose or invert sugar tolerance test

Twelve carbohydrate-sensitive and 12 normal men were selected for the study. Carbohydrate-sensitivity was based on an abnormal insulin response to a sucrose load. The subjects were fed a diet consisting of 45% of the calories as carbohydrate, 40% fat and 15% protein for 5 days prior to a sucrose or invert sugar tolerance test. In a crossover design, subjects were given 2 g/kg body weight of sucrose or invert sugar, and responses of insulin, glucose, fructose and gastric inhibitory polypeptide (GIP) were determined. Blood samples were taken at 0, 0.5, 1, 2 and 3 hours after being given the test loads. Insulin and glucose levels were significantly higher in carbohydrate-sensitive as compared to normal men. Glucose and GIP did not show any significant differences between the two carbohydrate loads. At 1 hour, the carbohydrate-sensitive men given sucrose had significantly higher insulin levels than carbohydrate-sensitive men given invert sugar (disaccharide effect). At 1, 2 and 3 hours, the disaccharide effect was shown in the fructose levels of the carbohydrate-sensitive men. In normal men, the disaccharide effect with levels of fructose was seen at 0.5 and 3 hours. This study indicates that the disaccharide effect on blood insulin cannot be explained by differences in gastric inhibitory polypeptide in unadapted human subjects.     

Effects of dietary fructose on plasma glucose and hormone responses in normal and hyperinsulinemic men

Twelve men with abnormally high insulin responses to a sucrose load and 12 normal men were fed diets containing 0, 7.5, or 15% of the calories as fructose for 5 weeks each. The diets contained approximately 43% of the calories as total carbohydrate, 42% as fat and 15% as protein. Mean insulin responses of the hyperinsulinemic men were initially 235% of control responses. Plasma glucose concentrations 1 hour after the sucrose load were significantly higher in hyperinsulinemic men than in controls. There were no initial differences between the two groups in glucagon or gastric inhibitory polypeptide (GIP) responses. Consumption of 7.5 and 15% Fructose diets increased fasting plasma glucose and GIP responses in both groups. Consumption of the 15% fructose diet resulted in significantly higher insulin and glucose responses than consumption of the other two diets. These results indicate that moderate levels of dietary fructose can produce undesirable changes in glucose metabolism of both normal and hyperinsulinemic men.     

早产儿静脉补糖时血糖及胰岛素的观察

36例早产儿随机分为两组,小剂量A组20例,高剂量B组16例,日龄2～10天,平均5.56±3.03天。静脉输糖速率分别为8mg·kg~(-1)/min及12mg·kg~(-1)/min,观察空腹时、补糖3h及停止补糖后3h的血糖及胰岛素水平。结果表明高剂量B组婴儿血糖值显著高于A组,高血糖发生率高达100％。两组各时项血清胰岛素值比较无显著性差异。提示早产儿胰岛素β细胞对较高剂量的葡萄糖输入缺乏合适的应答反应,为避免高血糖,早产儿静脉补糖时需控制补糖剂量。     

Metabolic effects of fructose and glucose: implications for food intake

Differential effects of fructose and glucose preloads on carbohydrate metabolism and later food intake were examined in both lean and obese subjects. In study 1, a preload of either 50 g of fructose or glucose was administered in solution, and food intake at a buffet lunch presented 2.25 h after preload was assessed. Significant differences in caloric intake were observed between load conditions with the fructose group consuming fewer calories than the glucose group. Obese subjects demonstrated significantly greater insulin responses to the preload compared with lean subjects, and insulin levels of obese subjects at 15, 30, and 45 min after preload were found to correlate significantly with amount consumed. Incorporation of fructose or glucose into a mixed meal format in study 2 revealed no differences in subsequent caloric intake as a function of either type of preload or percent overweight. Differing insulin levels are discussed as a possible mechanism for differential food intake.     

Palmitate turnover and its response to glucose infusion in weight-losing cancer patients

Palmitate turnover in weight-stable control subjects (n = 4) and weight-losing patients with progressive malignant disease (n = 4) has been determined. Measurements were made after an overnight fast and during glucose infusion (3.5 mg/kg/min). Turnover rates were calculated from plateau isotopic enrichment of palmitate in plasma during a continuous infusion of 1-13C palmitate. Palmitate turnover was higher in the cancer group before (180%) and during glucose loading (170%) compared with the control group. Palmitate turnover was reduced during glucose administration by approximately 34% in both groups. Plasma concentration of insulin was decreased and of cortisol was increased in the cancer group compared with the control group before and during glucose infusion. We conclude that cancer patients with weight loss have increased rates of fatty acid turnover indicative of enhanced mobilisation of body fat stores. Altered plasma concentrations of insulin and cortisol may mediate this effect. Nonetheless, even at more advanced stages of cachexia cancer patients have normal control mechanisms for inhibiting fatty acid turnover following administration of carbohydrate.     

Effects of starch, sucrose, fructose and glucose on chromium absorption and tissue concentrations in obese and lean mice

Forty-eight male genetically obese (OB) mice (C57BL/6J-OB) and 48 lean male littermates were randomly assigned within main plots (OB or lean) to one of eight diets. Diets were low chromium or supplemented with 1 mg chromium as CrCl3 per kg. Starch, sucrose, fructose or glucose comprised 50% of the diet, which met AIN recommendations except for chromium. Experimental diets and deionized water were available ad libitum for 26 d. Mice were fasted 10 h and were intubated 2 h before killing with 15 microCi of 51CrCl3 in a 25% carbohydrate solution (2 mg carbohydrate/g body wt) of either starch, sucrose, glucose or fructose corresponding to the diet previously fed. 51Cr concentrations were significantly higher in the blood, liver, spleen, epididymal fat pad, testes and femur of animals given their carbohydrate load as starch than in animals fed sucrose, fructose or glucose. Carbohydrate had a significant effect on chromium concentrations of testes, spleen, kidney and liver with values generally being higher with the starch diet. Chromium supplementation increased bone and kidney chromium concentrations and heart and muscle glycogen. These data indicate that the source of carbohydrate can alter chromium absorption and retention.     

Ingestion of guar gum hydrolysate, a soluble and fermentable nondigestible saccharide, improves glucose intolerance and prevents hypertriglyceridemia in rats fed fructose

Fructose feeding provides a dietary model of insulin resistance accompanied by hypertriglyceridemia. We examined the effects of guar gum hydrolysate (GGH), a soluble and fermentable nondigestible saccharide with low viscosity, on glucose intolerance and hypertriglyceridemia in rats fed high-fructose diets. Rats were fed either a dextrin-based or a fructose-based diet with or without GGH (75 g/kg) for 30 d. Oral glucose tolerance tests (OGTTs) were performed 0, 14, and 28 d after feeding. High-fructose feeding negatively affected glucose tolerance on d 14 and 28. The addition of GGH to the diets improved glucose intolerance on d 28. Fructose feeding induced hyperinsulinemia after an oral glucose load; this was also improved by GGH on d 28. The glycogen concentration in the gastrocnemius muscles of rats was lowered by dietary fructose, and GGH supplementation abolished this decrease. Triglycerides in the plasma and livers of rats fed fructose diets were elevated, and the increases were ameliorated by supplemental GGH. Regardless of the type of carbohydrate, GGH enlarged the cecum and increased the cecal SCFA pools. In conclusion, supplemental feeding of GGH to rats improved the glucose intolerance and hypertriglyceridemia induced by a high-fructose diet. Possible mediators of these beneficial effects of GGH are the SCFAs produced by microbial fermentation of GGH in the large intestine.     

Carbohydrate supplementation of horses during endurance exercise: comparison of fructose and glucose

To delay the onset of fatigue, endurance horses are often fed at rest stops during races. The resulting increase in blood insulin may adversely inhibit lipolysis. In humans, ingestion of fructose produces a smaller insulin rise than glucose. This study compared glucose and fructose as carbohydrate supplements for endurance horses. Three Arabian geldings were given 300 g of fructose (F), glucose (G) or 50% glucose: 50% fructose (GF), in 1.5 L water, by stomach tube. In the Resting Test, carbohydrate was administered at rest. Following treatment, blood samples were taken every 30 min for 8 h, and feces were collected for 24 h. Treatment did not affect fecal weight or water content. Plasma glucose and insulin responses did not differ among treatments. Post-treatment (60 min), plasma L-lactate tended to be higher (P = 0.06) after the F and GF treatments than after the G treatment. In the Exercise Test, two treadmill exercise bouts at 0 degrees incline (Bout 1: 90 min; Bout 2: 120 min) were separated by a 1-h rest period. A total distance of 36.84 km was covered at a mean speed of 2.9 m/s. Carbohydrate was administered 45 min before Bout 2. Plasma glucose and insulin at the start of Bout 2 were higher (P = 0.02 and 0.03, respectively) with the GF treatment than with the F treatment. However, during exercise, plasma glucose concentrations did not differ among treatments. We conclude that fructose is well-absorbed by horses and rapidly converted to glucose.     

Combination of erythritol and fructose increases gastrointestinal symptoms in healthy adults

Consumption of a large amount of dietary fructose induces gastrointestinal intolerance, and glucose has been known as an enhancer of fructose absorption. Erythritol is a nonglycemic sugar alcohol, and it has been suggested that erythritol is absorbed paracellularly. It was hypothesized that paracellular absorption of erythritol could also enhance paracellular absorption of fructose in healthy adults. This is one of the proposed pathways for how additional glucose enhances the absorption of fructose. Thirty-seven nondiabetic, healthy adults participated in a randomized, double-masked, controlled crossover study. After an overnight fast, participants consumed beverages containing either 50 g fructose and 50 g glucose, 50 g fructose and 33.3 g erythritol (an equimolar concentration of fructose), or 50 g fructose alone. Breath hydrogen response was determined for 8 hours postprandially. Gastrointestinal intolerance symptoms and the number and consistency of bowel movements were recorded for 24 hours postprandially. The breath hydrogen area under the curve (AUC) of the fructose and erythritol beverage was 2 times the AUC of the fructose beverage and 8.75 times the AUC of the fructose and glucose beverage (P < .001, respectively). Compared with fructose and glucose beverage and fructose alone, frequency of watery stools increased (P < .05) and gastrointestinal tolerance worsened (P < .05) when participants consumed fructose and erythritol. These data suggest that coingestion of equimolar concentrations of fructose and erythritol increased carbohydrate malabsorption.     

Preexercise feedings of glucose, fructose or sucrose: effects on substrate depletion in rats

Male Wistar rats (n = 72) trained to run on a treadmill were fasted overnight and fed by gavage 3 ml unsupplemented water or a solution containing 2 g of glucose, fructose or sucrose 30 min prior to exercise. Six rats from each dietary group were killed after 0, 1 or 2 h of exercise. Blood glucose levels decreased in all groups over the 2-h exercise period; however, the largest decline in blood glucose was exhibited by the rats fed unsupplemented water (-32.1%), followed by those fed fructose (-26.9%), sucrose (-13.9%) and glucose (-8.3%). The water-fed control rats also had the largest increase in circulating free fatty acids (+215.4%), followed by those fed fructose (+120.8%), sucrose (+69.2%) and glucose (+57.5%). The fructose-fed animals exhibited the greatest depletion of liver glycogen and the smallest decline in soleus and red vastus lateralis muscle glycogen of the rats fed the different carbohydrates. The data indicate that exercise-induced changes in substrate levels can be modified by the type of carbohydrate given prior to exercise.