Use of immunoresponsiveness to demonstrate that the dietary requirement for copper in young rats is greater with dietary fructose than dietary starch

Weaned male Lewis rats were pair-fed diets containing 62.7% fructose or starch and either 6-7 mg Cu/kg diet (adequate) or 0.7 mg Cu/kg diet (deficient) for 33 d. Antibody titers after primary immunization with sheep erythrocytes were significantly lower in rats fed copper-deficient diets. Compared to starch, fructose markedly attenuated antibody production in copper-deficient rats. Dietary carbohydrate did not affect the humoral immune response of rats fed diets with adequate copper. Concentrations of copper in thymus, spleen, liver and heart were also significantly lower in rats fed fructose with deficient copper (F-Cu) than in the group fed starch with deficient copper. Thymic hypogenesis was observed only in the F-Cu group. Tissue concentrations of copper were reduced before antibody production was impaired. Repletion of previously copper-deficient rats rapidly restored immunocompetence and stimulated thymic growth. Immunoresponsiveness and tissue concentrations of copper reached control levels in rats fed diets containing starch and fructose at 1.2-1.6 and 2.2-2.9 mg Cu/kg diet, respectively. The results demonstrate that the amount of dietary copper required for optimal function of the humoral immune system, thymic growth and maintenance of normal tissue levels of this essential micronutrient is greater when young rats are fed diets with fructose than with starch.     

Effect of retinoic acid on leptin, glycerol, and glucose levels in mature rat adipocytes in vitro

To elucidate the effects of retinoic acids (RAs) on adipogenesis and insulin sensitivity, we treated mature adipocytes with two different kinds of RA, 9-cis-RA and all-trans-RA. Both 9-cis- and all-trans-RA inhibited the secretion of leptin. However, the inhibition was significantly decreased at a higher dose of each RA. The inhibitory effect of 9-cis-RA was synergistically enhanced by the addition of rosiglitazone, a synthetic ligand for peroxisome proliferator-activated receptor (PPAR) gamma. 9-cis-RA also leads to adipogenesis in a dose-dependent manner. On the contrary, all-trans-RA does not increase adipogenesis in a dose-dependent manner. To clarify the antidiabetic effects of RA, glucose uptake was assessed by estimating glucose concentrations in the medium. 9-cis-RA reduced glucose levels in the culture media, but all-trans-RA did not. In conclusion, all-trans-RA does not alter adipogenesis and glucose uptake but does inhibit leptin secretion. 9-cis-RA, however, seems to increase both adipogenesis and glucose uptake through activation of the retinoid X receptor/PPARgamma heterodimer.     

Intestinal absorption and excretion of zinc in streptozotocin-diabetic rats as affected by dietary zinc and protein

65Zn was used to examine the effects of dietary zinc and protein on true zinc absorption and intestinal excretion of endogenous zinc by an isotope dilution technique in streptozotocin-diabetic and control rats. Four groups each of diabetic and control rats were fed diets containing 20 ppm Zn, 20% egg white protein (HMHP); 20 ppm Zn, 10% egg white protein (HMLP); 10 ppm Zn, 20% egg white protein (LMHP); and 10 ppm Zn, 10% egg white protein (LMLP). Measurement of zinc balance was begun 9 d after an i.m. injection of 65Zn. True zinc absorption and the contribution of endogenous zinc to fecal zinc excretion were calculated from the isotopically labeled and unlabeled zinc in the feces, duodenum and kidney. Results from the isotope dilution study indicated that diabetic rats, but not control rats, absorbed more zinc from 20 ppm zinc diets than from 10ppm zinc diets and that all rats absorbed more zinc from 20% protein diets than from 10% protein diets. Furthermore, all rats excreted more endogenous zinc from their intestines when dietary zinc and protein levels resulted in greater zinc absorption. In diabetic and control rats, consuming equivalent amounts of zinc, the amount of zinc absorbed was not significantly different, but the amount of zinc excreted by the intestine was less in the diabetic rats. Decreased intestinal excretion of endogenous zinc may be a homeostatic response to the increased urinary excretion of endogenous zinc in the diabetic rats and may also lead to the elevated zinc concentrations observed in some organs of the diabetic rats.     

Degree of starch gelatinization, digestion rate of starch in vitro, and metabolic response in rats

Glycemic response after ingestion of starchy foods varies. Starch in many common ready-to-eat foods is only partly gelatinized. In view of this, the relationships among degree of starch gelatinization, in vitro digestion rate, and in vivo metabolic response in rats were studied. Wheat starch with different degrees of gelatinization was used in the experiments. Plasma glucose and insulin responses as well as the rate of in vitro hydrolysis with alpha-amylase were strongly correlated to the degree of starch gelatinization (r = 0.88, r = 0.90, and r = 0.96, respectively). Plasma glucose and insulin responses were also positively correlated to the rate of hydrolysis with alpha-amylase in vitro (r = 0.98 and r = 0.76, respectively). These results suggest that the degree of starch gelatinization is an important determinant both for the rate of starch hydrolysis in vitro and for the metabolic response in vivo.     

Resistant starch attenuates colonic DNA damage induced by higher dietary protein in rats

Epidemiologic studies suggest that dietary complex carbohydrates are protective against colorectal cancer but dietary protein may increase risk. However, experimental data to support these relationships are scant. We have shown in rats that consumption of a high-protein (25% casein) diet for 4 wk resulted in a twofold increase in damage to colonocyte DNA compared with a low-protein (15% casein) diet. This was associated with thinning of the colonic mucous barrier and increased levels of fecal p-cresol. Addition of resistant starch as a high-amylose maize starch to the diet increased cecal short-chain fatty acid pools and attenuated DNA damage, suggesting protection against genotoxic agents. In humans, this could translate to altered risk of colonic cancer.     

Eucalyptus leaf extract inhibits intestinal fructose absorption, and suppresses adiposity due to dietary sucrose in rats

Sucrose is more lipogenic than starch, and the extreme ingestion of sucrose induces adiposity and obesity. The aim of this study was to examine the effect of the eucalyptus (Eucalyptus globulus) leaf extract (ELE) on adiposity due to dietary sucrose in rats. In addition, in this study, the effect of ELE on intestinal fructose absorption was also examined. Rats were fed a high-sucrose diet (75 % in calorie base) with or without ELE (10 g/kg diet) for 5 weeks. Body weight was lower in the rats receiving ELE than in the controls (342 (sd 37.9) v. 392 (sd 26.0) g (n 7); P<0.05). Furthermore, ELE resulted in decreases in the triacylglycerol concentrations in the plasma (1.44 (sd 0.448) v. 2.79 (sd 0.677) mmol/l (n 7); P<0.05) and liver (19.1 (sd 5.07) v. 44.1 (sd 16.28) micromol/g (n 7); P<0.05). In contrast, ELE did not show any significant effects in the rats fed a starch diet. When rats were orally given ELE 10 min before fructose administration, the intestinal fructose absorption, which was examined by measuring the elevated concentration of fructose in the portal vein at 30 min after the fructose administration, was significantly inhibited in a dose-dependent manner. Furthermore, in rats fed a high-fructose diet, the plasma and hepatic triacylglycerol concentrations were significantly decreased by ELE. These results indicate that ELE, which inhibits the intestinal fructose absorption, can suppress adiposity in rats that ingest large amounts of sucrose or fructose.     

Effects of dietary zinc levels, phytic acid and resistant starch on zinc bioavailability in rats

Summary Background Owing to its fermentability, it has been advocated that resistant starch (RS) has a positive effect on the absorption of minerals by increasing their solubility in the hindgut. In marginally zinc–deficient rats, the enhancement of zinc bioavailability by RS occurs mostly when the diet contains phytic acid. Aim of the study This study aims to investigate the effect of dietary zinc level and phytic acid on the cecal zinc pools and zinc bioavailability of rats fed RS. Methods Wistar rats (male, 3wk old) were divided into eight groups (n = 6), and fed diets containing either 5% cellulose (control fiber: insoluble and low fermentable) or 20 % RS (test fiber: soluble and fermentable), with or without the addition of 1% sodium phytate, at the 10 and 30 mg/kg dietary zinc levels, for 21 days. Results At 10 mg Zn/kg, RS increased femur zinc concentration only in the group receiving the phytate–containing diet, while at 30 mg Zn/kg it increased femur zinc concentration in rats fed both phytate–free and phytate–containing diets. The total content of zinc in the cecum was increased by the higher dietary zinc level and tended to be increased by the addition of phytate, which is assumed to impair zinc absorption in the small intestine. Feeding RS lowered cecal pH values, which correlated with increasing values of zinc solubility (r = –0.3471; P < 0.05). The later was, in turn, directly associated with zinc apparent absorption (r = 0.3739; P < 0.05). Conclusions The increase in zinc bioavailability by RS occurs when dietary zinc levels are adequate and/or zinc absorption is impaired in the small intestine, increasing the influx of unabsorbed zinc into the cecum and favoring the increase of zinc bioavailability when RS fermentation lowers the cecal pH.     

Relationships among crude fiber, neutral detergent fiber, in vitro dietary fiber, and in vivo (rats) dietary fiber in wheat foods.

The in vivo dietary fiber contents of wheat milling fractions and wheat foods, determined in rat feeding experiments, were compared with dietary fiber values determined in vitro with pronase alpha-amylase digestion. Both types of dietary fiber values were compared with crude fiber and neutral detergent fiber values in the same materials. Regression analyses indicated close correlation amongst all values determined. It appears that laboratory analysis for crude fiber, neutral detergent fiber, or in vitro dietary fiber accurately predicts in vivo dietary fiber (rats) for wheat milling fractions when the laboratory result is adjusted by means of an appropriate regression equation.     

Alteration of glucose tolerance by dietary L-tryptophan in rats.

L-Tryptophan is known to have pharmacological effects on carbohydrate metabolism. In a scrutiny for possible physiological relationships, intravenous glucose tolerance was measured in rats fed various diets of defined L-tryptophan-content. Within 14 days, animals which had been fed a tryptophan-deficient diet diet removed excess glucose from their blood at a reduced rate. This decreased tolerance to glucose was dose dependent to dietary L-tryptophan and the intolerance was reversed by feeding a complete diet. The intolerance was not dependent on dietary protein source, not reversed by added niacin or vitamin B-6, not a necessary consequence of decreased food consumption and growth, and not duplicated by a lack of dietary lysine. The results suggest that dietary L-tryptophan is active in physiological regulation of carbohydrate metabolism.     

Food additives such as sodium sulphite, sodium benzoate and curcumin inhibit leptin release in lipopolysaccharide-treated murine adipocytes in vitro

Obesity leads to the activation of pro-inflammatory pathways, resulting in a state of low-grade inflammation. Recently, several studies have shown that the exposure to lipopolysaccharide (LPS) could initiate and maintain a chronic state of low-grade inflammation in obese people. As the daily intake of food additives has increased substantially, the aim of the present study was to investigate a potential influence of food additives on the release of leptin, IL-6 and nitrite in the presence of LPS in murine adipocytes. Leptin, IL-6 and nitrite concentrations were analysed in the supernatants of murine 3T3-L1 adipocytes after co-incubation with LPS and the food preservatives, sodium sulphite (SS), sodium benzoate (SB) and the spice and colourant, curcumin, for 24 h. In addition, the kinetics of leptin secretion was analysed. A significant and dose-dependent decrease in leptin was observed after incubating the cells with SB and curcumin for 12 and 24 h, whereas SS decreased leptin concentrations after 24 h of treatment. Moreover, SS increased, while curcumin decreased LPS-stimulated secretion of IL-6, whereas SB had no such effect. None of the compounds that were investigated influenced nitrite production. The food additives SS, SB and curcumin affect the leptin release after co-incubation with LPS from cultured adipocytes in a dose- and time-dependent manner. Decreased leptin release during the consumption of nutrition-derived food additives could decrease the amount of circulating leptin to which the central nervous system is exposed and may therefore contribute to an obesogenic environment.     

Comparative changes of fat digestibility and fat accumulation by the carbon chain length of dietary glycerol tri-homogenous fatty acids in rats

The present study was undertaken to investigate the influence of the carbon chain length of dietary glycerol tri-homogenous fatty acid on fat digestibility and body fat accumulation in rats. Thirty-six Wistar male rats were divided into six groups and fed the semipurified C8, C10, C12, C14, C16, C18 triglyceride diets, respectively. Body weight was significantly lower (p<0.05) in rats fed the C14, C16 and C18 diets than in rats fed the C8, C10 and C12 diets. Weights of adipose tissues and apparent fat digestibility were markedly low in the C16 and C18 fed rats. In these groups, fat content of whole-body carcass was significantly lower (p<0.05), but moisture, ash and protein contents were significantly greater (p<0.05) than those of the other groups. Fatty acid profile of epididymal adipose tissue revealed that dietary C8:0 was not directly incorporated into adipose tissues, and only a small amount of dietary C10:0 was directly deposited as body triglycerides. Meanwhile, dietary C12:0 was extensively incorporated into adipose tissues when compared to those of C8 and C10 rats. The present study indicated that apparent fat and energy digestibilities of dietary glycerol tripalmitin and glycerol tristearin were remarkably lower than the glycerol tricaprylin, tricaprin, trilaurin and trimyristin, which results in lower fat accumulation in the C16 and C18 fed rats.     

Prenatal protein malnutrition in rats enhances serotonin release from hippocampus.

The effect of prenatal protein malnutrition on central serotonin metabolism was assessed in 220- to 240-d-old male rats. The malnourished rats (denoted 6,25 group) were males born to dams fed a 6% casein diet during pregnancy and fostered at birth to dams fed a control (25% casein) diet. They were compared with males born to dams fed 25% casein diet. Tissue concentrations of serotonin, 5-hydroxyindoleacetic acid, 5-hydroxytryptophan, L-tryptophan and catecholamines in the hippocampal formation in the 6,25 group were similar to those of well-fed controls (25,25 group). However, a twofold greater basal serotonin efflux from hippocampal slices of 6,25 rats compared with slices from 25,25 rats was observed during a 20-min incubation period. Hippocampal [3H]paroxetine binding indicated that there was no alteration of apparent maximal binding and affinity of the serotonin transporter in the 6,25 rats. In addition, there was no difference in serotonin receptor binding in hippocampal membranes from 6,25 and 25,25 rats. The results indicate that prenatal protein malnutrition causes selective changes in central serotonin metabolism.     

Availabilities of calcium,iron, and zinc from dairy infant formulas is affected by soluble dietary fibers and modified starch fractions

OBJECTIVE: Insoluble dietary fiber is a known inhibitor of mineral absorption, whereas the effects of soluble dietary fibers (including prebiotics) are less known. The aim was to study calcium, iron, and zinc availabilities from dairy infant formulas supplemented with soluble dietary fibers and modified starches in vitro. METHODS: Dairy infant formulas were supplemented with soluble dietary fibers (3%, dry wt) and modified starches (16% pregelatinized rice starch and 1.9% maltodextrin, dry wt) and kept in a well-controlled and defined environment in vitro. Pooled mature human milk was used as the reference standard. RESULTS: Calcium availability from standard formula was elevated by 30% after inulin supplementation (17.2%), whereas locust bean gum (11.9%) and high esterified pectin (11.7%) reduced availability by approximately 10%. Iron availability from standard formula was increased by pregelatinized rice starch (3.8%), whereas availability was reduced in the following order: high esterified pectin (2.3%), oligofructose (2.2%), and low esterified pectin (2.1%). Zinc availability was highest after the addition of pregelatinized rice starch (13.5%) but lowest with the addition of locust bean gum (6.8%) and maltodextrin (5.4%). CONCLUSIONS: This study showed that addition of soluble dietary fiber affects calcium, iron, and zinc availabilities in positive (inulin) and negative ways, depending on the type of the dietary fiber used.     

Net renal arginine flux in rats is not affected by dietary arginine or dietary protein intake.

Kidneys of adult animals serve as a major biosynthetic source of arginine. Recently, we demonstrated that kidneys of rats infused with citrulline responded to the elevated plasma citrulline concentrations by increasing citrulline uptake and producing greater quantities of arginine. The objective of the present study was to determine the effects of feeding adult male rats different levels of arginine or protein on renal arginine synthesis. Feeding arginine (0, 0.5 and 2.0%) for 1 wk increased circulating plasma concentrations of arginine 2.5-fold (196 mumol/L) in the 2.0% arginine group compared with the 0 and 0.5% arginine groups (73 and 81 mumol/L, respectively). However, the plasma citrulline concentration was unchanged. The renal uptake of citrulline and release of arginine were similar in all the three groups fed different levels of arginine. Feeding diets containing 5, 12 and 50% protein for 1 wk did not alter the circulating plasma concentrations of either citrulline or arginine, and there were no significant differences in the renal release of arginine. These results suggest that renal arginine synthesis is independent of dietary arginine or protein intake.     

Replacement of digestible wheat starch by resistant cornstarch alters splanchnic metabolism in rats.

Splanchnic metabolism was investigated in rats fed either a diet containing highly digestible wheat starch (DS diet) or amylase-resistant cornstarch (RS diet). In rats fed the latter diet, there was a considerable enlargement of the cecum and an increase in the production and absorption of volatile fatty acids (VFA), chiefly acetic and propionic acids. As a result, the major substrates absorbed from the digestive tract were glucose in rats fed the DS diet and both glucose and VFA in rats fed the RS diet. The liver removed about one-third of the absorbed glucose in rats fed the DS diet, whereas there was a slight release of glucose by the liver in rats fed the RS diet. Plasma insulin was higher in rats fed the DS diet, and there were smaller fluctuations of plasma insulin and liver glycogen between the fed and postabsorptive periods in rats adapted to the RS diet. In these animals, propionate was the major VFA taken up by the liver and approximately 50% of absorbed acetate was also removed by the liver. During the postabsorptive period, there was still a substantial contribution of VFA, especially propionate, to liver metabolism. A depressive effect of the RS diet on plasma triglycerides, cholesterol and free fatty acids was observed only during the postabsorptive period. Replacement of a large part of absorbed glucose by VFA apparently allows time for absorption of energy fuels to be extended and dampens the fluctuations of glucose metabolism during the light: dark cycle.     

Insulin insensitivity is rapidly reversed in rats by reducing dietary fat from 40 to 30% of energy.

The objective of this study was to determine the effect of reducing dietary fat content from 40 to 30% of total energy on body composition and insulin sensitivity in rats. Female Sprague-Dawley rats were fed either a control diet (30% energy as fat) or a high fat diet (40% energy as fat) for 10 wk. In vivo glucose tolerance tests indicated that both basal and glucose-stimulated insulin concentrations were elevated in rats fed the high fat diet. Two groups of rats offered the high fat diet were then fed the control diet (HF,C) and two that had received the high fat diet were then fed a diet (30% energy as fat) containing a fat-mimetic carbohydrate (HF,M). Two groups continued to receive the high fat diet and two groups continued to receive the control diet. Rats were killed 1 and 2 wk after the diet switch. In vivo glucose tolerance tests indicated that insulin sensitivity was corrected in HF,C and HF,M rats after 3 d. Body fat content was greater in rats fed the high fat diet and remained high after 7 d of consuming either diet with 30% of energy from fat. There was no effect of diet on liver fatty acid utilization or on diaphragm glucose oxidation. Adipocytes from all treatment groups were insulin resistant, possibly due to feeding status or age of the rats. The results of this study suggest that a moderate reduction in fat intake, from 40 to 30% of energy, can produce a rapid improvement of insulin sensitivity in insulin-insensitive rats, independent of changes in body fat content and irrespective of the means used to reduce dietary fat content.