EDTA disodium zinc has superior bioavailability compared to common inorganic or chelated zinc compounds in rats fed a high phytic acid diet

Different zinc (Zn) compounds have unique properties that may influence the amount of Zn absorbed particularly in the presence of phytic acid (PA), a common food component that binds Zn and decreases its bioavailability. In this study, 30-day-old male rats (n = 12/diet group) were fed diets supplemented with PA (0.8%) and low levels (8 mg Zn/kg diet) of inorganic (Zn oxide, Zn sulphate) or chelated (Zn gluconate, Zn acetate, Zn citrate, EDTA disodium Zn, Zn orotate) Zn compounds for 5 weeks. Two control groups were fed diets supplemented with low or normal (30 mg Zn/kg diet) Zn (as Zn oxide) without added PA. Control rats fed the low Zn oxide diet showed depressed Zn status. Addition of PA to this diet exacerbated the Zn deficiency in rats. Growth (body weight gain and femur length) and Zn concentrations in plasma and tissues were similar in rats fed Zn oxide, Zn sulphate, Zn gluconate, Zn acetate, Zn citrate or Zn orotate. Rats fed EDTA disodium Zn showed enhanced growth compared to rats fed Zn oxide or Zn gluconate and had higher Zn concentrations in plasma and femur compared to rats fed all other Zn compounds. Only the haematological profile of rats fed EDTA disodium Zn did not differ from control rats fed normal Zn. These data indicate that in rats fed a high PA diet, bioavailability of commonly used inorganic or chelated Zn compounds does not differ appreciably, but Zn supplied as an EDTA disodium salt has superior bioavailability.     

Iron,copper, and zinc status in rats fed supplemental nickel

Literature data concerning the effect of increasing dietary Ni concentrations on Fe, Cu, and Zn status in rats are sparse and, in part, controversial. Therefore, the effects of the addition of either 0, 3, 50, or 100 mg Ni/kg diet on Fe, Cu, and Zn status of rats were investigated in two separate experiments. Purified diets were used that were composed according to the established nutrient requirements of rats. Ni in kidney was increased with increasing Ni intakes. Dietary Ni did not significantly influence Fe concentrations in plasma, liver, kidney, femur, and spleen. Likewise, the addition of Ni to the diet did not alter Cu status. Zn concentrations in femur were significantly decreased after feeding the diets with 100 mg Ni/kg. However, Zn in plasma, liver, kidney, and spleen was not affected. It is concluded that variations in dietary Ni concentrations have no major impact on Fe, Cu, and Zn status in rats.     

Calcium exacerbates the inhibitory effects of phytic acid on zinc bioavailability in rats

BackgroundComplementary feeding of breastfed infants with foods high in bioavailable zinc (Zn) can help meet physiological requirements for Zn. Some infant cereals contain high concentrations of phytic acid (PA) and calcium (Ca) that may reduce absorbable Zn.ObjectivesThis study measured PA, Zn and Ca concentrations in selected infant cereals sold in Canada and investigated the effects of dietary PA and Ca at concentrations present in infant cereals on Zn bioavailability in rats.Methods and resultsMale Sprague-Dawley rats (36-day old) were fed a control diet containing normal Zn (29.1 mg/kg) and Ca (4.95 g/kg) or six test diets (n = 12/diet group). Test diets were low in Zn (8.91–9.74 mg/kg) and contained low (2.16–2.17 g/kg), normal (5.00–5.11 g/kg) or high (14.6–14.9 g/kg) Ca without or with added PA (8 g/kg). After 2 weeks, rats were killed and Zn status of the rats was assessed. PA, Zn and Ca concentrations in infant cereals (n = 20) differed widely. PA concentrations ranged from undetectable to 16.0 g/kg. Zn and Ca concentrations ranged from 7.0–29.1 mg/kg and 0.8–13.4 g/kg, respectively. The [PA]/[Zn] and [PA × Ca]/[Zn] molar ratios in infants cereals with detectable PA (16 of 20 cereals) ranged from 22–75 and 0.9–14.9 mol/kg, respectively, predicting low Zn bioavailability. Body weight, body composition (lean and fat mass), right femur weight and length measurements and Zn concentrations in serum and femur indicated that diets higher in Ca had a more pronounced negative effect on Zn status of rats fed a PA-supplemented diet. Addition of PA to the diet had a greater negative effect on Zn status when Ca concentration in the diet was higher.ConclusionThese results show that, in rats, higher concentrations of dietary Ca and PA interact to potentiate a decrease in bioavailable Zn and may suggest lower Zn bioavailability in infant cereals with higher PA and Ca concentrations.     

Zinc availability from zinc lipoate and zinc sulfate in growing rats

The purpose of this study was to investigate the effect of zinc lipoate and zinc sulfate on zinc availability in growing rats. 6 . 6 male albino rats were fed purified diets based on corn starch, egg albumen, sucrose, soy bean oil and cellulose over a 4-week period (diet Ia: 10 mg Zn/kg as zinc sulfate, diet Ib: 10 mg Zn/kg as zinc lipoate, diet IIa: 10 mg Zn/kg as zinc sulfate +0.4% phytic acid, diet IIb: 10 mg Zn/kg as zinc lipoate +0.4% phytic acid, diet IIIa: 20 mg Zn/kg as zinc sulfate + 0.4% phytic acid, diet IIIb: 20 mg Zn/kg as zinc lipoate + 0.4% phytic acid). Zinc lipoate and zinc sulfate both proved to be highly available zinc sources. When 0.4% phytic acid were present in the diets, apparent zinc absorption was generally depressed but was higher from zinc lipoate in tendency than from zinc sulfate. Comparable results were evident for femur zinc, plasma zinc and metallothionein concentrations in liver tissues. This indicates that zinc lipoate could be a valuable zinc source under conditions of low zinc availability. Nevertheless the absence or presence of phytic acid was a more important factor influencing zinc availability than the type of zinc source investigated.     

Cadmium accumulation, zinc status, and mineral bioavailability of growing rats fed diets high in zinc with increasing amounts of phytic acid

Five groups of individually housed albino rats (n=7, initial average weight=48 g) were fed diets based on egg albumen and cornstarch (basal diet 8.2 g Ca, 6.0 g P, 0.7 g Mg, 225 mg Zn, 150 mg Fe, 60 mg Mn, 8 mg Cu, and 5 mg Cd) over a 4-wk period. Group I (control) was fed the basal diet free of phytic acid (PA). In groups II, III, IV, and V, cornstarch was replaced by 3.5, 7.0, 10.5, and 14.0 g sodium phytate/kg diet, respectively. Daily gain, feed efficiency, Zn status (Zn in plasma, femur, testes, liver and kidneys, activity of the plasma alkaline phosphatase) and apparent absorption of Zn, Fe, Cu, and Mn remained unchanged by the different dietary treatments. PA decreased apparent Mg absorption significantly and apparent absorption of Ca in tendency. Increasing the amount of phytate caused a corresponding enhancement of amount of the digestible P. Cd accumulation in the liver was not significantly altered, and kidney Cd accumulation slightly increased owing to PA. In conclusion, it was shown that under conditions of high dietary Zn, PA had only little effect on the carryover of Cd in growing rats.     

Excess calcium increases bone zinc concentration without affecting zinc absorption in rats

We examined zinc (Zn) metabolism in rats given diets containing excess calcium (Ca). Rats were given phytate-free diet containing 5 g Ca/kg (control), 12.5 g Ca/kg, or 25 g Ca/kg for 4 wk in Experiment 1. The dietary treatment did not affect Zn concentration in the plasma, testis, kidney, spleen and liver; however, Zn concentration in the femur and its cortex was significantly higher in rats given diet containing 25 g Ca/kg than in other rats. Rats were given phytate-free diet containing 5 g Ca /kg or 25 g Ca /kg for 4 wk in Experiment 2. After 12-h food deprivation, rats were given a diet extrinsically labeled by 67Zn with dysprosium as a fecal marker for 4 h. Feces were collected from 1 d before administration of the labeled diet to 5 d after administration. Excess Ca did not affect the true absorption of Zn and its endogenous excretion but increased femoral Zn. These results suggest that excess Ca improves Zn bioavailability without affecting Zn absorption when diets do not contain phytate.     

Levels and distribution of zinc,copper, magnesium,and calcium in rats fed different levels of dietary zinc

Effects of altered dietary zinc on levels of zinc, copper, magnesium, and calcium in organ and peripheral tissues were studied. When rats fed a zinc-deficient diet (1.3 μg Zn/g) for 28 d were compared with rats fed a control diet (37.5 μg Zn/g), levels of zinc were slightly lower in plasma, hair, and skin and 50% lower in femur and pancreas, whereas the levels of copper were higher in all tissue except plasma. Magnesium levels were higher than controls in the heart and lower in the spleen, whereas the calcium levels were lower in plasma, lung, spleen, kidney, and skin and strikingly higher in brain, hair, and femur. When rats fed a zinc-supplemented diet (1.0 mg Zn/g) were compared to the same conrols, levels of zinc in these were higher in all organs and peripheral tissues studied, except heart, lung, and liver; copper levels were higher in liver, kidney, and spleen; magnesium levels were significantly higher in the spleen, but were little affected in other tissues, although calcium levels were higher in pancreas, spleen, kidney, and skin and lower in plasma and hair. These data indicate that overall copper organ and peripheral tissue levels are affected inversely, and zinc and calcium levels directly, by zinc nutriture.     

Redistribution of tissue zinc pools during lactation and dyshomeostasis during marginal zinc deficiency in mice

Zinc (Zn) requirements are increased during lactation. Increased demand is partially met through increased Zn absorption from the diet. It is estimated that 60–80% of women of reproductive age are at risk for Zn deficiency due to low intake of bioavailable Zn and increased demands during pregnancy and lactation. How Zn is redistributed within the body to meet the demands of lactation, and how Zn deficiency affects this process, is not understood. Female C57bl/6J mice were fed a control (ZA; 30 mg Zn/kg) or a marginally Zn deficient (ZD; 15 mg Zn/kg) diet for 30 days prior to mating through mid-lactation and compared with nulliparous mice fed the same diets. While stomach and plasma Zn concentration increased during lactation in mice fed ZA, mice fed ZD had lower stomach Zn concentration and abrogated plasma Zn levels during lactation. Additionally, femur Zn decreased during lactation in mice fed ZA, while mice fed ZD did not experience this decrease. Furthermore, red blood cell, pancreas, muscle and mammary gland Zn concentration increased, and liver and adrenal gland Zn decreased during lactation, independent of diet, while kidney Zn concentration increased only in mice fed ZD. Finally, maternal Zn deficiency significantly increased the liver Zn concentration in offspring but decreased weight gain and survival. This study provides novel insight into how Zn is redistributed to meet the increased metabolic demands of lactation and how marginal Zn deficiency interferes with these homeostatic adjustments.     

Efficacy of piperine, an alkaloidal constituent from Piper nigrum on erythrocyte antioxidant status in high fat diet and antithyroid drug induced hyperlipidemic rats

The main aim of this study was to investigate the effect of piperine on erythrocyte antioxidant status in high fat diet (HFD) and antithyroid drug induced hyperlipidemic rats. Male Wistar rats were divided into eight groups. The first four groups were fed a control diet and in addition were given respectively 1% carboxymethyl cellulose (CMC); 10 mg/kg body weight carbimazole (CM); 10 mg CM + 40 mg/kg body weight piperine and 10 mg CM + 2 mg/kg body weight atorvastatin (ATV). A similar pattern was followed for the next four groups except that they were all fed HFD instead of the control diet. Erythrocyte osmotic fragility, total cholesterol, phospholipids, lipid peroxidation products, enzymic and non-enzymic antioxidant status were studied in all experimental groups. Significantly increased osmotic fragility, total cholesterol/phospholipid ratio, thiobarbituric acid reactive substances and lipid hydroperoxides were observed in the plasma and erythrocytes of HFD fed and CM treated rats compared to the control. Superoxide dismutase, catalase, glutathione peroxidase, vitamin E and reduced glutathione in erythrocytes and vitamin C in the plasma were also significantly lowered in HFD fed, antithyroid drug treated rats compared to control animals. Concurrent piperine supplementation along with HFD and antithyroid drug administration normalized erythrocyte osmotic fragility, reduced lipid peroxidation, and improved the enzymic and non-enzymic antioxidant status compared to those rats that did not receive piperine. Thus, our results indicate that piperine supplementation markedly protects erythrocytes from oxidative stress by improving the antioxidant status in HFD fed antithyroid drug treated rats.     

Effect of zinc supplementation on metallothionein,copper, and zinc concentration in various tissues of copper-loaded rats

The present study was designed to investigate the effects of Zn administration on metallothionein concentrations in the liver, kidney, and intestine of copper-loaded rats. Male CD rats were fed a diet containing 12 mg Cu and 67 mg Zn/kg body wt. They were divided into either acute or chronic experimental protocols. Rats undergoing acute experiments received daily ip injections of either Cu (3 mg/kg body wt) or Zn (10 mg/kg body wt) for 3 d. Chronic experiments were carried out on rats receiving Cu ip injections on d 1, 2, 3, 10, 17, and 24, Cu injections plus a Zn-supplemented diet containing 5 g Zn/kg solid diet, or a Zn-supplemented diet alone. Rats injected Zn or Cu had increased MT concentrations in liver and kidney. Zn produced the most important effects and the liver was the most responsive organ. Rats fed a Zn-supplemented diet had significantly higher MT concentrations in liver and intestine with respect to controls. Increased MT synthesis in the liver may contribute to copper detoxification; the hypothesis of copper entrapment in enterocytes cannot be confirmed.     

The role of the pancreas in the regulation of zinc status

A low Zn diet resulted in subacute Zn deficiency in young rats. Thirty minutes after the intubation of a trace 65-Zn we determined the total tissue Zn activity in plasma, erythrocytes, liver, pancreas, bone, muscle, and proximal jejunum. Assuming the body behaved like a closed multicompartmental system in steady state, we estimated the initial Zn exchange between plasma, and the erythrocytes or these tissues. In comparison with control animals the exchanges between plasma and erythrocytes or pancreas increased threefold during subacufe Zn deficiency. In the pancreas the ratio also reversed from <1.0 to>1.0. This confirmed earlier, observations that the specific activity (kBq 65-Zn/mol Zn) increased mostly in the pancreas. By increased net Zn uptake during subacute deficiency, the pancreas Zn content remained constant in chronic Zn deficiency. We discussed the regulation of the Zn status by the pancreas. We hypothesize that the exocrine pancreas modulates Zn absorption by an exocrine ligand that enhances absorption in the jejunum during subacute deficiency: Unsaturated with Zn it binds dietary intraluminal Zn and increases the Zn absorption. The literature provides evidence in confirmation. This hypothesis explains also conflicting data on the inherited Zn malabsorption syndrome Acrodermatitis Enteropathica.     

Idiorrhythmic zinc dose-rate induction of intestinal metallothionein in rats depends upon their nutritional zinc status(dagger)

The idiorrhythmic dose-rate feeding experimental model was used to study the induction of intestinal metallothionein (iMT) by zinc (Zn) in the gastrointestinal (GIT) mucosa of young growing male rats relative to their nutritional Zn status. The idiorrhythmic approach requires that the average dietary Zn concentration, referred to as modulo (M), is kept constant across different groups over the whole experimental epoch (E). This is done by adjusting the Zn concentration of the supplemented diet to compensate for the reduction in the number of days on which this diet is fed, the latter being spread evenly over the whole experiment. Idiorrhythms (I) involve offering the diet with n times the overall Zn concentration (M) only every nth day with a Zn-deficient diet offered on other days. We studied three modulos (low-Zn, M3; adequate-Zn, M12; and high-Zn, M48), each M having 8 analogous idiorrhythms (I = Mx/1 to 8Mx/8); every I was fed over a 48-d idiorrhythmic E. Over the wide range of peak doses of dietary Zn (3-384 mg Zn/kg diet), the higher the modulo, the greater the capacity for iMT to be induced (M3 < M12 < M48; P < 0.05). Also, the ability of Zn to induce iMT increased proportionally with the progression of the idiorrhythms from I = Mx/1 to 8Mx/8 (P < 0.001). When rats were fed M3, less Zn was required to induce iMT than when they were fed M12 or M48. Thus, within the M and E limits of this study, the better the nutritional Zn status of the animal, the more Zn is required to induce iMT and vice versa. The fact that iMT was increased means that the amount of available Zn was not proportional with the actual steady state of its metabolism. This indicates that for any Zn supplementation program to be effective, it should progress gradually from a lower to a higher Zn dose relative to the given nutritional Zn status.     

Dietary zinc deficiency decreases plasma concentrations of vitamin E

Experiments were conducted to examine the effects of dietary zinc (Zn) upon plasma vitamin E (E) concentrations to test the hypothesis that there may be a significant dietary interaction between these two nutrients. Weanling female Sprague-Dawley rats were fed diets that were (i) Zn-deficient (less than 0.9 micrograms Zn/g diet) ad libitum; (ii) Zn-adequate (50.9 micrograms Zn/g diet), pair-fed to the Zn-deficient group; and (iii) Zn-adequate (50.9 micrograms Zn/g diet) ad libitum. Plasma E in Zn-deficient animals (4.02 +/- 1.20 micrograms/ml) was significantly reduced (P less than or equal to 0.05) compared with results in both Zn-adequate pair-fed (9.21 +/- 0.70 micrograms/ml) and Zn-adequate ad libitum-fed (9.47 +/- 0.90 micrograms/ml) animals. Zn deficiency in this model system also resulted in significant (P less than or equal to 0.05) reductions in femur and plasma Zn concentrations as well as in plasma retinol, plasma triglyceride, and plasma cholesterol concentrations. Plasma albumin and total plasma protein concentrations were normal in Zn-deficient animals. With dietary Zn deficiency, the decrease in plasma E appeared to be out of proportion to associated decreases in plasma triglyceride and plasma cholesterol concentrations. Since E is associated with plasma lipoproteins, these data suggest that lipid and/or E malabsorption may be a consequence of Zn deficiency. In response to increased dietary intake of E, increments of plasma E were lower in Zn-depleted than in Zn-adequate, pair-fed animals. These findings suggest that dietary Zn deficiency possibly may increase the nutritional requirement for E necessary to maintain adequate plasma concentrations.     

Clinical examination of weanling rats with early zinc deficiency

In order to gain experience about the detection of adverse effects during a scientific procedure, we carried out a clinical examination of rats with zinc deficiency. In weanling rats fed a zinc-deficient diet (30 mumol zinc/kg) for 10 days, the mean tibial concentration of zinc was reduced by 53% and body weight gain by 73% when compared with rats fed a diet containing an adequate amount of zinc (150 mumol zinc/kg). In a small open field on day 9 of the experiment, the deficient rats more frequently displayed the posture standing upright with elevated heels. On day 10 of the experiment a clinical examination was carried out at random and 'blind' by three independent assessors. Out of 20 variables scored quantitatively on each individual animal, only body size differed between normal and deficient rats. Other classical signs of zinc deficiency, such as alopecia, dermatitis and diarrhoea, were not detected. It is concluded that in this rat model of zinc deficiency, no evidence for extreme discomfort can be demonstrated.     

Moderate zinc deficiency negatively affects biomechanical properties of rat tibiae independently of body composition

To guide development of novel nutritional strategies aimed at reducing the incidence of stress fractures, we observed the effects of manipulating dietary zinc (Zn) content on bone integrity in Sprague–Dawley rats fed either a severely Zn-deficient (ZnD; 1 ppm), a moderately Zn-deficient (MZnD; 5 ppm) or a Zn-adequate (ZnAD; 30 ppm) diet for 6 weeks. At the completion of the diet period, body composition, bone mineral content (BMC), bone area (BA) and bone mineral density (BMD) were determined in vivo by using dual-energy X-ray absorptiometry. Following euthanasia, long bones were collected for determination of Zn content and biomechanical strength testing. Despite significant positive correlations between dietary Zn and both body weight (BW) and bone Zn content for the entire cohort (r=.77 and r=.83, respectively), rats fed MZnD or ZnAD diets did not differ in feed intakes, body composition, BMC, BA, BMD or BW. Tibial bones, but not femur bones, appear to be more responsive to dietary Zn manipulation, as all bone biomechanical strength indices in the ZnAD-fed rats were significantly greater than in rats fed the ZnD diets. Rats fed either MZnD or ZnAD diets had stronger tibiae (129% increase in maximum load and stress at maximum load, P<.01) compared with those fed ZnD diets. The load at breakage for the tibial bones of rats fed MZnD diets was not different from the ZnD rats, but lower (P<.05) than that of the ZnAD rats. These results suggest that since feed intakes, body composition, BMC, BA, BMD and BW were not significantly different between the MZnD- and ZnAD-fed animals, the reduced bone integrity observed in the MZnD-fed rats resulted from dietary Zn inadequacy, and not as a result of the reduced growth that is typically associated with Zn deficiency.     

Relationship between plasma zinc, angiotensin-converting enzyme, alkaline phosphatase and onset of symptoms of zinc deficiency in the rat

Recent evidence suggests that changes in plasma zinc concentration may play a central role in the development of early lesions of zinc deficiency. The aim of the following work was to better understand events occurring in plasma during the onset of zinc deficiency, and to investigate biochemical mechanisms by which plasma zinc may exert its effects. Fifty male weanling rats of 90 g weight were allocated to five treatment groups of ten rats each. Treatments were: 1, zinc deficient, mixed diet (1-2 mg Zn per kg): 2, zinc deficient, self-select diet; 3, zinc repleted; 4, control, pair fed; 5, control, ad libitum fed. With the exception of treatment 1, which consisted of a 25% casein diet, all rats were offered protein as a separate component of the diet. Control rats received zinc in the drinking water (100 mg l-1). The sequence of events following initiation of zinc deficiency were: reduced plasma zinc concentration (2 days), reduced plasma angiotensin-converting enzyme and alkaline phosphatase activities (3-4 days), reduced feed intake and growth (5-6 days) and reduced percentage protein intake (12 days). Plasma zinc concentration in the deficient rats was inversely correlated with the growth rate of the rat over the previous 24 h. Zinc repletion resulted in marked overshoot in plasma zinc concentration (300%) and converting-enzyme activity (150%) within 24 h, but a return to normal within 72 h. Alkaline phosphatase activity responded likewise, albeit more slowly. Protein self selection had no effect on the manifestations of zinc deficiency, although reduced protein intake was associated with lower plasma zinc concentration. The results provide evidence of a role for plasma zinc in the development of early clinical signs of zinc deficiency, possibly acting biochemically through reduced activity of zinc-dependent peptidases such as angiotensin-converting enzyme.     

Dietary pharmacological or excess zinc and phytase effects on tissue mineral concentrations, metallothionein, and apparent mineral retention in the newly weaned pig

Feeding pharmacological zinc (Zn) to weaned pigs improves growth, and dietary phytase improves P and Zn availability. Metallothionein (MT) increases in the duodenum, kidney, and liver of pigs fed 1000 mg Zn/kg with phytase or 2000 mg Zn/kg with or without phytase when fed for 14 d postweaning. The goal of this study was to determine the effects of feeding pharmacological Zn and phytase on tissue minerals, MT, mineral excretion, and apparent retention. Twenty-four newly weaned pigs (20 d; 7.2 kg) were individually fed twice daily, a basal diet supplemented with 0, 1000, or 4000 mg Zn/kg as Zn oxide, without or with phytase (500 phytase units [FTU]/kg) for 14 d, followed by a basal diet (100 mg Zn/kg) without phytase for 7 d. Pigs fed 4000 mg Zn/kg without phytase had higher (p=0.01) plasma, hepatic, renal Zn, renal Cu, and hepatic, renal, and jejunal MT than pigs fed the basal diet or 1000 mg Zn/kg. Duodenal MT was higher (p=0.0001) in pigs fed 1000 and 4000 mg Zn/kg than in pigs fed the basal diet. In pigs fed 1000 and 4000 mg Zn/kg, Zn loading occurred during the first 11 d of supplementation; by d 14, excess Zn was being excreted in the feces.     

Phytase supplementation increases bone mineral density,lean body mass and voluntary physical activity in rats fed a low-zinc diet

Phytic acid forms insoluble complexes with nutritionally essential minerals, including zinc (Zn). Animal studies show that addition of microbial phytase (P) to low-Zn diets improves Zn status and bone strength. The present study determined the effects of phytase supplementation on bone mineral density (BMD), body composition and voluntary running activity of male rats fed a high phytic acid, low-Zn diet. In a factorial design, rats were assigned to ZnLO (5 mg/kg diet), ZnLO+P (ZnLO diet with 1500 U phytase/kg) or ZnAD (30 mg/kg diet) groups and were divided into voluntary exercise (EX) or sedentary (SED) groups, for 9 weeks. SED rats were significantly heavier from the second week, and no catch-up growth occurred in EX rats. Feed intakes were not different between groups throughout the study. ZnLO animals had decreased food efficiency ratios compared to both phytase-supplemented (ZnLO+P) and Zn-adequate (ZnAD) animals (P<.01 compared to ZnLO). The ZnLO+P and ZnAD rats ran 56–75 km more total distance than ZnLO rats (P<.05), with the ZnLO+P rats running more kilometers per week than the ZnLO rats by Week 6. In vivo DEXA analyses indicate that rats fed phytase-supplemented diets had higher lean body mass (LBM) than those fed ZnLO diets; and that rats fed the Zn-adequate diets had the highest LBM. Body fat (%) was significantly lower in EX rats and was both Zn- and phytase insensitive. Rats fed phytase-supplemented diets had higher bone mineral content (BMC), bone area (BA) and BMD than rats fed ZnLO diets; and in rats fed ZnAD diets these indices were the highest. The dietary effects on BMC, BA and BMD were independent of activity level.We conclude that consuming supplemental dietary phytase or dietary Zn additively enhances Zn status to increase BMD, LBM and voluntary physical activity in rats fed a low-Zn diet. While the findings confirm that bone health is vulnerable to disruption by moderate Zn deficiency in rats, this new data suggests that if dietary Zn is limiting, supplemental phytase may have beneficial effects on LBM and performance activity.     

The effect of zinc deficiency on the body composition of rats

Body composition and the levels of some plasma metabolites were measured in zinc deficient and control rats with the aim of assessing the nature of the metabolic defects resulting from zinc deficiency. Two experiments, lasting 15 and 20 d, were carried out using 52 immature rats. Zinc deficient animals were fed a diet of 1–2 mg Zn/kg. Pair fed andad libitum control rats received the same diet with 100 ppm zinc added to the drinking water. Feed intake and growth rate were measured, and the carcasses were analyzed for protein, fat, and ash. In each experiment, a group of rats were killed on d 1 to provide pretreatment values and to allow for estimates of net deposition of carcass components. Lactate, urea, and zinc were assayed in plasma, as well as zinc concentration in carcasses and liver. The main effect of zinc deficiency was to reduce feed intake and efficiency of feed conversion, resulting in a reduced proportion of carcass wat because of the reduced feed efficiency, zinc deficiencyper se resulted in an increase in the proportion of fat in the carcass. Plasma lactate concentration was unchanged, but urea concentration increased in both pair fed and zinc deficient rats relative toad libitum fed control animals. The results indicate that a defect in protein synthesis and an increase in energy expenditure, perhaps resulting from increased protein turnover, underlies the reduced growth and efficiency of feed conversion of zinc deficiency.     

Consecutive zinc balance trials in growing rats

Rats were fed a purified egg white-based diet containing 5 ppm Cu and 2, 14, or 57 ppm Zn. Zinc and copper balances were determined for eight consecutive weekly trial periods. The zinc-deficient group almost ceased to gain weight and was in slightly negative zinc balance. Groups of rats fed 14 and 57 ppm Zn gained weight at equal rates. These groups were in strongly positive zinc balance for four weeks; thereafter, they fed 57 ppm Zn retained about two times as much zinc as did the group fed the diet containing 14 ppm Zn. All groups were in null or slightly negative copper balance throughout the trial. These results suggest that zinc accumulation may be homeostatically controlled to a level in excess of that needed for maximum growth.