The effect of past and current dietary Zn intake on Zn absorption and endogenous excretion in the rat

Effects of previous dietary Zn (or body Zn stores) and current dietary Zn intake on absorption and endogenous excretion of Zn were studied by using radioisotope dilution. Rats were fed diets containing 1.5, 12.6 or 50.3 mg Zn/kg for 19 d (dietary period I). Total body Zn in the three groups was 1870 +/- 340, 3953 +/- 698 and 4126 +/- 844 micrograms Zn/rat. Each group was divided into four subgroups fed 3.6, 12.6, 20.5 or 50.3 mg Zn/kg diet for 3 wk (dietary period II). Rats were injected intramuscularly with 65Zn after 7 d of dietary period II. True absorption and endogenous excretion were calculated by isotope dilution. Zinc intake, urinary and fecal excretion, balance and percent Zn absorption were significantly affected only by dietary Zn in dietary period II (P less than 0.01). Endogenous excretion was affected by both past dietary Zn deficiency (body Zn stores) and by dietary Zn in dietary period II (P = 0.0001). Total body Zn at the end of the experiment was significantly affected by both periods of dietary treatment (P less than 0.001), but total body Zn concentration was affected only by the final dietary treatment (P less than 0.05). These results show that Zn absorption is affected by the current diet, but that turnover of Zn (endogenous excretion) is regulated by both current Zn intake and past Zn intake, probably through an effect on body Zn stores.     

Metabolic adaptations to low zinc intakes in premenarcheal girls

BACKGROUND: Zinc deficiency is increasingly recognized as an important cause of mortality and morbidity. Children in developing countries are at especially high risk because of relatively low zinc intakes and poor bioavailability. OBJECTIVE: We assessed the effect of 2-wk adaptation to low zinc intake (4 mg/d) on fractional zinc absorption, endogenous fecal zinc excretion, and urinary zinc excretion. DESIGN: Sixteen healthy 9-14-y-old girls were studied twice in random order after 2-wk adaptation to diets providing either 12 mg/d (high) or 4 mg/d (low) zinc. Fractional zinc absorption and endogenous fecal zinc excretion were measured with use of established stable isotope techniques. RESULTS: Plasma zinc was not significantly lower during the low dietary intake period (1.06 +/- 0.18 mg/L) than during the high dietary intake period (1.14 +/- 0.23 mg/L, P = 0.30). Endogenous fecal zinc excretion was significantly lower during the low intake period (1.08 +/- 0.62 mg/d) than during the high intake period (1.82 +/- 0.95 mg/d, P < 0.026), but there was no significant change in fractional zinc absorption (30.6% +/- 12.4% compared with 26.6% +/- 9.0%, P = 0.32) or urinary zinc excretion (0.68 +/- 0.35 mg/d compared with 0.59 +/- 0.24 mg/d, P = 0.30). Approximate zinc balance was significantly lower during the low-intake period than during the high-intake period (P = 0.007) and significantly (P < 0.0001) less than zero. CONCLUSION: Short-term zinc restriction in premenarcheal girls leads to a significant decrease in endogenous fecal zinc excretion, which was inadequate to restore normal zinc balance.     

Zinc homeostasis during lactation in a population with a low zinc intake.

BACKGROUND: There is a major increase in endogenous zinc excretion, specifically via the mammary gland, in early human lactation. Whereas fractional absorption of dietary zinc has been reported to increase in early human lactation, it is not known to what extent adaptive mechanisms may maintain zinc homeostasis, especially when dietary zinc intake is relatively low. OBJECTIVE: The objective of this study was to quantitate major variables of zinc homeostasis during early lactation in subjects from a population whose habitual dietary zinc intake is low. DESIGN: We studied 18 free-living lactating women from a rural community of northeast China whose infants were exclusively breast-fed. The subjects were studied at approximately 2 mo of lactation with use of stable isotopes of zinc and metabolic collection techniques. Milk volume was measured with use of a deuterium enrichment method. RESULTS: The mean (+/-SD) secretion of zinc in milk was 2.01 +/- 0.97 mg/d, the intake of zinc was 7.64 +/- 1.61 mg/d, and the fractional absorption of zinc was 0.53 +/- 0.09, for a total daily zinc absorption of 4.00 +/- 0.71 mg/d. Endogenous zinc excretion in urine and feces was 0.30 +/- 0.10 and 1.66 +/- 0.97 mg/d, respectively. CONCLUSIONS: Zinc balance, including zinc secreted in breast milk, was maintained at approximately 2 mo of lactation in women whose habitual diet was low in zinc. Homeostasis was achieved by high fractional absorption of zinc and intestinal conservation of endogenous fecal zinc.     

Major variables of zinc homeostasis in Chinese toddlers

BACKGROUND: Measurement of the major variables of zinc homeostasis is an essential prerequisite for estimating human zinc requirements, which currently require a factorial approach. The data required for this approach have not been available for toddlers, whose requirements have been estimated by extrapolation from other age groups. OBJECTIVE: The objective of the study was to measure key variables of zinc homeostasis in rural and small-town Chinese toddlers. DESIGN: Zinc stable-isotope tracers were administered intravenously and orally with all meals for 1 d to 43 toddlers. Subsequent metabolic collections in the homes included duplicate diets, quantitative fecal collections, and spot urine sampling. Fractional absorption of zinc (FAZ) was measured by a dual-isotope tracer ratio technique, and endogenous fecal zinc (EFZ) was measured by an isotope dilution technique. RESULTS: No group or sex differences were found. Therefore, results were combined for 43 toddlers aged 19-25 mo whose major food staple was white rice. Selected results (x+/- SD) were 1.86 +/- 0.55 mg total dietary Zn/d; 0.35 +/- 0.12 FAZ; 0.63 +/- 0.24 mg total absorbed Zn/d; 0.67 +/- 0.23 mg EFZ/d; and 65.0 +/- 8.3 microg plasma Zn/dL. The molar ratio of dietary phytate to zinc was 2.7:1. CONCLUSIONS: The mean intake and absorption of zinc in this population are low in comparison with estimated average dietary and physiologic requirements for zinc, and plasma zinc values are consistent with zinc deficiency. Intestinal losses of endogenous zinc exceed previous estimates for toddlers, and only modest evidence exists of conservation in response to low zinc intake and absorption.     

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.     

Intestinal excretion of endogenous zinc in Guatemalan school children

The intestine is the major route of excretion of endogenous zinc (Zn) and has a key role in maintaining Zn homeostasis. The principal objective of this paper is to provide an interpretative report of quantities of endogenous fecal Zn (EFZ) excreted by rural Guatemalan school children fed either normal or low phytate maize as their principal food staple. EFZ was measured by a Zn stable isotope technique. EFZ did not differ between control and low phytate maize groups. The overall EFZ (n = 53) was (mean +/- SD) 1.56 +/- 0.69 mg Zn/d or 0.07 +/- 0.03 mg Zn x kg body wt(-1) x d(-1). EFZ was not correlated with the quantity of Zn absorbed. The estimated EFZ at the level of absorption that matched the physiologic requirement (EFZ(PR)) did not differ from the above mean value. The EFZ(PR) of 0.07 +/- 0.03 mg Zn/kg body wt is twice the value currently used in the estimation of Dietary Reference Intakes. Supported by other recent childhood data, these results suggest that the current estimates of EFZ(PR) used in the calculation of Zn requirements for children are misleadingly low.     

Dietary phytate reduction improves zinc absorption in Malawian children recovering from tuberculosis but not in well children

High dietary phytate content that compromises zinc nutriture is thought to be a major problem among children of the developing world. Zinc stable isotope techniques permit the quantitative assessment of the effect of phytate reduction on zinc homeostasis. We tested the hypothesis that zinc absorption would be increased in Malawian children fed a reduced-phytate corn-plus-soy diet compared with a standard high phytate diet. Twenty-three children hospitalized in Blantyre, Malawi, were enrolled. Children were selected from those recovering from tuberculosis and from well children (those with minor injuries, those awaiting elective surgery or healthy siblings). Children received a diet of corn-plus-soy porridge (either low phytate or high phytate) for a period of 3-7 d and then participated in a zinc stable isotope study. The study included the administration of oral and intravenous zinc stable isotopes and 7-d collections of urine and stool. The diet was maintained throughout the duration of specimen collection. Zinc isotopic enrichments in urine and stool were measured, and zinc fractional absorption, total zinc absorption, endogenous fecal zinc, net zinc retention and size of the exchangeable zinc pool were calculated. Among the 14 children recovering from tuberculosis, dietary phytate reduction resulted in higher fractional absorption (0.41 +/- 0.14 versus 0.24 +/- 0.09, mean +/- SD, P: < 0.05) and total zinc absorption (169 +/- 55 versus 100 +/- 46 microg/(kg. d), P: < 0.05). No effect of phytate reduction was seen in the well children (n = 9). Phytate reduction did not decrease the absolute endogenous fecal zinc, but it did decrease it relative to total absorbed zinc. These preliminary results indicate that phytate reduction may be beneficial in improving zinc nutriture in groups with increased zinc requirements who consume a cereal-based diet.     

A high oat-bran intake does not impair zinc absorption in humans when added to a low-fiber animal protein-based diet

Oat bran has a high phytate content and a low or inactivated phytase activity. A high intake of oat bran could therefore result in an impaired absorption of trace elements. The effect of a mean daily intake of 142 g of oat bran (102 g/10 MJ) on absorption of zinc was evaluated by the use of stable isotopes and fecal monitoring in 12 healthy subjects (6 males and 6 females). Each subject participated in two separate diet periods each of 21 d with identical low-fiber diets and with oat bran added in one of the periods. The oat bran was incorporated into bread and served at three daily main meals. The intake of zinc and phytate per 10 MJ was 138 micromol (9.0 mg) and 0.5 mmol, respectively, in the low-fiber period and 225 micromol (14.7 mg) and 4.0 mmol, respectively, in the oat bran period. Stable isotopes of zinc ((70)Zn) were added to the diets at d 7 of each period. The fractional absorptions (means +/- SD) of zinc from the low-fiber and oat bran diets were 0.48 +/- 0.11 and 0.40 +/- 0.15 (P = 0.07), respectively. The higher zinc content in the oat bran period resulted in a greater amount of zinc absorbed (64 +/- 19 micromol and 99 +/- 51 micromol, respectively, P = 0.009). Balance data suggest that the higher absorbed amount of zinc resulted in correspondingly higher intestinal endogenous excretion of zinc. In conclusion, the absorption of zinc was high and not affected by addition of oat bran.     

Endogenous zinc excretion in relation to various levels of dietary zinc intake in the mink (Mustela vison)

Endogenous zinc excretion was studied in adult male mink fed experimental diets for 73 d, including a collection period from d 69 to 73. Dietary zinc levels were 2.8, 26 or 121 mg/kg wet weight. In accordance with the results of a methodological study, also reported here, the animals had an intramuscular injection of 65ZnCl2 12 d before the start of the collection period. Total fecal (endogenous + unabsorbed) zinc excretion for d 69-73 in the three groups was 2.3, 20.4 and 91.0 mg. The endogenous zinc excretion was 1.3, 2.0 and 6.4 mg, corresponding to 80.8, 10.6 and 6.4% of the zinc intake. Thus, the endogenous excretion was mainly important for the zinc homeostasis at low zinc intake, whereas at high intake the homeostasis was regulated via absorption from the digestive tract. The overall conclusion of the experiment was that mink are comparable to other species (including man) in regard to mechanisms controlling zinc homeostasis.     

Dysprosium as a nonabsorbable fecal marker in studies of zinc homeostasis

BACKGROUND: Dysprosium is a nonabsorbable rare earth element that has had successful application as a marker for fecal excretion of unabsorbed zinc. OBJECTIVE: Our goals were 1) to evaluate the efficacy of administering dysprosium with all meals over several days as a method of determining the completeness of fecal collections, 2) to determine the similarity of gastrointestinal transit kinetics and excretion patterns of dysprosium and zinc tracer administered simultaneously over several days, and 3) to evaluate alternative methods of using the data for fecal excretion of orally administered zinc tracer and dysprosium to measure the fractional absorption of zinc. DESIGN: 70Zn and dysprosium were administered orally with all meals for 5 consecutive days to 7 healthy, free-living adults consuming a constant diet based on habitual intake. Additional tracers, 67Zn and 68Zn, were administered intravenously. Urine and fecal samples were collected during tracer administration and for 8 d after the last dose. Isotope ratios were measured in urine and feces, and total zinc and dysprosium were measured in fecal samples. RESULTS: The mean recovery of dysprosium was 101.3 +/- 2.4%. The zinc oral tracer and dysprosium had similar fecal excretory patterns; the correlation coefficient for 70Zn and dysprosium in fecal samples exceeded 0.99 (P < 0.0001) for each subject. Fractional zinc absorption measurements using various dysprosium methods correlated well (r > 0.95) with those from the fecal monitoring and dual-isotope-tracer ratio methods. CONCLUSION: Administration of dysprosium is a useful means of determining the completeness of fecal collections and of measuring zinc absorption.     

Calcium and zinc absorption from lactose-containing and lactose-free infant formulas

BACKGROUND: Calcium absorption is enhanced by the presence of lactose, but the quantitative significance of this effect in infant formulas is uncertain. It is also not known whether lactose affects zinc absorption. OBJECTIVE: We measured the absorption of calcium and zinc from infant formulas by using a multitracer, stable-isotope technique. DESIGN: Eighteen full-term infants (aged 8-12 wk at enrollment) were fed 2 partially hydrolyzed whey-protein-based formulas ad libitum for 2 wk per formula. The carbohydrate source was lactose in one formula and glucose polymers in the other (lactose-free). Infants were studied in a blinded crossover fashion after 2 wk of adaptation to each formula. Isotope absorption studies were conducted with a 4-tracer method in which (70)Zn and (44)Ca were provided orally and (67)Zn and (46)Ca intravenously. Zinc and calcium absorption was measured from the fractional excretion of the oral and intravenous isotopes in urine. RESULTS: Fractional and total calcium absorption was significantly greater from the lactose-containing formula than from the lactose-free formula. For total calcium absorption, the mean difference between formulas was 10.3% (P = 0.002) and 60 mg/d (P = 0.006). For zinc, fractional absorption (32 +/- 11%), total absorption, and intake did not differ significantly between the 2 formulas. CONCLUSIONS: The presence of lactose in a formula based on cow-milk protein increases absorption of calcium but not of zinc. Absorption of calcium from a lactose-free infant formula is, however, adequate to meet the calcium needs of full-term infants when the formula's calcium content is similar to that of lactose-containing, cow-milk-based infant formulas.     

Current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men

BACKGROUND: No studies have examined the independent effects of current and longer-term dietary zinc intakes on zinc absorption. OBJECTIVE: We determined the effects of current compared with longer-term zinc intake on fractional zinc absorption (FZA). DESIGN: We studied 9 men whose usual zinc intakes were >11 mg/d. FZA was measured at baseline, depletion (0.6 mg Zn/d for 1 wk and 4 mg Zn/d for 5 wk), and repletion (11 mg Zn/d for 4 wk with 20 mg supplemental Zn/d for first 7 d). During 2 successive days after each dietary period, subjects consumed either adequate-zinc meals (11 mg Zn/d) with a zinc stable isotope tracer for 1 d, followed by low-zinc meals (4 mg Zn/d) with zinc tracer, or vice versa. Five days after oral dosing, a zinc tracer was infused intravenously. FZA was measured with the use of a modified double isotope tracer ratio method with urine samples collected on days 5-7 and 10-12 of absorption studies. RESULTS: Plasma and urinary zinc did not vary by dietary period. Mean FZA was greater from low-zinc meals than from adequate-zinc meals (60.9% +/- 13.8% compared with 36.1% +/- 8.9%; P < 0.0001), whereas mean total absorbed zinc was greater from adequate-zinc meals than from low-zinc meals (3.60 +/- 0.91 compared with 2.48 +/- 0.56; P < 0.0001), regardless of the longer-term dietary period. CONCLUSIONS: FZA was inversely related to current zinc intake, but there was no detectable effect of longer-term dietary zinc. If longer- term zinc intake does modify FZA, such changes are smaller than those caused by current zinc intake, or they occur only after more severe zinc depletion.     

Plasma zinc and copper levels of infants fed different milk formulas

The plasma zinc and copper levels of 32 full-term healthy infants, aged 3-4 months, using different infant formulas, were measured. The plasma zinc levels of infants using soy formula (45.1 +/- 19.1 micrograms/dl) and iron-fortified cow's milk formula (61.6 +/- 12.9 micrograms/dl) were significantly lower than those of the infants using cow's milk formula not fortified with iron (77.5 +/- 13.4 micrograms/dl). The plasma copper levels of the infants using the different formulas were not significantly different from each other. Fortification of infant formulas with high levels of iron may reduce the zinc absorption from such formulas.     

The effect of dietary zinc status on biliary metal excretion of rats

The effect of dietary zinc status on biliary excretion of zinc, cadmium and mercury administered as a bolus of metal chloride (1 mg metal/kg body weight i.v.) was studied. Female rats were fed a purified diet containing either 9 micrograms/g (low), 45 micrograms/g (adequate) or 1150 micrograms/g (high) zinc for 8 d. Hepatic metallothionein (MT) was similar in low- and adequate-zinc groups, but was 18-fold higher in the high-zinc group than in the other two groups. Liver zinc content varied in relation to dietary zinc level. Biliary excretion of all metals studied was significantly lower in the high-zinc group than in the low-zinc group. The cumulative excretion of zinc, cadmium and mercury over 2.5 h in rats fed these two diets was 6.2 +/- 1.4 vs. 33.5 +/- 7.7, 0.006 +/- 0.02 vs. 22.8 +/- 8.4 and 1.6 +/- 0.6 vs. 14.9 +/- 5.3 micrograms/kg body weight, respectively. A relationship was found between the disposition of metal in liver and the extent of biliary metal excretion. Biliary metal excretion was highly correlated with liver cytosolic non-MT-bound metal; r = 0.999, 0.998 and 0.993 for endogenous + exogenous zinc, cadmium and mercury, respectively.     

Effect of low zinc intakes on basal metabolic rate, thyroid hormones and protein utilization in adult men

Basal metabolic rate (BMR), thyroid hormones and protein utilization were measured in six young men participating in a 75-d metabolic study of low zinc intakes. During metabolic period (MP) 1 (12 d) and MP 3 (9 d) the subjects received 16.5 mg Zn/d. During MP 2 (54 d) they received 5.5 mg Zn/d. Nitrogen intake averaged 12.6 g/d. Mean BMR significantly decreased from 1.00 +/- 0.06 to 0.91 +/- 0.05 kcal/(kg X h) (mean +/- SD) with the low zinc diet and tended to increase during period 3. Serum thyroid-stimulating hormone, thyroxine (T4) and free T4 tended to decrease during the low zinc period and to increase when the adequate zinc diet was fed; only the decrease in free T4 was significant at P less than 0.05, however. Among the measures of protein status, urinary urea excretion, serum prealbumin, albumin and retinol-binding protein levels all decreased significantly during the low zinc period. The results suggest that low zinc intakes may be associated with decreases in BMR. In addition, decreases in thyroid hormone levels and alterations in protein utilization may occur.     

Intrinsic and extrinsic stable isotopic zinc absorption by infants from formulas

The kinetics of fecal elimination and the extent of fractional absorption of intrinsic and extrinsic zinc from infant formula were studied in 11 human infants by using a direct, simultaneous dual-label method based on fecal monitoring of unabsorbed stable isotope labels. The relative positions of the two stable isotopic tags (67Zn, 70Zn) as extrinsic and intrinsic labels were reversed in two separate determinations of fractional absorption. Administration of doubly labeled formula for 24 h or less permitted elimination of unabsorbed labels before the end of a 72-h metabolic interval. The extent of enrichment and the kinetics of fecal elimination of unabsorbed extrinsic stable isotopic zinc tag were observed to agree closely with the corresponding values for the intrinsic tag. Fractional absorption of intrinsic and extrinsic tags was highly correlated and did not differ significantly. The ratio of fractional absorption of extrinsic tag to that of intrinsic tag was 1.05 +/- 0.19 (mean +/- SD). The results constitute strong support for validation of the use of enriched stable isotopes at low levels (less than or equal to 10%) of extrinsic addition to milk-based diets for studies of zinc absorption by humans.     

Zinc homeostasis in 1-4 year olds consuming diets typical of US children

Few data have evaluated Zn balance in young children after the first year of life. The objective of the present study was to study the relationships among Zn intake, absorption, endogenous faecal excretion, and retention in a group of healthy children. Thirty children, aged 15-48 months, were studied on a diet representative of their usual daily mineral intake. Zn absorption was assessed using a dual-tracer stable-isotope technique. Endogenous Zn faecal excretion and Cu absorption were determined in a subset of children. We found that Zn intake from the in-patient weighed dietary record (5.0 (SD 2.1) mg/d) was significantly greater than the current estimated average requirement (EAR; 2.5 mg/d; P 0.4, for all). Absolute Zn absorption was significantly related to Zn intake (r2 0.696; P < 0.0001), as was Zn retention (r2 0.506; P < 0.0001). Cu absorption was relatively high (75.1 (sd 10.8) %) despite the high Zn intake. The EAR for Zn based on this dataset would appear to be between 4.2 and 4.7 mg/d to allow for a net average retention of 120 microg/d consistent with growth needs. We concluded that at relatively high Zn intakes there was little evidence of down regulation of absorption or up regulation of urinary or endogenous faecal Zn excretion across the intake range studied. Zn retention was positively correlated with intake. A Zn intake between 4.2 and 4.7 mg/d should meet the requirement for normal growth for this age group.     

Dietary intake of lead, cadmium, copper and zinc by children from the German North Sea island Amrum

The dietary intake of metals was studied in seven male and seven female children at the age of 1.5 to 5.3 years living in a remote area of Germany, the North Sea island Amrum. The dietary intake of lead and cadmium was measured by a seven-day-duplicate study using atomic absorption spectrometry. The dietary intake of copper and zinc were calculated from food diaries. The median lead and cadmium intakes were 2.1 micrograms/(kgbw x week) [range: 0.63-5.1 micrograms/(kgbw x week)] and 2.7 micrograms/(kgbw x week) [range: 1.7-4.4 micrograms/(kgbw x week)]. The median daily intake of copper and zinc were 1.1 mg/d (range: 0.54-2.5 mg/d) and 5.7 mg/d (range: 2.7-14 mg/d). Compared to the provisional tolerable weekly intake (PTWI) of 25 micrograms/(kgbw x week) proposed by the WHO the dietary intake of lead was low. The median amounted to 8.5% and the maximum to 20% of the PTWI. The cadmium intake was comparatively high. The median amounted to 39% and the maximum to 63% of the PTWI [7 micrograms/(kgbw x week)]. The median intake of copper was in the range of the values recommended by the German Society of Nutrition (0.7-1.0 mg/d and 1.0-1.5 mg/d for children at the age of 1-< 4 years and 4-< 7 years). Twenty-three percent of the calculated intakes were below these values. The median intake of zinc however did not reach the recommended dietary intake of 7 and 10 mg/d for children at the age of 1-< 4 years and 4-< 7 years.     

Homeostatic regulation of zinc absorption and endogenous losses in zinc-deprived men

The mechanisms involved in the homeostatic regulation of zinc were studied in five male subjects by using stable 70Zn as a marker. When dietary zinc was reduced from 85 to 12 mumol/d, adaptation was achieved by a mean (+/- SEM) reduction in urine zinc of 48 +/- 7% and in fecal zinc of 46 +/- 12% over 25 d in four subjects. The latter was caused by an increase in the efficiency of zinc absorption from 38 +/- 3% to 93 +/- 1% after 15 d of zinic deprivation and by a reduction in intestinal endogenous losses of zinc. In a fifth subject, who had some evidence of a resolving alcohol-induced hepatitis, urine and fecal zinc were reduced by 64% and 41%, respectively, in 15 d and zinc absorption increased from 46% to 93%. More information on adaptive responses is needed to enable current dietary recommendations to be reconsidered.     

Fatty acid absorption in preterms on formulas with and without long-chain polyunsaturated fatty acids and in terms on formulas without these added

BACKGROUND/OBJECTIVE: Long chain polyunsaturated fatty acids have beneficial effects in preterm neurophysiological development and are semi-essential. Their levels and variation in plasma and red cells in term and preterms are better known than their intestinal absorption. In this paper the absorption of supplemented arachidonic acid (AA) and docosahexaenoic acid (DHA) is evaluated in a preterm group. DESIGN: Four newborn randomized groups were studied. Group T comprised 11 terms on regular formula. Preterms: group P (n=9) was on a classic preterm formula. Intervention: groups PA (n=9) and PB (n=13) were on the same formula but PB contained AA and DHA in similar proportion to breast milk. At 20 days a 3 day metabolic balance was taken for Ca, P(i), Mg, total fat and individual fatty acids (C8-C24, saturated unsaturated). RESULTS: Calcium absorption was (mean+/-s.d.) 51+/-13% in terms. In preterms it was respectively 45+/-18, 38+/-11 and 37+/-21%. Total fat absorption was 92.0+/-8.0% in terms, and from 95.0+/-2.0 to 91.0+/-8.0% in preterms. Absorption of 8:0, 10:0 and 12:0 showed a very high and constant rate despite significant intake differences (715-33 mg/kg/day). Linoleic acid and alpha-linolenic acid were absorbed in the three groups at around 94% regardless of a greater LA intake in group P. Details of absorption (mg/kg/day) were: for AA, intake 17+/-7, fecal excretion 5+/-4, net retention 12+/-5 (75.0+/-18%); for DHA, intake 10+/-3, fecal excretion 3+/-2, net retention 6+/-4 (62.3+/-30%). CONCLUSION: Intestinal absorption of fatty acids is high and is comparable in terms and preterms as regards the studied acids. Longer acids were less well absorbed. The supplemented amounts of AA and DHA were less well absorbed and probably not impairing calcium absorption. SPONSORSHIP: University of Alicante, University of Miguel Hernández.