INHIBITION OF INTESTINAL IRON ABSORPTION BY LAUNDRY STARCH

Transcription

1 G.....,. ~T A O E A O 71: L O G Y 1976 C o p y r@ i 1976 ~ h t hy The William. " Wilkins Co. Vol. 71. No. 6 Printrd in U.S.A. INHIBITION OF INTESTINAL IRON ABSORPTION BY LAUNDRY STARCH FRED B. THOMAS, M.D., JAMES M. FALKO, M.D., AND KENNETH ZUCKERMAN, M.D. Department of Medicine and Division of Gastroenterology, The Ohio State University Collf.'ge of Medicine, Columbw. Oh io The pathogenesis of iron deficiency anemia associated with amylophagia is usually attributed to dietary iron lack. However, large quantities of starch may inhibit intestinal iron absorption. Accordingly, studies were carried out to determine the effect of laundry starch on the intestinal absorption of inorganic and hemoglobin iron. In vitro, laundry starch bound 19 to 80% of the available stfeso. and 34 to 68% of the available "Fehemoglobin. Binding of both forms of iron was ph-dependent, with maximal binding at ph 7.0. In vivo, laundry starch significantly inhibited mucosal uptake of ItFeSO. from isolated duodenal loops. In nonanemic rats, administration of laundry starch (100 mg) 1 hr before a loo-ilg dose of ufeso. significantly decreased the absorption of "FeSO., as compared to saline or low iron chow controls (6.2 ± 2.0 versus 14.9 ± 2.1 and 11.8 ± 1.7, respectively, P < 0.(01). In anemic rats the absorption of either a l00-llg dose of "FeSO. or a 5OO-llg dose of "Fe-hemoglobin was also significantly decreased by prior administration of laundry starch. The data obtained indicated that laundry starch (1) binds appreciable quantities of inorganic and hemoglobin iron in vitro; (2) inhibits the mucosal uptake of inorganic iron by isolated intestinal loops; (3) inhibits the intestinal absorption of inorganic iron in normal nonanemic rats, and (4) blunts the compensatory increase in inorganic and organic iron absorption in anemic rats. Amylophagia is a relatively common form of pica in this country. The association of iron deficiency anemia with ingestion of large quantities of laundry starch is well documented. t. 2 Whether or not the associated anemia is a cause or an effect of amylophagia is unknown. Most studies have suggested that starch eating is the result of iron deficiency and that the anemia occurs primarily by dietary substitution of laundry starch for other nutrients. H However, it is possible that laundry starch binds dietary iron intraluminally and prevents its absorption from the small intestine. To answer this question, in vitro and in vivo studies were carried out in rats to determine the effect of laundry starch on the intestinal absorption of both inorganic and hemoglobin iron. The results obtained indicate that laundry starch (1) binds significant quantities of both inorganic and hemoglobin iron in vitro and (2) inhibits Received March Accepted June 8, This paper was presented in part at the American Federation (or Clinical Research Meeting, Atlantic City, New Jersey, May Address reprint requesta to: Fred B. Thomas. M.D., N 937 University H08pital, The Ohio State University, 410 West 10th Avenue, Columbus. Ohio Dr. Thomas is Associate Professor o( Medicine and Director. Division of Gastroenterology. The Ohio State University College of Medicine. Dr. Falko is a Major, United States Air Force, Fort Worth, Texas. Dr. Zuckerman is a Fellow in Hematology. Peter Bent Brigham Hospital, Boston, Massachusetts the intestinal absorption of inorganic and hemoglobin iron in normal and bled rats. Methods Materials. Test solutions of IOFeSO. (specific activity 10.0 mc per mg, New England Nuclear Corporation, Boston, Mass.) were prepared by dilution with nonlabeled ferrous sulfate. For in vivo studies the ph of the iron,olution was adjusted to 3.5 by addition of 0.1 N HC\. Hemoglobin labeled with IOFe was prepared according to methods previously described.' The final solution obtained had a hemoglobin concentration of 9.5 g per dl, and a specific activity of 100 counts per min per pg of hemoglobin. IOFe-Hemoglobin solutions of desired specific activity were obtained by dilution with an appropriate volume of non labeled hemoglobin. Suspensions of Argo laundry starch (ph 4.5, Best Foods Co., Englewood Cliffs, N.J.) and low iron rat chow (Teklad Test Diets, Madison, Wis.) were prepared by mixing with an appropriate volume of iron-free distilled water and continuously stirring on a magnetic mixer. After preparation, the ph of the suspensions was adjusted to 2. 5, or 7 by addition of either 0.1 N HCl or 0.1 N NaOH. In vitro binding studies. Experiments on the in vitro binding of ufeso. and "Fe-hemoglobin were carried out according to methods previously described.' Incubation flasks were prepared in duplicate at ph 2, 5, and 7 so that each flask contained 200 pg and 0.4 pc of ufeso. and 20, 100, 200, or 2000 mg of laundry starch. Control flasks containing identical quantities of inorganic iron but no laundry starch were also prepared in duplicate at ph 2, 5, and 7. Iron-free distilled water at the appropriate ph was added to a final volume of 10

2 December 1976 INHIBITION OF IRON ABSORPTION 1029 m!. Therefore, the final concentration of ilfeso. and starch were 20 Ilg per ml and 2, 10, 20, or 200 Ilg per ml, respectively. The flasks were shaken in a Dubnoff metabolic incubator at 37 C for 30 min. The contents of each flask were emptied and centrifuged at 10,000 x g for 15 min, and duplicate 2.0-ml aliquots ofthe supernatant were assayed for radioactivity along with appropriate standards in a Packard Auto-Gamma Spectrometer, model The percentage of radioiron bound by laundry starch was calculated by comparing the supernatant radioactivity with control flasks at the same ph and containing identical concentrations of "FeSO. without starch. In vitro binding studies with "Fe-hemoglobin were performed in a similar manner except that the incubation flasks contained 100 /lg of hemoglobin-iron (approximately 10,000 counts per min) and 10, 50, or 100 mg of laundry starch. In separate experiments, it was determined that incubations carried out for 1 hr did not significantly affect the binding; values were similar to those obtained for 3O-min incubations. Therefore, all in vitro incubations were carried out with a 30-min incubation period. The reversibility of "FeSO.-starch binding was assessed by washing the residue obtained after initial centrifugation three times with iron-free distilled water at its original ph, centrifuging at 10,000 x g for 15 min, and assaying the radioactivity in the supernatant fluid. In addition, the effect of changing ph on the reversibility of the binding was determined. After incubation, the final ph of the flask contents was decreased or increased by the addition of either 0.1 N HCl or 0.1 N NaOH, respectively. The contents of each flask was then centrifuged at 10,000 x g for 15 min, the supernatant was removed and assayed for radioactivity, and the percentage of binding was determined as described above. In vivo absorption studies. Female Sprague-Dawley rats (200 to 250 g) were used in these studies because they absorb inorganic and hemoglobin iron in a manner similar to that for man. 7 All animals were fed a diet of standard chow containing 7 mg of iron per 100 g of dry weight and were maintained in metabolic cages during the period of study. After a 16-hr overnight fast, absorption of inorganic iron was determined after the intragastric administration of 0.5 ml of FeSO. (1IlC, 100 Ilg) via a 17 -gauge olive-tipped needle. The ph of the test dose was adjusted to 3.5 by addition of 0.1 N He!. Animals in the experimental group were given an additional intragastric injection of laundry starch suspension, 100 mg per 2.0 ml, 1 hr before the administration of nfeso. Two control groups of animals were also studied. Animals in one control group received an identical volume of saline at the same ph as the starch suspension (ph 4.5). The second control group received a suspension of homogenized low iron rat chow (100 mg per 2.0 proximal 10 cm of small intestine were isolated between silk ligatures. The duodenal loops were drained and perfused free from intestinal contents with 30 ml of 0.9% saline. One milliliter of a solution containing 1.0 /lc of "FeSO. (50 Ilg) was then injected into the isolated loops. The experimental group received a concurrent intraduodenal injection of laundry starch, 50 mg per 1.0 ml, whereas control animals were given either 1.0 ml of 0.9% saline or 1.0 ml (50 mg) of homogenized low iron rat chow. After 30 min the loops were removed, drained, and flushed with 50 ml of 0.9% saline, and duplicate aliquots of the loop contents, the excised loops, and the individual carcasses were assayed for radioactivity. Mucosal tansfer was determined by dividing the amount of radioactivity recovered in the carcass by the amount injected into the isolated intestinal loop. Mucosal uptake was calculated by adding the percentage of recovery in the carcass to the percentage of recovery in the isolated loop.' The effect of laundry starch on the intestinal absorption of Fe-hemoglobin was determined in rats made anemic by prior phlebotomy. Animals were given a 0.5-ml intragastric dose of "Fe-hemoglobin containing 500 Ilg of hemoglobin. Animals in the experimental group were given laundry starch, 100 mg per 2.0 ml, 1 hr before study, whereas those in the control groups received either an identical volume of saline or homogenized low iron rat chow (100 mg). Absorption was measured by whole body retention of "Fe-hemoglobin as previously described. To determine whether the timing of starch administration significantly affected the intestinal absorption of inorganic or hemoglobin iron, further experiments were performed in which laundry starch, 100 ml per 2.0 ml, was given either concurrently with or 1 hr after the administration of "FeSO. (100 Ilg) or "Fe-hemoglobin (500 Ilg). For studies with "Fe-hemoglobin, rats were made anemic by prior phlebotomy. Statistical analysis. Results were analyzed by standard methods using the t-test for unpaired samples and are expressed as mean ± 1 SD. Probability values of 0.05 or less were considered significant. Results In vitro binding of 'FeSO. by laundry starch. The effect of ph on in vitro binding of 58FeSO. is shown in table 1. Binding of "FeSO. by laundry starch was ph-dependent, with large quantities of inorganic iron bound at ph 7. Binding was also dependent on the starch to iron concentration ratio. At ph 2 or 5 binding was increased with a starch to iron ratio of 10,000:1, compared to values obtained at ratios of 1,000: 1 or less. At ph 7.0 the percentage of binding of "FeSO. ml, ph 4.5) which supplied less than 2 ppm?f i ~ n ~. b S? r p decreased t! o n significantly with decreases in starch to iron was measured with a small whole body hquid scmtillatlon detector (Packard Armac, model 446) according to a modification of the method of Conrad and Schade.' The percentage of ratio on in vitro binding 0/ "FeSO. by laundry starch" TABLE 1. Effect 0/ ph and varying starch to "FeSO. concentration absorption was calculated as the ratio of net whole body counts retained at 7 days to those obtained 3 hr after administration of " "F.SO. bound' Starch' ufeso t ratio' the test dose. Enough counts were obtained to ensure a ph2 phi; phi counting error of less than 3%. The effect of laundry starch on absorption of ItFeSO. was also determined in rats made anemic by prior phlebotomy. For these experiments, absorption of nfeso. (l /lc, 100 /lg) was assessed in two groups of control animals as described above and in those given laundry starch. 100 ml per 2.0 ml, 1 hr before 10,000:1 (6) 1,000: I (12) 500:1 (6) 100:1 (6) 25.4 ± ± ± ± ± ± 4.7 IS.0± ± ± 9.1 SO.S ± ± S ± 6.2 administration of nfeso. To assess further the effect of laundry starch on iron absorption, additional studies were carried out with isolated duodenal loops in vitro. Laparotomy was performed and the " See text for conditions of incubation. Numbers in parentheses represent number of duplicate determina tions done at each ph. < Mean ± 1 SD.

3 1030 THOMAS ET AL. Vol. 71, No.6 concentration ratio. However, even at a concentration ratio of 100:1, appreciable quantities of inorganic iron were bound (28.5 ± 6.2%). Importantly, percentage of binding at the highest ratio of 10,000: 1 was not significantly different from that obtained at 1,000:1, 82.7 ± 9.1 and 80.5 ± 12.3%, respectively. Washing of the precipitated starch-iron residue did not alter binding significantly. In 12 studies only 5.1 ± 0.7% of the precipitated radioactivity was removed with repeated washing with iron-free distilled water (ph 7.0). In contrast, changing the final ph of the incubation mixture did cause a change in percentage of binding of IIFeSO. (table 2). After 30-min incubation, adjusting the ph from 7 to 5 or 2 produced significant decreases in the percentage of ufeso. bound by laundry starch. At any final ph, the percentage of binding was similar to values obtained when the ph remained constant (table 1). In vitro binding of,ofe-hemoglobin by laundry starch (table 3). Binding of life-hemoglobin by laundry starch was also ph-dependent, but in contrast to inorganic iron, significantly more life-hemoglobin was bound at ph 2 and 5 at all concentration ratios. At a ratio of 500:1 or 100:1, percentage of binding of life-hemoglobin was similar at ph 2 and 5. At a starch to life-hemoglobin concentration ratio of 1000:1, binding was maximal at ph 7, 67.6 ± 8.5%. At ph 7, lower concentration ratios of 500:1 and 100:1 resulted in decreased binding of IIFe_ hemoglobin, but even at the lowest concentration ratio, 41.0 ± 3.7% of the available life-hemoglobin was bound by laundry starch. Effect of laundry starch on ufesd. absorption from isolated duodenal loops in vivo (table 4). The simultaneous injection oflaundry starch and inorganic iron into TABLE 2. Effect of changing ph on in vitro binding of "FeSO, by laundry starch' ph Binding of "FeSO: Initial Final % Pi ± ± 8.0 (3) ± ± 5.6 (4) ± ± 18.6 (4) ± ± 20.0 (4) ± ± 0.8 (4), See text for experimental details. 'Mean ± 1 80; number in parentheses represents number of duplicate determinations. TABLE 3. In vitro binding of "Fe hemoglobin by laundry starch" Starch: hf'moglobin ratio ~ F e ~ bound' ph2 ph5 ph7 1000:1 (6) 34.2 ± ± ± :1 (6) 31.0 ± ± ± :1 (6) 17.4 ± ± ± 3.7 See text for experimental details. Number in parentheses represents number of duplicate determina tions done at each ph. 'Mean ± 1 SD. TABLE 4. Effect of laundry starch on "FeSO. absorption from isolated duodenal loops' Group No. of rats Mucosal uptake Controls Saline ± 3.5 Low iron chow ± 6.0 Starch treated ± 5.0 p' <0.001 See text for experimental details. 'Mean ± 18D. 'Saline controls versus starch treated. % administered radioactivity' Remaining in mucosa Mucosal transfer 19.0± ± ± ± ± ± 3.5 <0.05 <0.001 isolated duodenal loops resulted in a significant inhibition of mucosal uptake and transfer of IIFeSO., compared to either of the control groups. Although mucosal uptake and transfer were less in the low iron chow controls than in the saline conrols, the difference did not achieve statistical significance. Effect of laundry starch on the absorption of IIFeSO. and life-hemoglobin. Table 5 shows data on the effect of laundry starch on the intestinal absorption of inorganic iron in normal and bled rats and hemoglobin-iron absorption in bled rats only. In normal animals given a suspension of laundry starch 1 hr before administration of ufeso., there was a significant inhibition of iron absorption (P < 0.001) as compared to either saline or low iron chow controls (6.2 ± 2.0 versus 14.9 ± 3.1 and 11.8 ± 2.7, respectively). Inorganic iron absorption was also significantly inhibited by laundry starch pretreatment in bled anemic rats, as compared to the results obtained in either of the two groups of controls (P < 0.001). Hematocrit values were similar in all five groups of anemic animals and ranged between 30.0 and 31.3%. Pretreatment with laundry starch also resulted in a significant inhibition (P < 0.(01) of "Fe-hemoglobin absorption in anemic rats, as compared to saline controls or low iron chow controls. Although not significantly different from the saline controls,.ofeso. absorption was less in both normal and bled rats given a suspension of low iron chow 1 hr before the iron test dose. This slight decrease in absorption is probably related to the inhibitory effect of food on inorganic iron absorption.' When laundry starch was administered simultaneously with or 1 hr after sofeso. or "Fe-hemoglobin, there was no inhibition of absorption in either normal or bled rats; results were similar to those obtained in the two control groups. These observations are in contrast to those obtained with simultaneous intraduodenal injection and suggest that either differences in gastric emptying rate or minimal binding at low intragastric ph values are responsible for the observed difference. Discussion Previous studies in patients with amylophagia have suggested that this form of pica is probably the result of iron deficiency anemia rather than its cause. Garretson

4 December 1976 INHIBITION OF IRON ABSORPTION 1031 TABLE 5. Effect of laundry starch on the absorption of "FeSO. and,ofe hemoglobin in the rat" Group Treatment %_B_b_sorptlOn* Normal Bled Saline Low iron chow Laundry starch 1 hr before Laundry starch simultaneously Laundry starch 1 hr after Saline Low iron chow Laundry starch 1 hr before Laundry starch simultaneously Laundry starch 1 hr after 14.9 ± 3.1 (12) 11.8 ± 2.; (10) S.2 ± 2.0 (10) 12.5 ± I.S (10) 14.1 ± :1.0 (7) 40.7 ± 9.4 (8) 3:1.1 ± 4.1 ( ± 5.0 (8) 36.0 ± 6.1 ( ± ;.5 (S) 20.1 to 2.1 (S) 18.4 ± 2.:3 (6) 12.1 ± :1.0(8) 18.0 ± 1.9 (6) 22.5 ± :-1.2 (61 See text for experimental details. Animals received 100 jig of iron as.ofeso. or 500 jig of "Fe hemoglobin. Mean ± 1 SD; numbers in parentheses represent number of animals in each group;. not done. and Conrad were unable to demonstrate an inhibitory effect of starch on the absorption of inorganic iron in rats.' In these studies a relatively large test dose of Fe-Iabeled iron nitrate, 10.5 mg, was administered simultaneously with starch. However, these investigators found that iron-deficient animals fed a high starch diet absorbed significantly less inorganic iron, but attributed these results to protein depletion and a retarded growth rate. Talkington et al. found that the absorption of 5 mg of otfeso. as determined by percentage of Fe utilization, was not significantly affected by a 60-g starch solution administered 30 min after the iron test dose. 10 In contrast, Amine and Hegsted demonstrated that the absorption of 20 to 80 Ilg of inorganic iron in rats was inhibited by a high starch diet even when adequate protein continued to be supplied." Similar studies in humans, using smaller quantities of 69Fe, have shown that the ingestion of as little as 8 g of laundry starch per day inhibits the absorption of inorganic iron. 12 Our studies have demonstrated that in vitro significant quantities of both inorganic and hemoglobin iron are bound by laundry starch over a wide range of starch to iron concentration ratios. Binding of both forms of iron was ph-dependent, with maximal binding at ph 7.0. Although repeated washing of the precipitate ufeso. residue failed to remove significant amounts of iron, binding of inorganic iron was reversible when the ph of the solution was lowered from 7 to 2 or 5. It is pertinent to emphasize that binding of inorganic and hemoglobin iron wa'> greatest at or near the ph of the proximal small bowel. This suggests that at normal intraduodenal ph, iron absorption might be inhibited by starch ingestion. In vivo, prior intra gastric injection of laundry starch caused a significant decrease in the absorption of inorganic iron in normal nonanemic rats and in bled anemic rats. Although the mechanism of this inhibition of FeSO. absorption by laundry starch is probably related to intraluminal binding of inorganic iron by laundry starch, it is possible that starch-induced alterations in gastric emptying, intestinal motility, or intestinal secretion might have partly accounted for these results. To obviate any expected differences in rates of gastric emptying or effects on intestinal motility between saline and starch suspension, a suspension of low iron rat chow was administered to a second group of control animals. Inorganic iron absorption was slightly, but not significantly, less in the rat chow controls. This observation is consistent with the known inhibitory effect of food on inorganic iron absorption.' Although we did not actually quantitate gastric emptying, the suspensions of laundry starch and rat chow were equivalent in volume, weight, and ph. It is therefore unlikely that differences in the gastric emptying rates of starch and rat chow could account for the differences in absorption and whole body retention of a subsequently administered iron solution. The inhibitory effect of starch on the mucosal uptake and transfer of inorganic iron from isolated duodenal loops suggests that differences in intestinal motilitv in the control and starch-treated groups were not respo"nsible for the differences in iron absorption. Likewise. there were no significant differences in the volume of the isolated loop contents after the 30-min study period between the control and starch-treated intestinal loops. Thus, it is unlikely that decreased mucosal uptake and transfer of FeSO. in the starch-treated loops was due to nonspecific alterations in intestinal secretion induced bv laundry starch. - When the starch solution was administered simultaneously with or 1 hr after the iron test dose, there was no inhibitory effect on iron absorption. The failure of simultaneously administered starch to inhibit iron absorption is similar to an effect previously reported for cholestyramine. Because absorption was inhibited from isolated duodenal loops when laundry starch was administered simultaneously with.ofeso. (table 4), the failure of simultaneous intragastric starch administration to inhibit iron absorption suggests that (1) minimal binding of iron at normal intra gastric ph and/or (2) differences in the rates of gastric emptying of FeSO. and starch account for this observation. The lack of an inhibitory effect of laundry starch given 1 hr after the iron test dose is probably attributable to the rapidity of iron absorption after oral administration. Consequently, only small amounts of iron are then available for intraluminal binding. The failure of previous studies to

5 1032 THOMAS ET AL. Vol. 71, No. 6 show a conclusive effect oc laundry starch on iron absorption in man may be partially attributable to the fact that the starch solution was administered after the radioiron. Considering that the T" for gastric emptying of liquids is approximately 15 min in man. IS it is likely that much of the administered iron had been absorbed by the time starch was ingested, In addition to its effect on inorganic iron absorption, laundry starch also blunted the compensatory increase in "Fe-hemoglobin absorption in anemic rats. This inhibitory effect of laundry starch is similar in magnitude to that previously reported with cholestyramine. Experiments of hemoglobin-iron absorption in normal nonanemic rats were not performed, because only very small percentages of hemoglobin iron (1 to 3%) are absorbed in such animals." Laundry starch is a macromolecular polysaccharide composed of amylose and amylopectin. Both synthetic and naturally occurring pectins bind bile acids and cholesterol... I. Our studies demonstrate that inorganic and organic iron are also bound by laundry starch. We have no data which permit any firm conclusions regarding the mechanisms of the in vitro binding of inorganic and hemoglobin iron by laundry starch. In this connection. previous studies in our laboratory have shown that another macromolecule, cholestyramine, binds inorganic and hemoglobin iron in vitro in a ph-dependent manner and inhibits their intestinal absorption. I Binding of inorganic iron by both cholestyramine and starch is maximal at ph 7.0. At increasing ph levels ferrous iron may be present in a macromolecular polymeric form, II and it is possible that this form on inorganic iron was bound by starch. Similarly, binding of hemoglobin iron by starch was also ph-dependent. but significantly greater binding of hemoglobin iron occurred at ph 2 and 5, compared to inorganic iron. In summary, the present studies demonstrate that laundry starch (1) binds significant amounts of inorganic and hemoglobin iron at ph levels approximating those of the proximal small intestine. (2) inhibits inorganic iron absorption from isolated duodenal loops, (3) inhibits the intestinal absorption of inorganic iron in normal nonanemic rats, and (4) diminishes the intestinal absorption of inorganic and hemoglobin iron in anemic rats. The results obtained suggest that ingestion of large quantities oc laundry starch may also inhibit iron absorption in man and contribute to the development of iron deficiency anemia in patients with amylophagia. REFERENCES 1. Roselle HA, Englewood NJ: Association oclaundry starch and clay ingestion with anemia in New York City. Arch Intern Med 125:57-61, Keith L, Evenhouse H, Webster A: Amylophagia during preg nancy. Obstet Gynecol 32: Conrad ME, Foy AI., Williams HL, et al: Effect of starvation and protein on ferrokintics and iron absorption. Am J Physiol 213: , Ganetson FD, Conrad ME: Starch and iron absorption. Prot Soc Exp Bioi Med 126: , Brown EB, Rother ML: Studies of the mechanism of iron absorp. tion. II. Influence of iron deficiency and other conditions on iron uptake by rats. J Lab Clin Med 62: , Thomas FB, McCullough FS, Greenberger NJ: Inhibition of the intestinal absorption of inorganic and hemoglobin iron by choles. tyramine. J Lab Clin Med 78:70-80, Wheby MS, Suttle GE, Ford KT: Intestinal absorption of hemo globin iron. Gastroenterology 58: , Conrad ME, Schade SG: Ascorbic acid chelates in iron absorption. A role for hydrochloric acid and bile. Gastroenterology 55:35-45, Hallberg L: Oral iron therapy facton of affecting the absorption. In Iron Deficiency. Edited by L Hallberg, HG Harwerth, A Vannotti. London and New York, Academic Press, 1970, p Talkington KM, Grant NF, Scott DE. et al: Effect of ingestion of starch and some clays on iron absorption. Am J Obstet Gynecol 108: , Amine EK, Hegsted OM: Effect of diet on iron absorption in iron deficient rats. J Nutr 101: , Blum M, Orton CG, Rose L: The effect of starch ingestion on ezcessive iron absorption (abstr). Ann Intern Med 68: 1165, Meeroff Je, Go VLW, Phillips SF: Gastric emptying of liquids in man: quantification by duodenal recovery marker. Mayo Clin Proc 48: , Leveille GA, Sauberlich HE: Mechanisms of the cholesterol depressing effect of pectin in the cholesterol fed rat. J Nutr 88: , Calcraft BJ, Rhodes J, Cross S, et al: A study of amylopectin sulfate and bile damage to the gastric mucosal barrier. Am J Dig Dis 19: , Benjamin B, Cortell S, Conrad ME: Bicarbonate induced iron complexes and iron absorption: one effect of pancreatic secretions. Gastroenterology 53: , 1967