Fecal monitoring

Results from some recent studies (19-36) on the effects of fiber are summarized in Table I. For the most part, the results are from multi-day balance studies. However, Turnland et al. (36) used the stable isotope fecal monitoring method to assess zinc utilization and Simpson et al. (24) measured iron absorption from a single test meal. 

Zinc. Some recent studies on the effects of soy protein on zinc utilizaton are summarized in Table IV. Young and Janghorbani (4 4) and Istfan et al. (46) compared the effects of soy isolate or soy concentrate and dried skim milk as protein sources in multi-day feeding periods. Zinc absorptions, measured by fecal monitoring of the extrinsic label given, were equivalent and no deleterious effects of soy protein were observed. In a second study, Istfan et al. (47) fed egg protein diets for 10 days and then a soy concentrate diet for 82 days. Zinc absorptions were not decreased by feeding the soy concentrate diet. 

Eight subjects fed (10 days) formula diets with either (a) DSM or (b) soy protein concentrate as protein source extrinsic zinc label (fecal monitoring method)... 

Ten subjects fed (12 days) isonitrogenous diets with all protein from chicken meat or 50% from chicken and 50% from soy isolate intrinsic (chicken) and extrinsic labels used (fecal monitoring method)... 

Determination of Zinc Absorption in Young Men Using Zn and a Fecal Monitoring Method ... 

To determine the amount of isotope required for an absorption study using fecal monitoring, the length of time of fecal collections must be considered. Polyethylene glycol (PEG) and radioisotopes were used for to determine complete intestinal transit time in the studies described in this paper. In one study PEG and radioisotopes were fed simultaneously and excretion patterns were similar for the two (1>9). Most individuals eliminate all PEG or unabsorbed radioisotopes within 12 days, but a few individuals have longer transit times. Therefore 12 days collection time can be used for calculations. The amount of mineral expected in the 12 day collection is used to determine the amount of isotope to feed for best analytical precision. A mineral such as copper cannot be fed at a level to meet ideal enrichment conditions without greatly exceeding... 

Two critical aspects of fecal monitoring for absorption determinations are complete collection of unabsorbed isotopes and sample homogeneity. The times required for complete collections of unabsorbed isotopes vary markedly between subjects and also within the same subject. Therefore fecal makers are required to assure complete collections (9). The times required for complete elimination of a fecal marker have ranged from 6 to 18 days and included from 3 to 23 fecal samples in the experiments discussed later in this paper. Collection of only 80% of unabsorbed isotopes, particularly when absorption is low, will result in serious overestimation of absorption. In the case of iron, absorption of only 10% would appear to be nearly 3(, if 20% of the unabsorbed iron was not collected. A marker such as PEG, which can be measured quantitatively, must be used. Stools are collected until no trace of the inert marker can be detected. Recovery of less than 90% of the PEG... 

To determine iron absorption with tracers, a known amount of an iron tracer is given orally either by itself or with a meal. The appearance of the tracer, either in the feces or in whole blood, is monitored. In the fecal monitoring method, the feces are collected quantitatively. The collection period may last from as few as 3 (5) to as long as H days (6). Iron absorption is then estimated from the difference between the total amounts of tracer ingested and excreted. Probably, the most common and serious error in this method is introduced by incomplete fecal collection. 

The aim of this study was to further explore the potential and limitations of using stable iron isotopes as tracers and EI-MS in absorption studies. Procedures were developed for preparing iron acetylacetonate from both blood and fecal samples for mass spectrometric analysis. The precision and accuracy of ion abundance measurements were evaluated. In vivo use of stable iron isotope tracers was tested with a human study in which 54pe and 57pe were given orally and absorption was estimated with the fecal monitoring and hemoglobin incorporation methods. 

Fecal Monitoring Method. The subjects were instructed to bring their stool samples back to the metabolic unit as soon as was possible after collection. Each sample was carefully labelled with time, date, and subject identification, and was placed in a freezer in the metabolic unit. The samples were freeze-dried, and allowed to equilibrat for 24 hours under ambient conditions. The dry weights of the samples were taken, and the samples were powdered and mixed thoroughly to provide homogeneous portions for analysis. 

Table VII. Absorption of stable iron isotopes in orange juice measured with the fecal monitoring and hemoglobin incorporation...

Errors associated with iron quantification and abimdance measurements are common to both fecal monitoring and hemoglobin incorporation methods According to Janghorbani and Young (2 )> acceptable absorption estimates can be obtained if the precision of these measurements is kept below 5% The analytical procedures developed in this study are thus considered satisfactory since the relative standard deviation was 2 48% for total iron quantification and less than 2% for ion abimdance determinations ... 

Comparison of Absorption Data. Little correlation was found between the absorption data obtained with the hemoglobin incorporation and fecal monitoring methods with or without correction for PEG recovery (Table VII). There are several possible reasons for this poor correlation. 

Calculation of Absorption Absorption of isotope doses by tiuman subjects was calculated by fecal monitoring (5), that is> by determining the amount of stable isotope ingesteT compared to the amount excreted in the feces in excess of the natural abundance The fractional absorption A (I-F E)/I where I is the amount of isotope ingested F is the total metal in the... 

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