Phosphorus and magnesium intake, excretion, absorption, and retention values were not significantly different among the three groups. Palmitic acid was the major fecal fatty acid in most of the infants. We noted significant correlation between fecal calcium excretion and the excretions of fat and of the major fatty acids. Palmitic acid showed the highest correlation coefficient (r = 0.84), followed by oleic acid (r = 0.60) and linoleic acid (r = 0.51) (Fig. 1). Although in the present study design a systematic scoring of the degree of stool hardness and color was not included, differences were observed in the characteristics of the stools. Color and consistency of the “fresh” feces could be obtained from 8, 7, and 8 infants of the beta, intermediate, and regular groups, respectively. Consistency was significantly different among the groups (p = 0.003). In the beta group, 2 infants had soft feces, 6 had runny-soft feces, and none had hard stools. In the regular group, 4 infants had hard feces and 4 had soft feces. Infants fed the intermediate formula were in an intermediate condition; no infant had hard stools, 5 had soft feces, and only 2 had runnysoft feces. None of the infants had watery stools. The color of the feces was also statistically different (p = 0.026): All infants in the beta group had yellow feces (n = 8, 100%); the infants in the intermediate and regular groups had more brown and green feces (4 and 1 vs. 2 and 3, respectively).
Several studies have focused on the effect of the TG configuration on intestinal fat absorption in preterm infants (9-11). Only one group of investigators has studied the influence of the TG structure on the absorption of fatty acids in term infants (8); Filer et al. compared a formula based on natural lard (palmitic primarily at the β-position) with one based on a randomized lard. The infants fed the natural lard showed an improved absorption of all fatty acids, most markedly of palmitic and stearic acids, but calcium absorption was not improved. In our study using synthetic TG we compared fat in which palmitic is predominantly in β-position with fat in which palmitic is predominantly in α-position, whereas in the second diet used by Filer et al. (8), the fatty acids were randomized and thus equally distributed among the α- and β-positions. Our results confirm the finding of Filer et al. (8) of improved fat absorption in infants receiving the palmitic acid predominantly at the β-position, but we were also able to demonstrate a reduction in the fecal excretion of calcium. In term infants, absorption of calcium is clearly related to the absorption of fat (24-27). A possible explanation for the lack of effect on calcium absorption in the study of Filer et al. (8) might be the difference in calcium concentration between the formulas they used (69 and 72 mg/100 ml) and those used in our study (52.5-54.0 mg/100 ml) (Table 1). In our study, the fecal excretion of calcium exceeded the excretion of palmitic acid of ≈0.5 mmol · kg-1 · day-1 (Fig. 1). If the formulas had had a lower calcium content, the fecal calcium concentration would have been less and the palmitic acid calcium ratio higher (nearer 1:1). In such case, the effect of fecal palmitic acid (and of sn-2 palmitate) on calcium excretion might be more pronounced because of the larger percentage of calcium available for calcium palmitate formation and thus for fecal losses. Conversely, when the calcium concentration in formulas is more than double the amount in breast milk, the effect of fecal palmitate and of sn-2 palmitate on calcium absorption percentage would no longer be measurable.
Although we did not plan a systematic scoring of the degree of stool hardness and color differences, we decided to include such an evaluation when differences were noted in the stool samples of the first patients: The samples from the infants fed the beta formula were softer than the stool samples from infants fed the intermediate and the regular formulas. However, unlike in the recent study of Quinlan et al. (28) in which hardness of stools of breast-fed and formula-fed infants was compared, the variation in stool hardness in our study was not due to a significant difference in the water content of the infants' feces. Because this observation requires confirmation in future studies involving a larger number of infants, we may hypothesize that the lipid content of the stools, including the calcium soaps, has a much more pronounced effect on stool hardness than does its water content. The differences in total fecal output among the three feeding groups are difficult to explain. We know of no report in the literature describing a clearly lower fecal output in breast-fed infants than in formula-fed infants or in infants fed formulas of a composition relatively similar to those we used in our study. Although calcium absorption was greater in the beta group, we could not demonstrate a significant improvement in calcium and phosphate retention. Nonetheless, on the average, the infants fed the beta formula retained 16 mg · kg-1 · day-1 more calcium than the other two groups. This difference should be considered biologically significant and, if confirmed in a larger group of infants, certainly is further evidence of the importance of the structure of dietary TG. In term infants we showed that the isomeric position of fatty acids in dietary TG has a significant effect on the intestinal metabolism of the dietary FA. The use of beta formula containing TG with a structure more similar to those of HM fats than the currently available infant formulas is associated with an improvement in the intestinal absorption of the major saturated fatty acids and of total fat. Calcium excretion and absorption were also significantly improved. Formulas containing these novel TG similar in structure to HM lipids offer an advantage as compared with conventional formulas.
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