Heme iron absorption

Utilization of iron was not affected at levels of 9 to 26g bran/day from corn or wheat (19, 2J0 2 ) or bY 16 g of bran/day (25). Negative balances were observed by Morris and Ellis (21) during the first balance period with daily intakes of 36g bran but not during the second 5-day balance period. However, Simpson et al. (24) found a marked inhibition of non-heme iron absorption from a single test meal which included 6 g of wheat bran. With a diet which provided 35g/day of NDF (neutral detergent fiber from bran bread), iron balances were decreased (26) compared to the 9 or 22g/day intake levels. 

Removal of phytic acid from soy did not improve non-heme iron absorption (38)... 

Simpson et al. (24) did not observe increased non-heme iron absorption when dephytinzed bran was included in a test meal compared to the non-dephytinized bran. Removal of phytic acid from soy protein likewise did not improve non-heme absorption (38). Decreased iron balances, observed by Bodwell et al. (40) with soy isolate diets, did not appear to be associated with the level of phytic acid a tendency for zinc balances to decrease with increased phytic acid was observed. 

However, it has been estimated that about 80% of the daily dietary intake of iron is in the form of non-heme iron and only about 20% from heme iron. Hence, any product added to the diet which causes a significant decrease in non-heme iron absorption is of concern. 

The belief that soy protein, added to beef, caused a marked decrease in non-heme iron absorption, led to a... 

In a series of studies, Cook and co-workers (48,49,50) observed a marked decrease in non-heme iron absorption when soy protein was added to beef or protein mixtures or when soy protein was consumed as the primary protein source in test meals and compared to the effects of including egg albumen or beef alone in the test meal (Table III) Hallberg and Rossander (38J, however, found less of an effect when total iron absorption (heme plus non-heme iron) was considered. Likewise, in a study in which reconstituted textured soy was used to replace 30% of the beef, the absorptions of total iron were not greatly altered (51). In a study by Stekel et al. (52), replacing part of the beef with soy isolate or adding hydrated isolate to beef decreased non-heme iron absorption from 12.4% to 9.2 and 9.3%, respectively. In a related study, non-heme and total iron absorptions were low when soy isolate was the major protein source. 

Non-heme iron absorptions of 3.2, 8.4 and 4.8% and total iron absorptions of 0.18, 0.63 and 0.51 mg were observed for the basal meal, the basal meal plus beef, and the basal meal plus soy flour, respectively. The authors concluded that the amount of iron absorbed was "substantially augmented" by the addition of the soy flour which was high in iron. 

Nine or 10 subjects fed meal (a) basal containing maize, rice, and black beans, or the basal meal with (b) 75g beef added, (c) 15g soy flour added, or (d) iron (ferrous sulfate) added in an amount equivalent to that provided by the soy flour in (c) Non-heme iron absorptions of (a) 3.2, (b) 8.4, and (c) 4.8,-total iron absorptions of (a) 0.18, (b)0.63, (c)0.51 and (d)0.64mg. Soy product "substantially augmented" the amount of non-heme iron absorbed from basal meal (38)... 

Lynch et al. (5 7) found non-heme iron absorptions, as measured by single test meals, for black beans, lentils, mung beans split peas, and whole soybeans to be low (0.84 to 1.91%). This suggests that many commonly consumed legumes are poor sources of iron whether legumes other than soy may have an "offsetting" enhancing effect on heme-iron absorption cannot be predicted. 

Precision The precision of the absorption value depends upon tfe precision of P, and E measurements This method for isotopic enrichment measurements by mass spectrometry has a precision of 2% as does the measurement of F by atomic absorption This precision is adequate for absorption and bioavailability studies with zinc and copper (Table I) since zinc and copper absorption are in the range of 30-70% Only fairly large changes in iron absorption can be discerned because non-heme iron absorption is typically less than 10% This may not be a serious problem in bioavailability studies since it is doubtful that very small changes in iron absorption from single foods are biologically significant ... 

Level of ascorbic acid in the diet has been found to be an important factor in determining non-heme iron absorption (6,10,11). Ascorbic acid intake has been found to be more closely correlated to several biochemical parameters of iron nutritional status than was total iron Intake (12). However, timing of consumption is equally important. If non-heme iron absorption is to be increased via this factor, then both the non-heme iron and the ascorbic acid must be consumed at the same time. Considering that important sources of ascorbic acid are all of plant origin, the chances that a shift from more animal-based foods to more plant-based foods will lead to Increased consumption of ascorbic acid are good indeed. However, this is not necessarily the case if the shift moves toward a diet based solely, for example, on highly polished cereals. 

Hallberg L, Brune M, Erlandsson M, Sandberg AS and Rossander-Hulten L (1991) Calcium ffect of different amounts on non-heme and heme iron absorption in humans. Am J Clin Nutr 53 112-119. 

Samman S, Sandstrom B, Toft MB, Bukhave K, Jensen M, Sorensen SS, Hansen M. Green tea or rosemary extract added to foods reduce non-heme iron absorption. Am J Clin Nutr 2001 73 607-612. 

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