Plant foods are the major staples of diets in developing countries, in which the consumption of animal-source foods is often low because of economic and/or religious concerns. However, such plant-based diets are often associated with micronutrient deficits, exacerbated in part by poor micronutrient bioavailability. Diet-related factors in plant foods that affect bioavailability include: the chemical form of the nutrient in food and/or nature of the food matrix; interactions between nutrients and other organic components (e.g. phytate, polyphenols, dietary fibre, oxalic acid, protein, fat, ascorbic acid); pretreatment of food as a result of processing and/or preparation practices. Consequently, household strategies that reduce the content or counteract the inhibiting effects of these factors on micronutrient bioavailability are urgently needed in developing-country settings. Examples of such strategies include: germination, microbial fermentation or soaking to reduce the phytate and polyphenol content of unrefined cereal porridges used for young child feeding; addition of ascorbic acid-containing fruits to enhance non-haem-Fe absorption; heating to destroy heat-labile anti-nutritional factors (e.g. goitrogens, thiaminases) or disrupt carotenoid-protein complexes. Such strategies have been employed in both experimental isotope-absorption and community-based studies. Increases in Fe, Zn and Ca absorption have been reported in adults fed dephytinized cereals compared with cereals containing their native phytate. In community-based studies in rural Malawi improvements in dietary quality and arm-muscle area and reductions in the incidence of anaemia and common infections in young children have been observed. Bioavailability: Plant foods: Household: Micronutrients: PhytateIn developing countries plant foods are the major staples of the diet and consumption of animal-source foods is often low because of economic and/or religious concerns. Such plant-based diets are, however, often associated with deficits in Ca, Fe, Zn and some vitamins. A major factor contributing to these deficits, particularly for diets based on unrefined cereals and legumes, is that bioavailability, which can be defined as the proportion of an ingested trace element in food that is absorbed and utilized for normal metabolic and physiological functions or storage (Jackson, 1997), is poor. Bioavailability is influenced by both dietary and host-related factors (Fairweather-Tait & Hurrell, 1996). The present review addresses the dietary factors and summarizes food preparation and processing practices that can be used in the household to enhance nutrient bioavailability. Examples of efficacy studies employing these strategies in developing countries are also given. Diet-related factors in plant foods that affect bioavailabilitySeveral dietary factors may affect the nutrient bioavailability of plant foods when they are consumed, including:(1) the chemical form of the nutrient in the food and the nature of the food matrix; (2) interactions occurring betwe...

Complementary foods used in the Philippines are predominantly rice-based, although enrichment with mung beans and sesame seeds is recommended despite their high content of phytic acid, a potent inhibitor of iron and zinc absorption. We have investigated the effect of soaking on the inositol penta-(IP5) and hexaphosphate (IP6) (analysed by HPLC), zinc, iron and calcium (via AAS) content of rice-based complementary foods with and without the addition of mung beans and sesame seeds. Soaking rice¯our for 1, 6 and 12 h at 30°C reduced the content of IP5 IP6 by 60, 65 and 98% respectively, with only slight changes in zinc, iron and calcium. Levels of IP5 IP6 were reduced by 10 and 47% by soaking mung bean¯our, but not whole beans, for 1 and 6 h respectively. In conclusion, soaking can be used to reduce the IP5 and IP6 content of complementary foods based on mung bean our and/or rice¯our and thus enhance the bioavailability of iron and zinc. INTRODUCTIONRice (Oryza sativa L) is the staple food of the Philippines and is consumed by all age groups. 1 Even complementary foods in the Philippines are predominantly rice-based, 2,3 although enriching them with mung beans and sesame seeds is recommended to enhance their energy and protein density. 4 Rice, mung beans and sesame seeds are known to contain phytic acid (myo-inositol hexaphosphate; IP6) and small amounts of inositol pentaphosphate (IP5). These higher inositol phosphates form insoluble complexes with zinc, iron and calcium at the physiologic pH of the gastrointestinal tract, thus reducing their bioavailability. 5±7 As well, for iron, even the lower inositol phosphates (eg IP4 and IP3) inhibit non-haem iron absorption to some degree. 8,9 The inhibitory effect of phytates on non-haem iron absorption is dose-dependent, 10 whereas for zinc it occurs when the phytate/zinc ([Phy]/[Zn]) molar ratio is 15 or above. 11 High levels of calcium potentiate the inhibitory effect of phytate on zinc absorption by forming a zinc± calcium±phytate complex that is even less soluble than the zinc±phytate complexes alone, further reducing the bioavailability of zinc. 12 Several methods have been advocated to reduce the IP5 and IP6 content of cereal-based complementary foods, thereby increasing the bioavailability of calcium, iron and zinc. These include milling, soaking, fermentation and germination of cereal grains. 13 Some

Intakes of macronutrients (energy, protein, fat, and carbohydrate) and vitamins (vitamin A, thiamin, riboflavin, niacin, and vitamin C) (per day and per 100 kcal) from complementary foods by a cohort of Filipino breast-fed infants and toddlers (n=1794) were studied at 10, 16, and 22 months of age using a single 24-h recall. With the exception of protein, intakes of energy and vitamins for all age groups were below the World Health Organization estimated needs and desired nutrient densities from complementary foods regardless of breast-feeding frequency. Nutrient deficits were greater for rural children compared with urban children, and were attributed to low intakes of energy, as well as cellular animal protein, fruits and vegetables.

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Philippine complementary foods are predominantly plant-based, with a low content of readily available iron, zinc, and calcium, and a relatively high amount of phytate, a potent inhibitor of mineral absorption. Some of the phytate is water soluble, and hence can be removed by soaking. In this study we have compared the iron, zinc, and calcium content, and estimated iron and zinc bioavailability of rice- and maize-based Filipino complementary foods prepared with and without soaking and/or enrichment with chicken liver, egg yolk, small soft-boned fish, and mung bean grits. Analysis of iron, zinc, and calcium were performed by atomic absorption spectrometry, and phytate (based on hexa-(IP6) and penta-inositol phosphate (IP5) by HPLC; corresponding [Phy]/[Fe] and [Phy]/[Zn] molar ratios were calculated as predictors of iron and zinc bioavailability. Addition of chicken liver, followed by egg yolk, resulted in the greatest increases in iron and zinc content for both the rice- and maize-based complementary foods, whereas addition of small dried fish with bones had the greatest effect on calcium. The IP5 + IP6 content and [Phy]/[Zn] molar ratios were higher in the maize- than rice-based complementary foods, and were reduced by soaking, although only the maize plus mung bean grits, with and without soaking, had [Phy]/[Zn] molar ratios above 15. Enrichment with animal protein or soaking has the potential to enhance the content of absorbable iron, zinc, and probably calcium to varying degrees in rice- and maize-based Philippine complementary foods.