Iron content in beans
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Iron Content in Beans: Concentration and Variability
Research shows that the iron content in common beans (Phaseolus vulgaris) varies widely depending on the variety and genetic background. Studies have found total iron concentrations in common beans ranging from 32 to 115 parts per million (ppm), or about 34 to 144 mg/kg, with an average around 55 mg/kg in large collections of bean varieties Hoppler2014Beebe2020Beebe2000+1 MORE. Fava beans (Vicia faba) also show a broad range, with iron content between 1.8 and 21.3 mg/100 g (or 18–213 mg/kg) depending on the cultivar . Tepary beans and other less common varieties can also have iron concentrations ranging from about 30 to 78 µg/g (30–78 mg/kg) .
Iron Forms in Beans: Ferritin and Nonferritin Iron
Iron in beans exists in different forms, mainly as ferritin-bound iron and nonferritin-bound iron. Ferritin iron makes up about 13% to 35% of the total iron in beans, but most of the iron in high-iron beans is nonferritin-bound. The proportion of ferritin iron increases only slightly in beans with higher total iron content, suggesting limited potential for breeders to increase ferritin iron specifically .
Iron Biofortification in Beans
Efforts to biofortify beans have successfully increased their iron content. Breeding programs have developed high-iron bean varieties with up to 10 mg iron per 100 g (100 mg/kg), which can help address iron deficiency in populations that rely on beans as a staple food Beebe2020Petry2015. However, breeding progress is sometimes slow due to natural plant mechanisms that regulate iron uptake and storage .
Iron Bioavailability: Impact of Antinutrients and Cooking
Despite high iron content, the bioavailability of iron from beans is often low. This is mainly due to the presence of antinutritional factors such as phytic acid and polyphenols, which inhibit iron absorption Eckhof2024Petry2015Huertas2022+1 MORE. Phytic acid levels tend to increase with iron biofortification, further reducing absorption . Cooking methods also affect iron bioavailability, with significant iron losses (up to 40%) occurring when beans are boiled and the cooking water is discarded . In vitro studies show that less than 5% of iron in raw beans is bioavailable after digestion, though zinc is more bioavailable .
Improving Iron Status with Biofortified Beans
Despite low absorption rates, regular consumption of iron-biofortified beans has been shown to improve iron status in humans. For example, a study in Rwandan women found that eating iron-biofortified beans (86 mg Fe/kg) significantly increased hemoglobin and ferritin levels compared to standard beans (50 mg Fe/kg) over 128 days . Consuming 100 g of biofortified beans daily can provide 30%–50% of the daily iron requirement for iron-deficient women Petry2015Haas2016.
Differences Among Bean Types and Cultivars
There are substantial differences in iron content and bioavailability among bean types and cultivars. For example, white tepary beans have higher iron bioavailability than brown tepary or common beans, likely due to lower levels of polyphenols and phytic acid . Among fava bean cultivars, only some provide adequate iron bioavailability, highlighting the importance of cultivar selection for nutritional benefit .
Conclusion
Beans are a valuable source of dietary iron, with significant variation in iron content and bioavailability depending on the species, variety, and processing methods. While biofortification can increase iron content, absorption is limited by antinutritional factors. Nonetheless, regular consumption of iron-rich or biofortified beans can help improve iron status, especially in populations at risk of deficiency. Selecting the right bean varieties and optimizing preparation methods can further enhance the nutritional benefits of beans as a source of iron Hoppler2014Beebe2020Labba2021+7 MORE.
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