Siriporn Tuntipopipat. Efffect of commonly consumed spices and herbs in Thai diets on human iron absorption. Doctoral Degree(Nutrition). Mahidol University. : Mahidol University, 2006.
Efffect of commonly consumed spices and herbs in Thai diets on human iron absorption
Abstract:
Iron deficiency is a major public health problem in tropical regions where diets are plant
based and rich in several spices and herbs. Being rich in phenolic content of spices and herbs,
the food would be expected to bind iron in the intestine and inhibit iron absorption in humans.
The objective of this study was to evaluate the impact of the most commonly consumed
spices and herbs in Thai diets on human iron absorption, using stable isotope techniques. The
most relevant spices/herbs were identified by a pilot dietary survey in Khonkaen and Ubon
Ratchathani provinces. The relevant spices/herbs were collected to analyze iron absorption
inhibitors and enhancers. Chili, garlic, Pak-ka-yeng, shallot, tamarind, turmeric and green
curry paste, all containing high polyphenol content, were selected to measure their iron
binding capacity through simulated gastrointestinal digestion by iron dialyzability. All spices
and herbs except tamarind reduced iron dialyzability by dose dependent manner. Because
chili and turmeric are two of the most common spices and herbs consumed in Asia. Three
experiments were conducted on healthy young women (10 women per study) to assess the
effect of them on iron absorption, using a vegetable rice-based meal, seasoned with iron
fortified fish sauce. Iron absorption was determined by erythrocyte incorporation of stable
isotopes (57Fe/58Fe) using a randomized cross-over design. Addition of 4.2 g freeze dried chili
powder or 14.2 g fresh weight (25 mg polyphenols gallic acid equivalents) reduced iron
absorption from the meal by 38 % (6.0 % with chili vs. 9.7% without chili, p=0.0017). No
inhibition of iron absorption was observed for turmeric (0.5g dry powder, 50 mg polyphenols,
p=0.91). A possible effect of chili on gastric acid secretion was indirectly assessed by
comparing iron absorption from acid soluble 57Fe pyrophosphate relative to water soluble
58FeSO4 from the same meal in the presence and absence of chili. No indication for an
enhancing effect of chili on gastric acid secretion was observed. Relative iron bioavailability
of ferric pyrophosphate was 5.4% in the presence of chili and 6.4% in the absence of chili (p
= 0.47). This shows that iron binding by phenolics in chilli is the primary mechanism
affecting dietary iron absorption. Despite the much higher amount of phenolics in the
turmeric meal, its effect on iron absorption was insignificant. We conclude that both phenolic
quality and quantity determine the inhibitory effect of phenolic compounds on iron
absorption.