Garlic Increases Bioavailability of Iron and Zinc from Grains and Legumes (Beans and Lentils)
Not only does seasoning with alliums such as garlic and onions add flavor to a dish but it may also add additional nutrients. Adding garlic or onions to grains or legumes increased the absorption of zinc and iron. Bioavailability of trace minerals such as zinc and iron is low in high fiber plant foods like grains, beans and lentils. As a result, it is common for vegetarians and vegans to be deficient in zinc and iron. This study offers a good argument to add some garlic to your bean dip.
Picture: Red Rezan garlic bulbs sunbath on rocks outside garlic barn. Warning: don't let your garlic bulbs cure in the intense sun or they will get sunburn.
Gautam et al. (2010) looked at raw or cooked grains, rice and sorghum, and pulses (dried legumes), whole green gram (a dried bean like legume) and chickpea. Grain/legumes were either plain (10 g) or had two levels of garlic (0.25 and 0.5 g/10 g of grain/legume) or onion (1.5 and 3 g/10 g of grain/legume). Onions and garlic were whole fresh and raw. Bioavailability of zinc and iron from each sample was determined using a simulated gastrointestinal digestion procedure.
Garlic enhanced iron absorption in all four foods studied. Adding garlic to grains increased the bioavailability of iron in raw rice by 12.6%, cooked rice by 13.5-16.2%, and raw sorghum by 13.9-37.6%. There was no difference in absorption in cooked sorghum. Adding garlic to legumes increased iron bioavailability in raw green grams by 15.6-20.5%, cooked green grams by 60.6-73.3%, raw chickpeas by 12.3% and cooked chickpea by 10-17.2%.
Garlic enhanced zinc absorption in cooked rice by 61-71%. There was no change in uncooked rice. Garlic increased zinc uptake in uncooked sorghum by 32.5-54.5%, cooked sorghum by 157-159%, raw green gram by 9.8%, and cooked green gram by 14.5-19.1%.
Onion enhanced iron absorption in all four foods studied. Adding garlic to grains increased the bioavailability of iron in raw rice by 37.5-41.2%, cooked rice by 21.5-30.3%, raw sorghum by 31.9-49.4% and cooked sorghum by 27.2-65.9%. Adding onion to legumes increased iron bioavailability in raw green grams by 17%, cooked green grams by 17.2-32%, raw chickpeas by 39.3-48% and cooked chickpea by 21.2-26.3%.
Onions enhanced zinc absorption in raw rice by 10.4%, cooked rice by 47-58.4%, raw sorghum by 26.4-35.2%, cooked sorghum by 14.5%, and cooked green gram by 13.6-19.2%. There was no change in raw green gram.
In all the above cases, the higher absorption percentages in the stated range were from the greater percentage of onion or garlic in the grain or legume. In other words, in general the more garlic or onion added the greater the bioabsorption of zinc or iron.
Mechanism: Sulfur compounds in garlic and onion may increase mineral absorption (Snedeker et al. 1983).
Take home message: Adding garlic, onions or both alliums to grain and legume dishes will increase absorption of the minerals zinc and iron. It will also make your food tastier!
Men need more zinc than women (except pregnant or nursing women). Zinc is used to make hormones including testosterone. This mineral is found in many enzymes, plays a structural role in proteins (zinc finger motif) and plays a regulatory role in gene expression and cell signaling.
Zinc RDA in adults: men 11 mg, women 8 mg, pregnant women 11-13, and nursing women 12-13 mg. One recent study of people over 65 years old (n=102) found that 52% of men and 34% of women were deficient in zinc. Twenty percent had extremely high zinc deficiencies (Madej et al. 2013).
- Impaired growth and development in children, boys may not go through puberty
- Increased risk of infections
- Loss of appetite
- Skin rashes
- Night blindness
- Inability to taste
- May cause up to 450,000 deaths in children worldwide (4.4% of childhood deaths)
Zinc deficiency can cause a decrease in ability to taste. If you are a middle aged or older man who notices that 'food doesn't taste the same as it used to' try taking a zinc supplement.
Zinc deficiency may even be a factor with taste in younger guys. One study found that in young men adequate dietary zinc intake was important in determining the taste of food (McDaid et al. 2007). Men receiving inadequate zinc had less ability to detect sour and bitter flavors. In women, but not in men, higher zinc intake corresponded to a increased sensitivity to salt in food.
Personal example of zinc deficiency: My aunt complained that my uncle was not as appreciative of her food as he had been in the past. He kept whining that 'food didn't taste good' and that the food from the grocery store didn't have the same taste as it did in the past. This complaining was about to have a major impact on my aunt's desire to cook any food for my uncle (and may also have resulted in bodily harm to my uncle). I suggested that she try giving him a zinc supplement. She gave him 25 mg zinc gluconate per day (zinc RDA for men is 11 mg). Two weeks later she reported to me that his taste was back (and so were the compliments on her cooking!)
Women need more iron than men. Up to 25% of women may be iron deficient. See Why you Should Worry About Iron for more about iron deficiency.
- Gautam S, Platel K, Srinivasan K. Higher bioaccessibility of iron and zinc from food grains in the presence of garlic and onion. J Agric Food Chem. 2010:28;58:8426-9. Pubmed. doi: 10.1021/jf100716t
- Madej D, Borowska K, Bylinowska J, Szybalska A, Pietruszka B. Dietary intakes of iron and zinc assessed in a selected group of the elderly: are they adequate? Rocz Panstw Zakl Hig. 2013;64:97-104. Pubmed.
- McDaid O1, Stewart-Knox B, Parr H, Simpson E. Dietary zinc intake and sex differences in taste acuity in healthy young adults. J Hum Nutr Diet. 2007;20:103-10. Pubmed.
- Snedeker SM, Greger JL. Metabolism of zinc, copper and iron as affected by dietary protein, cysteine and histidine. J. Nutr. 1983:113, 644–652. Pubmed. Full text.