Tamale: the research is all about the masa

There is no research on the tamale. Every record our corpus returns under that name is the city of Tamale in Ghana. What exists instead is a literature on masa, the lime-cooked corn dough the thing is made of, and it starts with what the lime bath takes out. When visibly mouldy maize was nixtamalized, fumonisin B1 and B2 fell by 95 percent and zearalenone by 89 percent, while fumonisin B3 and deoxynivalenol dropped below detection in the grain. Then 40 adults in Kliptown, Soweto, ate either that maize or control maize, and urinary fumonisin B1, zearalenone and its metabolites came out no different between the groups (p > 0.05). Behind that null sit 40 people, a short intervention, and background exposure from other foods that stayed high the whole time. The cleaning happened in the corn. Whether it reaches the person eating is a separate question, and this trial did not show that it does. The bath also loads the corn with calcium, and phytate holds much of that calcium back. In 5 healthy women fed about 140 g of tortillas in place of breakfast, calcium absorption ran at 0.50 from an experimental low-phytate maize against 0.35 from the matching ordinary maize (P = 0.003). That is five women, one test meal each time, and a hybrid maize no tortilleria buys.

The numbers, per 100 g

What your body absorbs

• The lime bath that makes masa also loads it with calcium, and phytate then holds much of that calcium back: in 5 women, tortillas from low-phytate maize gave 50% absorption against 35% from ordinary maize. — 5 healthy adult women, each fed about 140 g of tortillas in place of breakfast on two occasions a month apart, with calcium absorption traced by stable isotopes (n = 5) Evidence C source
  Fractional calcium absorption 0.50 (SD 0.03) from low-phytate maize tortillas against 0.35 (SD 0.07) from the matching wild-type maize, P = 0.003
• Masa holds onto iron: in Guatemalan girls aged 12 to 13 eating corn tortillas with black bean paste, only 5.5% of added ferrous sulfate was absorbed, rising to 9.0% when the same iron came as NaFeEDTA. — Guatemalan girls aged 12 to 13 in a crossover trial, fed meals of corn tortillas and black bean paste fortified with ferrous fumarate, ferrous sulfate or NaFeEDTA, absorption traced by stable isotopes at 14 days Evidence B source
  Geometric mean iron bioavailability 5.5% to 6.2% from ferrous fumarate, 5.5% from ferrous sulfate and 9.0% from NaFeEDTA (P = 0.009), with Na2EDTA adding nothing to ferrous fumarate
• The cheap iron powder used to fortify corn masa barely gets in: in 24 children aged 5 to 7 only 3.8% of it was absorbed from tortillas, and adding EDTA did not fix that. — two groups of 12 children aged 5 to 7 years, fed tortillas made from corn masa flour with 3 mg per 100 g of isotopically labelled hydrogen-reduced iron, with or without Na2EDTA (n = 24) Evidence B source
  Geometric mean bioavailability of reduced iron 3.8% (range 2.7 to 5.3), rising only to 5.1% (2.8 to 9.2) with Na2EDTA, P = 0.18

What cooking and storage change

• Soaking maize in lime before grinding it into masa stripped 95% of fumonisin B1 and B2 and 89% of zearalenone out of visibly mouldy grain, yet in 40 adults the mycotoxins measured in urine came out the same either way. — 40 healthy adults from an informal settlement in Kliptown, Soweto, randomly assigned to eat control maize or visibly mouldy maize that had been nixtamalized (n = 40) Evidence B source
  Fumonisin B1 and B2 down 95%, zearalenone down 89%, fumonisin B3 and deoxynivalenol to undetectable levels in the maize, with no significant difference between groups in urinary fumonisin B1, zearalenone or its metabolites (p > 0.05)

Safety, limits and interactions

• Aflatoxin rides along with the masa: in 915 Mexican adults over 40, every extra maize tortilla went with 2.0% more of the aflatoxin marker in blood, and tortillas from homemade masa carried 2.8%. — 915 adults aged 40 and over in a representative sample from south and eastern Mexico in 2018 to 2019, intake by food frequency questionnaire, aflatoxin B1-lysine adduct measured in serum (n = 915) Evidence C source
  Plus 2.1% (95% CI 0.9 to 3.4) in aflatoxin B1-lysine per 30 g of maize, 2.0% (0.6 to 3.4) per tortilla and 2.8% (1.1 to 4.6) per homemade masa tortilla, with minimal estimates for tortilleria or maize flour tortillas

What people believe that the data does not support

• Folic acid was allowed into corn masa flour in the United States on a voluntary basis, and by 2017 to 2018 blood folate in Hispanic women of reproductive age had not moved overall, with a rise only among the least acculturated. — 2070 Hispanic women of reproductive age aged 12 to 49 in NHANES, 1643 before voluntary fortification in 2011 to 2016 and 427 after it in 2017 to 2018 (n = 2070) Evidence C source
  No change overall in red blood cell folate or in the proportion at risk of neural tube defects, with a rise from 894 to 1018 nmol/L in women born abroad and resident under 15 years and from 941 to 1034 nmol/L in primarily Spanish-speaking women

What is still unknown

• Eight studies covering 20123 women are the whole published record on folic acid fortified foods among Hispanic women in the US, and the review that gathered them graded the certainty of every outcome as low to very low. — 8 studies with 20123 Hispanic women of reproductive age in the US, searched from inception to September 2024 (n = 20123) Evidence C source
  Certainty of evidence low to very low across all outcomes, neural tube defect rates 7.5 per 10000 live births in Hispanic against 7.1 in non-Hispanic White women after fortification, and no significant rise in folic acid intake from voluntary fortification

The bottom line

Masa is a poor place to put iron. In Guatemalan girls aged 12 to 13 eating corn tortillas with black bean paste, 5.5 percent of added ferrous sulfate was absorbed, against 9.0 percent when the same iron came as NaFeEDTA (P = 0.009). Those were adolescent girls in one country on one meal pattern, and the abstract does not say how many of them there were. The cheap hydrogen-reduced iron powder that real fortified masa flour uses does worse. In 24 children aged 5 to 7 fed tortillas carrying 3 mg of labelled reduced iron per 100 g, 3.8 percent was absorbed (range 2.7 to 5.3), and adding Na2EDTA moved it only to 5.1 percent (P = 0.18). The authors point out that their labelled powder had a smaller particle size than commercial elemental iron, so absorption from flour off the mill would look worse still. Folic acid was allowed into corn masa flour in the United States on a voluntary basis, and the blood tests do not show it arriving. Among 2070 Hispanic women of reproductive age aged 12 to 49 in NHANES, red blood cell folate did not differ between 2011 to 2016 and 2017 to 2018, and neither did the proportion at risk of neural tube defects. Folate rose only in the least acculturated groups, from 894 to 1018 nmol/L in women born abroad and resident under 15 years, and from 941 to 1034 nmol/L in primarily Spanish-speaking women. Because the fortification is voluntary, how much fortified masa reached any of these women is unknown, and two survey cycles is a short window to look through. The whole published record on the question is 8 studies covering 20123 women, and the review that gathered them graded the certainty of every outcome low to very low. One caution here, and it belongs to the corn rather than to the cook. Among 915 Mexican adults aged 40 and over surveyed in 2018 to 2019, every maize tortilla consumed went with 2.0 percent more aflatoxin B1-lysine in serum (95% CI 0.6 to 3.4), and 2.8 percent (1.1 to 4.6) for a tortilla made from homemade masa. That is a cross-sectional survey, which cannot say the tortilla caused the level, and the adduct it measures marks recent exposure rather than any disease. The estimates for tortillas from a tortilleria or from maize flour were minimal, so where the maize came from and how it was stored is the part worth caring about. Past that our shelf is thin, and thin in a particular way. What we hold on children is the two absorption trials above, in children aged 5 to 7 and in girls aged 12 to 13, and what we hold anywhere near pregnancy is the folic acid work in women of reproductive age. On tamales alongside a medicine we hold nothing at all, because the interaction layer behind these pages is organised by nutrient and a dish has no entry in it. Our two USDA rows are a Navajo tamale and a Hopi masa and pork tamale, both legacy records, so we can give you no measured spread between samples and no retention figure for what steaming does. Nothing in the corpus studies the tamale itself, the filling, the fat, the husk or the portion.

Sources

1. tml-r2-02 · controlled feeding trial
   Calcium fortification of maize has been achieved for millennia in Central America by the process of nixtamalization. Bioavailability of calcium is, however, compromised by phytate, which is present in large quantities in maize kernels and is only modestly reduced by nixtamalization...Mean fractional absorption of calcium from tortillas prepared from the low-phytate maize (0.50 +/- 0.03) was significantly (P = 0.003) greater than that from tortillas prepared from the control maize (0.35 +/- 0.07).
   Am J Clin Nutr, 2005 · checked 2026-09-24
2. tml-r2-03 · randomised controlled trial
   Geometric mean iron bioavailability from test meals fortified with ferrous sulfate was 5.5% and was significantly higher in test meals fortified with NaFeEDTA (9.0%; P = 0.009, paired t test).
   Am J Clin Nutr, 2002 · checked 2026-09-24
3. tml-r2-04 · randomised controlled trial
   When normalized to 40% absorption of the reference dose, the geometric mean (+/-range 1 SD) bioavailability of reduced iron in tortilla was 3.8% (2.7-5.3). The addition of Na(2)EDTA, tended to increase it (P = 0.18) to 5.1% (2.8-9.2).
   J Nutr, 2004 · checked 2026-09-24
4. tml-r2-01 · randomised controlled trial
   Nixtamalization achieved a reduction in fumonisin B3 and deoxynivalenol (DON) to unquantifiable or undetectable levels in maize, while reducing fumonisin B1 (FB1), fumonisin B2, and zearalenone (ZEN) by 95%, 95%, and 89%, respectively...Biomarker analysis revealed that after consumption of either control or nixtamalized maize, urinary levels of FB1, ZEN, and its metabolites α- and β-zearalenol (α- and β-ZEL) did not show significant differences between groups (p > 0.05).
   Toxins (Basel), 2025 · checked 2026-09-24
5. tml-r2-05 · cross-sectional study
   After multivariable adjustment, for every 30 g of maize consumed (1 tortilla equivalent), circulating AFB1-lys incremented by 2.1% [95% confidence interval (CI): 0.9%, 3.4%]. For every maize tortilla consumed, the concentration of circulating AFB1-lys was 2.0% (95% CI: 0.6%, 3.4%) higher. The corresponding estimate for homemade masa tortilla was 2.8% (95% CI: 1.1%, 4.6%).
   Am J Clin Nutr, 2025 · checked 2026-09-24
6. tml-r2-06 · cross-sectional study
   RBC folate concentration (adjusted geometric mean) among Hispanic women of reproductive age did not differ between 2011-2016 and 2017-2018, though RBC folate concentration increased significantly among lesser acculturated Hispanic women consuming ECGP only...By subpopulation, we observed no significant changes in the proportion at risk of NTDs (<748 nmol/L) and no changes in the model-based estimated NTD rates following voluntary corn masa fortification.
   Nutrients, 2021 · checked 2026-09-24
7. tml-r2-07 · systematic review of observational evidence
   The certainty of evidence, assessed using the Grading of Recommendations, Assessment, Development, and Evaluations framework, ranged from low to very low across outcomes.
   BMC Public Health, 2025 · checked 2026-09-24