Corn tortillas: mostly measured for what was added to them

Most of what has been measured about the corn tortilla is not the tortilla. It is what someone tried to add to it. The trials here put iron and zinc into corn flour and then asked whether the body takes any of it out again. Zinc it takes. In ten Mexican women the share absorbed held at 0.35 with no added zinc, 0.36 with zinc oxide and 0.37 with zinc sulfate. That number is a share of what the meal held, not a total. A steady share of a flour that carries more zinc still hands the body more zinc, so what the trial showed is that the added forms were absorbed as readily as the zinc already in the corn. In the second half of the same trial the women absorbed 4.8, 4.5 and 4.8 mg of zinc a day at 0, 30 and 60 mg of added iron per kg of flour, so the iron did not push the zinc out. With iron, the compound decides the result. Elemental reduced iron reached 3.8 percent bioavailability in Mexican children aged 5 to 7. In Guatemalan girls aged 12 and 13 eating tortillas with black bean paste, switching from ferrous sulfate to NaFeEDTA lifted iron absorption from 5.5 to 9.0 percent, and that gap is unlikely to be chance (P = 0.009). That trial never reports how many girls took part, so how precise those two numbers are cannot be judged from here. None of that describes the tortilla on a shelf in the United States. A 2019 survey of 43 corn masa and tortilla products found folic acid in three masa flours and in none of the corn tortillas.

What your body absorbs

• The share of zinc absorbed from corn tortilla was 0.35 to 0.37 in adult women, a fraction of the meal rather than a total, whether the flour carried added zinc oxide, zinc sulfate or no added zinc. — 10 healthy Mexican women aged 21 to 51, single test meals, stable isotope method (n = 10) Evidence B source
  Fractional absorption 0.35 (no zinc), 0.36 (zinc oxide), 0.37 (zinc sulfate), no significant difference
• Adding 30 or 60 mg of iron per kg of corn flour left zinc absorption from the tortilla unchanged at about 4.5 to 4.8 mg per day. — 10 healthy Mexican women, second phase of the same isotope crossover trial (n = 10) Evidence B source
  Zinc absorbed 4.8, 4.5 and 4.8 mg/day at 0, 30 and 60 mg/kg added iron
• Elemental reduced iron added to corn masa flour reached only 3.8 percent bioavailability in tortillas eaten by 5 to 7 year old children. — 24 Mexican children aged 5 to 7 in two groups of 12, tortillas with 3 mg iron per 100 g, 14 day isotope follow-up (n = 24) Evidence B source
  Geometric mean bioavailability 3.8 percent (range 2.7 to 5.3), rising to 5.1 percent with Na2EDTA (P = 0.18)
• In meals of corn tortillas with black bean paste, iron bioavailability rose from 5.5 percent with ferrous sulfate to 9.0 percent with NaFeEDTA. — Guatemalan girls aged 12 to 13, crossover design, erythrocyte isotope incorporation 14 days after intake (n = not stated in the abstract) Evidence B source
  5.5 percent versus 9.0 percent, P = 0.009 (paired t test)

What it does to your health

• Corn tortilla intake stayed the same on both arms of a 6 week Mexican-style diet trial, so the A1c gain of the low glycaemic index arm (P < 0.008) came from other foods. — 14 overweight adults with type 2 diabetes who completed a crossover of two 6 week diets with a 6 week washout (n = 14) Evidence B source
  A1c improved on the low glycaemic index diet, P < 0.008, with tortilla intake equal in both arms

Safety, limits and interactions

• In the 2008 Salmonella Saintpaul outbreak in the United States, eating corn tortillas carried a matched odds ratio of 2.3, and the investigators traced the source to raw peppers served with them. — 1500 case subjects across the United States, three case-control studies of cases not linked to restaurant clusters (n = 1500) Evidence C source
  Matched odds ratio 2.3 (95% CI 1.2 to 5.0) for corn tortillas, against 4.0 for pico de gallo salsa

Who this works differently for

• Observational data from rural Honduras link a median intake of four or more corn tortillas a day with 1.75 times the odds of a functional gastrointestinal disorder. — 815 adults interviewed in rural Western Honduras, Rome IV questionnaire plus diet history (n = 815) Evidence C source
  Odds ratio 1.75 (95% CI 1.22 to 2.50) for any functional gastrointestinal disorder

What is still unknown

• A 2019 national survey of 43 unique corn masa and tortilla products found folic acid in three masa flours and in none of the corn tortillas. — 132 product photographs from 28 United States states, collected through a social media campaign (n = 43 unique products) Evidence C source
  3 of 43 products fortified, 0 of the corn tortilla products

The bottom line

Eat tortillas because they are the bread of the meal you are making. The evidence in front of us gives you no reason beyond that. It gives you nothing against them either, and that is because nobody in our base has measured the tortilla itself, not because it has been checked and cleared. Two findings get read as warnings, and both say something narrower than they look. In the 2008 Salmonella Saintpaul outbreak in the United States, corn tortillas carried a matched odds ratio of 2.3 across 1500 cases, and the investigators traced the source to the raw peppers served with them. In a six week crossover of two Mexican style diets, 14 overweight adults with type 2 diabetes improved their A1c on the low glycaemic index arm, and tortilla intake was equal on both arms, so the tortillas were not what moved it. One finding stays open. In rural Western Honduras, adults reporting four or more tortillas a day had 1.75 times the odds of a functional gastrointestinal disorder. That is 815 people answering a questionnaire once, with the diet and the symptoms recorded at the same moment, so it cannot tell you which one came first. Nobody has fed anyone tortillas and watched what happened to their gut, and until someone does, this number is a reason to pay attention rather than a reason to stop. What is missing from this page is bigger than what is on it. We hold no USDA record for this food in this cohort, so there is no composition table here and no number for what a tortilla contains. Nixtamalization, the lime cooking that turns corn into masa and is the most interesting thing about this food, has no card in our base, and neither does portion size or what varies between one tortilla and the next. The one card standing in the safety section is an outbreak the investigators traced to raw peppers, so nothing here measures the safety of the tortilla itself: no upper amount, no mould toxins, no allergen work, nobody named who should be careful. A silent section is not a clean bill of health. Two of the three studies on absorption above ran on children and on girls aged 12 and 13, so if you are an adult reading them, you are reading across an age gap that nobody has closed. We would rather say all of this than fill the space.

Sources

1. cotor-r5-01 · RCT crossover
   The mean (+/- SEM) fractional zinc absorption from unfortified tortilla, tortilla fortified with zinc oxide, and tortilla fortified with zinc sulfate did not differ among treatments: 0.35 +/- 0.07, 0.36 +/- 0.05, and 0.37 +/- 0.07, respectively.
   Food Nutr Bull, 2012 · checked 2026-09-23
2. cotor-r5-02 · RCT crossover
   The three treatment groups with 0, 30, and 60 mg/kg of added iron had similar fractional zinc absorption (0.32 +/- 0.04, 0.33 +/- 0.02, and 0.32 +/- 0.05, respectively) and similar amounts of zinc absorbed (4.8 +/- 0.7, 4.5 +/- 0.3, and 4.8 +/- 0.7 mg/day, respectively).
   Food Nutr Bull, 2012 · checked 2026-09-23
3. cotor-r5-03 · RCT
   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).
   J Nutr, 2004 · checked 2026-09-23
4. cotor-r5-04 · RCT crossover
   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 2026-09-23
5. cotor-r5-05 · RCT crossover
   There were no differences in the amount of carbohydrates consumed, such as corn tortillas and dairy products. At the end of the study periods, A1c was improved on the low- compared with the high-GI diet (P < 0.008).
   Diabetes Care, 2003 · checked 2026-09-23
6. cotor-r5-07 · case-control
   eating at a Mexican-style restaurant (matched odds ratio, 4.6; 95% CI, 2.1 to ∞) and eating pico de gallo salsa (matched odds ratio, 4.0; 95% CI, 1.5 to 17.8), corn tortillas (matched odds ratio, 2.3; 95% CI, 1.2 to 5.0), or salsa (matched odds ratio, 2.1; 95% CI, 1.1 to 3.9)
   N Engl J Med, 2011 · checked 2026-09-23
7. cotor-r5-06 · cross-sectional
   Subjects with a median daily intake of ≥ 4 corn tortillas had 1.75 (95% CI 1.22-2.50) times the odds of having any FGID.
   Dig Dis Sci, 2021 · checked 2026-09-23
8. cotor-r5-08 · prevalence survey
   People from 28 states shared photos of 132 products, including 43 unique corn masa flour or corn tortilla products. Of those, only three corn masa flour products included folic acid: (a) Maseca Instant White (4.4 lb bag); (b) Masa Brosa Instant; and (c) Masa Brosa Instant Blue. None of the corn tortilla products were fortified.
   Birth Defects Res, 2019 · checked 2026-09-23