Tortillas: the lime, the zinc and the outbreaks

A corn tortilla is maize cooked in lime. How much of the calcium in it reaches you is settled by the grain. In five women who ate about 140 g of tortillas on two days a month apart, half of the calcium eaten was absorbed when the tortillas were made from low-phytate maize, 0.50 against 0.35 from ordinary maize. Five women is a small trial. Take the direction seriously and treat the size of the gap as open. Low-phytate maize is also a rare thing to find in a shop, so this is a fact about the grain and not a way to shop. Fortification we can describe only from one snapshot. In January 2019, three years after the FDA allowed folic acid in corn masa flour, people photographed 43 products across 28 states for a campaign run on social media. Three masa flours carried folic acid and no corn tortilla did. Whoever answered that call is not a random sample of the shelf, and the shelf has had years to change since. One more thing before you read the rest. Two of the ten studies on this page were run on tortilla chips, a fried salted snack from another aisle, and what they found belongs to chips. Our USDA table holds eight tortilla records, corn and flour and whole wheat, and one of them exists only to mark flour tortillas with no calcium added.

The numbers, per 100 g

How much is actually in it

• Three years after the FDA allowed folic acid in corn masa flour, a nationwide survey of 43 unique products found three fortified masa flours and no fortified corn tortillas at all. — 132 product photographs from 28 US states collected through a social media campaign in January 2019 (n = 43) Evidence C source
  3 of 43 unique corn masa or tortilla products carried folic acid, and none of the corn tortilla products did

What your body absorbs

• Zinc from corn tortilla fortified with zinc oxide was absorbed as well as zinc from tortilla fortified with zinc sulfate, with fractional absorption of 0.36 against 0.37 in 10 women. — 10 healthy adult women aged 21 to 51 years in Mexico City, stable isotope method (n = 10) Evidence B source
  Fractional zinc absorption 0.35 unfortified, 0.36 with zinc oxide, 0.37 with zinc sulfate, no difference between treatments
• Adding 30 or 60 mg of iron per kg of corn flour to a zinc fortified tortilla left zinc absorption unchanged at about 4.8 mg a day. — 10 healthy adult women in Mexico City, second phase of the same crossover trial (n = 10) Evidence B source
  Fractional zinc absorption 0.32, 0.33 and 0.32 and absorbed zinc 4.8, 4.5 and 4.8 mg a day at 0, 30 and 60 mg of added iron per kg
• Tortillas made from low-phytate maize gave 0.50 fractional calcium absorption against 0.35 from ordinary maize, so the phytate of the grain, and not the lime cooking alone, sets how much calcium gets in. — 5 healthy adult women, two test meals of about 140 g of tortillas a month apart (n = 5) Evidence B source
  Fractional calcium absorption 0.50 against 0.35, P = 0.003

What cooking and storage change

• Replacing 30 percent of the refined flour in a tortilla with soy flour lowered blood glucose at 90 to 120 minutes after eating (p = 0.0009) and did not cost the product its taste rating. — 17 adults aged 21 to 45 with overweight or obesity, of whom 10 completed the tortilla arm (n = 10 (tortilla arm)) Evidence B source
  Lower plasma glucose at 90 to 120 min for tortillas, p = 0.0009; insulin, hunger and satiety unchanged (all p > 0.05)
• Tortilla chips were the only food associated with illness in a 2015 outbreak in one Wyoming facility, and markers of rancidity, hexanal and peroxide, were found in them. — residents and staff of a correctional facility in Wyoming, October 2015 Evidence C source
  Tortilla chips the only food item associated with illness in multivariate logistic regression; symptoms within 1 to 3 hours

What it does to your health

• A 250 kcal snack of tortilla chips, a fried salted snack and not a tortilla, raised glucose and insulin higher than the same calories of pecans in 20 adults with overweight or obesity, while hunger and the size of the next meal stayed the same. — 20 adults with overweight or obesity, mid-morning snack after a standardised breakfast (n = 20) Evidence B source
  Glucose and insulin significantly more elevated after tortilla chips; appetite ratings and food intake unchanged

Safety, limits and interactions

• In a Finnish school outbreak of 2023 with 721 people ill, flour tortillas carried an adjusted odds ratio of 3.3 for illness, and three samples held over 24000 mg of calcium propionate per kg against a legal ceiling of 2000. That is one manufacturer over the limit by more than 12 times, and not a property of tortillas as a food. — 721 pupils and staff in 17 schools of one Finnish municipality, August 2023 (n = 721) Evidence C source
  Adjusted odds ratio 3.3 (95% CI 1.4 to 7.4) for tortillas; calcium propionate above 24000 mg/kg against a limit of 2000 mg/kg
• Each maize tortilla a day was linked to 2.0 percent higher circulating aflatoxin adduct in 915 Mexican adults, and the figure was somewhat higher for tortillas made from homemade masa (2.8 percent, 95% CI 1.1 to 4.6). This is a cross-sectional snapshot from one country and one maize supply, and the adduct is a marker in blood, not a diagnosis and not a risk figure. — 915 adults aged 40 and over in south and eastern Mexico, 2018 to 2019, representative sample (n = 915) Evidence C source
  2.0 percent higher AFB1-lysine per tortilla (95% CI 0.6 to 3.4), 2.8 percent for homemade masa tortillas (95% CI 1.1 to 4.6)

Who this works differently for

• A breakfast tortilla filled with 135 g of beans kept 35 older adults as full as the same tortilla filled with 80 g of beef, with no difference in what they ate later that day. — 35 community dwelling older adults, mean age 72.4 years, BMI 25.1, in Guelph, Canada (n = 35) Evidence B source
  Appetite area under the curve, ad libitum lunch intake and 24 h energy intake did not differ between black bean, red kidney bean and beef meals

The bottom line

On minerals the zinc question has a clear answer. In ten women in Mexico City, zinc from a corn tortilla fortified with zinc oxide was absorbed as well as zinc from one fortified with zinc sulfate, 0.36 of what was eaten against 0.37, with 0.35 from the plain tortilla. The cheaper salt does the job. Adding iron to the same tortilla, 30 or 60 mg per kg of corn flour, left absorbed zinc sitting at about 4.8 mg a day, so a flour carrying both minerals does not have to give up one for the other. Ten women, one city, one crossover trial. That is enough to plan a fortification programme around and not enough to call the matter closed. Two things change what a tortilla does to you at the table. Replacing 30 percent of the refined flour with soy flour lowered blood glucose 90 to 120 minutes after eating (p = 0.0009), and people rated the taste no worse. Insulin, hunger and fullness stayed where they were. Ten people finished that arm of the trial, so this is an early finding and not yet a reason to shop differently. The filling matters too. A breakfast tortilla holding 135 g of beans kept 35 older adults, average age 72, as full as the same tortilla holding 80 g of beef, and they ate no more than usual for the rest of the day. Tortilla chips behave like the snack they are. A 250 kcal serving of them raised glucose and insulin higher than 250 kcal of pecans in 20 adults with overweight or obesity, while hunger and the size of the next meal were unchanged. Everything our cards hold under safety is about contamination, and it is worth your time. In 17 Finnish schools in August 2023, 721 people fell ill, and flour tortillas carried an adjusted odds ratio of 3.3 for illness (95% CI 1.4 to 7.4). Three samples of them held more than 24000 mg of calcium propionate per kg against a legal ceiling of 2000. That was one manufacturer failing badly, and it says nothing about tortillas as a food. In a Wyoming correctional facility in October 2015, tortilla chips were the only food linked to illness, hexanal and peroxide were found in them, and people were sick within one to three hours. In that one outbreak the chips were the only food linked to illness and they carried markers of rancidity. That is what the report says, and it says nothing about rancid food in general. In 915 Mexican adults, each maize tortilla a day went with 2.0 percent more aflatoxin bound in the blood (95% CI 0.6 to 3.4), rising to 2.8 percent when the masa was homemade. That is an observational finding in one country, from one maize supply, and nobody has shown what a difference of that size does to a person. The holes in this page are worth naming out loud. Nothing we have says who should be careful with tortillas for a reason of their own, whether that is a medicine, a pregnancy or a kidney problem, so if that is your question, read this page as unanswered and ask someone who knows your case. We found no study of what an ordinary portion of tortillas amounts to in a real day of eating, no entry in the health claim registries under this name, and no trial that took any of the common beliefs about tortillas and tested it. No study here followed anyone long enough to say what eating tortillas does to health over years.

Sources

1. tortl-r3-10 · prevalence survey
   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
2. tortl-r3-01 · randomised crossover trial
   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
3. tortl-r3-02 · randomised crossover trial
   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
4. tortl-r3-03 · clinical trial, crossover feeding study
   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 2026-09-23
5. tortl-r3-04 · randomised crossover trial
   Compared with the control condition, substituting 30% of refined flour with soy flour significantly reduced the area under the concentration-time curve for postprandial glucose for breads (p = 0.03) and arepas (p = 0.04), and reduced plasma glucose concentrations at 90-120 min for tortillas (p = 0.0009).
   Nutrients, 2026 · checked 2026-09-23
6. tortl-r3-09 · case-control study
   Consuming lunch at the facility on October 11 was highly associated with illness; multivariate logistic regression analysis found that tortilla chips were the only food item associated with illness. Hexanal and peroxide, markers for rancidity, were detected in tortilla chips and composite food samples from the lunch.
   MMWR Morb Mortal Wkly Rep, 2016 · checked 2026-09-23
7. tortl-r3-06 · randomised crossover trial
   VAS ratings, energy, food intake and macronutrient composition did not differ between treatment conditions, but glucose and insulin were significantly more elevated after tortilla chips.
   Nutrients, 2024 · checked 2026-09-23
8. tortl-r3-07 · retrospective cohort study
   In a questionnaire-based retrospective cohort study, consumption of flour tortillas and vegetable filling served at lunch were statistically associated with illness (adjusted odds ratio (aOR) = 3.3; 95% confidence interval (CI): 1.4-7.4 for the tortillas and aOR = 1.5; 95% CI: 1.1-2.1 for the filling).
   Euro Surveill, 2026 · checked 2026-09-23
9. tortl-r3-08 · cross-sectional study
   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 2026-09-23
10. tortl-r3-05 · randomised crossover trial
    Appetite sensation AUCs, ad libitum pizza intake, and 24-h energy intake did not significantly differ between the test meals.
    J Nutr, 2025 · checked 2026-09-23