Corn tortilla: plain bread, mostly studied as a carrier for added minerals

The strongest trial touching the corn tortilla is about the cooking behind it. Nixtamalization, the alkaline cooking that turns maize into masa, cut fumonisin B1 in moldy maize by 95 percent and zearalenone by 89 percent in a randomized trial of 40 adults in Soweto, South Africa. They ate the maize as porridge over a short 5-day design, and their urine markers ended up no different from people eating control maize, which the authors read as exposure brought down to the control level. Most other trials use the tortilla as a vehicle for added minerals. In a randomized crossover trial of 10 Mexican women eating single test meals, tortillas from zinc-fortified flour delivered more absorbed zinc than unfortified ones, with zinc oxide as good as zinc sulfate. In Guatemalan girls aged 12 and 13, a tortilla and black bean meal fortified with NaFeEDTA gave 9.0 percent iron absorption against 5.5 percent with ferrous sulfate (P = 0.009), and the abstract does not say how many girls took part. The tortilla itself is plain food. USDA survey data give 218 calories, 6.3 g fiber, 81 mg calcium and 45 mg sodium per 3.5 oz (100 g), one averaged record with no spread.

The numbers, per 3.5 oz (100 g)

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• In USDA survey data 3.5 oz (100 g) of corn tortilla gives 218 calories, 44.6 g carbohydrate, 6.3 g fiber, 5.7 g protein, 2.9 g fat, 81 mg calcium and 45 mg sodium. — USDA FNDDS Tortilla, corn (52215100) (n = 1 record) Evidence E source
  Per 100 g: energy 218 calories; carbohydrate 44.64 g; fiber 6.3 g; protein 5.7 g; fat 2.85 g; calcium 81 mg; sodium 45 mg

What a real portion looks like

• A medium corn tortilla weighs 0.99 oz (28 g) in USDA survey data, about 61 calories, a small one 18 g and a large one 44 g. — USDA FNDDS Tortilla, corn (52215100) (n = 5 measures) Evidence E source
  1 small 18 g; 1 medium 28 g (about 61 calories, 22.7 mg calcium); 1 large 44 g; 1 extra large 65 g; quantity not specified 77 g

What your body absorbs

• In 5 women eating about 4.9 oz (140 g) of tortillas, calcium absorption was 0.50 from low-phytate maize against 0.35 from ordinary maize. The authors note that nixtamalization only modestly reduces phytate. — healthy adult women, two test meals of about 140 g tortillas one month apart, dual calcium isotopes (n = 5) Evidence C source
  Fractional calcium absorption 0.50 +/- 0.03 (low-phytate) vs 0.35 +/- 0.07 (control maize), P = 0.003
• In a randomized crossover isotope trial in 10 women, tortillas from zinc-fortified flour delivered more absorbed zinc than unfortified ones, with zinc oxide as good as zinc sulfate. — 10 healthy Mexican women aged 21 to 51, flour with 20 mg/kg zinc as oxide or sulfate, single test meals (n = 10) Evidence B source
  Absorbed zinc significantly lower from unfortified tortilla; fortified with oxide and sulfate similar
• In Guatemalan girls aged 12 to 13, iron from a corn tortilla and black bean meal was absorbed at 9.0% with NaFeEDTA against 5.5% with ferrous sulfate. — Guatemalan girls aged 12-13, fortified corn tortilla and black bean paste meals, erythrocyte isotope incorporation at 14 days (n = not stated in the abstract) Evidence B source
  Geometric mean iron bioavailability 9.0% (NaFeEDTA) vs 5.5% (ferrous sulfate), P = 0.009

What cooking and storage change

• In a randomized trial in 40 adults in Soweto, nixtamalization, the alkaline cooking behind tortillas, cut fumonisin B1 in moldy maize by 95% and zearalenone by 89%. — 40 healthy adults in Soweto, South Africa, 300 g maize porridge portions on 2 days, control (18) or nixtamalized moldy maize (22) (n = 40) Evidence B source
  Fumonisin B1 and B2 reduced 95%, zearalenone 89%, fumonisin B3 and DON to unquantifiable; urinary biomarkers not different from control maize

Safety, limits and interactions

• Among 54 pregnant adolescents in Guadalajara, corn tortillas were the most eaten food, reported by 93-96%, while iron, calcium and zinc intakes were low in the younger ones. — pregnant adolescents aged 12-19, Guadalajara, food frequency and cultural beliefs survey (n = 54) Evidence C source
  Corn tortilla consumption 93-96%; low iron, calcium and zinc intake in early and middle adolescence

What is still unknown

• A 2019 US survey of 43 corn masa and tortilla products found no fortified corn tortillas, so the authors advise Hispanic women of reproductive age to take a daily supplement with at least 400 mcg of folic acid. — 132 product photos from 28 US states, social media campaign, January 2019 (n = 43 unique products) Evidence C source
  0 corn tortilla products fortified; 3 masa flours fortified

The bottom line

A medium corn tortilla weighs 0.99 oz (28 g) in US survey data, about 61 calories recalculated from the 100 g value, and sizes run from 18 g for a small one to 44 g for a large one. Nixtamalization only modestly reduces phytate, which holds back calcium. In 5 women eating about 4.9 oz (140 g) of tortillas, the share of calcium absorbed was 0.50 from low-phytate maize and 0.35 from ordinary maize, in a small study that does not describe the meal order as randomized. Who should take care. We have no safety card on allergy, children or medicines for this food, and the only card on what the tortilla itself might carry is the mold toxin trial above, which used porridge. It shows that nixtamalized maize carries far less fumonisin, and says nothing about a given packet of tortillas. Pregnancy is where the tortilla matters. A 2019 US survey of 43 corn masa and tortilla products, gathered from photos people shared online, found folic acid in 3 masa flours and in no corn tortilla. Its authors advise Hispanic women who could become pregnant to take a daily supplement with at least 400 mcg of folic acid. Among 54 pregnant teenagers in Guadalajara, corn tortillas were the most eaten food, reported by 93 to 96 percent, and the younger ones had low intakes of iron, calcium and zinc, in a small one-time survey.

Compared with other foods

Sources

1. ctrt-daily-r5-01 · food composition dataset
   Tortilla, corn, FNDDS 52215100, fdc_id 2707823, per 100 g: Energy 218 kcal | Carbohydrate, by difference 44.64 g | Fiber, total dietary 6.3 g | Protein 5.7 g | Total lipid (fat) 2.85 g | Calcium, Ca 81 mg | Sodium, Na 45 mg
   USDA FNDDS (FoodData Central survey 2024-10-31), Tortilla, corn, food code 52215100, fdc_id 2707823 · checked 2026-09-29
2. ctrt-daily-r5-02 · reference dataset
   Tortilla, corn, FNDDS 52215100, fdc_id 2707823: 1 small 18 g | 1 medium 28 g | 1 large 44 g | 1 extra large 65 g | Quantity not specified 77 g
   USDA FNDDS (FoodData Central survey 2024-10-31), Tortilla, corn, food code 52215100, fdc_id 2707823 · checked 2026-09-29
3. ctrt-daily-r5-03 · controlled clinical trial
   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 2026-09-29
4. ctrt-daily-r5-04 · randomized crossover trial
   The subjects absorbed significantly less zinc with CT than with fortified tortillas, and absorption from both fortified tortillas (CT + ZnO and CT + ZnSO4) was similar.
   Food Nutr Bull, 2012 · checked 2026-09-29
5. ctrt-daily-r5-05 · randomized crossover 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 2026-09-29
6. ctrt-daily-r5-06 · randomized 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.
   Toxins (Basel), 2025 · checked 2026-09-29
7. ctrt-daily-r5-08 · cross-sectional
   The iron, calcium and zinc intake was also deficient in the early/middle stage; meanwhile, the folic acid consumption was very low in the late stage of adolescence. Corn tortillas were the most consumed cereal and food (93-96%)
   Arch Latinoam Nutr, 2008 · checked 2026-09-29
8. ctrt-daily-r5-07 · prevalence survey
   Until folic acid fortification of corn masa products is implemented fully in the country, Hispanic women of reproductive age should take a daily vitamin supplement which includes at least 400 mcg of folic acid to prevent spina bifida and anencephaly.
   Birth Defects Res, 2019 · checked 2026-09-29