Corn or flour tortilla: what each one carries

In a randomized trial on adult women, about 35 percent of the zinc in a corn tortilla was absorbed, and adding zinc oxide or zinc sulfate to the masa did not change that share. Mexican children aged 5 to 7 absorbed 3.8 percent of the reduced iron powder added to masa tortillas, and since the trial used iron finer than the commercial kind, real absorption may be lower still. We found no trial that fed people corn tortillas against flour tortillas and measured blood sugar, weight or cholesterol. So the comparison on this page is about what goes into each one. The flour tortilla is the bigger unit. A medium one weighs 1.6 oz (45 g) in US survey coding against 28 g for a medium corn tortilla, roughly 60 percent heavier. In lab tests of 25 store brands from one US region, flour tortillas made with phosphorus or aluminum additives carried more of both than corn ones.

How much is actually in it

• Laboratory tests of 25 US store brands found wheat flour tortillas with phosphorus additives carried about 50 percent more phosphorus per 30 g than corn tortillas, relevant for kidney patients. — 13 wheat flour and 12 corn tortilla brands bought in Southern California, 2019-2020 (n = 25) Evidence D source
  About 50% more phosphorus per 30 g serving in wheat flour tortillas, p=0.049; wheat with phosphorus additives 63 +/- 6.0 mg per 30 g
• Across 6 USDA samples of dry masa harina, the flour for corn tortillas, calcium ranged from 72 to 162 mg per 3.5 oz (100 g) and fiber from 5.7 to 9.4 g. — USDA Foundation Foods samples, Corn flour, masa harina, white or yellow, dry (n = 6) Evidence E source
  Calcium 71.8-162.0 mg (median 108.5); fiber 5.69-9.38 g (median 6.735); iron 1.13-3.65 mg (median 1.31) per 3.5 oz (100 g)

What a real portion looks like

• In US survey coding a medium corn tortilla weighs 0.99 oz (28 g) and a medium flour tortilla 45 g, so the flour one is roughly 60 percent heavier. — USDA FNDDS 52215100 Tortilla, corn (fdc_id 2707823) and 52215200 Tortilla, flour (fdc_id 2707824) Evidence E source
  Corn: small 18 g, medium 28 g, large 44 g; flour: small 33 g, medium 45 g, large 71 g, extra large 104 g

What your body absorbs

• In 10 women, about 35 percent of zinc was absorbed from corn tortillas whether they were unfortified or fortified with zinc oxide or zinc sulfate. — adult women, corn tortillas with 20 mg/kg zinc oxide, zinc sulfate or no added zinc; stable isotopes (n = 10) Evidence B source
  Fractional zinc absorption 0.35 +/- 0.07 (unfortified), 0.36 +/- 0.05 (oxide), 0.37 +/- 0.07 (sulfate); iron at 30-60 mg/kg did not change it
• Children aged 5 to 7 absorbed only 3.8 percent of the reduced iron powder added to corn masa tortillas, and EDTA did not significantly raise it. — Mexican children aged 5-7 years, 2 groups of 12, tortillas with 3 mg/100 g H2-reduced iron (n = 24) Evidence B source
  Bioavailability 3.8% (range 2.7-5.3) vs 5.1% (2.8-9.2) with Na2EDTA, P=0.18
• In Guatemalan girls aged 12 to 13, iron absorption from corn tortilla and bean meals was 5.5 percent with ferrous sulfate and 9.0 percent with NaFeEDTA. — Guatemalan girls aged 12-13 years, fortified corn tortilla and black bean paste meals Evidence B source
  Geometric mean iron bioavailability 5.5% (ferrous sulfate) vs 9.0% (NaFeEDTA), P=0.009; ferrous fumarate 5.5-6.2%
• Zinc absorption from tortillas made of ordinary corn was 13 to 15 percent, and rose to 28 to 38 percent with low-phytate corn hybrids. — 10 healthy adults fed maize tortillas as the only food for 2 days (n = 10) Evidence C source
  Fractional zinc absorption 0.38 and 0.28 (low-phytate) vs 0.15 and 0.13 (wild-type); negative relation with phytate, P<0.001

What cooking and storage change

• Nixtamalization adds calcium to corn but only modestly reduces phytate, and in 5 women calcium absorption from ordinary tortillas was 35 percent versus 50 percent from low-phytate corn. — 5 healthy adult women, about 140 g tortillas as breakfast, dual calcium isotopes (n = 5) Evidence C source
  Fractional calcium absorption 0.35 +/- 0.07 (typical maize) vs 0.50 +/- 0.03 (low-phytate maize), P=0.003

What it does to your health

• In 10 adults with overweight, swapping 30 percent of the wheat flour in a tortilla for soy flour did not significantly lower the glucose area under the curve. — adults aged 21-45 with overweight or obesity, tortilla arm of 10, portions with about 70 g carbohydrate (n = 10) Evidence B source
  Glucose AUC 30% soy vs control tortilla F(2,18) = 2.16, p = 0.1; lower glucose only at 90-120 min

Safety, limits and interactions

• Wheat flour tortillas made with aluminum leavening held about 8.9 mg aluminum per 30 g in lab tests, while corn tortillas held 0.02 to 0.45 mg. — 25 US commercial tortilla brands (13 wheat flour, 12 corn) (n = 25) Evidence D source
  Aluminum 8.86 +/- 3.98 mg per 30 g (wheat with aluminum additives) vs 0.02-0.45 mg (soft corn), 0.15-0.31 mg (hard corn)
• In a 2023 Finnish school outbreak, eating flour tortillas carried 3.3 times the odds of acute stomach illness, and samples held over 24,000 mg/kg calcium propionate against a 2,000 mg/kg limit. — 721 ill pupils and staff in 17 schools, Finland, August 2023 (n = 721) Evidence C source
  Adjusted OR 3.3 (95% CI 1.4-7.4) for flour tortillas; calcium propionate >24,000 mg/kg vs EU maximum 2,000 mg/kg
• Among 915 Mexican adults aged 40 and over, each corn tortilla a day was linked with 2.0 percent higher blood aflatoxin adducts, mostly from homemade masa. — 915 adults aged 40+ in south and eastern Mexico, 2018-2019 (n = 915) Evidence C source
  +2.0% (95% CI 0.6-3.4) AFB1-lysine per tortilla; +2.8% (1.1-4.6) for homemade masa tortillas

What people believe that the data does not support

• A systematic review of 8 observational studies found that voluntary folic acid fortification of US corn masa flour from 2016 did not significantly raise folic acid intake in Hispanic women. — Hispanic women of reproductive age in the US, 8 studies, n = 20,123 (n = 20123) Evidence C source
  No significant rise in folic acid intake; NTD 7.5 vs 7.1 per 10,000 live births (Hispanic vs non-Hispanic White) after fortification
• FDA allows manufacturers to add up to 0.7 mg of folic acid per pound of corn masa flour, the base of corn tortillas, but this fortification is voluntary. — corn masa flour products sold in the US Evidence E source
  Up to 0.7 mg folic acid per pound of corn masa flour

The bottom line

Lab tests of 25 brands bought in one region of Southern California found that flour tortillas listing a phosphorus additive carried about 50 percent more phosphorus per 30 g than corn tortillas, a point the authors raise for people with kidney disease. The same tests found 8.86 mg aluminum per 30 g in flour tortillas made with aluminum leavening, against 0.02 to 0.45 mg in soft corn tortillas, and they measured products with no health outcome in anyone. Six USDA samples of dry masa harina, the flour behind corn tortillas, ranged from 72 to 162 mg calcium and from 5.7 to 9.4 g fiber per 3.5 oz (100 g) of dry flour, with calcium depending on how much lime went in. Cooking corn in lime, called nixtamalization, adds calcium and only modestly lowers phytate. In 5 women in a non-randomized study, calcium absorption was 35 percent from ordinary tortillas and 50 percent from a low-phytate corn. In 10 adults eating only tortillas for two days, in groups of 4 to 6, zinc absorption was 13 to 15 percent from ordinary corn and 28 to 38 percent from low-phytate hybrids. The two zinc studies used different designs, and their numbers do not line up. In Guatemalan girls aged 12 to 13 eating corn tortillas with bean paste, iron absorption was 5.5 percent with ferrous sulfate and 9.0 percent with NaFeEDTA. The one glucose trial here changed the flour tortilla itself. In 10 adults with overweight, a tortilla made for the study with 30 percent of the wheat flour swapped for soy flour did not significantly lower the glucose area under the curve, p = 0.1. FDA lets makers add up to 0.7 mg folic acid per pound of corn masa flour, and doing so is voluntary, while enriched US wheat flour has been fortified by rule since 1998. A systematic review of 8 observational studies covering 20,123 Hispanic women of reproductive age found that the voluntary step did not significantly raise their folic acid intake, on evidence graded low to very low. Who should be careful. If you have kidney disease, the phosphorus gap above concerns you. In a 2023 Finnish outbreak across 17 schools with 721 ill pupils and staff, eating flour tortillas carried 3.3 times the odds of acute stomach illness (95% CI 1.4 to 7.4). Samples from that one batch of one maker held over 24,000 mg/kg calcium propionate against an EU limit of 2,000. Among 915 Mexican adults aged 40 and over, each corn tortilla a day was linked with 2.0 percent higher blood aflatoxin adducts, and 2.8 percent for homemade masa, in a cross-sectional survey where adducts mark exposure and say nothing about disease. For women who could become pregnant, the relevant fact is the folic acid gap above, and for children it is the low iron absorption. We have no card on wheat allergy or celiac disease, and flour tortillas are made from wheat flour.

Sources

1. cfto-daily-r4-06 · food analysis
   Further analysis of phosphorus concentrations reveals that wheat flour tortillas generally contained approximately 50 % more phosphorus (per 30 grams serving) than corn tortillas when a source of phosphorus was listed on the ingredients label (p = 0.049).
   Food and Humanity, 2026 (dietary burden of phosphorus and aluminum in tortillas) · checked 2026-09-29
2. cfto-daily-r4-14 · food composition dataset
   USDA Foundation Foods Corn flour, masa harina, white or yellow, dry, 6 samples: Calcium 71.8-162.0 mg (median 108.5) | Fiber, total dietary 5.69-9.38 g (median 6.735) | Iron 1.13-3.65 mg (median 1.31) per 100 g
   USDA FoodData Central, Foundation Foods, release 2026-04-30, Corn flour, masa harina, white or yellow, dry · checked 2026-09-29
3. cfto-daily-r4-13 · reference dataset
   FNDDS 52215100 Tortilla, corn (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; FNDDS 52215200 Tortilla, flour (fdc_id 2707824): 1 small 33 g | 1 medium 45 g | 1 large 71 g | 1 extra large 104 g | Quantity not specified 56 g
   USDA FNDDS (FoodData Central survey foods), codes 52215100 and 52215200 · checked 2026-09-29
4. cfto-daily-r4-01 · randomized crossover absorption 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 2026-09-29
5. cfto-daily-r4-02 · randomized absorption 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 2026-09-29
6. cfto-daily-r4-03 · randomized crossover absorption 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
7. cfto-daily-r4-05 · controlled feeding study
   The mean (+/-SD) FAZ values from tortillas prepared from ND-LP, lpa1-1-LP, lpa1-1-WT, and ND-WT were 0.38 +/- 0.07, 0.28 +/- 0.04, 0.15 +/- 0.07, and 0.13 +/- 0.05, respectively.
   Am J Clin Nutr, 2004 · checked 2026-09-29
8. cfto-daily-r4-04 · controlled feeding study
   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.
   Am J Clin Nutr, 2005 · checked 2026-09-29
9. cfto-daily-r4-10 · randomized crossover trial
   Plasma glucose AUC was also reduced following the 30% soy arepa compared with control (F(1,7) = 6.1, p = 0.04), whereas no significant difference was observed between the 30% soy tortilla and control tortilla (F(2,18) = 2.16, p = 0.1) (Table 3).
   Nutrients, 2026 · checked 2026-09-29
10. cfto-daily-r4-07 · food analysis
    The aluminum content ranged from 0.15 to 0.31 mg per 30 g serving, less than wheat flour tortillas with aluminum additives (8.86 ± 3.98 mg per 30 g serving; mean ± SEM) (Table 2) and comparable to soft corn tortillas (0.02–0.45 mg per 30 g serving, Table S4).
    Food and Humanity, 2026 (dietary burden of phosphorus and aluminum in tortillas) · checked 2026-09-29
11. cfto-daily-r4-08 · outbreak investigation
    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 2026-09-29
12. cfto-daily-r4-09 · cross-sectional survey
    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 2026-09-29
13. cfto-daily-r4-11 · systematic review
    Voluntary fortification did not significantly increase folic acid intake or reduce the proportion with inadequate intake; however, monolingual Spanish-speakers demonstrated higher intake and RBC folate concentrations.
    BMC Public Health, 2025 · checked 2026-09-29
14. cfto-daily-r4-12 · regulatory decision
    Manufacturers may add folic acid to corn masa flour at a level of up to 0.7 milligrams per pound.
    US FDA, Fortifying Corn Masa Flour Products with Folic Acid (content current as of 2024-06-03) · checked 2026-09-29