Cassava flour: almost all carbohydrate, and the cyanide risk sits in the soaking

In a randomized trial in 176 Nigerian preschool children, yellow biofortified cassava eaten for 17 weeks lifted median vitamin A intake to 536 mcg RAE a day against 301 mcg with white cassava, in local dishes that included flour-based ones. Ordinary white flour has almost no provitamin A. UK tables give gari, a fermented and roasted cassava flour, 361 calories and 95.1 g carbohydrate per 3.5 oz (100 g) with 0.7 g protein. The question most people bring is cyanide. The data on harm come from Central African villages where bitter roots were soaked too briefly. In rural Zaire, children eating flour from roots soaked one day had urinary thiocyanate of 757 µmol/l against 50 µmol/l where roots were soaked three days, and the community with konzo was the one eating short-soaked flour. It is an old, small comparison of two communities.

The numbers, per 3.5 oz (100 g)

How much is actually in it

• Across 8 USDA samples of cassava flour, iron ranged from 0.3 to 19.5 mg per 3.5 oz (100 g) around a median of 1.1 mg, and calcium from 28 to 224 mg. — — (n = 8) Evidence E source
  Iron mean 3.99 mg (0.306-19.5, median 1.075), calcium 74.6 mg (28.1-224.0), fiber 4.8 g (0-8.6), fat 0.49 g (0.32-0.85) per 3.5 oz (100 g)
• UK tables list gari (cassava flour) at 361 calories and 95.1 g carbohydrate per 3.5 oz (100 g) with only 0.7 g protein and 2.02 mg iron. — — Evidence E source
  Per 100 g: 361 calories, carbohydrate 95.1 g, protein 0.7 g, fat 0.2 g, AOAC fiber 4.6 g, calcium 41 mg, iron 2.02 mg, water 9.3 g
• In an RCT in 176 Nigerian preschool children, yellow biofortified cassava for 17 weeks lifted median vitamin A intake to 536 ug RAE a day against 301 ug with white cassava. — 176 Nigerian pre-school children, white vs yellow cassava for 17 weeks (n = 176) Evidence B source
  Median RAE intake 536 vs 301 ug/day (P < 0.0001), below EAR 9% vs 29%

What a real portion looks like

• In Mozambique, schoolchildren in konzo-affected sites had a calculated maximum cassava intake of over 700 g a day, against under 5.3 oz (150 g) of cassava flour a day in sites without konzo. — schoolchildren at 4 sites, 2 with and 2 without recent konzo, Mozambique Evidence C source
  Calculated maximum intake over 700 g/day vs under 150 g/day

What your body absorbs

• In a 3-month trial in 43 Indonesian adolescent girls with anemia, cookies from iron-fortified cassava composite flour did not raise hemoglobin more than control cookies. — Indonesian adolescent girls with anemia at a boarding school, 27 intervention, 16 control, 3 months (n = 43) Evidence B source
  Hemoglobin rose in both groups, no significant difference between groups
• In an RCT in 342 Kenyan schoolchildren, yellow cassava for 18.5 weeks raised serum retinol by 0.04 umol/L and serum beta-carotene by 524%. — 342 children aged 5-13, 6 days a week for 18.5 weeks, about 371 g cassava a day (n = 342) Evidence B source
  Serum retinol +0.04 umol/L (95% CI 0.00 to 0.07), beta-carotene +524% (448% to 608%)

What cooking and storage change

• In rural Zaire, children eating flour from cassava soaked only one day had urinary thiocyanate of 757 umol/l against 50 umol/l where roots were soaked three days, and the short-soaking community had konzo. — 31 children in a konzo-affected and 46 in an unaffected population, rural Zaire (n = 77) Evidence C source
  Urinary thiocyanate 757 vs 50 umol/l
• A 2024 review of DR Congo data reports that a wetting method cut cassava flour cyanide from 19-41 to 8-12 mg HCN per kg, mostly under the WHO limit of 10 mg/kg. — villages in Boko, DR Congo, intervention program Evidence C source
  Mean flour cyanide 19-41 down to 8-12 mg HCN eq/kg, median 12.5 mg/kg estimated
• Laboratory data suggest soaking cassava roots in water with plant extracts before making flour kept hydrogen cyanide under the FAO/WHO threshold of 10 mg/kg. — cassava flour samples from 11 soaking treatments and 2 controls, Nigeria Evidence D source
  HCN held below 10 mg/kg dry weight in treated flours

What it does to your health

• In 19 volunteers, dental plaque pH did not drop after eating the two main Amazonian cassava flours, unlike after a fruit sweet. — 19 volunteers, crossover with 4 foods, plaque pH over 60 min (n = 19) Evidence C source
  Plaque pH unchanged after flours (p > 0.05), fell after sweet (p < 0.05)

Safety, limits and interactions

• Observational data from a konzo-affected area of Congo link higher cyanogen content of household cassava flour, averaging 52 ppm against a WHO cut-off of 10 ppm, with poorer motor and overall development in children aged 1-4. — 114 mother-child dyads, children 12-48 months, Kahemba, DR Congo (n = 114) Evidence C source
  Flour cyanogen mean 52.18 ppm (SD 32.79), adjusted coefficients -0.08 to -0.15 (p < 0.01) for fine motor and neurodevelopment
• A 2024 model estimates that cyanide in DR Congo cassava flour costs children under 5 a median of 2.37 cognitive score points, rising to 8.02 points at the 95th percentile of exposure. — children under 5 in DR Congo, modeled from flour cyanide data Evidence C source
  CAC decrement mean 3.12, median 2.37, 95th percentile 8.02 points
• In 1231 Brazilian schoolchildren, 91% of whom ate cassava flour, daily intake was not linked to iodine deficiency (OR 1.43, not significant). — 1231 schoolchildren aged 6-14, public schools, Bahia, Brazil (n = 1231) Evidence C source
  Iodine deficiency OR 1.43 (95% CI 0.72 to 2.82), p = 0.29
• In Nigerian type 2 diabetes patients on chlorpropamide, a cassava flour meal gave a poorer glycemic response than maize or yam flour meals. — Nigerian patients with type 2 diabetes, 250 mg chlorpropamide, three standard meals Evidence C source
  Better glycemic response with maize and yam flour meals than cassava flour meal

What people believe that the data does not support

• In Brazil, spina bifida rates were 1.4 times higher in the 10 years after cassava flour was added to folic acid fortification than in 2005-2010, in a registry comparison. — Brazilian live births, SINASC registry, 2005-2010 vs 2011-2020 Evidence C source
  Rate ratio 1.4 (95% CI 1.34 to 1.45)

The bottom line

Mineral numbers vary a lot between bags. Across 8 USDA samples, iron ran from 0.3 to 19.5 mg per 3.5 oz (100 g) around a median of 1.1 mg, a spread that suggests milling or soil contamination in some samples, and calcium ran from 28 to 224 mg. Adding iron did not show in the one trial we found. Cookies of iron-fortified cassava composite flour, eaten for 3 months by 43 Indonesian schoolgirls with anemia, raised hemoglobin no more than control cookies, with high dropout and low compliance. Fresh yellow cassava did move vitamin A status. In 342 Kenyan schoolchildren, about 371 g a day for 18.5 weeks raised serum retinol by 0.04 µmol/L (95% CI 0.00 to 0.07). Processing decides the cyanide. A 2024 review of DR Congo data reports that a wetting method cut flour cyanide in Boko villages from 19 to 41 mg HCN per kg down to 8 to 12 mg, most samples under the WHO limit of 10 mg/kg. That is a secondary summary of the original studies. Laboratory data from Nigeria suggest soaking roots in water with plant extracts kept the flour under the same threshold. Quantity matters as well. In Mozambique, schoolchildren at sites with recent konzo had a calculated maximum of over 25 oz (700 g) of cassava a day, against under 5.3 oz (150 g) of cassava flour at sites without it, figures derived from biomarkers. The cautions concern children and heavy dependence. In Kahemba, DR Congo, household flour averaged 52 ppm cyanogens against a WHO cut-off of 10, and observational data from 114 mother and child pairs link higher levels with poorer fine motor and overall development at ages 1 to 4. A 2024 model estimates a median loss of 2.37 cognitive score points in children under 5 in DR Congo, rising to 8.02 at the 95th percentile of exposure. Both describe poorly processed bitter cassava in subsistence diets, and we found no data on cyanogens in cassava flour sold in US or EU shops. In a small Nigerian study of people with type 2 diabetes taking chlorpropamide, a cassava flour meal gave a poorer glycemic response than maize or yam flour meals. In 1231 schoolchildren in Bahia, Brazil, daily cassava flour was not significantly linked to iodine deficiency (OR 1.43, 95% CI 0.72 to 2.82), in a setting with iodised salt. In 19 volunteers, dental plaque pH did not drop after the two main Amazonian cassava flours and fell after a fruit sweet, a 60 minute measure that says nothing direct about cavities. Brazil saw spina bifida rates 1.4 times higher in the decade after cassava flour joined folic acid fortification. That is a registry comparison that changes in recording confound, and it does not show that fortification caused harm.

Sources

1. cafl-r7-01 · food composition dataset
   Flour, cassava: Iron, Fe 3.988 MG range 0.306-19.5 (median 1.075), samples 8; Calcium, Ca 74.55 MG range 28.1-224.0 (median 60.65), samples 8; Fiber, total dietary 4.834 G range 0.0-8.6 (median 5.405), samples 8; Total lipid (fat) 0.4938 G range 0.32-0.85, samples 8
   USDA FoodData Central Foundation Foods, 'Flour, cassava' (FDC 2512377), release 2026-04-30 · checked 2026-09-30
2. cafl-r7-02 · food composition dataset
   Flour, gari (cassava flour) (11-899): Energy (kcal) 361; Carbohydrate (g) 95.1; Protein (g) 0.7; Fat (g) 0.2; AOAC fibre (g) 4.6; Calcium (mg) 41; Iron (mg) 2.02; Water (g) 9.3
   CoFID 2021 (Public Health England), code 11-899 · checked 2026-09-30
3. cafl-r7-11 · randomized controlled trial
   During intervention, median RAE intake was 536 µg/d in the YC group and 301 µg/d in the WC group (P < 0·0001).
   Br J Nutr, 2021 · checked 2026-09-30
4. cafl-r7-07 · observational study
   In two sites with recent konzo cases, 84% and 93% of school children consumed cassava the previous day, and the calculated maximum daily consumption of cassava was over 700 g. In two sites without recent konzo cases, about 50% of school children consumed cassava the previous day and the calculated daily consumption of cassava flour was less than 150 g.
   Int J Food Sci Nutr, 2004 · checked 2026-09-30
5. cafl-r7-10 · randomized controlled trial
   The average haemoglobin level increased from baseline to middle line, with a significant difference observed in both groups (p < 0.05), but no significant difference between the groups (p < 0.05).
   Nutr Hosp, 2026 · checked 2026-09-30
6. cafl-r7-12 · randomized controlled trial
   Both yellow cassava and β-carotene supplementation increased serum retinol concentration by 0.04 μmol/L (95% CI: 0.00, 0.07 μmol/L); correspondingly, serum β-carotene concentration increased by 524% (448%, 608%) and 166% (134%, 202%).
   Am J Clin Nutr, 2016 · checked 2026-09-30
7. cafl-r7-04 · observational study
   The affected population consumed flour made from short-soaked (one day) cassava roots and thus had high dietary cyanide exposure (urinary thiocyanate in 31 children = 757 mumol/l) compared with the unaffected population (urinary thiocyanate in 46 children = 50 mumol/l) that ate cassava that had been soaked for three days before consumption.
   Lancet, 1992 · checked 2026-09-30
8. cafl-r7-05 · modeling study
   Recently, a wetting method has been proved to be an effective intervention in reducing levels of cyanogens in cassava flour in DRC. For example, significant reductions of cyanide content were observed in different villages in Boko of DRC: the mean cyanide content in cassava flour reduced from 19–41 to 8–12 mg HCN eq/kg during an intervention program, and most of the samples were below the WHO safe limit of 10 mg/kg [26,30,31].
   PLOS Glob Public Health, 2024 · checked 2026-09-30
9. cafl-r7-14 · food chemistry experiment
   Most importantly, the experimental outcomes revealed that, the treatments were able to suppress the flour’s HCN levels within the recommended threshold of 10 mg/kg DW (1 mg/100 g DW) by FAO/WHO, basically for cassava and its derived products, which is considered safe for human consumption (56).
   Front Nutr, 2025 · checked 2026-09-30
10. cafl-r7-09 · controlled feeding study
    In vivo, plaque pH decreased significantly after the consumption of the sweet (p < 0.05), increased after the fish (p < 0.05), but did not change after intake of the flours (p > 0.05).
    Caries Res, 2002 · checked 2026-09-30
11. cafl-r7-03 · cross-sectional study
    The mean (SD) and median (IQR) of cyanogen content of cassava household flour were above the WHO cut-off points of 10 ppm (52.18 [32·79]) and 50 (30-50) ppm, respectively.
    PLoS One, 2018 · checked 2026-09-30
12. cafl-r7-06 · modeling study
    The estimated average CAC decrement was 3.12 points in children population. The median estimate of CAC decrement was 2.37 points at the median and increased to 8.02 points at 95th percentile.
    PLOS Glob Public Health, 2024 · checked 2026-09-30
13. cafl-r7-08 · cross-sectional study
    We found that daily cassava flour intake did not significantly raise the risk of iodine deficiency (ID) (odds ratio [OR] = 1.43 [confidence interval (CI) 0.72-2.82]; p = 0.29)
    Biol Trace Elem Res, 2021 · checked 2026-09-30
14. cafl-r7-15 · clinical pharmacology study
    Analysis of the results demonstrated a better glycaemic response with meals A and C compared with meal B.
    Eur J Drug Metab Pharmacokinet, 2008 · checked 2026-09-30
15. cafl-r7-13 · cross-sectional study
    Furthermore, comparing 10 years after additional cassava flour folate fortification, the rate ratio increased to 1.4 (95% CI 1.34-1.45; p < 0.01).
    Childs Nerv Syst, 2023 · checked 2026-09-30