Plant-Based Mineral Absorption: Phytates, Oxalates, Soaking, Sprouting and Fermenting
What phytates and oxalates do to zinc, iron and calcium absorption from plant foods, and what studies found about soaking, sprouting, fermenting and boiling, with no universal rules.
Content last updated . This page has not been medically reviewed.
Phytates and oxalates are natural compounds in plants that can bind minerals in the gut, so the body absorbs less of the zinc, iron and calcium in those foods. Soaking, sprouting, fermenting and boiling can lower these compounds in laboratory and household studies. But the sources we read also say that in a varied diet these interactions probably have little or no nutritional consequence for many people. There is no universal rule, and the foods that contain phytates are also good sources of minerals.
What the terms mean
- Phytate (phytic acid) is the storage form of phosphorus in plants. It binds minerals such as zinc in the intestine and forms an insoluble complex that limits absorption. [1] It is the major storage form of phosphorus in cereals, legumes, oil seeds and nuts, and humans lack the enzyme phytase to break it down. [2]
- Oxalic acid (oxalate) can bind calcium into indigestible salts. Foods high in it include spinach, collard greens, sweet potatoes, rhubarb and beans. [3]
What research and official sources found
| Question | What the source found | Label |
|---|---|---|
| Zinc from plant-heavy diets | Absorbed zinc ranges from 5% to more than 50% of intake, depending on how much plant food (phytate) the diet contains. [1] | Established nutritional role |
| Calcium from spinach vs milk | Absorption was only 5% for spinach and 27% for milk. Broccoli, kale and cabbage, which lack these compounds, are similar to milk per unit absorbed, though they supply less calcium per serving. [3] | Established nutritional role |
| Iron | Iron bioavailability is about 14% to 18% from mixed diets with meat, seafood and vitamin C, and 5% to 12% from vegetarian diets. [4] Phytate and certain polyphenols in cereals and legumes lower nonheme iron absorption. [4] | Established nutritional role |
| Mixed meals | When people eat many different foods, the oxalic and phytic acid interactions probably have little or no nutritional consequence. [3] | Established nutritional role |
| Phytate in infant-type plant foods | Unrefined cereals and legumes were highest at about 600 mg per 100 g dry weight, refined cereals about 100, and roots and tubers under 20. [5] | Preclinical (food analysis) |
| Removing phytate in people | Adults fed cereals with phytate removed absorbed more iron, zinc and calcium than from cereals with native phytate. [6] | Review of absorption studies |
Soaking, sprouting and fermenting
The reviews list germination, fermentation and soaking among ways to reduce phytate in unrefined cereal porridges for young children. [6] A review of grain processing names fermentation, soaking, germination and treatment with phytase enzyme. [2]
- Soaking. ODS says vegetarians and vegans might use soaking beans, grains and seeds in water for several hours before cooking to reduce zinc binding. [1] In a cowpea study, long soaking (16 hours) in bicarbonate solution caused a remarkable reduction in antinutritional factors. [7]
- Fermenting. ODS says organic acids in fermented foods might increase zinc absorption. [1] In a laboratory maize study, spontaneous fermentation cut phytate by 51.8% and lactic acid fermentation of soaked, germinated grain by up to 85.6%. The authors estimated improved iron and zinc bioavailability from molar ratios; they did not measure absorption in people. [8]
- Limits. A review of complementary foods in low-income countries said removing phytate alone is probably not enough to close the shortfall in iron, zinc and calcium in those foods; enrichment with animal-source foods or mineral fortification is also needed. [5]
Proper evidence not found in the sources we read for a household soaking time, sprouting length or fermentation method that reliably increases mineral absorption in healthy adults eating a mixed diet. We searched PubMed for soaking, germination and fermentation with phytate and mineral bioavailability, and read the NIH ODS fact sheets for zinc, iron and calcium.
Boiling and oxalate
In nine vegetables analyzed for oxalate, boiling reduced soluble oxalate by 30% to 87%, more than steaming (5% to 53%), and the cooking water held about all the oxalate lost. [9] The authors suggested this may help people prone to kidney stones, since about 75% of kidney stones are mainly calcium oxalate. [9] That is a laboratory finding about vegetable oxalate, not a trial of stone prevention. People with stones should ask their clinician or dietitian; see calcium, heart disease and kidney stones.
Frequently asked questions
Do phytates make plant foods useless as mineral sources?
No. They lower absorption of some minerals, such as zinc, but beans, nuts and whole grains still contain zinc, and ODS says interactions with oxalic or phytic acid probably have little or no consequence when many foods are eaten. [1][3]
Does soaking beans increase mineral absorption?
ODS says soaking beans, grains and seeds for several hours may reduce zinc binding. We did not find a trial giving a household soaking time that reliably raises absorption in healthy adults. [1]
Is spinach a good calcium source?
It contains calcium, but absorption was only 5% versus 27% for milk because of oxalic acid. Broccoli, kale and cabbage are absorbed about as well as milk. [3]
Does boiling vegetables lower oxalate?
In one study of nine vegetables, boiling lowered soluble oxalate 30% to 87%, with the oxalate ending up in the water. [9]
Should vegetarians take extra zinc or iron?
That is a clinician's decision. ODS says vegetarian diets give lower iron bioavailability (5% to 12%) and lower zinc intakes, but supplements carry upper limits and interactions. [4][1]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
How to read the evidence labels
Labels used on this page: established nutritional role (documented in NIH ODS fact sheets), preclinical (measured in food samples or laboratory processing, not in people) and insufficient evidence (not found in what we read).
Who it matters for, and cautions
- Vegetarians and vegans usually have lower zinc intakes and serum zinc than nonvegetarians, ODS says, and may have lower selenium intakes. [1][10] See iron for vegetarians and vegans, dairy-free calcium and vegetarian and vegan supplements.
- Beans, nuts and whole grains still supply zinc, though less bioavailable than from animal foods. [1] Do not drop them from fear of phytate without advice.
- Infants and young children. Complementary-food research is about plant-based foods in low-income countries; ask a clinician about your child's diet.
- Pregnancy, kidney or liver disease, and medicines. Ask a clinician or pharmacist before changing diet or adding supplements; see medication interactions.
- Do not diagnose a deficiency from symptoms. Low iron is a clinician-led diagnosis; see anemia and iron deficiency. For how minerals compete, see mineral interactions and absorption.
References
- NIH Office of Dietary Supplements, Zinc Fact Sheet for Health Professionals. Read 2026-10-22 as an Internet Archive copy dated 2026-01-01 because the live ODS page blocked automated download.
- Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains (2015). PubMed abstract. Read 2026-10-22.
- NIH Office of Dietary Supplements, Calcium Fact Sheet for Health Professionals. Read 2026-10-22 as an Internet Archive copy dated 2026-01-01 because the live ODS page blocked automated download.
- NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals. Read 2026-10-22 as an Internet Archive copy dated 2026-01-02 because the live ODS page blocked automated download.
- A review of phytate, iron, zinc, and calcium concentrations in plant-based complementary foods used in low-income countries (2010). PubMed abstract. Read 2026-10-22.
- Improving the bioavailability of nutrients in plant foods at the household level (2006). PubMed abstract. Read 2026-10-22.
- Effect of soaking, germination, cooking and fermentation on antinutritional factors in cowpeas (2002). PubMed abstract. Read 2026-10-22.
- Enhancing iron and zinc bioavailability in maize through phytate reduction (2024). PubMed abstract. Read 2026-10-22.
- Effect of different cooking methods on vegetable oxalate content (2005). PubMed abstract. Read 2026-10-22.
- NIH Office of Dietary Supplements, Selenium Fact Sheet for Health Professionals. Read 2026-10-22 as an Internet Archive copy dated 2025-12-30 because the live ODS page blocked automated download.