Tannins
What it is and what it does
- Tannins are phenolic compounds with molecular weights above 500 daltons. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- There are two groups: hydrolysable tannins (such as gallotannins and ellagitannins) and condensed tannins (proanthocyanidins). (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Tannins can bind and precipitate proteins. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- When eaten, tannins form complexes with proteins, which inactivates many digestive enzymes and lowers protein digestibility. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Tannin interferes with iron absorption (ICMR-NIN notes this for tea and coffee). (ICMR-NIN. Dietary Guidelines for Indians 2024)
Why it matters
- The poorer iron availability seen in brown finger millet varieties has been attributed to their higher tannin content. (Abioye VF, Babarinde GO, Ogunlakin GO, Adejuyitan JA, Olatunde SJ, Abioye AO (2022). Varietal and processing influence on nutritional and phytochemical properties of finger millet: A review. Heliyon 8(12):e12310 (peer-reviewed review; PMC9800331; open access) (DOI 10.1016/j.heliyon.2022.e12310))
- When present in large amounts, tannins can affect the colour, flavour, nutrient digestibility, mineral absorption and quality of finger millet foods. (Abioye VF, Babarinde GO, Ogunlakin GO, Adejuyitan JA, Olatunde SJ, Abioye AO (2022). Varietal and processing influence on nutritional and phytochemical properties of finger millet: A review. Heliyon 8(12):e12310 (peer-reviewed review; PMC9800331; open access) (DOI 10.1016/j.heliyon.2022.e12310))
General information, not medical advice — for your own needs, ask a doctor or dietitian.
How much is needed
| Who | Amount | What the figure is | Whose figure |
|---|---|---|---|
| India, all groups | no value set | No ICMR-NIN 2020 value | ICMR-NIN 2020 |
Sources: ICMR-NIN Expert Group. Short Report of Nutrient Requirements for Indians: Recommended Dietary Allowances and Estimated Average Requirements - 2020
Absorption and food
- ICMR-NIN advises avoiding tea and coffee for at least one hour before and after meals, because their tannin interferes with iron absorption. (ICMR-NIN. Dietary Guidelines for Indians 2024)
- Tannin content falls when soluble tannin leaches out during soaking and germination. (Abioye VF, Babarinde GO, Ogunlakin GO, Adejuyitan JA, Olatunde SJ, Abioye AO (2022). Varietal and processing influence on nutritional and phytochemical properties of finger millet: A review. Heliyon 8(12):e12310 (peer-reviewed review; PMC9800331; open access) (DOI 10.1016/j.heliyon.2022.e12310))
- In one study, pressure-cooking lowered the tannin content of black gram (urad) and improved its protein digestibility. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Milling removes the bran, and with it tannins and phytic acid. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Lactic acid fermentation may lower tannin levels and so increase iron absorption, except in some high-tannin cereals. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Tannins are concentrated in beverages, pomegranate, berries and cocoa beans, and are also found in cereals such as sorghum and barley. (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- Peanuts and millets contain condensed tannins (proanthocyanidins). (Samtiya M, Aluko RE, Dhewa T (2020). Plant food anti-nutritional factors and their reduction strategies: an overview. Food Production, Processing and Nutrition 2:6 (peer-reviewed review; open access, CC BY 4.0) (DOI 10.1186/s43014-020-0020-5))
- White-grained finger millet varieties have less tannin (about 0.05%) than brown and dark varieties. (Abioye VF, Babarinde GO, Ogunlakin GO, Adejuyitan JA, Olatunde SJ, Abioye AO (2022). Varietal and processing influence on nutritional and phytochemical properties of finger millet: A review. Heliyon 8(12):e12310 (peer-reviewed review; PMC9800331; open access) (DOI 10.1016/j.heliyon.2022.e12310))