Why iron may not be absorbed — and why food is the place to start
Iron is an essential mineral: your body needs it to make haemoglobin, the protein that carries oxygen in your blood. Low iron is one of the most common nutrition problems worldwide, especially for women of reproductive age, children and people with chronic health conditions. Oral iron supplements are a common option, but they don’t always work as well as hoped because absorption is poor. Iron from food can be poorly absorbed too. The main reasons are low stomach acid, missing “helper” nutrients, a diet high in processed food and changes in the gut microbiome.
That’s why it makes sense to look at your diet and gut health alongside any supplements.
Low stomach acid
Non-haem iron (Fe³⁺), the form found in plant foods and some supplements, needs an acidic stomach to be converted into the more absorbable form (Fe²⁺). This happens in the stomach and the upper part of the small intestine, where iron is taken up by special transport proteins. When stomach acid is low — because of conditions such as atrophic gastritis, or medicines such as proton pump inhibitors (PPIs), H2 blockers or antacids — iron absorption can drop by up to 50%. PPIs, often used for reflux, noticeably reduce stomach acid, which makes it harder for iron to dissolve and be absorbed.
Missing helpers
Some nutrients help iron get into your cells. The best studied is vitamin C. It converts Fe³⁺ into Fe²⁺ and binds with iron in a way that makes it easier to absorb. So it’s worth adding a squeeze of lemon, an orange or a handful of spinach to iron-rich meals.
Another helper:
Beta-carotene: improves how much iron you absorb, especially from plant foods. Carrots, pumpkin and sweet potato can increase iron absorption several times over.
Processed food
What you eat plays a key role. Processed foods often contain fewer of the nutrients iron needs and more of the compounds that block it, such as:
Phytates: found in whole grains, legumes, nuts and seeds. Phytic acid binds iron into compounds your body can’t absorb. Soaking, fermenting, long cooking and sprouting cut phytates significantly.
Polyphenols: tannins in tea, coffee, cocoa and some fruit are strong blockers. Black tea can reduce iron absorption by 79–94%, coffee by 39% and cocoa — including chocolate — by 71%.
Calcium: a high calcium intake, especially from dairy, gets in the way of iron. So it’s best not to have iron-rich foods or iron supplements together with dairy.
Soy: soy proteins form compounds with iron that are hard to absorb. Tempeh is the exception, because it’s fermented.
Processed foods such as refined oils, ultra-processed cereals and ready meals tend to contain less vitamin C and other helpers, and more blockers — not a great combination for iron.
Changes in the gut microbiome
Some gut bacteria, such as bifidobacteria, can convert non-haem iron into a more absorbable form.
Prebiotic fibres such as fructo-oligosaccharides, inulin and pectin (in bananas, cabbage, onion, garlic, beetroot, apples and chicory) feed beneficial bacteria and help you absorb more iron.
Fermented foods such as sauerkraut, kimchi, coconut yoghurt and kombucha also improve iron absorption, even when phytates are present.
On the other hand, an imbalanced microbiome — for example, more unfriendly bacteria — can reduce iron absorption and cause gut inflammation. Iron supplements themselves can shift the balance of gut bacteria. Prebiotics and probiotics from food are a great way to add balance.
Other factors that affect iron absorption:
Gut health: conditions such as coeliac disease, Crohn’s disease and ulcerative colitis inflame the gut lining and reduce iron absorption.
Alcohol: drinking alcohol can reduce how much iron your body absorbs.
And remember: good digestion starts with managing stress and relaxing your diaphragm. Without this, tension and sluggish digestion and bile flow will keep slowing things down.
Want a plan that fits your body and your routine? Book a session →
General information only, not medical advice. If you have a health condition or low iron, please talk to your GP.
That’s why it makes sense to look at your diet and gut health alongside any supplements.
Low stomach acid
Non-haem iron (Fe³⁺), the form found in plant foods and some supplements, needs an acidic stomach to be converted into the more absorbable form (Fe²⁺). This happens in the stomach and the upper part of the small intestine, where iron is taken up by special transport proteins. When stomach acid is low — because of conditions such as atrophic gastritis, or medicines such as proton pump inhibitors (PPIs), H2 blockers or antacids — iron absorption can drop by up to 50%. PPIs, often used for reflux, noticeably reduce stomach acid, which makes it harder for iron to dissolve and be absorbed.
Missing helpers
Some nutrients help iron get into your cells. The best studied is vitamin C. It converts Fe³⁺ into Fe²⁺ and binds with iron in a way that makes it easier to absorb. So it’s worth adding a squeeze of lemon, an orange or a handful of spinach to iron-rich meals.
Another helper:
Beta-carotene: improves how much iron you absorb, especially from plant foods. Carrots, pumpkin and sweet potato can increase iron absorption several times over.
Processed food
What you eat plays a key role. Processed foods often contain fewer of the nutrients iron needs and more of the compounds that block it, such as:
Phytates: found in whole grains, legumes, nuts and seeds. Phytic acid binds iron into compounds your body can’t absorb. Soaking, fermenting, long cooking and sprouting cut phytates significantly.
Polyphenols: tannins in tea, coffee, cocoa and some fruit are strong blockers. Black tea can reduce iron absorption by 79–94%, coffee by 39% and cocoa — including chocolate — by 71%.
Calcium: a high calcium intake, especially from dairy, gets in the way of iron. So it’s best not to have iron-rich foods or iron supplements together with dairy.
Soy: soy proteins form compounds with iron that are hard to absorb. Tempeh is the exception, because it’s fermented.
Processed foods such as refined oils, ultra-processed cereals and ready meals tend to contain less vitamin C and other helpers, and more blockers — not a great combination for iron.
Changes in the gut microbiome
Some gut bacteria, such as bifidobacteria, can convert non-haem iron into a more absorbable form.
Prebiotic fibres such as fructo-oligosaccharides, inulin and pectin (in bananas, cabbage, onion, garlic, beetroot, apples and chicory) feed beneficial bacteria and help you absorb more iron.
Fermented foods such as sauerkraut, kimchi, coconut yoghurt and kombucha also improve iron absorption, even when phytates are present.
On the other hand, an imbalanced microbiome — for example, more unfriendly bacteria — can reduce iron absorption and cause gut inflammation. Iron supplements themselves can shift the balance of gut bacteria. Prebiotics and probiotics from food are a great way to add balance.
Other factors that affect iron absorption:
Gut health: conditions such as coeliac disease, Crohn’s disease and ulcerative colitis inflame the gut lining and reduce iron absorption.
Alcohol: drinking alcohol can reduce how much iron your body absorbs.
And remember: good digestion starts with managing stress and relaxing your diaphragm. Without this, tension and sluggish digestion and bile flow will keep slowing things down.
Want a plan that fits your body and your routine? Book a session →
General information only, not medical advice. If you have a health condition or low iron, please talk to your GP.
