Iron from plants: what helps, what gets in the way

Animal foods carry mostly haem iron. Plants carry non-haem iron, which the body takes up less readily.¹ Dietary reference values assume that about 14–18 % of the iron in a mixed diet is absorbed and 5–12 % in a vegetarian diet, for people with no iron stores.² Your own iron status has a greater effect on uptake than the make-up of the meal.²

The EU’s scientific reference intake for adults is 11 mg of iron a day for men and for women after the menopause, and 16 mg for women before it.³

Peppers, citrus fruit, broccoli and strawberries are good sources of vitamin C, which helps the body take up non-haem iron. EFSA has assessed this and concluded that a cause-and-effect relationship has been established.⁴

How much does it help? In short-term trials, adding vitamin C to a test meal raised iron absorption by about six percentage points on average.⁵ Across a whole diet the effect is far less pronounced than in single meals.⁶ So treat it as a useful habit, not a trick.

Beta-carotene, which gives carrots, pumpkin and sweet potato their colour, has been studied too. One trial in 100 adults found higher iron absorption from cereal-based meals with beta-carotene,⁷ while a later review calls the role of carotenoids unresolved.²

Garlic and onion are often named too. In a laboratory digestion model, adding them raised the share of iron that dissolves from cereals and pulses by roughly 9–73 %.¹³ That is a test-tube result, not a trial in people.

In the kitchen that means: lemon over the finished dish, a raw pepper salad on the side, parsley at the end.

The polyphenol effect is large. In one trial with a bread meal, black tea cut iron absorption by 79–94 %, peppermint tea by 84 % and camomile tea by 47 %; cocoa and coffee inhibited it too.¹¹ If iron is on your mind, keep tea and coffee apart from the meal rather than with it.

Soaking and sprouting lower phytate. In a laboratory study on sorghum, soaking cut it by 24–32 % and sprouting by 25–35 %.¹² Legumes and whole grains stay on the plate all the same: research has generally supported eating more of them.⁸

The usual suspects: legumes (lentils, beans, chickpeas, peas), whole grains, quinoa and amaranth, leafy greens such as spinach and kale, and seeds such as sesame, pumpkin and hemp. The amount per portion varies a lot, and a list of foods is not a ranking.

In a 1986 study, twenty foods were cooked in iron and in non-iron pans. Ninety per cent of them contained significantly more iron when cooked in iron, and acidity, moisture and cooking time made a difference,⁹ which points to long-simmered, acidic dishes such as tomato sauces.

Whether that changes anyone’s iron status is less clear: a systematic review found three trials, mostly in developing countries, with some evidence of higher haemoglobin in people who were iron deficient.¹⁰

Tiredness has many causes, and low iron is found with a blood test, not with a menu. These groups are at higher risk of low iron: pregnant women, growing children, people with heavy periods, people who eat no meat and people with some gut conditions.¹

If you think your iron may be low, talk to a doctor before you take supplements: the body has no way to excrete extra iron.²