Have you ever wondered why two people following the same dietary advice have completely different results?

Take Rina and Mitu, for example. Both have a low haemoglobin level, and both have started eating more iron-rich foods, just as their doctors advised. Slowly, Rina’s condition is improving but Mitu’s haemoglobin levels barely change. She is trying just as hard as Mitu, so what could be going wrong? Is the problem with her food? The answer may lie in the mechanism behind iron absorption in our bodies. Sometimes getting enough iron from food is not the whole story. And our bodies need to be able to take it in and use it.

Iron in our diet comes in two main forms: haem iron and non-haem iron. Haem iron is found in animal foods such as beef, liver, fish and chicken, while non-haem iron is found mainly in plant foods, including masoor dal, chhola, beans and leafy vegetables such as lal shak, palong shak and kolmi shak. Our bodies generally absorb haem iron more efficiently than non-haem iron. As a broad estimate, around 15–35% of haem iron may be absorbed, compared with approximately 2–20% of non-haem iron. These figures vary depending on a person’s iron status, the foods eaten together and other dietary factors. This does not mean that plant-based foods are poor sources of iron. Rather, the iron they contain is more sensitive to other substances present in our regular meals.

For our bodies to absorb non-haem iron effectively, it needs to remain in a form that can be taken up by the intestine. Certain dietary components can help this process, while others can interfere with it.

A simple way to improve non-haem iron absorption is to combine plant-based sources of iron with foods rich in vitamin C. Vitamin C keeps iron in solution and helps the body to absorb it more readily. To make better use of the iron in plant foods, squeeze lemon over dal or shak, eat guava or amla after a meal or include tomatoes and green chillies in vegetable dishes.

Tea and coffee are almost a non-negotiable part of our lives on a daily basis. A cup of coffee after breakfast or tea with evening snacks. But both contain natural compounds called polyphenols, which can bind iron in the digestive tract and reduce its absorption, especially when taken with meals. If you are concerned about iron deficiency, consider drinking tea or coffee between meals rather than alongside your breakfast or dinner. Leaving an interval of around one to two hours is a reasonable approach.

Food preparation can also make a difference. Soaking, germinating and fermenting grains and legumes can reduce phytates, naturally occurring compounds that limit iron absorption. For example, soaking chola before cooking, allowing mung beans to sprout, or fermenting rice and lentil batter to prepare traditional foods such as dosa or chitoi pitha can help reduce phytate levels. Similar principles can be applied to preparing pulses and other plant-based foods commonly eaten in Bangladesh.

However, low haemoglobin doesn’t necessarily mean a person is eating too little iron or absorbing it poorly. Low haemoglobin can also be caused by other nutritional deficiencies, bleeding and some medical conditions. If you continue to have low levels of haemoglobin after making these dietary changes, you should see a healthcare professional to find out why.

Ultimately, good nutrition is not just about the amount of a nutrient listed on a food label. It is also about how much of that nutrient our bodies can absorb and utilise. Scientists call this bioavailability, and understanding it helps us make more informed food choices. Sometimes improving nutrition does not require changing our entire diet. It can start with learning the science behind the food already on our plates.