Haem iron versus non-haem iron
Iron in food comes in two forms, and your body treats them differently.
• Haem iron is found in animal foods, especially meat, poultry and seafood. Your body absorbs it more efficiently, and other foods in the meal affect it less.
• Non-haem iron is found in plant foods, fortified foods and some animal foods. It matters most for athletes who eat little or no meat, and how well you absorb it depends more on what else is on your plate.
This does not mean plant iron is second best, and you do not need to eat meat to meet your needs. It simply means that what you pair your food with can make a real difference.
What happens to iron after you eat it?
Iron does not travel straight from your plate to your muscles. It has to be absorbed in your gut, enter your bloodstream and be delivered to the tissues that need it.
Non-haem iron first has to be converted into a form that is easier to absorb at the surface of your small intestine. A transporter called DMT1 then helps move it into the intestinal cells. Haem iron takes a different route, and scientists have not yet fully mapped how it is absorbed in humans. Either way, the iron ends up in the body ' s cellular iron pool. It can then leave the intestinal cells through a protein called ferroportin and travel in your blood, mostly attached to a protein called transferrin. Transferrin delivers it to your tissues, including your bone marrow, where red blood cells are made.
One of the key regulators here is hepcidin, a hormone made in your liver. It controls ferroportin, which means it influences how much iron moves into your circulation from your gut and from your iron stores. After hard training, hepcidin can rise for a while, and that may reduce how much iron you absorb or release. How big that effect is depends on when you trained, your iron status and other factors, so there is no single meal timing rule that suits every athlete.
Why does iron matter for performance?
Iron does several important jobs, and every one of them counts when you train.
• Oxygen transport: iron is part of haemoglobin, the protein in your red blood cells that carries oxygen from your lungs to your tissues.
• Muscle function: iron is part of myoglobin, which helps store oxygen and make it available inside your muscle.
• Energy production: iron is involved in the enzymes and processes in your mitochondria, where your cells make energy.
• Recovery and general wellbeing: enough iron supports normal body function, including the production of red blood cells.
If you are a runner, cyclist, swimmer or other endurance athlete, this is especially relevant. You might notice unusual fatigue, breathlessness during exercise, reduced endurance, trouble holding your usual pace or a dip in the quality of your training. These signs are not proof of iron deficiency. Poor sleep, not eating enough, illness, too much training load and other medical conditions can cause very similar problems.
Which athletes need to pay extra attention?
Iron deficiency can affect anyone, but some athletes are more vulnerable than others.
• Endurance athletes: high training volumes, eating less than your energy demands and iron losses through training can all add up. Menstruating athletes: blood loss during your period raises your iron needs, particularly when your periods are heavy.
• Vegetarian and vegan athletes: a plant diet can give you plenty of iron, but it is mostly non-haem iron, so your food choices and meal combinations deserve some thought.
• Athletes with low energy availability: if you eat too little to support your training and normal body functions, it becomes very hard to meet your iron needs.
• Adolescents: growth raises nutritional demands, and young athletes are often training hard too.
• Athletes training at altitude: your iron needs can rise as your body adapts and makes more red blood cells.
This is not a reason to assume every endurance athlete needs an iron supplement. It is a reason to pay attention to what you eat, how you feel and, when there is a clinical reason, to test.
How can you improve iron absorption through food?
You do not need to overhaul your whole diet. A few practical changes can help you get more from the iron already on your plate.
Pair non-haem iron with vitamin C. Vitamin C helps keep iron in a form that dissolves more easily and supports its conversion into a form your body can absorb. Some easy combinations:
• Lentils with tomato and peppers
• Chickpeas with lemon juice
• Fortified cereal with kiwi or berries
• Tofu with broccoli
• Beans in a tomato sauce
You do not need a vitamin C supplement for this. Everyday foods will do the job.
Be mindful of tea and coffee around your iron-rich meals. The polyphenols in tea and coffee can reduce how much non-haem iron you absorb when you have them with a meal. If your iron stores are low, try having your tea or coffee between meals rather than alongside your main iron meal.
NUTRITION
Calcium can affect iron absorption in some meals, but we do not yet know much about its effect on iron status over time, so there is no need to cut out dairy.
Spinach and other leafy greens do contribute iron, but how much you absorb depends on the food itself and on other compounds in the meal. They are a useful addition, but not necessarily the best strategy on their own for correcting low iron stores.
Should athletes take iron supplements?
Not automatically. A supplement can be the right call when deficiency has been confirmed and a healthcare professional recommends treatment. But taking iron you do not need will not necessarily improve your performance, and it can cause nausea, constipation and stomach discomfort. Too much iron can also be harmful.
If you have ongoing fatigue, a noticeable drop in performance, unexplained breathlessness or any other concern, speak to a healthcare professional. Depending on your situation, they may recommend:
• A full blood count to assess haemoglobin and other blood cell measures
• Serum ferritin to assess your iron stores
• Transferrin saturation and other iron studies when needed
• Inflammatory markers or further tests if the results need more interpretation
Ferritin is an important marker, but it can rise with inflammation or illness, so your results need to be read in context and not as one number on its own. Please do not diagnose yourself with iron deficiency because you are tired, and do not start large doses of iron just because you are training hard.
The takeaway
Iron is essential for oxygen transport, muscle function and energy metabolism. Both haem and non-haem iron count towards your needs, and you can get iron from a varied diet that includes animal foods, plant foods or both.
The practical approach is simple. Eat enough to support your training, include iron-rich foods regularly, pair plant sources with vitamin C where you can and pay attention to ongoing symptoms or unexplained changes in performance.
You do not need to fear food or eat a perfect diet. You need to understand what your body is asking for, make informed choices and investigate when there is a good reason to.
Push past your possible.
When your iron stores run low, your body may struggle to keep up with demand. If deficiency progresses to anaemia, the ability of your blood to carry oxygen can drop. But iron deficiency can affect some aspects of exercise capacity even before anaemia develops. |
Phytates, found in wholegrains, legumes and seeds, can also reduce absorption. That does not mean you should avoid these nutritious foods. Soaking, fermenting and cooking all change phytate levels, and your overall diet matters more than any single ingredient. |
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