Iron-Rich Foods: What to Find in Them and How to Supplement Them Properly

You can find iron-rich foods among animal and plant sources. These include liver, beef, legumes, seeds, or oats. However, the amount of iron your body actually utilizes is not determined solely by the number in the table. It also depends on its form and what you eat it with.

Key findings:

• The highest iron content is found in liver, duck and sesame seeds, beef, legumes, and oats. For a regular diet, however, the amount in a typical serving is more important than the value per 100 g.
• Heme iron from meat and fish is absorbed better than non-heme iron from plant foods. The absorption of non-heme iron is improved by vitamin C, while coffee and tea can reduce it.
• Ferritin indicates iron stores, not just "iron in the blood." Therefore, during prolonged fatigue, it is wiser to first get a blood test rather than supplement blindly.
• When supplementing, the form, dosage, and tolerability matter. Hemoglobin improves within weeks, replenishing stores takes months, and a higher dosage does not speed up the process.

Fatigue doesn't have to be just from overexertion

Stairs that you used to climb without thinking suddenly require a break. In the afternoon, you struggle to concentrate and even after a decent nap, you don't feel rested. Such periods are familiar to almost everyone. Sometimes they are caused by ordinary overexertion, but at other times, something like iron deficiency can be one of the reasons.

The first advice is usually simple: have a steak, spinach, or just reach for a nutritional supplement. However, with iron, it pays to consider what and why you are supplementing. Its deficiency can make a person's ordinary day unpleasant, but an excess is also not beneficial. So let's go through which foods contain iron, how to facilitate its absorption, and when a regular diet may not be enough for its supplementation.

🩸 What does iron do in our body and why might we be lacking it?

Iron is part of hemoglobin, a protein in red blood cells that carries oxygen. You can also find it in myoglobin, a protein that stores oxygen in muscles, and in enzymes that help the body obtain energy from food. When it decreases, it can manifest during an ordinary day just as much as during sports (1, 2).

Iron deficiency and anemia are not the same. Anemia, medically known as anemia, means that the blood contains too little hemoglobin, and therefore struggles to distribute oxygen. Our body helps itself from stores for a certain period, so hemoglobin can remain normal even when iron is decreasing.

Anemia can develop later, when there is not enough for the necessary production of hemoglobin. That is why a normal blood count (basic blood test) may not reveal low stores (3).

The cause may not only lie on the plate. Iron may be lacking due to blood losses, poor absorption, or increased demands on the body. Attention should be paid especially to:

• heavy menstruation,
• pregnancy,
• regular blood donation,
• certain digestive diseases,
• long-term restricted diet (1, 4).

When a deficiency is detected, the doctor also looks for its cause (3).

How much iron do we need daily?

The European Food Safety Authority (EFSA) provides these recommendations for daily intake. This is known as the population reference intake, meaning the amount that covers the needs of most healthy people (5):

Group	Recommended daily iron intake
Adult men	11 mg
Women after menopause	11 mg
Women before menopause	16 mg

This refers to the total iron intake from food, not a recommendation to swallow the same strong tablet every day (5).

🥩 What is iron and why is it not absorbed equally?

In foods, you encounter two forms of iron:

• Heme iron is found in meat, fish, and seafood. It is usually absorbed better, and the composition of the surrounding meal affects it less (1).
• Non-heme iron is found in plant foods; it is also present in animal sources. Its utilization significantly depends on what you eat it with (1).

Two meals with the same iron content may not provide the same usable amount to the body.

TIP: A serving of lentils with vegetables containing vitamin C may be more useful for iron supplementation than the same serving washed down with strong tea (1).

Iron-rich foods – table of values and portions

Which foods contain the most iron and how much a typical serving brings, is shown in the table below. The values come from the Czech food composition database. Portions are practical examples, not prescribed doses. For liver, the weight refers to raw material before preparation, for lentils and beef cuts to cooked meals (6).

Food and state	Iron per 100 g	Example portion	Iron in portion
Pork liver, raw	15.3 mg	100 g before preparation	15.3 mg
Duck seeds, dried	15.0 mg	20 g	3.0 mg
Sesame seeds	9.9 mg	10 g	1.0 mg
Beef liver, raw	8.4 mg	100 g before preparation	8.4 mg
Chicken liver, raw	6.7 mg	100 g before preparation	6.7 mg
Cooked beef cut	4.9 mg	120 g	5.9 mg
Oats, dry	4.4 mg	60 g	2.6 mg
Lentils, cooked in unsalted water	2.3 mg	180 g	4.1 mg
Tofu	1.9 mg	150 g	2.9 mg

Note: Indicative database values; specific food may vary by variety, production, and preparation. Portion calculations are rounded. The table shows the ingested, not absorbed iron. Liver is consumed cooked and is not suitable during pregnancy (6, 7).

Notice the amount of iron in sesame. At 100 grams, it looks excellent, but a spoonful on bread brings about a milligram. On the other hand, a typical serving of lentils can provide around four. For a regular diet, it is therefore more useful to monitor the portion than to look for a single winner in the table (6).

Similarly, do not compare dry legumes with cooked ones. When cooked, they absorb water, so the iron content per 100 grams decreases even with just a slight dilution. One hundred grams of dry lentils and one hundred grams of cooked lentils are two very different portions of the original raw material.

WARNING: Liver can be part of a varied diet, but due to its high vitamin A content, do not make it a daily solution. During pregnancy, liver and products made from it are avoided (7, 8).

🥗 How to supplement iron naturally?

You don't have to look for iron in one special dish. It is much more practical to spread its sources throughout the day and mix them during the week. And if you have never liked liver, you don't have to force yourself to eat it just because of the high number in the table.

Practically, it can look like this:

• Breakfast: 60 g of oats and 20 g of duck seeds, along with kiwi or strawberries. Mix everything into 150g of Greek yogurt. The oats with seeds provide approximately 5.6 mg of iron before accounting for the other ingredients (6).
• Lunch: 180 g of cooked lentils with a side dish of your choice and a salad of fresh peppers.
• Dinner: 150 g of tofu with vegetables and rice, or a portion of beef with potatoes and vegetable salad.

What helps absorption and what hinders it:

• Vitamin C increases the absorption of non-heme iron. Therefore, for plant meals, it makes sense to add fresh peppers, citrus fruits, kiwi, or another source of it (1).
• Coffee and tea can reduce iron absorption; if you are addressing low stores, it is better to have them between meals (1).
• Legumes and whole grain foods do not eliminate absorption due to their content of substances that reduce absorption. They still provide iron and other valuable nutrients (1).

WARNING: In confirmed anemia, simply changing the diet often isn't enough. It is an important part of the solution, but treatment must correspond to the size of the deficit and its cause (3).

🔍 How to recognize iron deficiency and what do blood tests say?

Fatigue, weakness, paleness, shortness of breath during usual exertion, or heart palpitations can raise suspicion. Changes in nails, hair loss, or unusual cravings for ice can also occur. However, none of these symptoms alone proves a deficiency (4).

When fatigue persists, it is wiser to get a blood test rather than purchase supplements blindly. For orientation, the following are used:

• Blood count and hemoglobin: help reveal anemia (3).
• Ferritin: indicates the state of iron stores (3).
• Transferrin saturation: adds information about the availability of iron for the body (3).
• CRP and other tests as needed: help interpret results, for example, in inflammation (3).

In otherwise healthy adults, ferritin below 15 µg/l indicates depleted stores; a value below 30 µg/l already generally indicates low stores. However, during inflammation, ferritin may rise even when usable iron is lacking. Therefore, one number is evaluated together with other results and symptoms (3, 9).

The "iron in the blood" is also not the same as stores. Its value fluctuates, and an isolated result is not enough to decide whether you need supplements. The result needs to be interpreted together with ferritin and other findings (10).

💊 When to use iron and how to choose the right supplement?

When considering what to supplement with iron, it pays to look beyond just the number of milligrams. The form and tolerability are also important. Especially if you need to supplement regularly, you don't want to think about how your stomach will react to the next capsule every time.

Traditional forms include iron sulfate, fumarate, and gluconate, which may have their place in treating deficiency, but their use can be accompanied by nausea, constipation, or abdominal pain. And absorption may not come close to the values that modern chelated supplements have.

Currently, one of the best forms with high absorption is iron bisglycinate. A chelated form where iron is bound to two molecules of the amino acid glycine (3, 11).

Clinical data also exist for this form. In a randomized study of 80 pregnant women, 25 mg of iron daily in the form of bisglycinate provided comparable protection against iron deficiency and anemia as 50 mg in the form of sulfate. The group using bisglycinate reported fewer gastrointestinal issues. The result relates to specific dosages and the monitored group, but it well illustrates why this form also has its justification when choosing a supplement (11).

For regular supplementation, bisglycinate is a well-thought-out choice, especially if other iron preparations haven't suited you.

Iron Supp+

Our supplement Iron Supp+ is based on high-quality iron bisglycinate. The composition is also suitable for vegans.

Ingredient	Amount in 1 plant capsule	Function
Iron (iron bisglycinate)	20 mg	main active ingredient
Vitamin C	100 mg	supports iron absorption
Folic acid	400 µg	contributes to normal blood formation (blood cell production)
Vitamin B12	5 µg	contributes to normal red blood cell formation

The result is a practical combination of chelated iron and related vitamins in one capsule. Iron Supp+ makes sense for everyone looking for a carefully chosen form, clear composition, and easy use when supplementing iron.

The recommended use is one capsule daily, preferably with food, taken with a sufficient amount of water. If you are already using a multivitamin or another iron preparation, also account for its content. The product is not intended for children under 12 years; pregnant and breastfeeding women should consult their doctor before use.

When to take iron – in the morning or evening?

For the question of when is the best time to take iron, the specific time of day is not the most important. For some medicinal preparations, for example, iron sulfate, it is recommended to take them on an empty stomach, as food can reduce absorption. However, if it irritates your stomach, it may paradoxically be better to take it with food.

For a specific supplement, follow its instructions. In the case of our Iron Supp+, use one capsule right with food. For long-term use, you also need a regimen that you tolerate well and can adhere to (12).

How to use iron in practice:

• Usually take the tablet with water (12).
• A two-hour interval is generally recommended from coffee, tea, dairy products, and calcium-containing supplements (12).
• If you are using levothyroxine (a thyroid medication), certain antibiotics, or medications for stomach acidity, check the exact interval in the package information or with your pharmacist. It varies with different medications (13).
• Do not double up on a missed dose (12).

Vitamin C in food supports absorption, but automatically adding another high dose of vitamin C to the treatment is not necessary (1, 14).

Why do some doctors recommend iron every other day?

After a higher dose of iron, hepcidin, a hormone, temporarily limits further absorption. For some people, therefore, an every-other-day regimen may improve the utilization of the dose and tolerability (15, 16).

This approach applies to specific treatment regimens, often with higher doses. Therefore, there is no reason to arbitrarily change the dosing of a regular supplement or prescribed medication based on this (3).

⏳ How long does it take for iron to work?

After the first capsule, you usually won't notice anything significant. The body needs time to utilize the supplied iron for blood formation and gradually replenish stores.

With effective treatment, changes in hemoglobin may show during the first weeks, and monitoring is usually done within four weeks. Subjective relief often comes about three to four weeks later, but it depends on the cause of the symptoms and the depth of the deficiency. Replenishing stores takes longer, usually months (3, 17).

Therefore, treatment is often continued for approximately three months after normalizing hemoglobin levels. If results do not respond, dosing, regularity, absorption, and ongoing blood losses are addressed. In certain situations, intravenous iron may be indicated in a healthcare setting (3, 18).

🤰 What applies to iron during pregnancy and in sports?

Pregnancy

During pregnancy, the body needs iron for fetal development and changes in the mother's body. However, the initial stores are not the same for all women. Therefore, the process relies on pregnancy check-ups, blood results, and specific recommendations from the gynecologist (1).

You may encounter various recommendations for daily intake: the European EFSA states 16 mg during pregnancy, while American recommendations suggest 27 mg. The difference arises from different assumptions about stores and increased absorption. For a specific woman, her initial state and the course of pregnancy are more important than trying to pick a higher number from tables (1, 5).

Also check how much iron is already in the prenatal supplement before adding more. And avoid liver due to vitamin A, even if it looks appealing in the iron content table (1, 7).

Sports

Especially endurance athletes and sportswomen may be more prone to deficiency, especially when high exertion is combined with limited food intake. A long-term unexplained drop in performance is a reason to check iron, not automatically add more training (19).

However, if you have enough iron, further supplementation will not boost performance (19). About how to choose supplements according to actual needs, you can also read in the article Dietary Supplements for Runners: What Makes Sense and What is Marketing.

⚠️ What are the side effects and risks of iron overdose?

Nausea, abdominal pain after iron, constipation, or diarrhea are among the known undesirable effects. If they occur, it makes sense to discuss with a doctor or pharmacist the tolerability, form, or regimen of use. There is no need to endure long-term discomfort; sometimes adjusting the regimen or changing the preparation can help (20).

Dark to black stools after iron are common. Tar-like, sticky stools, blood, or concurrent weakness and abdominal pain may indicate bleeding and require prompt investigation. Do not automatically attribute every change to the tablet (20).

A higher dose does not automatically mean a quicker return of energy. EFSA has set a safe level for healthy adults of 40 mg daily from all sources for long-term total intake. This is not a recommended dose or a sharp boundary for toxicity and does not apply to treatment under medical supervision (21).

How to recognize iron overdose? Typically, it manifests as severe abdominal pain, vomiting, or diarrhea and can be dangerous, especially for children. If you suspect excessive dosing, do not wait for symptoms: call the Toxicological Information Center at 224 919 293 or 224 915 402, or in serious cases, 155. Store preparations out of reach of children (1, 12, 22).

⚡ Summary for practice

👉 Include iron-rich foods and also monitor portion sizes.

👉 Add a food with vitamin C to plant sources.

👉 Do not address long-term fatigue with iron blindly; ferritin indicates stores in connection with other tests.

👉 In confirmed deficiency, address supplementation and its cause.

👉 When choosing a product, look for the dosage of iron itself, tolerability, and intervals from medications or drinks.

👉 Give supplementation time to replenish stores and do not increase the dose in an attempt to speed everything up.

With iron, a little patience pays off. A well-structured diet, possibly appropriately chosen supplementation, and monitoring results will tell you more than the feeling after the first two capsules. The goal is for the body to have enough of what it needs, and to manage an ordinary day without unnecessary exhaustion.