Last updated: August 3, 2026.
Short answer: heme iron is the form found in animal foods (liver, red meat, organ meats, shellfish), and your body absorbs it at roughly 15–35%. Non-heme iron is the form in plants, fortified cereals and most supplement tablets, and it absorbs at roughly 2–20%, with the low end being common. Heme iron absorbs better, by a factor of two to three, and it's far less bothered by the coffee, tea and calcium that sabotage the plant form.
Here's what that actually means for your plate, and where non-heme iron still earns its keep.
Two forms, one mineral
All iron does the same job once it's in your blood. The difference is the packaging on the way in. Heme iron comes bound inside hemoglobin and myoglobin, the molecules that carried oxygen in the animal you're eating. Your gut has a dedicated uptake route for it, which is why absorption stays high and steady. Non-heme iron is the free, unbound form in spinach, lentils, fortified cereal, and iron salts like ferrous sulfate. It has to be shepherded through a fussier absorption process, which is where the losses happen.
What the NIH Says About Heme vs Non-Heme Iron Absorption
The National Institutes of Health iron fact sheet is blunt about the gap: heme iron is more bioavailable than non-heme iron, and adding heme-containing foods to a meal even increases how much non-heme iron you absorb from everything else on the plate.
The NIH puts total iron bioavailability at roughly 14 to 18 percent from mixed diets that include meat and seafood, versus 5 to 12 percent from vegetarian diets. Classic absorption research behind those averages estimates heme iron absorption at roughly 15 to 35 percent, against 2 to 20 percent for non-heme iron, with the exact figure depending on your iron stores and what else you ate. Source: NIH Office of Dietary Supplements, Iron Fact Sheet for Health Professionals.
What is heme iron?
Heme iron is the form of iron bound inside a heme molecule, the same ring structure that carries oxygen in haemoglobin and myoglobin. It occurs only in animal foods: red meat, organ meats, poultry and seafood. Because it is absorbed through its own dedicated pathway in the gut, it bypasses most of the dietary factors that block the other form.
What is non-heme iron?
Non-heme iron is iron that is not bound into a heme molecule. It is the form in plants (spinach, lentils, beans, fortified grains) and in almost every standard iron tablet, usually as a salt like ferrous sulfate. It is the majority of the iron in most diets, and the minority of the iron people actually absorb.
Why is non-heme iron harder to absorb?
Because it has to be converted before your body can take it up, and that conversion is easy to interfere with. Phytates in grains and legumes, polyphenols in tea and coffee, calcium, and some fibres all bind non-heme iron in the gut and carry it straight through you. Vitamin C pushes in the other direction and improves uptake, which is why the standard advice is to pair plant iron with citrus. Heme iron is largely indifferent to all of this, which is the entire absorption gap in one sentence.
The absorption gap, in real numbers
Heme iron: roughly 15–35% absorbed. Non-heme: roughly 2–20%, and the conditions have to cooperate to reach the top of that range. Coffee or tea with the meal, calcium alongside, or a sensitive stomach can push non-heme absorption toward the floor. Heme iron largely shrugs those off.
This gap explains a common frustration: someone eats an iron-conscious diet (spinach, legumes, fortified oats) or dutifully swallows a tablet, and their energy stays flat. Swallowing iron and absorbing iron are two different transactions. A modest amount of heme iron can outperform a larger amount of non-heme on what actually reaches your blood.
Why the plant list keeps failing you
The 2–20% non-heme range isn't random. It's driven by compounds that ride along in the same foods. Spinach is the famous case: roughly 3.6 mg of iron per 100 g cooked, bound up by oxalates that form complexes your gut can't absorb. The iron mostly passes through. Phytates (in the grains, legumes, nuts and seeds that anchor most "iron-rich" meal plans) are worse: a landmark review by Hurrell and Egli in the American Journal of Clinical Nutrition (2010) found a single phytate-containing meal can cut non-heme absorption by 50–80%. And polyphenols finish the job: research in the European Journal of Clinical Nutrition shows a cup of tea with a meal can reduce non-heme uptake by 60–70%. None of these meaningfully touch heme iron, which uses its own transport pathway.
What actually reaches your blood
Run the absorbed-milligram math and the label numbers invert:
- Beef liver, 85 g cooked: ~5.8 mg iron, heme-dominant → roughly 1.45–2.0 mg absorbed
- Spinach, 180 g cooked: ~6.4 mg iron, non-heme + oxalates → roughly 0.13–0.32 mg absorbed
- Lentils, 200 g cooked: ~6.6 mg iron, non-heme + phytates → roughly 0.13–0.33 mg absorbed
- Fortified cereal, one serving: ~18 mg added ferric iron → poor uptake, and the high dose is what irritates guts
Same "6 mg of iron" on paper; a ten-fold difference in what lands. There's also a bonus effect working for the animal side: heme iron enhances absorption of the non-heme iron eaten in the same meal, the "meat factor" documented by Hallberg and colleagues. Liver next to your lentils improves the lentils.
The Canadian picture
This gap is why iron deficiency stays the most common nutrient deficiency in Canada despite decades of fortified cereal. Statistics Canada's nutrition data puts roughly 12–16% of women aged 19–50 in iron-deficient territory, with many more sitting in the "borderline" zone that never earns a diagnosis. Fatigue, poor exercise tolerance and brain fog can show up while hemoglobin still reads normal. If that's you, ask for serum ferritin, not just hemoglobin: many practitioners now treat ferritin under 30 ng/mL as symptomatic insufficiency. And if you're eating the spinach-and-lentils list while drinking coffee with every meal, the math above is likely the reason nothing's moving.
Where each form lives
- Heme: beef liver is the standout at roughly 6.5 mg per 100 g cooked, with B12, folate and copper in the same food. Red meat, organ meats and shellfish follow.
- Non-heme: lentils, beans, spinach, tofu, fortified cereals, and nearly every iron pill on the pharmacy shelf, including ferrous sulfate and ferrous gluconate.
Worth knowing: Health Canada's recommended iron intake for women 19–50 is 18 mg per day, versus 8 mg for men. When your target is that high and your absorption rate is doing the heavy lifting, the form matters more than the label total.
In defence of non-heme iron
Fairness break. Non-heme iron isn't useless. Most of the world's dietary iron is non-heme, and pairing it with vitamin C meaningfully improves uptake. Plant-forward eaters can absolutely manage their iron; it just takes more attention and more milligrams to land the same absorbed amount. And when a practitioner prescribes therapeutic iron for diagnosed deficiency (often 60–200 mg per day), that's non-heme doing a job food can't. Form is a lever, not a religion.
The practical shortcut
If you want heme iron daily but liver isn't joining your dinner rotation, capsules solve the logistics. Rise Grass-Fed Beef Liver Capsules are one ingredient (freeze-dried grass-fed, grass-finished beef liver), NPN certified with Health Canada. Four capsules deliver 3,000 mg of freeze-dried liver; the 120-capsule bottle is $39.99 and covers 30 days, about $1.33 a day. It's the heme form, from the densest heme food, without the frying pan.
FAQ
Which foods have heme iron?
Animal foods: liver (the densest source, roughly 6.5 mg per 100 g cooked), red meat, organ meats and shellfish. Plants contain only non-heme iron.
Why does non-heme iron absorb so poorly?
It's the free form of the mineral and depends on a fussier uptake process that coffee, tea and calcium can interfere with. Absorption runs roughly 2–20%, versus roughly 15–35% for heme iron, which has its own dedicated route.
Does vitamin C help iron absorption?
It helps the non-heme form. Pairing plant iron or tablets with vitamin C improves uptake. Heme iron doesn't need the assist.
Is supplement iron heme or non-heme?
Almost all standard iron tablets (ferrous sulfate, ferrous gluconate and similar salts) are non-heme. Freeze-dried liver capsules are the practical supplement route to heme iron, because they're simply the food in capsule form.
Written by the team at Rise Nutrition, Toronto, Canada's single-ingredient ancestral nutrition brand. Whole foods, freeze-dried, one ingredient per label. Questions? ray@risenutritions.ca
