Probably the best known nutrition fact about iron is that meats—particularly red meats—are rich in iron. You will see some familiar animal foods on our list of iron sources below.
While this is true, it is also true that a number of plant foods are also rich in iron. It may come as a surprise that researchers have found that people eating plant-based diets eat as much or more iron as people who regularly rely on animal foods. And, you'll see that our list of excellent iron sources is largely dominated by plant foods.
Without question, more human health problems worldwide are caused by iron deficiency than by lack of any other nutrient. Less well known is the fact that excessive iron stores are also responsible for a large burden of illness worldwide. As such, iron is a very important nutrient to understand not only for researchers and nutritionists but everyone, since we need to be aware of finding the right iron balance from our foods.
Five of the World's Healthiest Foods rank as excellent sources of iron and nine foods rank as very good sources. Additionally, 30 foods rank as good sources. Added together, over one-third rank as good, very good, or excellent sources of iron.
All of the tissues in our body need a near constant supply of oxygen to maintain life. We maintain this oxygen delivery by the red cells in our blood. These have an iron-containing protein called hemoglobin, which is a perfect transporter for oxygen, in that it both picks up and releases oxygen in an exact and targeted way.
The average man has about 2 grams of iron in his blood cells at any given time while women have about 1.6 grams. If the dietary iron intake falls below daily needs and this storage amount goes down, the ability to tolerate bursts of exercise will deteriorate. The reduction in blood count related to having low iron stores (or other nutrient deficiencies, including of vitamin B12, folate, copper, and vitamin A) is called anemia.
In addition to the key role iron plays in transporting oxygen to tissues, it also is necessary to support proper metabolism for muscles and other active organs. Almost all of the cells in our body burn dietary calories to create energy through a process that requires iron. When iron stores get low, this process gets compromised, and generalized fatigue can occur.
This lag in energy production tends to occur earlier than changes in blood cell production, so the muscle fatigue and changes in concentration are likely to be noticeable long before laboratory testing shows low blood cell production.
You may be surprised to see no animal foods listed among our excellent or very good sources of iron. There are two related reasons for this result.
First, as we discussed above, it is a common misconception that plant foods are not rich sources of iron. In fact, many plant foods contain more than 10% of a daily iron requirement per serving. Some—lentils and spinach, for example—contain as much as one third of the daily requirement.
Second, plant foods tend to have fewer calories per serving than animal foods. Since we base our food ratings on nutrient richness (or amount of nutrient per calorie), the least energy dense foods look the best in our assessment model.
Among plant foods, legumes and leafy green vegetables are consistently among our best sources. Several spices are surprisingly strong sources of iron. Whole grains can also be good contributors to iron nutrition.
While not included as one of our World's Healthiest Foods, blackstrap molasses—the thick syrup that remains after sugars have been extracted from sugar cane through boiling and filtering—provides about 1 milligram of iron per teaspoon. This amount is somewhat unusual among sweeteners and much greater than the amount found in a teaspoon of honey, maple syrup, or brown sugar.
All of this is not to say that animal foods are not concentrated sources of iron, as well. Many of the animal foods represented in the World's Healthiest Foods list contain at least 2 mg of iron per serving. Included among these are lamb , sardines, and grass-fed beef.
|World's Healthiest Foods ranked as quality sources of|
|Swiss Chard||1 cup||35.0||3.96||22||11.3||excellent|
|Beet Greens||1 cup||38.9||2.74||15||7.0||very good|
|Collard Greens||1 cup||62.7||2.15||12||3.4||very good|
|Bok Choy||1 cup||20.4||1.77||10||8.7||very good|
|Asparagus||1 cup||39.6||1.64||9||4.1||very good|
|Mustard Greens||1 cup||36.4||1.22||7||3.4||very good|
|Turnip Greens||1 cup||28.8||1.15||6||4.0||very good|
|Leeks||1 cup||32.2||1.14||6||3.5||very good|
|Chili Peppers||2 tsp||15.2||0.93||5||6.1||very good|
|Romaine Lettuce||2 cups||16.0||0.91||5||5.7||very good|
|Sesame Seeds||0.25 cup||206.3||5.24||29||2.5||good|
|Garbanzo Beans||1 cup||269.0||4.74||26||1.8||good|
|Lima Beans||1 cup||216.2||4.49||25||2.1||good|
|Navy Beans||1 cup||254.8||4.30||24||1.7||good|
|Kidney Beans||1 cup||224.8||3.93||22||1.7||good|
|Black Beans||1 cup||227.0||3.61||20||1.6||good|
|Pinto Beans||1 cup||244.5||3.57||20||1.5||good|
|Pumpkin Seeds||0.25 cup||180.3||2.84||16||1.6||good|
|Green Peas||1 cup||115.7||2.12||12||1.8||good|
|Brussels Sprouts||1 cup||56.2||1.87||10||3.3||good|
|Green Beans||1 cup||43.8||0.81||5||1.9||good|
|Summer Squash||1 cup||36.0||0.65||4||1.8||good|
|Black Pepper||2 tsp||14.6||0.56||3||3.8||good|
|Sea Vegetables||1 TBS||10.8||0.56||3||5.2||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%
Iron in animal foods appears to be very resilient to different methods of cooking. Minor changes may occur to the absorbability of iron, with fully cooked meats having slightly more iron in its most absorbable forms. This is probably not terribly important to overall nutrition, however, as the iron from animal foods is already more available on average than that from plant sources.
In contrast, the iron in plant foods is much more likely to be pulled out in the processing or cooking of foods. Whole grains, by way of example, can lose up to three-quarters of their iron content when their outer layers are removed during the production of refined flours. Avoiding this loss of nutrients is one of the reasons we recommend consumption of grains in their whole form—and not only grains but grain flours as well. Unless a bread label states "100% whole grain" (or "100% whole wheat" in the case of one specific grain like wheat), it is best to assume that the grains have been refined and that nutrients have been lost.
In addition, iron can be removed from plant foods by way of the water in which foods are cooked. For instance, boiling spinach for over three minutes in a large pot removes almost 90% of iron from the leaves. To minimize iron loss from cooking, we recommend shorter cooking times and the use of smaller amounts of water..
Cast iron cookware can release relevant amounts of absorbable iron into foods. This amount is likely to be a milligram or two in a meal prepared under most circumstances, but may provide far greater amounts under certain conditions. In particular, more acidic foods appear to pull iron from cookware more efficiently. This cookware-provided iron appears to be absorbable as well, and in some studies, researchers have been able to link health benefits with the use of iron cookware.
There is currently some debate in the research world about how to define iron deficiency. Many researchers believe that iron deficiency is only important when it causes low blood counts. This is indicative of a severe deficiency and will potentially take years of an iron-deficient diet to develop.
Recent research, however, suggests that symptoms related to iron deficiency—specifically fatigue, muscle weakness, and excessive menstrual blood flow—can occur at iron storage levels seen in women with normal blood counts.
The risk of iron deficiency in women is substantial. In fact, according to the World Health Organization, iron deficiency is the most common nutrient-related condition in the world.
In the U.S., the numbers are a little more encouraging, but iron deficiency still affects about 10% of women of childbearing age. Symptomatic iron deficiency is quite rare in men and post-menopausal women.
Young children are the other major at-risk group for iron deficiency, with close to 15% of kids developing deficiency by age 2. These numbers tend to improve until the rapid period of growth in adolescence.
Although some popular sources suggest otherwise, researchers have not consistently found that vegetarian or largely plant-based diets lead to significant increases in the risk of iron deficiency anemias. In fact, at least one research group found that the intake of iron across the US population was higher in people that did not include meat in their diet.
As an example of iron richness in a plant-based diets, consider two of our plant-based recipes: Spicy Healthy Sautéed Tofu and Black Bean Chili. are two of our all-plant recipes that provide roughly 50% of the daily requirement for iron.
Increased blood loss, including from blood donation, will increase your daily iron needs. Up to 50% of repeat female blood donors, and 20% of males, have evidence for compromised iron status on routine screening tests.
Endurance exercise can increase iron losses by up to 50% each day. This is a commonly reported problem, particularly in younger women. A couple of iron-packed recipes that might be particularly good for training time include Oyster and Clam Chowder and Broiled Rosemary Chicken over Puréed Lentils and Swiss Chard.
Gastrointestinal problems, including malabsorption diseases and low stomach acid production, can impair iron absorption. In people with autoimmune intestinal disease, for instance, the correlation between dietary iron intake and risk of low iron stores is much stronger than in the rest of the population.
Note that in each of these risk groups, dietary iron should still be sufficient to keep stores in a healthy range, as long as you are careful to regularly include iron-rich foods in your daily diet. In fact, adding extra sources of iron in the form of fortified foods or supplements may make gastrointestinal symptoms worse for some people.
Consuming vitamin C together with iron-containing meals can increase or optimize iron absorption. In fact, adding 50 milligrams of vitamin C—about the amount found in one-half of a grapefruit—to an iron-rich meal may make it possible to triple the absorption of iron. Put in another way, if vitamin C deficiency is severe, it may be necessary to address this issue before iron stores can be restored to normal. Note that the effect of vitamin C on iron absorption is much stronger on iron from plant foods than on animal foods.
Advanced deficiency of vitamin A can impair the ability to use iron to make red blood cells. For this reason, researchers have been exploring combined vitamin A and iron interventions in many parts of the non-industrialized world. The level of vitamin A deficiency necessary to affect iron nutrition needs to be severe, however, and does not appear to be common in the industrialized world.
Copper is necessary to mobilize iron from storage for use in blood cells and other areas. Because of this, deficiency of copper may play a role in anemia. Legumes like soybeans and lentils are simultaneously high in iron and copper, and as such may be a particularly good choice for keeping a strong supply of both of these at-risk minerals.
Oddly, although in short-term experiments calcium and iron compete for absorption, researchers have been unable to demonstrate that this is a common problem in human nutrition. At least according to one prominent research group, it appears that our bodies are able to compensate for this issue by increasing iron absorption accordingly. At this time, it does not appear that you need to be careful to eat iron-rich foods away from foods rich in other minerals to enhance or optimize absorption.
Many food constituents can inhibit iron absorption by binding it in the gastrointestinal tract. Prominent examples include phytic acid found in many whole grains and some of the polyphenols found in black tea. In general, consumption of foods like whole grains and black tea does not appear to cause iron-related problems for healthy persons who are not at special medical risk for iron deficiency. But in certain medical situations—for example, iron deficiency anemia or iron storage disease—these interactions might have a significant impact and foods with iron-binding components might need to be avoided We encourage you to consult with your healthcare provider if you have any medical concerns in this regard.
For most healthy persons, the checks and balances on iron absorption and excretion appear to keep our body stores in a fairly narrow range. This is a good thing since too much stored iron can help to foster free radical damage to the liver and other organs.
However, relatively new research studies have pointed to a possible connection between some very common health problems—including obesity, insulin resistance, and metabolic syndrome—and imbalances in iron metabolism. Somewhat paradoxically, these health problems appear to simultaneously result in altered aspects of iron status that reflect iron deficiency, and other altered aspects that reflect iron excess. Dysmetabolic iron overload syndrome (DIOS) is the name that has been given to factors related to excess. Based on this recent research, it may make sense for persons diagnosed with the above conditions to consult with their healthcare provider and take a closer look at their iron status for issues related to either deficiency or excess before making a final decision about the place of iron-rich foods in their meal plan.
It's important to point out that DIOS is not the same as hemochromatosis. Hemochromatosis is a genetic predisposition in which excess iron retention and storage can occur. It is also estimated to affect between 1-6% of all persons in the U.S. For persons diagnosed with hemochromatosis, restriction of dietary iron is a key part of medical treatment..This restriction not only includes foods that are naturally rich in iron, but also foods that have been enriched or fortified with iron during processing. It also typically includes avoidance of cast iron cookware.
One additional non-food note about iron supplements: Iron supplements represent one of the most common poisoning risks in children. If you are taking an iron supplement, make sure and keep it out of the reach of children.
In 2000, the Institute of Medicine at the National Academy of Sciences established Dietary Reference Intake (DRI) standards for iron. These DRI standards included Adequate Intake (AI) level for infants up to 6 months old and Recommended Dietary Allowances (RDA) for all other age categories. These standards are as follows:
The Tolerable Upper Intake Limit (UL) for iron is 45 mg per day for all adults. Given that even the most iron-rich foods have less than 5 mg per serving, it would be very difficult to exceed this regularly through diet alone.
There is also a Daily Value (DV) for iron of 18 mg. This is the standard you'll see reported on food labels, and it is also the standard we adopted at the World's Healthiest Foods as our recommended daily amount.