06 September, 2011
Does the Oxalic Acid in Spinach Inhibit the Absorption of Iron?
The term “nutrient-dense food” perfectly describes spinach, which has few calories per serving but is rich in many nutrients, including iron. However, as with iron from all plant sources, the iron in spinach is present as non-heme iron. This form of iron is not absorbed as efficiently as heme iron, the iron found in meat and animal sources. Additionally, the oxalic acid in spinach binds with iron, which further inhibits iron absorption. You can improve the absorption of iron from spinach by eating it with foods that enhance iron absorption.
Iron Content of Spinach
According to the USDA National Nutrient Database, 100 grams of raw spinach contains 2.71 milligrams of iron, whereas the same amount of boiled spinach contains 3.57 milligrams of iron. Adult men, 19 to 50 years, require 8 milligrams of iron daily, while menstruating women aged 19 to 50 years need 18 milligrams of iron daily. Part of these needs can be met by eating spinach. However, the University Health Center of the University of Georgia recommends that vegetarian women may need to eat 33 milligrams of iron daily, because of less iron being absorbed from plant foods.
Oxalic Acid in Spinach
Oxalic acid content in vegetables varies from 0.1 to 1.7 grams per 100 grams of the vegetable. Except for parsley, chives, purslane, cassava and amaranth, which contain more oxalic acid than spinach, most other vegetables contain less oxalic acid than spinach. According to the USDA Agricultural Research Services, 100 grams of spinach contains about 1 gram of oxalic acid. Because the high content of oxalic acid combines with iron and reduces its bioavailability, the Center for Disease Control and Prevention states that eating spinach with foods that contain a high amount of vitamin C improves the absorption of iron.
Increasing Iron Absorption
In addition to consuming vitamin-C-rich fruits such as oranges, grapefruits, strawberries and cantaloupes to enhance iron absorption from spinach, you can plan your meals to include meat, fish or poultry along with spinach. These sources of heme-iron-rich food improve the absorption of non-heme iron from spinach. Other vegetables such as broccoli, Brussels sprouts, tomatoes, tomato juice, potatoes and green and red peppers also improve absorption of iron from spinach.
Other Nutrients in Spinach
Apart from iron, spinach is rich in other minerals such as calcium, manganese, magnesium and potassium. It is also an exceptional source of vitamin A, vitamin B-2, vitamin B-6, vitamin C, vitamin K and folic acid. Additionally, spinach contains flavonoid compounds that promote health. Because spinach is readily available in the raw, canned or frozen forms, you can easily improve the nutritive value of your meal by adding it to many dishes, including soups and stews, or eat it raw in salads and sandwiches.
- USDA: Nutrient Data Laboratory
- HealthCastle; Is Spinach a Good Source of Iron; Gloria Tsang, R.D.; May 2006
- USDA; Agricultural Research Service; Oxalic Acid Content of Selected Vegetables
- Center for Disease Control and Prevention: Vegetable of the Month: Spinach
- University of Georgia; The University Health Center; Iron facts
- Lilechka75/iStock/Getty Images