Ever get a weird fuzzy feeling on your tongue or the roof of your mouth when you eat cooked spinach?
While some claim this sensation is more pronounced with unwashed vs. washed cooked spinach, it is more likely to be the effect of oxalic acid.
Spinach, as well as other greens and some other foods, contain oxalic acid. Oxalic acid binds with iron and calcium, and leads to reduced absorption rates of these minerals in your body.
When you chew spinach, the calcium in your saliva interacts with the oxalic acid in the spinach, forming calcium oxalate crystals. The calcium oxalate crystals are what gives you that gritty mouthfeel.
Other high oxalate vegetables include:
- Wax & dried beans
- Beets & beet greens
- Collard greens
- Dark leafy green: kale, Swiss chard, watercress
Oxalic acid isn’t the only compound that lowers iron absorption. Phytates and phytic acid from whole grains, and tannins found in teas can also reduce iron absorption.
It is believed that somewhere between 15-30 percent of heme-iron (from meat, fish and poultry) is absorbed, whereas only about 5 percent of non-heme iron (from plant sources) is absorbed.
If you have low iron stores or have been diagnosed with iron deficiency anemia, it may be difficult to achieve adequate iron intake levels from foods alone, and you might consider taking an iron supplement to fill the gap.
The Institute of Medicine’s Dietary Reference Intake (DRI) for iron is 18 mg per day for females age 19-50 and 8 mg per day for males age 19+. One cup of boiled, drained spinach has 6.5 mg of elemental iron, but again, you only absorb a small portion of that.
On the other hand, vitamin C helps enhance iron absorption. Eating a piece of citrus fruit or other vitamin C-containing fruit or vegetable can boost the iron absorption from the foods you eat, or the iron supplement pill you take.