Phytic acid, also known as inositol hexaphosphate or IP6, is a naturally occurring compound found predominantly in plants. It serves as the primary storage form of phosphorus within plant seeds. Phytic acid is found in various parts of plants, including the bran of grains, and within the protein bodies of legumes and oilseeds.
Foods Rich in Phytic Acid
All edible seeds, grains, legumes, and nuts contain phytic acid. The concentration of phytic acid can differ significantly based on the specific food type, growing conditions, and processing methods.
Whole grains are a notable source of phytic acid, particularly in their outer bran layers. Examples include oats, wheat, barley, brown rice, and corn. Wheat germ and wheat bran can contain 1.1–3.9% and 2.0–5.3% phytic acid, respectively, while rice bran may contain up to 8.7%.
Legumes, such as black beans, kidney beans, pinto beans, lentils, chickpeas, and soybeans, also contain considerable amounts of phytic acid. The phytic acid content in whole legume seeds typically ranges from 0.2% to 2.9%, with higher concentrations, often exceeding 3.7%, found in their cotyledons. Peanuts are another legume that serves as a source of phytic acid.
Nuts, including almonds, walnuts, pecans, cashews, and Brazil nuts, naturally contain phytic acid. For instance, almonds can have a phytic acid content ranging from 0.4% to 9.4%, and Brazil nuts from 0.3% to 6.3%. Seeds like sesame seeds, flax seeds, and sunflower seeds are also rich in this compound. Some root vegetables and tubers, such as potatoes, turnips, beets, and carrots, contain smaller amounts of phytic acid compared to grains and legumes.
Understanding Phytic Acid’s Role
In plants, phytic acid is broken down when seeds sprout, releasing phosphorus for the young plant to utilize. This compound also serves as an energy reserve and a source of cations for the seedling.
When consumed by humans, phytic acid can interact with certain minerals in the digestive tract. It binds to essential minerals like iron, zinc, calcium, and magnesium, forming insoluble complexes (phytates) that can reduce their absorption in the small intestine. The human digestive system generally lacks the enzyme phytase, which is needed to break down phytic acid efficiently, thus making the bound minerals less bioavailable.
Phytic acid also possesses other properties. It acts as an antioxidant, helping to protect cells from oxidative damage. This antioxidant capacity is partly due to its ability to bind iron, which can otherwise catalyze oxidative reactions. Phytic acid may also aid in the regulation of blood sugar levels and support colon health.
Strategies to Modify Phytic Acid Content
Traditional food preparation methods can reduce phytic acid content in plant-based foods, improving mineral bioavailability. These methods activate naturally occurring enzymes, primarily phytase, which break down phytic acid.
Soaking grains, legumes, and nuts in water is a common technique. Soaking activates endogenous phytase enzymes present in the food, which then begin to hydrolyze phytic acid. For example, soaking sorghum flour for 24 hours can reduce phytic acid levels by 16–21%. Adding an acidic medium like lemon juice or vinegar during soaking can further enhance this process.
Sprouting is another effective method. This process significantly activates phytase, leading to a substantial breakdown of phytic acid. Sprouting can reduce phytic acid content in various grains and legumes, with reported reductions ranging from 37% to 81%. For instance, sprouting oats can lead to a 98% reduction in phytic acid, rye by 84%, and barley by 58%.
Fermentation, such as lactic acid fermentation used in sourdough bread, also contributes to phytic acid reduction. Organic acids produced during fermentation create an acidic environment that promotes phytate breakdown. This method can significantly increase the amount of soluble iron, zinc, and calcium in fermented foods.
Prolonged cooking can also reduce phytic acid to some extent. Combining methods, such as soaking followed by cooking, or sprouting combined with fermentation, can lead to even more significant reductions in phytic acid content. These strategies make the minerals within these nutritious foods more accessible for absorption by the body.