What Exactly Are Phytates?
Phytates, the salt form of phytic acid, function as the primary storage form of phosphorus in the edible parts of many plants, including seeds, grains, legumes, and nuts. When a seed germinates, the phytate is broken down to release its stored phosphorus and fuel the new plant's growth. Because humans and other non-ruminant animals lack the enzyme (phytase) to fully break down phytates, these compounds can bind to minerals like zinc, iron, calcium, and magnesium in the digestive tract, forming insoluble complexes that reduce mineral absorption. This chelation process led to their classification as 'antinutrients' in the past. However, modern research highlights a more nuanced view, acknowledging both the mineral-binding properties and the potential health benefits of phytates, such as their antioxidant effects and protective role against certain diseases.
Phytates in Whole Grains
Whole grains are a significant source of phytates, particularly in the outer bran and germ layers. Refining grains removes most of the bran and germ, along with the bulk of the phytates, but also eliminates valuable fiber and other nutrients. Therefore, while refined flours are low in phytates, whole grain flours and products contain higher levels. Common whole grains that contain phytates include:
- Wheat (especially bran and germ)
- Oats
- Rice (especially brown rice and rice bran)
- Barley
- Corn
- Rye
- Sorghum
Phytates in Legumes
Legumes, including beans, peas, and lentils, are another major source of phytates. The phytates in legumes are predominantly found in the endosperm's protein bodies. This is a key reason why preparation methods like soaking and cooking are traditionally used for legumes, as they can significantly reduce the phytate content. Examples of legumes containing phytates are:
- Soybeans and soy products (tofu, tempeh)
- Kidney beans
- Lentils
- Chickpeas
- Peas
- Black beans
Phytates in Nuts and Seeds
Nuts and seeds are often consumed in their raw, unprocessed state, and are high in phytates. This is where the practice of 'activating' nuts and seeds by soaking or sprouting originates, as these methods can help neutralize phytic acid and improve nutrient bioavailability. Some of the nuts and seeds with notable phytate content include:
- Almonds
- Walnuts
- Brazil nuts
- Sesame seeds
- Flaxseeds
- Pumpkin seeds
- Cashew nuts
Phytates in Tubers and Roots
While grains, legumes, nuts, and seeds are the primary sources, certain root vegetables and tubers also contain smaller amounts of phytates. Examples include potatoes, sweet potatoes, and beets.
Reducing Phytates: Preparation Methods
Given that phytates can inhibit mineral absorption, especially for individuals with a diet heavily reliant on these foods, various preparation techniques can help reduce their concentration. For most people on a balanced diet, the inhibitory effect is minimal and outweighed by the nutritional benefits of the food.
- Soaking: A simple and effective method for legumes and grains. Soaking overnight in water (ideally with a splash of acid like lemon juice or vinegar) helps activate phytase enzymes that break down phytic acid.
- Sprouting: Also known as germination, sprouting triggers the plant to break down its own phytates. This process significantly reduces phytic acid content in seeds, grains, and legumes.
- Fermentation: Lactic acid fermentation, as used in making sourdough bread or fermented vegetables, produces organic acids that aid in phytate breakdown.
- Cooking: Standard cooking methods, particularly cooking legumes and grains for a prolonged period, can also degrade some phytic acid.
Comparison of Phytate Levels in Different Food Groups
The following table illustrates the general range of phytic acid content (as a percentage of dry weight) across major food categories. Actual levels can vary depending on factors like growing conditions and processing.
| Food Category | Examples | Phytic Acid (% Dry Weight) | Key Takeaway |
|---|---|---|---|
| Whole Grains | Wheat bran, rice bran, oats, maize | 0.4%–8.7% | Bran and germ contain the highest concentrations; processing removes most phytates. |
| Legumes | Soybeans, kidney beans, lentils, chickpeas | 0.2%–2.9% | Content is significant but can be reduced with proper cooking and soaking. |
| Nuts | Almonds, walnuts, cashews, peanuts | 0.17%–9.42% | Content varies widely; soaking or sprouting is effective for reduction. |
| Seeds | Sesame seeds, flaxseeds, sunflower seeds | 1.44%–5.4% | High content, can be reduced by soaking, sprouting, or fermentation. |
| Tubers/Roots | Potatoes, sweet potatoes | Lower levels | Not a major source of dietary phytates compared to other food groups. |
Conclusion
Numerous healthy, plant-based foods contain phytates, a compound that has long been misunderstood. While phytates can reduce the absorption of certain minerals, the foods in which they are found are often rich in other nutrients, antioxidants, and fiber. For individuals consuming a varied and balanced diet, the mineral-binding effect is not a significant concern. For those on high-phytate, plant-heavy diets, or with existing mineral deficiencies, simple preparation techniques like soaking, sprouting, and fermenting can help mitigate this effect. Ultimately, the health benefits of consuming whole grains, legumes, nuts, and seeds far outweigh the minimal concerns surrounding their phytate content for the vast majority of people.
For more in-depth nutritional information and preparation tips, resources like the Harvard T.H. Chan School of Public Health's Nutrition Source are invaluable.
