What are Phytates and Why Do They Matter?
Phytic acid, or phytate, is a compound found in the seeds, grains, and legumes of plants, where it serves as the main storage form of phosphorus. For humans, however, phytates are classified as "anti-nutrients" because they can bind to essential minerals, such as iron, zinc, magnesium, and calcium, in the digestive tract. This chelation process forms insoluble complexes that make these minerals poorly absorbed by the body. For individuals with diets rich in whole grains and legumes, particularly those in developing countries or following vegetarian and vegan diets, high phytate consumption can contribute to mineral deficiencies. Conversely, in a balanced diet, phytates may offer health benefits due to their antioxidant properties.
The Effect of Heat on Phytates
Heat is one of several processing methods used to reduce phytic acid levels. However, its effectiveness depends on the specific cooking method, duration, temperature, and the food itself. General cooking methods like boiling or microwaving can cause a reduction in phytate content, but this is often modest compared to other techniques. The primary mechanism for phytate reduction during cooking is leaching into the cooking water. Consequently, discarding the cooking water, as is common when boiling legumes, enhances the overall reduction.
Boiling and Autoclaving
Research has explored the impact of various high-heat methods. Boiling, a common practice for cooking legumes and grains, has been shown to reduce phytic acid. For instance, boiling mung beans resulted in a 59.1% reduction in phytate concentration. A double-boiling process, where the initial water is discarded, is even more effective for some beans. Autoclaving, which involves high-pressure steam at temperatures above the boiling point, can be more effective than simple boiling. A study on soybeans demonstrated that autoclaving at 121°C for 15 minutes was more effective at reducing phytic acid than boiling for 30 minutes.
Pressure Cooking
Pressure cooking is a particularly effective heat-based method for tackling phytates. One study found that pressure cooking soaked peas reduced phytic acid by 54%, which was nearly twice as effective as boiling them (29% reduction). The combination of high temperature and pressure breaks down the phytic acid more efficiently than standard boiling. The pressure cooking process is also often shorter, making it a time-saving option for dephytinization.
The Role of Phytase
Many plant-based foods, such as grains and legumes, contain the enzyme phytase, which is responsible for breaking down phytic acid. This enzyme becomes active during soaking or germination. For example, soaking oats activates their intrinsic phytase, which then begins to break down phytates. However, it is important to note that heating or cooking foods can inactivate this natural phytase enzyme, especially if not pre-soaked. This is why simply cooking certain foods without a prior soaking step may not achieve the same level of phytate reduction as soaking first.
The Synergy of Soaking and Heat
Combining soaking with subsequent heat treatment is often the most effective strategy. Soaking, especially in warm or slightly acidic water, can activate the phytase enzyme and begin the degradation process. When these foods are then cooked, the heat finishes the job by further breaking down the remaining phytate and promoting its leaching into the water. This two-step approach is particularly effective for legumes. For example, soaking followed by cooking has been shown to be substantially more effective than just cooking alone.
A Simple Guide to Reducing Phytates
Here is a simple, step-by-step process for minimizing phytates in common foods:
- Select Your Grain or Legume: Choose a whole grain, such as brown rice or oats, or legumes like black beans or chickpeas.
- Soak Overnight: Place the food in a bowl and cover it with warm water. For extra effectiveness, add a slightly acidic medium like a splash of lemon juice or vinegar for grains, or a sprinkle of baking soda for legumes.
- Drain and Rinse: The next day, drain the soaking water and rinse the food thoroughly. This step is crucial as it removes the phytic acid that has leached into the water.
- Cook with Fresh Water: Cook the food as you normally would, using fresh water. This prevents the reabsorption of any residual phytates.
- Consider Fermentation: For grains like oats, try making sourdough, as lactic acid fermentation is known to be very effective at breaking down phytic acid.
Comparison of Phytate Reduction Methods
| Method | Primary Mechanism | Effectiveness | Best For | Considerations |
|---|---|---|---|---|
| Boiling | Leaching into water, heat degradation | Low to Moderate | Legumes, Grains | Must discard cooking water. Less effective alone. |
| Pressure Cooking | High heat and pressure | High | Legumes | Faster cooking, very effective on soaked foods. |
| Soaking | Activates phytase, leaches into water | Moderate to High | Grains, Legumes, Nuts | Dependent on the food's natural phytase content. Requires time. |
| Sprouting | Activates phytase | High | Seeds, Grains, Legumes | Requires time, specific conditions. Can reduce volume. |
| Fermentation | Produces organic acids that degrade phytate | High | Grains (sourdough), Legumes | Requires a starter culture and time. Adds flavor. |
Conclusion
While heat can reduce phytates to some extent, it does not destroy them on its own, and its effectiveness varies significantly based on the cooking method. For maximum reduction, a combination of techniques is recommended. The most powerful approach is to combine soaking, sprouting, or fermentation with a final heat treatment, such as boiling or pressure cooking. This two-pronged strategy ensures that both enzyme activation and heat-driven degradation work in tandem to minimize phytic acid and maximize the bioavailability of essential minerals from your food. Remember, for a generally healthy diet, phytate levels are not a major concern, but understanding how to prepare foods correctly can help those at risk of mineral deficiencies. For further information on the effects of different heat treatments on phytic acid, explore research from reliable sources such as the National Institutes of Health.
Conclusion
Ultimately, the question isn't whether heat destroys phytates, but rather how effectively it does so in combination with other preparation methods. For optimal nutrient absorption from whole foods, relying on heat alone is insufficient. Instead, embracing traditional cooking techniques like soaking and fermentation, followed by a cooking step, is the most scientifically supported way to manage phytate levels. This approach allows for a balanced diet that maximizes the health benefits of whole grains, legumes, and seeds while mitigating the effects of anti-nutrients.
