Understanding the 'Antinutrients' in Nuts
Nuts are a cornerstone of many healthy diets, offering an abundance of healthy fats, protein, fiber, vitamins, and minerals. However, they also contain naturally occurring compounds often referred to as 'antinutrients.' The two most relevant for calcium absorption are phytates and oxalates. These substances, which serve important functions for the plants themselves, can interfere with mineral absorption in the human digestive tract.
What are Phytates?
Phytates, or phytic acid, are found in the seeds of plants, including nuts, grains, and legumes. Phytates possess a strong ability to bind to mineral cations, such as calcium, zinc, and iron, forming insoluble complexes that the body cannot easily absorb. The impact of phytates on calcium absorption is most pronounced when high-phytate foods are consumed simultaneously with high-calcium foods. However, this is primarily a concern with consuming large amounts of high-phytate foods over time, rather than a single meal, for individuals on an otherwise balanced diet.
What are Oxalates?
Oxalates, or oxalic acid, are present in a variety of plant foods, including nuts, leafy greens, and certain vegetables. Similar to phytates, oxalates can bind with calcium to form calcium-oxalate crystals. This binding reduces the amount of calcium available for absorption in the intestines. The binding effect is most significant within a single food source that contains both high levels of oxalate and calcium, like spinach. However, if oxalate-rich nuts are eaten with a separate calcium-rich food, the effect on calcium from that other source is less significant.
Bioavailability of Calcium in Nuts
While nuts contain these antinutrients, it's important to recognize that they also provide calcium. However, the bioavailability—the proportion of a nutrient that is absorbed from the diet and used for bodily functions—can vary. For example, almonds are often praised for their high calcium content, but studies have shown the bioaccessibility is relatively low due to the presence of phytates. In contrast, other nuts like macadamia and pistachios may have a higher percentage of their calcium absorbed, even if the total amount is lower. It's crucial to view nuts as part of a varied diet rather than a primary source of bioavailable calcium.
Strategies to Maximize Calcium Absorption
For those concerned about mineral absorption, especially individuals following a largely plant-based diet, several simple kitchen techniques can help reduce antinutrient levels in nuts:
- Soaking: Soaking nuts in water for a few hours can help reduce their phytic acid content. Rinsing the nuts after soaking is also recommended. This process activates enzymes that break down the phytates.
- Sprouting or Germinating: Sprouting nuts can increase nutrient bioavailability by activating phytase enzymes, which break down phytic acid.
- Cooking: Cooking nuts, like roasting, can also help to degrade some of the phytic acid content.
- Meal Timing: For those with specific concerns or mineral deficiencies, consuming high-calcium foods and high-antinutrient foods at separate times can help. For most people on a balanced diet, however, this is not necessary.
Balancing Benefits and Concerns
Despite the potential for reduced calcium absorption, the overall nutritional value of nuts is substantial. They offer healthy fats that support heart health and contain magnesium, a mineral that is critical for calcium absorption and bone health. The key is to consume nuts as part of a varied and balanced diet that includes other robust sources of bioavailable calcium, such as dairy products, fortified plant milks, and leafy greens with lower oxalate content like kale.
Comparison of Nutrients and Absorption
| Feature | Nuts (e.g., Almonds) | Other High-Calcium Foods (e.g., Dairy) |
|---|---|---|
| Calcium Content | Varies by nut, almonds are high | Generally high per serving |
| Antinutrients Present | Phytates and oxalates | None related to calcium absorption |
| Bioavailability of Calcium | Potentially lower due to antinutrients | Generally higher (~30%) |
| Other Key Nutrients | Healthy fats, fiber, magnesium | Protein, Vitamin D (often fortified) |
| Preparation to Maximize Absorption | Soaking, sprouting, cooking | None required to maximize calcium absorption |
Conclusion
To answer the question, do nuts interfere with calcium absorption? The answer is yes, but the effect is generally minor for individuals on a balanced and varied diet. The presence of phytates and oxalates in nuts can bind to calcium, but this shouldn't be a reason to avoid these nutrient-dense foods. By including a diverse range of food sources and using simple preparation techniques like soaking, you can minimize any potential interference. The overall benefits of incorporating nuts into your diet, including their contributions to heart health and bone health through other minerals like magnesium, make them a valuable addition to your nutrition plan. Focusing on a well-rounded diet with multiple calcium sources, rather than eliminating any single healthy food, is the most effective approach for optimal mineral intake and overall health.
For more in-depth information on nutrition, the Harvard T.H. Chan School of Public Health's Nutrition Source is an excellent resource.
