When it comes to nutrition, few topics generate as much debate as anti-nutrients. These natural substances have sparked controversy among both experts and devoted soy enthusiasts. No wonder! If you eat a plant-based diet, you may add one or more soy-based foods to your plate. For example, tofu and tempeh (a fermented soy food) are popular among vegetarians and vegans. However, some sources say the anti-nutrients in soy foods are problematic. Let’s look at some anti-nutrients in soy and other plant-based foods, and whether you should be concerned about them.
Lectins: Fact and Fiction
One group of plant compounds in soy is lectins. Like phytates, they’ve generated some controversy. These compounds have been accused of hindering mineral absorption, particularly calcium, iron, phosphorus, and zinc. Some even claim they threaten gut health by binding to intestinal epithelial cells, potentially compromising gut permeability, leading to “leaky gut” and autoimmune conditions.
However, the evidence supporting these claims is limited and involves isolated lectins or raw beans fed to animals. Human research remains scarce. Plus, lectins are heat-sensitive, meaning cooking destroys them. So, lectins aren’t an issue unless you’re eating food raw. Plus, fermenting and sprouting also reduce the lectin content of soy and other plant-based foods.
Protease Inhibitors: Balancing Act
Soy and other legumes also contain compounds called protease inhibitors. Their purpose is to protect plants against insects. Although some animal studies raise questions about whether protease inhibitors interfere with protein digestion, cooking destroys them and reduces any negative effects they might have. Plus, they’re not all bad. Studies show that protease inhibitors have anti-inflammatory benefits, too.
Phytates: Balancing Act
Another group of anti-nutrients is phytates, which are referred to as phytic acid. Soybeans and soy-based products have various levels of phytates. Why are they under scrutiny? When you consume soy and other phytate-rich foods, the compounds form complexes with essential minerals like iron, zinc, calcium, magnesium, and potassium. The result? Reduced bioavailability of these crucial nutrients, potentially raising concerns about mineral deficiencies.
But don’t be so quick to demonize phytates. They have their upsides. For example, they have antioxidant and anti-inflammatory properties. Moreover, phytate’s effects on blood glucose and cholesterol levels have piqued the interest of scientists, offering potential benefits in managing these aspects of health.
You can also reduce the phytate content of foods, like nuts and seeds, by soaking them overnight or sprouting them. Fermenting soy, to make tempeh or miso, reduces their phytate content too. If you’re trying to maximize the nutritional benefits you get from soy, fermented soy sources such as miso or tempeh are better choices than tofu, an unfermented soy food.
However, some processed foods incorporate phytases, enzymes that break down phytate, to improve bioavailability. So, the impact of phytate on nutrition largely depends on how soy is prepared and consumed.
What about the Oxalates in Soy and Other Plant-Based Foods?
Oxalates, compounds in soy and numerous other plant-based sources, reduce mineral absorption and increase the risk of kidney stones if you have a history of calcium oxalate stones. However, the oxalate content of soy foods varies with how they’re processed. In general, extensively processed soy products have lower oxalate levels. Conversely, minimally processed alternatives such as soy flour, soy nuts, and edamame may contain higher concentrations of oxalates.
If you have a history of calcium oxalate kidney stones, it’s best to reduce the number of oxalates in your diet and choose low-oxalate plant-based foods. You can find lists of low-oxalate plant-based foods online. Combine a low-oxalate diet with drinking plenty of water to avoid painful kidney stones. If you don’t have a history of kidney stones, eating moderate quantities of oxalates is unlikely to be a problem. Some cooking methods, particularly boiling, also reduce oxalates.
Saponins: Multifaceted Compounds
Soy and other legumes also contain saponins, versatile bioactive compounds known for their antimicrobial, antifungal, and immune-modulating properties. While some claim that saponins block nutrient absorption and disrupt endocrine function, evidence supporting their negative effects is scant.
In reality, saponins offer a range of potential health benefits. They may lower cholesterol levels by forming insoluble complexes with cholesterol and bile acids in the gut. Additionally, saponins may help regulate blood glucose levels and exhibit anticancer properties, particularly against colon cancer cells. Their effects on nutrient absorption depend on individual metabolism and dietary context.
Take a Balanced Approach to Antinutrients
In the realm of nutrition, it’s crucial to take a balanced and evidence-based approach when evaluating the impact of anti-nutrients. Soy, as a staple in many healthy diets worldwide, showcases the complexity of this issue. While anti-nutrients in soy can indeed affect nutrient bioavailability, the impact varies with factors such as food preparation and individual dietary patterns.
Rather than demonizing specific foods or food components, choose a variety of healthy, whole foods and eat a varied and balanced diet. Anti-nutrients are part of the nutrition conversation, but they aren’t something to obsess over, especially if you’re eating many types of plant-based foods.
Therefore, when it comes to soy and its anti-nutrient content, a nuanced perspective is key. By understanding the interplay between anti-nutrients and your diet, you can enjoy the healthful benefits of this versatile legume without unnecessary worry. Keep in mind that everyone responds differently to specific foods, so listen to your body!
References:
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- Sutardi and Ken A. Buckle. “Reduction in Phytic Acid Levels in Soybeans During Tempeh Production, Storage and Frying.” Journal of Food Science 50 (2006): 260-263.
- Wen Y, Liu A, Meng C, Li Z, He P. Quantification of lectin in soybeans and soy products by liquid chromatography-tandem mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci. 2021 Nov 15;1185:122987. doi: 10.1016/j.jchromb.2021.122987. Epub 2021 Oct 13. PMID: 34656828.
- Kårlund A, Paukkonen I, Gómez-Gallego C, Kolehmainen M. Intestinal Exposure to Food-Derived Protease Inhibitors: Digestion Physiology- and Gut Health-Related Effects. Healthcare (Basel). 2021 Aug 5;9(8):1002. doi: 10.3390/healthcare9081002. PMID: 34442141; PMCID: PMC8394810.
- Savage, Geoffrey P. and Warinporn Klunklin. “Oxalates are Found in Many Different European and Asian Foods – Effects of Cooking and Processing.” Journal of Field Robotics 7 (2018): 76.
- Today’s Dietitian. Vol. 23, No. 4, P. 22. April 2021.
- Mohamad, Alaa Alshikh and Joumaa Al- Zehouri. “The effect of the boiling process on the Oxalic acid content of some vegetables in the Syrian local market.” Research Journal of Pharmacy and Technology (2021): n. pag.
- Sharmin F, Koyama T, Koyama H, Ishizaki S. Cholesterol-binding ability of saponin from Japanese starfish. J Food Sci Technol. 2021 Aug;58(8):3056-3064. doi: 10.1007/s13197-020-04809-4. Epub 2020 Sep 25. PMID: 34294968; PMCID: PMC8249638.
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