A Look at Soybean Nutritional Value and Chronic Kidney Disease

Apr
30

A Look at Soybean Nutritional Value and Chronic Kidney Disease

Just like eggs, soy has a long history of being known as “good” or “bad” with different headlines coming out once every few years. A controversy like this can be confusing on whether or not soybean products have a good nutritional value and if you should be avoiding them. Even more so when you aren’t sure of its effects on certain chronic diseases, such as kidney disease or diabetes. 

What is soy?

Soybeans are a type of legume, living within the same family of beans and lentils. They grow within fuzzy green pods, which you may recognize if you’ve ever enjoyed edamame

Soybeans and other soy products are popular foods across many Asian countries, but quickly found a place among many other cuisines as the trend of plant-based diets has increased in recent years.

Popular soy products

Within the US, the most popular and well-known soy products are:

Non-fermented

  • Soy milk
  • Tofu
  • Edamame
  • Soy nuts
  • Sprouts

Fermented

  • Miso
  • Tempeh
  • Natto
  • Soy sauce

Certain soybean products such as tofu and soy milk are commonly fortified with calcium, which can help reduce deficiencies in those following plant-based diets and boost nutritional value. Textured Vegetable Protein (TVP) is also a popular product for food manufacturers to use within vegetarian and vegan products to mimic the taste and texture of items like chicken nuggets, burger patties, bacon, and more. 

Soybean Nutritional Value and Health Benefits

Soybeans are very nutritionally dense. The following percentages are typical makeups of soybeans by seed weight (1,2): 

  • 35-40% protein
  • 20% fat
  • 30% carbohydrate
  • 15-20% water, fiber, etc.

Fat

The fat soybeans provide mostly consists of unsaturated fats, and is specifically high in linoleic acid. (1). Research has shown that replacing saturated fat with unsaturated fats, especially linoleic acid, is linked to lower coronary heart disease deaths (3). 

Most Americans could benefit from increasing their unsaturated fat to saturated fat ratio, specifically by getting more Omega-3 fatty acids in their diet. While switching out butter for soybean oil in cooking can have a positive health effect, do not rely solely on it for all of your needs.

Soybean oil does not provide much Omega-3 fatty acid content, so be sure to reach for other sources that will provide a more significant amount such as walnuts and walnut oil, flaxseeds and flaxseed oil, and of course fatty fish such as salmon or mackerel (4). 

Protein

Animal-based proteins have always been highly regarded due to their complete amino acid profile (AKA protein building blocks). This means that protein sources derived from animals (meat, dairy, and eggs) contain all of the necessary types of protein building blocks that the human body needs. The human body can use around 95% of the animal-based protein it digests (5). 

Soy is currently the most popular mass-produced plant-based protein in the food industry, and for good reason. The nutritional value of soybean protein is the closest a plant-derived protein has come to an animal-based protein. It has a complete amino acid profile similar to whey protein, often used in protein shake powders, and has a 95-98% digestibility rate (5). 

While soy protein technically contains all nine essential amino acids, it is relatively low in methionine, so it is important to vary your protein routine to be sure you are getting all of your essential amino acids (6). Other plant-based sources you can pair with soy to get more methionine include rice, wheat, oats, rye, and beans (7). 

Carbohydrate

Soybeans are well-known for their protein and fat content, but their carbohydrate content is often overlooked. Most food manufacturers use soybeans to either squeeze out oil or isolate the protein. 

Sucrose, otherwise known as sugar, makes up as high as 25-35% of the total carbohydrate (8). The presence of sugar in soybeans doesn’t necessarily make them an unhealthy option with no nutritional value by default. Many vegetables, including carrots, beets, and bell peppers, contain natural sugars!

The other main carbohydrate component in soybeans is fiber. Soybeans are rich in insoluble fiber, which helps regulate bowel movements. They also contain a specific type of carbohydrate that acts as a prebiotic. Prebiotic substances essentially “feed” our gut bacteria so they can continue to thrive and promote healthy bacteria to grow. 

Moreover, soybeans are a growth promoter of Bifidobacterium. Research has shown this type of bacteria to be beneficial to the body. According to a 2021 study, some of the primary benefits of this substance are (9):

  • Acting as an anti-inflammatory agent
  • Boosting immune function
  • Supporting healthy bowel movements in the intestine
  • Maintaining a healthy pH balance in the intestine to prevent the growth of harmful bacteria
  • Reducing the impact of insulin resistance 

What are the concerns with soy?

Isoflavone & Phytoestrogen Impact on Testosterone Levels

Isoflavones are a type of plant substance that is very chemically similar to that of the human-produced hormone estrogen. They are classified as phytoestrogens for this reason. Soybeans are unique in that they contain a very high content of isoflavones compared to other plant foods (10).

As you may know, estrogen is the dominant female hormone. Therefore, concerns have been raised that men consuming soy-based foods would experience feminizing effects. A research review analyzing the outcomes of 41 studies completed in 2021 found no statistically significant impact on testosterone levels in men consuming soy. While there may still be select case reports out there that claim otherwise, it is important to note the level of consumption when looking at the effects. Many of these reports come from rare situations, such as consuming 360mg per day of isoflavones, compared to the typical 30-50mg per day (10).

Less than 10 percent of Asians consume more than 75mg of isoflavones per day, which is equal to about three servings of traditional soy foods. Therefore, 75mg would be considered the cutoff for high intake. 

Serving sizes of traditional soy foods:

  • 1 cup soymilk
  • ½ cup tofu
  • 1-ounce soynuts

To summarize, although isoflavones have not been shown to have a significant impact on testosterone levels, they have been found to have many positive effects on the body. There is a wealth of research on the benefits of isoflavones for women during menopause, including reducing hot flashes, providing antidepressant effects, and lowering the risk of breast and prostate cancers (9,10, 11). 

Phytic Acid

Phytic acid is the stored form of phosphorus in plant-based foods (12). Many types of legumes and grains contain naturally occurring phytic acid ranging from about 0.5 to 7 percent. On average, soybeans have about 2.5% phytic acid content (9). 

Phytic acid is a compound that is often considered an antinutrient because humans lack the enzyme necessary to properly break it down. As a result, it can reduce the body’s ability to absorb important minerals such as iron, zinc, and calcium. Despite this, it does have many beneficial properties as well. For example, it contains powerful antioxidants and anticancer agents, and can help lower levels of fat in the blood (9). 

In conclusion, phytic acid is both a pro and a con within itself. For those living with chronic kidney disease, it may be beneficial to increase phytic acid intake as its interference with mineral absorption can help reduce the formation of kidney stones (13). 

Oxalates

Oxalates are another naturally occurring substance in plant foods. If you are living with kidney disease, you have likely heard to stay away from them. A combination of too much oxalate and too little liquid in the body can cause kidney stones. Below is a table depicting the oxalate levels in various soy foods:

Food ItemServing SizeOxalate CategoryOxalate Value
Soy Milk1 CupLow4mg
Soy Sauce1 TablespoonLow3mg
Soybeans1 cupModerate7mg
Soy Burger3.5 ozHigh12mg
Soy Flour1 cupVery High94mg
Soy Protein Isolate1oz Very High27mg
*Information within above table obtained from the University of California at Irvine Kidney Stone Center

Generally, anything over 10mg of oxalate per serving is considered high. In addition to the table above, a separate study sampling various soy products concluded that tempeh, soynut butter, and textured vegetable protein were all considered high in oxalate (14). 

Potassium

Limiting potassium is a common concern for those living with Chronic Kidney Disease due to the increased risk of potassium buildup in the body. In general, foods with over 200mg per serving are considered high in potassium, and anything under 200mg is considered low. 

Raw soybeans are very high in potassium, with over 3,000mg of potassium in just 1 cup (2). However, most people are not typically casually enjoying raw soybeans on the daily. Below is a table breaking down the potassium nutritional value of common soybean foods.

Food Item*Serving SizePotassium CategoryPotassium Value
Miso1 tablespoonLow36mg
Soy sauce1 tablespoonLow70mg
Tofu, firm**3 ozLow135mg
Soy milk, original1 cupHigh379mg
Edamame, frozen, no salt added1 cupHigh410mg
Soy protein powder1 (45mg) scoopHigh420mg
Tempeh, cooked100gHigh401mg
*Nutrtional value for these food items were derived from USDA FoodData Central accessed on April 24th, 2024
**Tofu potassium content calculated as the mean between three different brands

While some of the products listed in the table above are low in potassium, they may also be high in sodium, which can also be harmful in excess. Be sure to choose low-sodium options when available and keep track of your daily sodium intake. Learn more about the link between sodium and heart health in my other blog post here

Summary

To sum up, soy can be a controversial topic. Current research shows that the nutritional value of soybean products makes them a great, healthy option to add to your diet as a source of highly digestible lean protein and healthy fats. Be sure to check if the soy-based product you are buying is fortified with calcium, especially if you need to monitor your calcium intake with chronic kidney disease. If you are consuming a largely plant-based diet, pair soy foods with complementary plant-based proteins such as rice and other grains to meet all your amino acid needs. 

Last of all, the three primary concerns that are associated with soy are testosterone-lowering effects in men and high phytic acid, oxalate, and potassium content. Studies have shown no significant impact on testosterone levels with soy consumption and a benefit to the high phytic acid content in those with CKD. Finally, we know that high oxalate and potassium content in soy foods depends on the product, and research analyses have shown soy milk and soy sauce to be considered low in oxalate. 

Sources

  1. Kahraman A. 2017. Nutritional value and foliar fertilization in soybean. J. Elem., 22(1): 55-66. DOI: 10.5601/jelem.2016.21.1.1106 
  2. Fooddata Central Search Results. FoodData Central. (n.d.). https://fdc.nal.usda.gov/fdc-app.html#/food-details/174270/nutrients 
  3. Clifton, P., & Keogh, J. (2017). A systematic review of the effect of dietary saturated and polyunsaturated fat on heart disease. Nutrition, Metabolism and Cardiovascular Diseases, 27(12), 1060-1080. https://doi.org/10.1016/j.numecd.2017.10.010 
  4. Santos, H. O., Price, J. C., & Bueno, A. A. (2020). Beyond Fish Oil Supplementation: The Effects of Alternative Plant Sources of Omega-3 Polyunsaturated Fatty Acids upon Lipid Indexes and Cardiometabolic Biomarkers—An Overview. Nutrients, 12(10), 3159. https://doi.org/10.3390/nu12103159
  5. Qin, P., Wang, T., & Luo, Y. (2022). A review on plant-based proteins from soybean: Health benefits and soy product development. Journal of Agriculture and Food Research, 7, 100265. https://doi.org/10.1016/j.jafr.2021.100265
  6. Friedman M, Brandon DL. Nutritional and health benefits of soy proteins. J Agric Food Chem. 2001 Mar;49(3):1069-86. doi: 10.1021/jf0009246. PMID: 11312815.
  7. https://www.sciencedirect.com/topics/food-science/methionine#:~:text=Examples%20are%20corn%20(21%20mg,(14%20mg%2Fg)
  8. Al Loman, A., & Ju, L. (2017). Enzyme-based processing of soybean carbohydrate: Recent developments and future prospects. Enzyme and Microbial Technology, 106, 35-47. https://doi.org/10.1016/j.enzmictec.2017.06.013 
  9. Kim, I., Kim, C., & Yang, W. (2021). Physiologically Active Molecules and Functional Properties of Soybeans in Human Health—A Current Perspective. International Journal of Molecular Sciences, 22(8), 4054. https://doi.org/10.3390/ijms22084054 
  10. Reed, K. E., Camargo, J., Hamilton-Reeves, J., Kurzer, M., & Messina, M. (2021). Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reproductive Toxicology, 100, 60-67. https://doi.org/10.1016/j.reprotox.2020.12.019 
  11. Kim, I. (2021). Current Perspectives on the Beneficial Effects of Soybean Isoflavones and Their Metabolites for Humans. Antioxidants, 10(7), 1064. https://doi.org/10.3390/antiox10071064
  12. Gupta, R. K., Gangoliya, S. S., & Singh, N. K. (2015). Reduction of phytic acid and enhancement of bioavailable micronutrients in food grains. Journal of Food Science and Technology, 52(2), 676-684. https://doi.org/10.1007/s13197-013-0978-y 
  13. Upadhyay, J., Tiwari, N., Durgapal, S., Jantwal, A., & Kumar, A. (2022). Phytic acid: As a natural antioxidant. Antioxidants Effects in Health, 437-450. https://doi.org/10.1016/B978-0-12-819096-8.00015-X 
  14. Al-Wahsh IA, Horner HT, Palmer RG, Reddy MB, Massey LK. Oxalate and phytate of soy foods. J Agric Food Chem. 2005 Jul 13;53(14):5670-4. doi: 10.1021/jf0506378. PMID: 15998131. 

SHARE THIS POST

Leave a Reply

Your email address will not be published. Required fields are marked *

Meet Edith

Registered Dietitian with over 10 years of experience sharing nutrition knowledge that you can use to enjoy food again

The Shop

RESOURCES TO HELP YOU BETTER YOUR HEALTH

FIND ME ELSEWHERE

Grab Your Guide

Complete the form below for instant access