The final two areas I would like to touch on in regards to soy are trypsin inhibitors and phytates. Trypsin is a pancreatic enzyme released in response to protein-containing meals and assists in breaking down long protein chains into peptides and amino acids. This is critical for the digestion and absorption process because whole proteins and long peptide chains usually cannot be and should not be absorbed as a whole. If we infer a little, we can assume that inhibiting the enzyme that assists in protein digestion would cause us to absorb less of the protein we eat. This mechanism is actually a natural deterrent from animals and insects that would normally consume the soybean. This protective mechanism can be seen in many other forms like protective hulls, saponins, essential oils, caffeine, capsaicin and atropine. These are all naturally occurring substances in plants that deter insects and animals from eating them, having effects ranging from in-digestibility to toxicity. The opposite of this would be seed bearing plants like fruit which want to be eaten so their seeds can be spread when passed through animal stool with the fruit inviting consumption while the seed itself is not digested so it can grow elsewhere.
There have been many studies conducted on trypsin inhibitors in humans and animals. The evidence suggested that chronic ingestion of products like soy, which contain these trypsin inhibitors can and do limit protein utilization. The degree often varies but if soy is an individual's main protein source, then they can limit their intended protein intake by up to 20%. Raw soy products like soy flour are the largest culprit in this, with heat treated soy products and fermented soy products being less of an issue. When comparing trypsin inhibition to whole, unprocessed soybeans, the following amounts were found:
Soy Sauce: 0.8%
Soy Proteins: 8.5-26.5%
Raw Soy Flour: 99%
Raw soybeans and soybean flour are the major products to be avoided here, if trypsin inhibition is a concern. Next would be soy milk followed by tofu. Tofu comes in various forms, some raw and some fermented so it would be safer to look for fermented tofu products. Soy sauce and miso are both heavily fermented products and contain a negligible amount of trypsin inhibitors so those should not be a concern for most people.
Phytates are related to trypsin inhibitors because in addition to blocking mineral absorption, they also act as enzyme inhibitors. Phytic acid is present in grains, legumes and nuts/seeds. It is the storage form of phosphorous in the plant and digested in animals with multiple stomachs (like cows) but not in humans. In addition to this, the phytic acid also blocks mineral absorption like calcium, magnesium, iron and zinc. In regards to enzyme inhibition, phytates not only block trypsin but pepsin and amylase which are used to digest proteins and starches, respectively.
Phytates are another naturally occurring substance that can have some surprising affects on the body. Since the phytates are inhibiting some vitamin and mineral absorption, people can develop nutritional deficiencies that may take years to notice. Phytates can inhibit calcium and Vitamin D absorption which, in large amounts, can lead to rickets and lack of bone formation. Inhibition of minerals like magnesium and zinc, along with iron can lead to not only decreased bone density but tooth decay and anemia. Minerals like magnesium also assist in digestive peristalsis and zinc helps to block aromatization in men (leads to decreased testosterone), so there are many under the surface issues that can arise an be exacerbated over time.
The Weston A. Price foundation suggests that children are most at risk when consuming high amounts of phytates and should not make up a large part of the diet. Some good news is that phytates can be deactivated with a few supplements. Increasing calcium intake has been shown to assists in phosphorous absorption and Vitamin C can inhibit the iron depleting effects of phytates. Thus, increasing ingestion of foods or supplements high in calcium like dairy products and high in Vitamin C, like dark greens can mitigate some of these effects. Vitamin A and beta-carotene have also been shown to work similarly like Vitamin C in regards to iron and are also encourage to be consumed.
FOOD SOURCES OF PHYTIC ACID As a percentage of dry weight
|Sesame seed flour||5.36||5.36|
|Soy protein concentrate||1.24||2.17|
|Whole wheat bread||0.43||1.05|
WHAT TO DO?
Since phytates are found it not only soybeans but nuts, seeds and legumes, phytates are certainly not the main culprit in soy. However, trypsin inhibitors are much more active in soy than other foods and this can be a major concern if soy is making up the majority of protein in your diet. My major recommendations in regards to chronic soy consumption would be the following, taking all of the studies and risk factors into consideration:
-Consume other protein products in place of or in addition to soy
-Consume more fermented soy products and fewer raw soy products
-Consume foods high in calcium, Vitamin C, Vitamin A and beta-carotene
-Consider taking supplemental magnesium and zinc for their anti-estrogenic effects
-Avoid high amounts of raw soy of you have poor thyroid function
-Avoid eating large amounts of soy AND goitrogenic vegetables together to limit thyroid down- regulation (kale, cabbage, Brussels sprouts, turnips)
-Replace or limit extra phytate consuming foods(nuts, seeds, legumes, grains) in your diet if also consuming large amounts of soy
A diet high in cooked and raw vegetables can help to mitigate many of the adverse effects of a diet high in soy and should be prioritized over consuming more grains and legumes. Potatoes are a safer choice and actually, white rice with the hull removed has fewer phytates than brown rice, so Jasmine, Arborio and other white rices may be a good starchy carbohydrate choice. Some people may need to consider taking extra minerals if they feel they exhibit any of the symptoms of low testosterone and make smarter vegetable choices if they have existing thyroid issues. Lastly, supplementing with a non-soy protein may help to boost overall protein content and limit exposure to some of these side affects for the person not wanting to consume any animal products. Some possible choices are non-GMO rice and pea proteins, or if you are willing to try, there are a few organic and grass-fed milk proteins out there that come from well-raised cattle.
Soy in and of itself will not wreak total havoc on your health and there are studies to prove it's benefits and dangers. It is largely the amount consumed that has the adverse affects we are trying to avoid and over-reliance on any one food is never recommended. Traditional Japanese cuisine, although known for soy products, consists of very little soy on a day to day basis, anywhere from a few ounces or less per person. This is important to note because all of this information must be taken in the context of how much is being consumed. If we looked at the health of the Japanese and attributed it all to soy, we would be missing the point because it makes up so little of their total calories; likewise if we said soy was completely detrimental to health but fed people a diet consisting of 50% soy. As always, use this information to make informed decisions and pay attention to your health to clue you in as to what areas of your diet may need changing.
Nagel, Raimie(March 26, 2010). Living With Phytic Acid
Weston A. Price Foundation, May 2013. <http://www.westonaprice.org/food-features/living-with-phytic-acid>
Y, Miyagi et al (October 1997). Trypsin Inhibitor Activity In Commercial Soybean Products In Japan.
Pubmed, May 2013. <http://www.ncbi.nlm.nih.gov/pubmed/9505242>.
Liener, Irvin (1995). Possible Adverse Affects of Soybean Carcinogens.
Pubmed, May 2013. Journal of Nutrition 125: 744-750.
Wolf, Walter and Anderson, Robert(1995). Compositional Changes in Trypsin Inhibitors, Phytic Acid,
Saponins and Isoflavones Related to Soybean Processing.
Pubmed, May 2013. Journal of Nutrition 125: 581-588.
Freeman, B.C. and G.A. Beattie. 2008. An Overview of Plant Defenses against Pathogens and Herbivores. The Plant Health Instructor. DOI: 10.1094/PHI-I-2008-0226-01