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Antinutrients and Thyroid Health

Grains, nuts, seeds, and legumes have numerous health benefits. However, many people are unaware that these foods also contain antinutrients which can interfere with the absorption of other nutrients you consume.  And so while I love eating nuts and seeds, and I’m not “anti-grain”, I do think it’s important for people to realize why they should minimize their consumption of these foods.  And so what I plan on doing in this blog post is to discuss the most common antinutrients, and hopefully after reading this you will have a better understanding as to why you should only eat minimal amounts of these foods.

Before I discuss these antinutrients, you might be wondering “why do these foods have anti-nutrients?”.  Well, some of these antinutrients are included in plants as a form of protection.  This includes lectins, protease inhibitors, and saponins.  These secondary metabolites help to ensure the survival of the seed.  However, they have other functions as well.  What I’d like to do now is discuss some of the more common antinutrients.

Lectins. These are probably the most well known of the different antinutrients, and I have put together a separate article on this entitled “Should People With Thyroid And Autoimmune Thyroid Conditions Avoid Foods With Lectins? [1]“.  Lectins are carbohydrate binding glycoproteins which can affect the turnover and loss of gut epithelial cells, damage the luminal membranes of the epithelium, interfere with nutrient digestion and absorption, stimulate shifts in the bacterial flora and modulate the immune state of the digestive tract (1) [2]. Systemically, they can disrupt lipid, carbohydrate and protein metabolism, promote enlargement and/or atrophy of key internal organs and tissues and alter the hormonal and immunological status (1) [2]. At high intakes, lectins can seriously threaten the growth and health of consuming animals (1) [2].  In summary, lectins can have a negative effect on the lining of the gastrointestinal tract, as well as the gut flora, which in turn can affect the absorption of nutrients.  Plus they can also affect the breakdown of fats, carbohydrates, and proteins.

Phytic acid. This is a major phosphorus storage compound found in nuts and seeds, as well as grains and legumes.  Phytic acid has the strong ability to chelate certain minerals, especially zinc, calcium, and iron (2) [3]. There is also evidence that phytic acid can bind to magnesium and affect its absorption as well (3) [4].  The binding can result in very insoluble salts that are poorly absorbed from the gastrointestinal tract, which results in poor bioavailability of minerals (2) [3].  In summary, phytic acid will affect the absorption of numerous minerals, which obviously isn’t a good thing.

Protease Inhibitors. These can inhibit the proteolytic activity of certain enzymes.  In other words, they will interfere with the breakdown of protein.  For example, certain legumes such as navy beans, red kidney beans, and adzuki beans have trypsin inhibitors (4) [5].  Soybeans and chickpeas also have trypsin inhibitors (5) [6].  Trypsin is an enzyme which breaks down numerous proteins.  What’s important to understand is that eating a lot of foods with trypsin inhibitors can affect the breakdown of proteins.

Oxalates.  These are naturally-occurring substances which belong to a group of molecules called organic acids.  Some of the foods with high amounts of oxalates include spinach, blueberries, blackberries, and almonds.  Foods high in oxalates can affect the absorption of certain nutrients, such as calcium.  Most people can eat normal amounts of foods with oxalates, although people with certain conditions, such as enteric and primary hyperoxaluria, need to eat a low oxalate diet.  I mentioned that spinach and blueberries are high in oxalates, and for those who routinely make smoothies, adding some spinach and/or blueberries is fine for most people.  However, you probably want to avoid adding large amounts of these foods to your smoothies, especially if you have one or two smoothies on a daily basis as I do.  I spoke about oxalates in a blog post I wrote entitled “Should Spinach Be Avoided In People With Thyroid Conditions? [7]

Saponins.  These are naturally occurring compounds that are widely distributed in all cells of legume plants, and derive their name from their ability to form stable, soaplike foams in aqueous solutions (6) [8].  Although saponins have some health benefits, they also can impair the digestion of protein and the uptake of vitamins and minerals in the gut, and can also cause hypoglycemia (7) [9].  They can also lead to the development of a leaky gut (8) [10].

Solanine.  This is a glycoalkaloid found in species of the nightshades, which include foods such as potatoes, tomatoes, eggplant, and peppers.  Although many people who eat these foods seem to do fine, because they can lead to inflammation and other problems, most autoimmune diets don’t include the nightshade vegetables.  One of the best articles I’ve read on the nightshades is from Dr. Garrett Smith of the Weston Price Foundation [11].

These are some of the most common antinutrients, although there are a few I didn’t list.  A couple of additional ones worth mentioning are tannins and salicylates.  Tannins might inhibit the digestion of dietary proteins, and might also have some systemic effects.  Salicylates are phytochemicals found in fruits, vegetables, some other foods, and in some over-the-counter medications and prescription drugs.  Most people can eat normal amounts of salicylates, but some people are unable to tolerate smaller amounts.

How Do Antinutrients Affect Thyroid Health?

Loren Cordain has a wonderful article entitled “Cereal Grains: Humanity’s Double-Edged Sword [12]“.  In this article he talks about some of the antinutrients and focuses on the risks of cereal grains.  Towards the end of this article he discusses how cereal grain consumption can lead to the development of autoimmune conditions.  As he discusses in his article, the genetic component that is most closely associated with the expression of autoimmune conditions are those genes which code for the human leukocyte antigens (HLA).  The HLA is subdivided into different classes, and Dr. Cordain discusses how lectins are potent inducers of HLA class II molecules.  I also mentioned earlier how certain antinutrients, such as lectins and saponins, can potentially cause a leaky gut, which in turn can trigger an autoimmune response.

In his article Dr. Cordain also talks about how these antinutrients “might induce cross-reactivity and hence autoimmunity by virtue of peptide structures homologous to those in the host”.  In other words, the structures of these antinutrients might be similar to certain structures in the human body, and as a result the body might produce autoantibodies.  This is known as molecular mimicry, which has been proposed as a pathogenic mechanism for autoimmune disease.

There isn’t much evidence when it comes to direct effects of these anti-nutrients on thyroid health.  In other words, while consuming some of these anti-nutrients might cause a leaky gut and trigger an autoimmune response, they don’t seem to directly stimulate or inhibit thyroid activity.  However, there is evidence that soyasaponins, which were isolated from soybeans, increased the levels of serum thyroid hormones, which lead to lipid peroxidation (9) [13].  Lipid peroxidation involves damage to the membranes of fats, and has been implicated in conditions such as atherosclerosis, irritable bowel disease, retinopathy of prematurity (ROP), borderline personality disorder, asthma, Parkinson’s disease, kidney damage, preeclampsia and other conditions (10) [14].

Is It Best To Completely Avoid These Foods?

I definitely don’t think that most people permanently need to avoid nuts, seeds, and beans.  But I do think it’s a good idea to minimize one’s consumption of these foods.  I love nuts and seeds, and I can easily eat a few cups per day, but most people probably should limit their consumption to half a cup per day total.  As for grains, although there are some healthy nutrients in grains, we don’t need to eat grains to survive.  Plus, although there are some healthy nutrients in grains, remember that the antinutrients will reduce the absorption of these nutrients.  With that being said, I think that eating a small amount of grains is fine for many people, preferably gluten free grains.  On the other hand, many people seem to thrive when eliminating grains from their diet.

Soaking And Sprouting Can Improve Nutrient Absorption

Soaking and sprouting nuts, seeds, beans, and grains can help to reduce the anti-nutrient content of these foods.  This in turn can improve the contents of certain essential amino acids, total sugars and B-group vitamins (11) [15].  Of course many people aren’t willing to take the time to do this, and keep in mind that this won’t completely eliminate the anti-nutrient content of these foods.  As a result, it’s best to minimize your consumption of these foods, and if someone has gut issues then it’s probably a good idea to avoid eating them altogether until the gut is healed.  With that being said, if someone is a vegetarian or vegan it can be challenging to follow a gut repair diet and completely eliminate all of the foods with antinutrients, and so eating soaked nuts, seeds, beans, and grains can make it a lot easier to follow such a diet.  I’ve had some people follow a gut repair diet and do okay while eating small amounts of these soaked and sprouted foods.  On the other hand, some people aren’t able to heal the gut unless if they completely eliminate these foods from their diet.

In summary, due to the antinutrients present in nuts, seeds, legumes, and grains, one wants to try to minimize their consumption of these foods.  The reason is because these antinutrients can interfere with the absorption of certain nutrients such as zinc, calcium, iron, and magnesium, and can also lead to certain health issues, such as a leaky gut.  Although all people need to be careful not to eat too many of these foods, people with autoimmune conditions such as Graves’ Disease and Hashimoto’s Thyroiditis will especially want to reduce their intake, and in many cases it’s best to avoid these foods altogether.