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Can Eating Nuts and Seeds Be Detrimental To Thyroid Health?

There is no question that nuts and seeds are my favorite type of whole food. I ate my share of junk food growing up, but nuts and seeds were one of the few “healthy” foods I consumed on a regular basis. Okay, I admit they weren’t too healthy, as I usually ate them out of a can, which of course included the unhealthy oils. In any case, eating nuts and seeds can be a healthy part of one’s diet. However, one needs to be cautious about eating too many nuts and seeds, and sometimes it is a good idea to completely avoid eating them.

Let’s begin by discussing some of the health benefits of nuts and seeds. First of all, nuts are an excellent source of protein. For example, one cup of almonds provides about 20 grams of protein. In fact, nuts and seeds can be a main source of protein for vegans and vegetarians. Nuts and seeds can also be a good source of certain minerals. Most nuts and seeds have a good amount of magnesium. And some nuts, such as almonds, are good sources of calcium. Nuts and seeds are also excellent sources of fiber. Yet another benefit is that nuts and seeds have a low glycemic index. So there are many great benefits of eating nuts and seeds.

Which Nuts and Seeds Are The Healthiest For You?

Almonds. Almonds are one of the healthiest nuts you can eat. They are high in many different nutrients. Some of the cardioprotective nutrients found in almonds include alpha-tocopherol, arginine, magnesium, copper, manganese, calcium, and potassium (1) [1]. They are an excellent source of protein, and are high in fiber. There have been numerous studies on the health benefits of almonds. One study showed that almond consumption may decrease total cholesterol and does not significantly affect LDL or HDL cholesterol, triglycerides, or the LDL:HDL ratio (2) [2]. Another study showed that almonds used as snacks in the diets people with high lipid levels significantly reduce coronary heart disease risk factors (3) [3].

Walnuts. Compared to most other nuts, which contain higher amounts of monounsaturated fatty acids, walnuts are unique because they are rich in omega 3 and omega 6 polyunsaturated fatty acids (4) [4]. Walnuts contain multiple health-beneficial components, such as having high levels of arginine, folate, fiber, tannins, and polyphenols (4) [4]. One study showed that walnuts have a large antioxidant capacity (5) [5]. There is even evidence that eating walnuts might help to prevent breast cancer (6) [6]. Due to the high content of omega-3 fatty acids, eating walnuts might also help to improve learning and memory functions (7) [7].

Cashews. Cashews are by far my favorite nut. Although I can’t say that they are the healthiest of all of the nuts, they still have numerous nutrients (i.e. manganese, tryptophan, magnesium), are high in protein and fiber, and taste great when covered with dark chocolate (of course just about every type of nut tastes better when covered with dark chocolate!). Unfortunately I couldn’t find too many studies regarding the health benefits of cashews, although there is some evidence that they might have anti-diabetic properties (8) [8].

Brazil nuts. Brazil nuts are well known for having high levels of selenium. In fact, there are numerous studies which show that eating only one or two Brazil nuts per day can help to improve selenium status (9) [9] (10) [10] (11) [11].

Macadamia nuts. These are also pretty yummy. The protein content of macadamia nuts isn’t as high as other nuts. Studies have demonstrated that eating macadamia nuts can help to lower both total and LDL cholesterol (12) [12] (13) [13]. Another study showed that short-term macadamia nut consumption improves the biomarkers of oxidative stress, thrombosis and inflammation (14) [14], which are risk factors for coronary artery disease.

Sunflower seeds. Sunflower seeds are also very healthy, as they have high levels of protein and dietary fiber. They are also high in vitamin E, thiamin, folate, manganese, copper, magnesium, selenium, and other nutrients. However, sunflower seeds (along with peanuts, flaxseed, and linseed) can also have high levels of cadmium (15) [15].

Pumpkin seeds. Pumpkin seeds consist of high amounts of potassium, magnesium, manganese, selenium, copper, chromium, and molybdenum (16) [16]. In the past I’ve discussed how pumpkin seeds can act as a natural aromatase inhibitor, and it also can benefit men who have benign prostatic hyperplasia (17) [17] (18) [18]. There is also evidence that pumpkin seed oil exhibits antihypertensive and cardioprotective effects (19) [19].

Pistachios. I love pistachio nuts. Like most other nuts, pistachios have high amounts of protein and are a good source of dietary fiber. Among nuts, pistachios contain the highest levels of potassium, gamma-tocopherol, vitamin K, phytosterols, and xanthophyll carotenoids (20) [20]. One study showed that a diet consisting of 15% of calories as pistachio nuts (about 2-3 ounces per day) over a four week period can favorably improve some lipid profiles in subjects with moderate hypercholesterolemia and may reduce risk of coronary disease (21) [21]. This was confirmed by another study, which also showed that pistachios can increase serum antioxidants, such as lutein, gamma-tocopherol, and beta carotene (22) [22].

Pecans.Let’s not forget about pecans. They are lower in protein when compared to other nuts, but they have a high amount of dietary fiber, and they are a good source of magnesium, zinc, manganese, and iron. Just like many other nuts, there is evidence that eating a pecan-enriched diet can help lower total and LDL cholesterol, and increase HDL cholesterol levels (23) [23]. Pecans can also help to increase plasma postprandial antioxidant capacity (24) [24]. So I guess there are some benefits to eating pecan pie!

One thing you’ll notice is that even though nuts are high in fat, there are numerous studies which demonstrate that eating nuts and seeds can potentially decrease the risk of cardiovascular disease.

What’s The Deal With Peanuts?

Peanuts aren’t considered to be a nut, as they are classified as a legume. There is a lot of controversy over whether peanuts are healthy to eat. One of the reasons for this is because peanuts contain aflatoxins, which are natural toxins produced by the fungi Aspergillus flavus and Aspergillus parasiticus. Aflatoxins are associated with an increase in liver cancer and impaired growth in young children (25) [25]. However, the levels of aflatoxins produced in peanuts differs with the genetic variety of the plant and with the species and strain of the fungus (26) [26]. In other words, not all peanuts have high amounts of aflatoxins. Of course it can be a challenge to know whether the peanuts you’re eating have high amounts of aflatoxns.

The FDA requires the aflatoxin levels to be 20 parts per billion or less in both organic and non-organic peanut butters sold by retail stores. Keep in mind that this doesn’t apply to grinding your own peanut butter at the health food store, and so you’re probably better off buying an organic, pre-packaged peanut butter. Whole Foods claims to test all of their batches of the “365” brand of peanut butter for aflatoxins, and says that they keep it between 0 to 10 parts per billion (27) [27].

Even with the aflatoxins, there are some health benefits of eating peanuts. They are high in protein, and have high amounts of certain nutrients, such as manganese, tryptophan, vitamin E, and folate. They are a good source of fiber. They also have a small amount of resveratrol, which has many health benefits. Assuming someone doesn’t have a peanut allergy then I think in many cases it’s fine to eat organic peanuts (including organic peanut butter) on an occasional basis.

Getting back to the subject of aflatoxins, it’s important to understand that peanuts aren’t the only source of these toxins. Aflatoxins can be found in pecans, almonds, Brazil nuts, and other nuts, seeds, and legumes. They can also be found in other types of foods such as corn and wheat. Consuming small amounts of aflatoxins probably isn’t a big issue with most people, although you of course still want to be cautious, and this is yet another reason to consider buying organic food, as while it won’t completely eliminate the risk of aflatoxins, it will minimize the risk of exposure.

The Risks Of Eating Too Many Nuts And Seeds

I can easily eat a few cups of nuts and seeds per day. However, it usually isn’t wise to eat such a large amount on a daily basis. One of the biggest reasons is that nuts and seeds are high in omega 6 fatty acids. While it’s true that some nuts do have a decent amount of omega-3 fatty acids, pretty much all nuts and seeds have a higher amount of omega-6 fatty acids. These days most people have an imbalance of the ratio of omega-3 and omega-6 fatty acids, and so while it’s fine for most people to eat some nuts and seeds per day, you probably don’t want to exceed one cup per day, and it might be best to limit it to 1/2 cup on most days.

Nuts, Seeds, and Thyroid Health

I’ve spoken about goitrogens in the past, and certain nuts and seeds seem to have a small amount of goitrogenic activity. Some of the nuts and seeds which supposedly have goitrogenic activity include almonds, cashews, flax seeds, peanuts, pumpkin seeds, and walnuts. I couldn’t find much research on this, and most of the research I found showing that certain nuts and seeds are goitrogens were conducted many decades ago, and were performed on rats. This doesn’t mean that these studies weren’t valid, but it would be nice to have at least a few updated studies on this. Plus, roasting nuts and seeds apparently reduces the goitrogenic activity. With that being said, in my opinion, eating “normal” amounts of raw nuts and seeds shouldn’t inhibit thyroid function in most people.

However, there is another reason why some people with thyroid and autoimmune thyroid conditions need to be cautious about eating nuts and seeds. In past articles and blog posts I’ve spoken about how an increase in intestinal permeability (a leaky gut) is a potential cause of Graves’ Disease and Hashimoto’s Thyroiditis. Nuts and seeds contain lectins and phytic acid, which make them very difficult to digest. And there is evidence that lectins can cause an increase intestinal permeability. As a result, most people with gut problems will want to consider avoiding nuts and seeds until the health of their gut is restored back to normal. Soaking nuts and seeds can help to reduce the antinutrient content, and thus make them easier to digest. However, doing this won’t completely eliminate the lectins and phytic acid. In the past I put together a blog post entitled “Should People With Thyroid and Autoimmune Thyroid Conditions Avoid Foods With Lectins? [28]

In summary, nuts and seeds have numerous health benefits, as they are an excellent source of fats, protein, fiber, and have other beneficial nutrients. Although nuts and seeds have a high fat content, just about all of them offer cardioprotective benefits. Peanuts are actually classified as a legume, and although they also have numerous health benefits, some peanuts tend to have high levels of aflatoxins. One does need to be cautious about eating large amounts of nuts and seeds, as they are high in omega 6 fatty acids, are difficult to digest, and might also possess goitrogenic activity. On the other hand, for most people, eating a small amount of nuts and seeds on a daily basis can provide some great benefits to their health.