Soy usually falls into two camps. If you are vegetarian or vegan it has been hailed as the savior for those consuming diets too low in protein and too high in carbohydrates. The polar opposite end of the spectrum usually belongs to those interested in sports performance and physique enhancement that view soy as the weak man's protein. I won't pass any judgment here as I have been in both camps myself and see why both arguments can be made.
Without delving right into the research, let's look at some of the generic information on soy. A half a cup of firm tofu(126grams) contains the following:
Soy also has a glycemic load of 1, which is extremely low. It is actually pretty low in most vitamins and nutrients but high in calcium and manganese. Consider that a one-pound package of tofu costs between $3 and $4. You can find it cheaper at an Asian market but assuming you get most of yours at a big-box grocery store, you can expect to pay that amount. At 2g protein per ounce, a one pound block contains 32 g protein, so each ounce of protein costs between 9 and 13 cents.
Taking a look at a favorite among the strength and physique crowds, a typical 1/2 chicken breast serving(118grams) of chicken breast contains the following:
Chicken breast has a glycemic load of 0. It is high in vitamin B6, pantothenic acid, niacin, phosphorous and selenium. Considering that soy is a plant and chicken is an animal, it is hard to compare vitamin and mineral contents because the foods are molecularly very different. Based on the macronutrient ratio, though, it appears that chicken wins over soy for protein. It is higher in calories per serving but if you tripled the soy serving to get a similar protein content, you would end up with 264 calories, so soy truly isn't lower-calorie when you match protein content. And protein content is why vegan and vegetarians eat soy, for the most part.
If you buy chicken breast at $3 a pound, a one pound serving contains 96 grams of protein and ends up costing about 3 cents per gram of protein.
Well, that solves that, right? Soy is more expensive per ounce, is higher in calories gram for gram of protein and doesn't contain a superhuman amount of vitamins and minerals compared to chicken. In reality, though, who cares? If you are vegan or vegetarian then the reality of the matter is that you aren't going to eat chicken, beef or pork no matter how nutritionally dense or inexpensive it is. So the real argument comes next....
Is Soy BAD for Us?
Recently, there has been a movement to expose soy as not only inadequate when compared to animal protein, but potentially damaging to our health. The argument is that soy is estrogenic, goitrogenic and contains trypsin inhibitors. Phytoestrogens in soy are said to mimic physiological estrogen which is bad news for men in terms of libido, fat mass and muscle mass. Goitrogens are chemicals that inhibit your thyroid from making adequate thyroid hormone. Low thyroid hormone can present as low energy, sensitivity to cold, dry skin, weakness, weight gain and depression. Trypsin inhibitors are chemicals that prevent the enzyme trypsin from cleaving proteins into amino acids, which is why soy is considered a low quality protein by some. Generally, the protein in soy has about a 60% absorption rate, which is pretty low compared to animal proteins.
Without looking any further into these claims, the three reasons noted above were enough to dissuade me from eating soy completely in the last few years. Research has opened my eyes to a few things so let's quickly address two of our three areas.
Phytoestrogens are plant derived compounds that behave as estrogen mimics in the human body. The two major phytoestrogens in soy are lignans and isoflavones. Dietary estrogens are weak compared to the ones your body produces and do not bind as readily to estrogen receptors in the body. The real question is how much of an effect they have on the human body and in what doses. Turns out that isoflavones, the compound in question in regards to estrogen mimicry, is metabolized differently depending on the person and age. A study comparing baseline levels of estradiol in men and women before and after consumption of soy shows significant increases in plasma isoflavones. Men hovered around 50 pg/Ml while mid-cycle women were closer to 1,000 pg/Ml. After ingestion of soy, the adults on average increased circulating levels of isoflavones to 1,000,000! So the phytoestrogen levels increased men by by 20,000 and mid-cycle women by 1,000. The circulating levels are hard to interpret, though because of the unknown level of effects the isolfavones have on the body. However, even at low physiological effects, a 20,000 increase in men is food for thought.
Ok, so isolfavones from phytoestrogens could potentially mimic estrogen. Hang in there because one isolfavone in particular, genistein, has actually been shown to be an antioxidant, anti-proliferative and inhibit cytokines and growth factors. These actions of isoflavones have been linked to inhibiting prostate cancer growth as well as breast cancer and reducing inflammation.
The question becomes what level of soy ingestion helps decrease risk of cancer and inflammation without artificially increasing estrogen to harmful levels? In reality, there is no definitive research that says dietary phytoestrogens from soy increase the body's estrogen levels, especially to a degree where it would impact a man's sex-hormone levels to deleterious effects. If we look at animal models though, ingestion of genistein actually promote growth of tumor cells in some studies while showing a decrease in tumor cells in others. Part of this is linked to the dosage, where low dose genistein increased cell growth while high doses inhibited it.
I wouldn't take the animal models as gospel, and the results are so inconclusive that it is hard to say whether the animal studies translate to humans. Combined with pro and con test results, it seems that following human studies makes more sense for us, which point isoflavones as being largely beneficial. The data is confusing and for good reason. Tests are done on both animal and humans with no definitive results in either category. While I find it intriguing that soy ingestion can increase phytoestrogens to such a degree, without definitive proof that it raises your circulating estrogen levels to a dangerous point and binds to active cell receptors, I cannot condemn it just yet.
Goitrogens are a more common element in foods we eat today. Their basic mechanism is inhibiting iodine absorption, which leads to a decrease in the production of T3 and T4 by the thyroid gland. T4 is more involved in energy storage while T3 is the “active” form of thyroid hormones, resulting in energy usage and mitochondrial activation. As listed above, low thyroid presents as a host of symptoms, ultimately making you feel and look pretty lousy. Obviously it would make sense to avoid all goitrogenic foods, right? Aside from soy products, other goitrogens include most cruciferous vegetables like brocolli, cauliflower, kale, cabbage, brussels sprouts, bok choy, mustard greens and turnips. Before you turn your back on all these foods, take note that these foods contain small amounts of goitrogens and much of that is inactivated through cooking. Soy presents a problem because it is higher in goitrogens and is probably consumed on a much more frequent basis for vegans and vegetarians than the vegetables are consumed.
The most important reason for possibly avoiding soy is for people with hypothyroidism, or low thyroid function. If you already have low thyroid, then you will be much more sensitive to goitrogens. Case in point is a study conducted on 60 patients with sub-clinical hypothyroidism, half with high dose phytoestrogens and half with low dose. With the addition of 30grams of soy protein every day for 8 weeks, 6 of these high-dose patients moved into overt hypothyroidism, which reflects the power of these naturally occurring chemicals. As noted in the estrogen section, there are almost always pros and cons to these tests: although these women experienced full hypothyroidism, the phytoestrogens actually decreased insulin resistance, blood pressure and inflammatory markers. The low-dose half experience no overt hypothyroidism but also did not get the benefits of decreased insulin resistance, blood pressure and inflammation.
There have been a plethora of studies on humans connecting soy intake and thyroid disfunction. In the 1960s, a group of teenagers with autoimmune conditions involving the thyroid were studied. Those fed soy milk formula as infants had double the risk of thyroid diseases. Another study focused on adults who added 30g of pickled soybeans experienced goiter and thyroid dysfunction in as little as one month. Noted throughout quite a few studies is the increased sensitivity to soy's negative thyroid and estrogen effects on infants and children. Also, soy products are marketed towards post-menopausal women for relief of symptoms. This makes sense because progesterone becomes one of the dominant hormones in the absence of estrogen and progesterone is very thermogenic, contributing to hot flashes. While increasing estrogen helps relieve these symptoms, the increased soy consumption can negatively affect the thyroid.
Lastly, a research review of the safety of soy for the thyroid found mixed results. In observation of 530 children in India with iodine deficiency and consuming soy products, almost all had goiters. In contrast, the authors cite 5 different studies that show adult men and women consuming 54-90mg genistein daily (the active isoflavone in soy) did not experience adverse thyroid function. The authors did conclude that the combination of isoflavones, age and gender do contribute to the results which is why both positive and negative results have surfaced regarding these studies.
There seems to be enough evidence to support the fact that consuming soy products can and does affect thyroid function in some people, especially post-menopausal women, children and those with hypothyroidism. These three groups should be most careful in regards to soy consumption.
…...in a second installment, I will cover trypsin inhibitors and also touch on phytates.
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