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Soy’s Dirty Little Secret, Part 1

Many Americans think of soy products as a niche within the health food industry. While this may have been true 20 years ago, it isn’t any more. Soy products hit sales of more than $4.1 billion in 2008.

Those sales mean that Americans are eating more soy than ever. And it’s no wonder. Every time a study even hints soy may be healthy, the industry blankets the media with the news.

But the truth about soy is more complicated than they’ve been telling you. Soy has a “dark side,” too. In this article, you’ll discover some of the risks of soy. In a second, we’ll uncover the truth about soy’s “feminizing” effects. And in a follow-up, I’ll tell you which forms of soy are the best for your health – and why.

Soy Protein – Not All It’s Cracked Up to Be

The soy industry trumpets soy as a good source of protein and an excellent meat substitute. But what you don’t hear them mention is that soy isn’t a complete protein. It’s lacking in the essential amino acid methionine.1

Methionine is your body’s main source of sulfur. It’s critical for healthy hair, nails and skin. Sulfur also helps your liver lower cholesterol. It’s even linked to ridding your body of toxic heavy metals.

But methionine is important for another reason. Low levels of this amino acid in women’s diets have been linked to serious nervous system defects in babies.2

Soy is also low in another essential amino acid: lysine.1 Your body needs lysine to produce serotonin, a key neurotransmitter. Serotonin helps regulate sleep, mood, appetite, memory and several other functions.

For example, in a Japanese animal study, denying subjects lysine for just four days produced marked anxiety.3

But it’s not just what soy lacks that should cause you concern. There are other ways soy can put your health at risk, too.

Disappearing Minerals

Here’s a shocker you won’t hear from the food industry: Soy interferes with your body’s ability to absorb minerals.

You probably know that vegetarians have a greater risk of iron deficiency than meat eaters. But research shows that eating soy makes the problem even worse.

Scientists at National Taiwan University looked at a group of healthy students. Some ate meat, while others were vegetarians. Soy foods were a regular part of the vegetarians’ diet.

When they analyzed iron intake, the researchers found that the male students – whether vegetarian or not – got about the same amount of iron in their diets. But vegetarian women took in about a third more iron than the meat-eating ladies.

However, when the scientists tested the students blood, they found that the vegetarians had iron levels half that of their meat-eating counterparts! And that included the vegetarian women who got so much more iron in their diets.4

A study at the USDA’s Children’s Nutrition Research Center came to the same conclusion.5 Except this study looked at more than just iron. These researchers found that soy inhibits zinc absorption, too. The subjects in this study absorbed only two-thirds as much zinc when eaten in a soy-based meal.

Incomplete protein… lower mineral absorption… Those two items alone should make you rethink your level of soy intake. But soy’s “healthy” isoflavones will give you another reason – especially if you’re a man.

Soy Effects Thyroid Function

Genistein is one of soy’s active compounds. Some studies have reported that it helps promote heart-health. But it has effects on other parts of the body, too.

Czech researchers found that eating soy raises the levels of thyrotropin in men.6 Thyrotropin is also known as “thyroid stimulating hormone” (TSH), because it causes the thyroid to grow and produce more hormones. Since thyroid hormones regulate growth and metabolism, you don’t want an excess floating around in your system.

The good news is that the increase in TSH is temporary. The researchers found when their subjects stopped eating soy, TSH levels returned to normal. But most people who eat soy, eat it regularly.

Should You Give Up Soy Foods?

With all these problems, you may be torn about soy foods. After all, soy offers so many health benefits, right?

Maybe not as many as you’ve been told. In fact, C.W. Xiao of Health Canada’s Food Directorate calls the support for soy’s health claims “inconsistent or inadequate.” And that’s backed up by an American Heart Association review of 22 soy studies.

Xiao points out that the studies showed soy had no effect on lipoproteins, triglycerides, blood pressure or HDL cholesterol – all markers of heart health. And soy only lowered LDL cholesterol “slightly.”7

So cutting back on soy probably won’t do you any harm, but rather it will do you a world of good.

Soy milk accounts for a quarter of all soy product sales in the US… and it’s one of the soy products I recommend you consider dropping from your diet. Soy ice cream? Forget it. Enjoy an ounce of dark chocolate instead. As for tofu, you can do without.

If you want to eat soy, I recommend fermented soy foods such as natto, tempeh and miso. These foods can have a significant positive impact on your health. I’ll tell you about their benefits in a later article. But next time, you’ll discover another important reason to cut back on soy foods in general.

Best Life Herbals Wellness Team
Best Life Herbals


1 Friedman M, Brandon DL. Nutritional and health benefits of soy proteins. J Agric Food Chem. 2001 Mar;49(3):1069-86.
2 Shoob H, et al. Dietary Methionine Is Involved in the Etiology of Neural Tube Defect–Affected Pregnancies in Humans. Journal of Nutrition. 2001;131:2653-2658.
3 Smrigal M, et al. Dietary L-Lysine Deficiency Increases Stress-Induced Anxiety and Fecal Excretion in Rats. J. Nutr. 132:3744-3746, December 2002.
4 Shaw NS, et al. A vegetarian diet rich in soybean products compromises iron status in young students. J Nutr 1995;125:212-219.
5 Etcheverry P, et al. Effect of Beef and Soy Proteins on the Absorption of Non-Heme Iron and Inorganic Zinc in Children. Journal of the American College of Nutrition, Vol. 25, No. 1, 34–40 (2006).
6 Hampl R, et al. Short-term effect of soy consumption on thyroid hormone levels and correlation with phytoestrogen level in healthy subjects. Endocr Regul. 2008 Jun;42(2-3):53-61.
7 Xiao CW. Health effects of soy protein and isoflavones in humans. J Nutr. 2008 Jun;138(6):1244S-9S.

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