Soy

From Mercola.com:
It is crucial, however, to make a distinction between the health effects from fermented versus non-fermented soy, which I will go over toward the end of this comment, because as you will see, fermented soy dishes do have some redeeming qualities that conventional soy products lack.
Perfect Food or Brilliant Propaganda?
In recent years soy has emerged as a 'near perfect' food, with supporters claiming it can provide an ideal source of protein, lower cholesterol, protect against cancer and heart disease, reduce menopause symptoms, and prevent osteoporosis, among other things.
But how did such a 'perfect' food emerge from a product that in 1913 was listed in the U.S. Department of Agriculture (USDA) handbook not as a food but as an industrial product?
Lipid specialist and nutritionist Mary Enig, PhD shed some light on this issue when she said, "The reason there's so much soy in America is because they [the soy industry] started to plant soy to extract the oil from it and soy oil became a very large industry. Once they had as much oil as they did in the food supply they had a lot of soy protein residue left over, and since they can't feed it to animals, except in small amounts, they had to find another market."
In short, the soy industry CREATED a market where there was none, to profit from their waste products. It required multi-million dollar advertising campaigns and intense lobbying to the Food and Drug Administration (FDA), but now about three-quarters of U.S. consumers believe soy products are healthy.
It's like a re-run of the water fluoridation propaganda machine, which began in the 1940s as solution to the fluoride pollution from aluminum plants. The disposing of fluoride had become a costly problem that needed a radical solution. The solution was to create the false belief that fluoride had some health benefit, and today, not only are you likely consuming this toxic waste product in your municipal tap water, but you may even believe it's good for your teeth, AND industry is getting PAID rather than paying for toxic waste removal…
Soy has become a grossly misunderstood food category, to be added to the ranks of coconut oil, saturated fats and vegetable oils. The two former have gained a negative reputation where a good one actually applies, whereas vegetable oil, along with soy, have emerged with sparkling reputations that cover up an unsavory truth.
The Truth About Soy
For just a brief look at what's really going on, consider that numerous studies have found that soy products can actually:

• Increase thyroid damage, especially in women
• Increase the risk of breast cancer in women, brain damage in both sexes, and cause abnormalities in infants
• Contribute to thyroid disorders, especially in women
• Promote kidney stones
• Weaken your immune system
• Cause severe, potentially fatal food allergies

Despite these findings, many people still want to believe the hype, thinking that these studies must somehow be wrong. But the content of soy itself should be a clue. For example, non-fermented soy products contain:

• Phytoestrogens (isoflavones) genistein and daidzein, which mimic and sometimes block the hormone estrogen
• Phytates, which block your body's uptake of minerals
• Enzyme Inhibitors, which hinder protein digestion
• Haemaggluttin, which causes red blood cells to clump together and inhibits oxygen take-up and growth
• High amounts of omega-6 fat, which is pro-inflammatory

Furthermore, most soybeans are grown on conventional farms that use toxic pesticides and herbicides, and many are from genetically engineered plants. When you consider that two-thirds of all processed food products contain some form of soy, it becomes clear just how many Americans are consuming GM products, whose long-term effects are completely unknown.
Like Feeding Birth Control Pills to a Baby
One of the most disturbing ill effects of soy has to do with its phytoestrogens, which can mimic the effects of the female hormone estrogen. These phytoestrogens have been found to have adverse effects on various human tissues, and drinking just two glasses of soy milk daily for one month has enough of the chemical to alter a woman's menstrual cycle.
The FDA regulates estrogen-containing products, however no warnings exist on soy.
Soy products are particularly problematic for infants, and soy infant formulas should be avoided at all cost. It's been estimated that infants who are fed soy formula exclusively receive the equivalent of five birth control pills worth of estrogen every day!
When testing the blood of soy formula-fed infants, concentrations of isoflavones have been found to be 13,000 to 22,000 times higher than natural estrogen concentrations in early life. It should be obvious that the potential damage to your child can be quite significant. Not to mention the fact that soy formula lacks other vital nutrients for normal and healthy brain- and biological development.
Soy Also Contributes to Dangerously Lopsided Intake of Essential Fats
One of the most important things you can do for your overall health is to balance your intake of omega-3 and omega-6 fats. These two types of fat are both essential. However, the typical American consumes far too many omega-6 fats in their diet while consuming very low levels of omega-3.
The ideal ratio of omega-6 to omega-3 fats is probably close to 1:1. But the ratio of omega-6 to omega-3 today averages from 20:1 to 50:1!
That spells serious danger for your health. Even the mainstream health media is now reporting that lack of high quality omega-3 is one of the most serious health issues plaguing contemporary society.
The primary sources of omega-6 are corn, soy, canola, safflower and sunflower oil; oils that are overabundant in the typical American diet. And when you consider the fact that some form of soy or corn (oftentimes both) is found in just about every processed food product on the market, it really helps to explain these excessive omega-6 levels.
What About Soy as a Source of Protein?
While soybeans are relatively high in protein compared to other legumes, they are still a poor source of protein because other proteins found in soybeans act as potent enzyme inhibitors.
These "anti-nutrients" block the action of trypsin and other enzymes needed for protein digestion, effectively cancelling out any potential benefit you may have thought it had.
Regular soy consumption can also lead to chronic deficiencies in amino acid uptake.
It is believed that it is this ability to interfere with enzymes and amino acids that might be one of the reasons for why soy has such a negative effect on your brain. Isoflavones in tofu and other soy foods might exert their influence by interfering with the tyrosine kinase-dependent mechanisms required for optimal hippocampal function, structure and plasticity.
High amounts of tyrosine kinases are found in your hippocampus, a brain region involved with learning and memory. One of soy's primary isoflavones, genistein, has been shown to inhibit tyrosine kinase in the hippocampus, effectively blocking the mechanism of memory formation.
If You Want to Benefit From Soy, Make Sure it is Fermented !
There are some redeeming qualities to soy, however these are found primarily in fermented soy products like tempeh, miso, natto and soybean sprouts. If you want to get some health benefits from soy, stick to these four forms and pass on ALL processed soy milks, tofu, soy 'burgers', soy 'ice cream', soy 'cheese', and the myriad of other soy junk foods that are so readily disguised as health foods.
The study above affirms this as well, showing that consumption of tempeh was related to better memory, particularly in participants over 68 years of age. Their explanation for this difference between (unfermented) tofu versus (fermented) tempeh is that the fermentation process produces high amounts of folate, which might have a protective effect against the phytoestrogens.
Additionally, not only does the fermentation process blunt the anti-nutritive effect of the soybeans' phytic acid, it also produces probiotics -- the "good" bacteria your body is absolutely dependent on – that increase the quantity, availability, digestibility and assimilation of nutrients in your body.
As a side note, formaldehyde (used as a preservative) was also introduced as a potential culprit rather than the tofu itself in this article. Granted, formaldehyde is somewhere at the very bottom of the list of things you want to consume for good health, but even so, there are so many studies confirming the benefits of fermented soy and the dangers of non-fermented soy products in general that I believe preservatives play a secondary role in the outcome, if any.
Soy is a broad and deep subject that cannot be fully covered in a single article, so for further reading, I recommend you review my related articles below as well as my Soy Index Page, which contains links to many of my best articles and important research findings on soy.