Here's a trivia question straight from the crypt: what ingredients found in many packaged food can neuter babies while still in the womb? And here's another: what ingredients commonly found in everyday packaged food has been shown in animals to destroy their hormones and reproductive health at relatively low dosages?
Sound unbelievable? Well, here is a partial list of the hormonal vampires:
All of these ingredients have several things in common: they are used in the food industry as "flavor enhancers" but are under the covers what biologists call excitotoxins and contain either aspartate or glutamate. Glutamate is the most studied of the two compounds, but aspartate is definitely glutamate's evil little sibling.
Together these two have something in common: when ingested, they love to destroy neurons. And, just as bad, when they destroy neurons in the right places, they can take out your entire hormonal cascade, including testosterone.
Animal studies, and not at overly high doses by the way, have shown that when pregnant mothers are fed glutamate the offspring is born normally but then during puberty a host of reproductive issues surface including shrunken testes. In other words, these molecules would better be called eunuch-o-toxins.
Interestingly, these key molecules are actually used by your brain for energy and as a type of neurotransmitter. In fact, they are involved in the switching mechanism of your neurons and are called excitotoxins because they literally overexcite the neurons to death if ingested in even relatively small quantities. Neurons that receive too much glutamate or aspartate allow a flood of calcium - calcium is used for turning neurons on and off - into the cell. The neurons under these conditions become swollen and damaged and eventually die. So a little glutamate and aspartate is essential for the brain but too much is neuronal death. Yes, your cells can literally get overexcited to death.
Furthermore, animals that are fed relatively low levels of glutamate can actually develop too many synaptic connections. The brain becomes literally miswired. In fact, studies show animals on glutamate become hyper and unable to perform normal tests of intelligence (for animals of course). This, of course, is because their brains are slowly getting mangled. It is like taking a race horse or an elite bodybuilder and forcing him to work out until the muscles are literally shredded irreparably.
The tragedy is that many otherwise health-conscious people think that MSG, or monosodium glutamate, is only a health problem because it contains extra sodium or causes allergic-type reactions in sensitive people. And probably an even greater tragedy is that many people, trying to be healthy by drinking diet sodas, are soaking their hypothalmuses (and in some cases brains) with excitotoxins. (Aspartame is so named because of the aspartate in its chemical composition which is released upon digestion in the stomach.)
So what do the studies show? One animal study in a prestigious European journal already found "a statistically significant, dose-related increase in lymphomas and leukaemias in females" at about the equivalent level of three diet sodas per day.  This study was conducted on 1,800 rats and the control animals had no lymphomas. In contrast, the animals aspartame had 10 malignant gliomas, 1 medulloblastoma and 1 malignant meningioma. Yet somehow pro-aspartame proponents argue that this is not statistically significant!
Before I go on, I need to mention that, while I had read some basic information about excitotoxins, the book that really opened my eyes was Russell Blaylock's The Taste That Kills. I cannot possibly do justice to this book in just one web page, but keep in mind that the author is a neurosurgeon and has packed this book with studes and references.
So why, you might ask, would the FDA allow these excitotoxins into our food supply? Well, here is the FDA's (extremely weak) argument: the brain is protected by the blood-brain barrier which does not allow the passage of either glutamate or aspartate into your precious grey matter. This is deadly and foolish thinking, because there are parts of your brain completely unprotected by the blood-brain barrier. Secondly, the blood brain barrier is not perfect and will under certain circumstances allow passage of glutamate and aspartate sized molecules directly into the brain.
But let's focus on the problem that is going to be an issue for almost everyone. There is a very key region of the brain where MSG and aspartate can march in and rape and pillage during their stay: the hypothalamus. This region of the brain essentially couples the nervous system and the endocrine system together. The hypothalamus pumps many key "factors" into the pituitary and the pituitary in turn controls your many of the hormones that you hold most dear as a male, including leutinizing hormone, i.e. LH, follicle-stimulating hormone, i.e. FSH, and growth hormone, i.e. GH. And I should mention that testosterone is strongly effected by leutinizing hormone and, to a lesser extent, growth hormone.
Thus, it would stand to reason that damage to the hypothalamus from glutamate (and aspartate) could negatively effect all these key hormones effecting masculinity and fertility. And that is exactly what the animal studies have found. Growth hormone, leutinizing hormone, prolactin and several other hormones are all hit by the ravages of glutamate  resulting in animals that are so damaged that they obese with decreased fertility and often shrunken testes and pituitaries.
Do you know the foods and drinks that boost Nitric Oxide and repair the veins and artieries to your penis? Then check out the Peak Erectile Strength Diet Program where I show you how to dramatically improve your erectile strength.
By the way, I should mention that these changes do not necessarily show up right away. They often show up only when the animal goes through puberty. In other words, the excitotoxin damage can sit their dormant for years, relatively unnoticed, yet hitting your body years later like a freight train. How many middle aged guys out there have wondered why their testosterone has vaporized in middle age seemingly inexplicably due to the ravages of MSG ingestion during their formative years? We will never know the answer to that question and, more importantly, nor should we have had to.
Regardless, the damage to us middle aged and beyond guys from glutamate and aspartate is probably rather extensive. Throughout the 60's, many manufacturers laced baby food with glutamate! (And you older guys wonder why you've been having problems, eh?) In addition, many women probably at more glutamate at meals during the very vulnerable first trimester when our entire brain is much more exposed to all that our moms ate and drank. Again, animal studies show horrific brain damage from just these situations.
Okay, you can't the past - we all know that. But how do you protect yourself from excitotoxins from this point forward? First of all, do NOT ever consume any of the items on the list at the top of this link. That's a no-brainer - no pun intended. In fact, I strongly recommend that you do not consume these even in minute amounts.
You also must be extremely careful when it comes to packaged foods (and eating out). Somehow the food manufacturers got the FDA to not only allow MSG but to allow it in many foods without being labeled. Monosodium glutamate can be added to your food under labels like "spices", "natural flavorings" and so on in many cases without actually labelling it glutamate or anything similar. You also get substantail amounts of MSG generally in "sodium casseinate", "autolyzed yeast extract" and "maltodextrin". So beware! The only way to really protect yourself is to buy foods packaged without absolutely no ambiguous or vague entries whatsoever.
NOTE: I have documented some of the Fast Food Chains and Restaurants that Pack their Foods with MSG.
Remember that you probably have considerable damage to your hypothalamus and possibly other regions of your brain from the past decades of your life. Many neurological diseases are based on a critical threshold being passed. For example, in the case of Parkinson's, one can have 50, 60 or even 70% of the cells in a certain area of the brain destroyed without any symptoms showing up. But once we you pass the 80% threshold, that is when the devastating symptoms of Parkinson's manifest themselves.
There are probably many areas of your brain where you probably at the 50% point. The last think you want to do is anything that may take you down the home stretch to neurological disease and possibly dementia. Remember: your brain and your hypothalamus in particular sit vulnerable and exposed like a little child. You are the only one that can protect them. I highly recommend that you read my link on the Brain as well for other critical ways to protect yourself.
NEWS FLASH: Researchers have just linked kidney decline to diet drink consumption.  Aspartame, the artificial sweetener in most diet drinks such as Diet Coke and Diet Pepsi, breaks down into formaldehyde. Formaldehyde can accumulate in the kidneys and other organs and cause damage. This can potentially have far-reaching consequences as kidney decline has been linked with cognitive decline and loss of memory in seniors.  Kidney decline has also been linked to an increase in phosphorous  and ensuing heart disease. 
The bottom line: preserve what you got! "Your grey matter is all that matters".
1) Eur J Oncol, 2005, (10)(2):00-00
2) Neuroendocrinology, 1978, 26:220-228; 1986, 42:158-166; 1980, 30:280-284
3) American Society of Nephrology (2009, November 2). Diets High In Sodium And Artificially Sweetened Soda Linked To Kidney Function Decline. ScienceDaily. Retrieved November 2, 2009, from http://www.sciencedaily.com /releases/2009/11/091101132543.htm
4) Neurology, 2009, 73:920-927, "Kidney function is associated with the rate of cognitive decline in the elderly"
5) http://esciencenews.com/articles/2009/11/05/small.increases.phosphorus. mean.higher.risk.heart.disease
6) http://esciencenews.com/articles/2009/11/05/kidney.function.decline. increases.risk.heart.failure.and.premature.death