James Price’s breasts had been painful and swollen. It looked as if gum balls were implanted underneath each nipple. The slightest touch triggered throbs.

For Price, a retired U.S. Army intelligence officer who once flew attack helicopters in Vietnam, these changes were more than just physically uncomfortable.

“Men aren’t supposed to have breasts,” he says today in a quiet Texas drawl. “It was like my body was feminizing.”

A lean and wiry man, the breast development stood in stark contrast to the rest of his body. But it was not Price's only symptom.

His beard growth had slowed, he’d lost hair from his arms, chest, and legs, and he’d stopped waking up with morning erections.

“My sexual desire disappeared,” he says. “My penis—I won’t say it atrophied, but it was so flaccid that it looked very small in comparison with the way it used to be. Even my emotions changed.”

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The first three doctors Price consulted diagnosed him with gynecomastia, or the abnormal enlargement of the mammary glands in men.

Tests further revealed that estrogen levels in his bloodstream were eight times higher than the normal limits for men, higher even than the levels typically seen in healthy women. Price’s estrogen was so high, in fact, that the doctors were at a loss to explain it. One physician became so frustrated he eventually accused Price of secretly taking estrogen.

“He thought I was a mental case,” says Price, still angry as he recalls the experience.

Dispirited and in pain, he decided to try one more doctor, this time a fellow military man.

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He made an appointment with Lieutenant Colonel Jack E. Lewi, M.D., chief of endocrinology at the San Antonio Military Medical Center. During that first meeting, neither doctor nor patient had any inkling of just how long and complex this medical mystery would prove to be.

Dr. Lewi initially checked for “usual suspect” lifestyle factors known to trigger gynecomastia, from alcoholism to certain herbal ingredients, like tea-tree oils and lavender. With those ruled out, Dr. Lewi was left with a more dreaded suspect: an estrogen-secreting tumor.

Over the next few months, Dr. Lewi ran multiple tests, checking Price for cancer of the testicles, adrenal glands, chest, and lungs.

The good news: When the final test came back negative, Price was in the clear on all fronts. The not-so-good news: Dr. Lewi still had no clue what was causing his patient’s hormones to go haywire. But he was determined not to be the fourth doctor to leave James Price in limbo.

In the classes that Dr. Lewi teaches to medical students and residents, he has long offered this advice: If you’re not finding the right answers, you’re not asking the right questions.

Though he’d asked Price about his lifestyle and habits innumerable times, he decided to go back once again, and this time to make his questions as specific as possible.

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“I said, ‘Let’s go over your diet, meal by meal, and you tell me every single thing you eat and drink.’ He said, ‘Sure, Dr. Lewi. I get up and usually have some cereal.’ I said, ‘Do you put anything on it?’ He said ‘Soy milk.’”

Price explained that he’d developed lactose intolerance in recent years and had switched to soy milk exclusively. It had, in fact, become one of his favorite drinks, a great thirst quencher in the Texas heat.

Dr. Lewi suddenly felt his excitement building. He asked Price how much soy milk, on average, he drank each day.

“He told me, ‘Probably about 3 quarts,’” recalls Dr. Lewi about the moment that changed everything.

Over the past decade, soy foods and good health have become inextricably linked in the national consciousness.

According to annual U.S. consumer attitude surveys by the United Soybean Board, 85 percent of those polled in 2008 rated soy products as “healthy,” a significant increase from the 59 percent who in 1997 thought this was the case. Many men, to be sure, are hard pressed to explain why soy is supposed to be so healthy, but they take it on faith that they should embrace the bean.

“It’s something you need to train yourself to like, you know, for the health benefits," my friend Larry, a distance runner, opined recently.

“Tofu’s the modern equivalent of cod liver oil,” added another buddy, Bill. Three times a week, his wife stir-fries tofu with chard. “It’s this gunk she calls superfood. I call it soylent green.”

He pauses a beat before adding, “I guess I’m grateful she gets me to eat it.”

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Long the foundation of a vegetarian diet, tofu provides protein with little of the saturated fat and none of the moral indigestion that comes with meat.

Moreover, in the past decade, research has emerged suggesting that scarfing down soy may also play an active role in extending our lives. In 1999, soy protein earned a highly coveted FDA-allowed health claim: Diets that include 25 grams—about a pound of tofu—a day may reduce the risk of heart disease.

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Add to this the number of studies showing that soy protein might also help protect against prostate cancer, and suddenly the stuff starts looking like powerful medicine for men.

Of course, most medicines have side effects.

And when you consume soy protein, you’re actually courting the Mr. Hyde side of two natural drugs: genistein and daidzein. Both act so similarly to estrogen that they’re known as phytoestrogens (plant-produced estrogens).

Soybeans couldn’t care less about human sex characteristics—genistein and daidzein may have evolved to act as chemical defenses against fungi and grazing animals. (They aren't very effective deterrents, apparently, since soy meal is widely used to feed livestock.)

But when humans consume these compounds in high enough quantities, they may experience gender-bending nightmares like James Price’s.

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What’s more, studies of these phytoestrogens in leading peer-reviewed medical journals suggest that even lower doses—such as the amount in the 25-gram soy protein target cited by the FDA—have the potential to wreak hormonal havoc.

Here are a few of the recent findings across the life stages of men.

Babies: Weaned On the Bean

A whopping 35 percent of bottle-fed babies in the United States receive at least some of their protein from soy.

The American Academy of Pediatrics (AAP) is taking steps to change this: It recommends that all infants who cannot be breastfed be given cow’s-milk formulas as the first preferred alternative. Healthy full-term infants should be given soy formula only when medically necessary, the AAP’s 2008 report states.

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Babies with an extreme form of lactose intolerance fall into this category, but many others who suffer from colic and excessive crying are switched to soy formula despite a lack of proven benefits.

Paul Cooke, Ph.D., a reproductive biologist at the University of Illinois, has studied mice raised on enough genistein to make their blood levels comparable to those of human infants fed soy formula.

Among other worrisome findings, he discovered significant shrinkage of the thymus gland, a key part of the immune system. “The thymus,” says Cooke, “is like a finishing school for white blood cells—it’s where they go to mature.”

Whether the same effect occurs in human infants is difficult to say, but a 2001 study in the Journal of the American Medical Association surveyed over 800 adults, ages 20 to 34, who were fed either soy-based or cow’s-milk formulas during their infancy.

One of the few differences to emerge was that the group raised on soy formula regularly used more asthma and allergy medications in adulthood. Was this just a quirk of the sampling—or could it represent a subtle impairment of immune function?

“I don’t know the answer,” says Cooke. “But the point is I don’t think anyone knows. There are 20 million people in the United States alone who have consumed soy formula as infants. When people ask me about doing experiments, I tell them we already are—with a large chunk of the country’s population.”

For now, at least, the United States is gambling that widespread use of soy formula won’t lead to long-term consequences.

In 2005, Israel’s health ministry recommended that soy products be limited in young children and, if possible, avoided altogether in infants. In issuing such a caution, Israel joined France, New Zealand, and Australia in officially embracing a better-safe-than-sorry approach for the next generation.

Teens to 20s: Faux Muscle Fuel

Most weightlifters, whether they’re dedicated competitors or occasional gym rats, understand the importance of protein in muscle building and repair. And research has shown that the timing of when you swallow that protein is just as critical—a fact that’s created a market for easy-to-consume protein supplements.

Related: Workout Nutrition: What and When to Eat to Build Muscle

“It’s kind of hard to throw a steak down right before or after a strength workout,” says William Kraemer, Ph.D., a professor of kinesiology and a preeminent researcher of strength training and human performance at the University of Connecticut.

Protein supplements allow an athlete to dump a scoop of powder in with some juice and chug what he needs, when he needs it.

Giant canisters of the stuff line the shelves at GNC and similar health-food stores nationwide, each brand touting its unique muscle-building properties. The most common sources of protein used in them are soy, whey, and casein.

But the latter two, which come from animal sources, are more expensive to produce than soy. The question currently being debated by strength trainers and researchers is this: Does soy’s relative affordability come at a cost to muscle gains?

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In a 2005 study in the Journal of Nutrition, researchers comparing soy to casein concluded that “the biological value of soy protein must be considered inferior to that of casein protein in humans.”

Among other disadvantages, the researchers found, a significantly larger portion of soy is degraded to the waste product urea. Moreover, it contributes to less protein synthesis in the body.

"A protein like whey has much more robust biological effects than soy,” acknowledges Kraemer.

In terms of strength gains, however, he says more research is needed before he can provide definitive guidelines.

“But my personal opinion is that soy protein is cheaper and whey protein is higher quality,” he says. “There are also concerns that soy might decrease a man’s testosterone production and increase his estradiol production, which we tend to associate with female hormone production.”

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After retiring from military service, James Price and his wife, Donna, moved to a small farm in Texas.

He had a commercial pilot’s license and split his time between flying and working the land. His passion was raising and training quarter horses that he broke himself. Price lived the kind of cowboy lifestyle that few of his friends, even those decades younger, had the stamina to sustain.

Donna cooked well-balanced meals, nothing fancy, just standard American fare. It was a good life.

Then Donna developed glioblastoma multi-forme, a lethal type of brain cancer. When she died, Price, then 55, was left to cope not only with his grief but a radical change in his daily routine. Not surprisingly, the diet of the new widower took a hit.

“All of a sudden,” he says, “I was living on not-so-healthy meals I’d make for myself.”

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He saw a product advertised on TV called Ensure; it was supposed to provide adults all the vitamins and minerals and other vital nutrients necessary for health. He also started drinking milk, a favorite from his childhood that he figured would supply protein and other nutrients.

Unfortunately, Price soon discovered he was lactose intolerant.

“I switched to soy milk because it’s lactose-free,” he says, “and I had heard that soy milk is supposed to be good for you.”

He tried it and liked it. Soon soy milk became a regular item on his shopping list, something he bought on autopilot.

In the wake of Donna’s death, Price’s body as well as his emotions began to change, often in ways that were hard to separate from normal grief.

Mood swings and a decrease in libido are not unusual companions to bereavement. But Price had a nagging sense that something was off.

“I was becoming much more sentimental,” he recalls, describing his emotions as almost feminine. “I’d break out and cry at a sad movie, that kind of thing. It just wasn’t like me.”

When Price began dating again, it was as if the sexual aspect had evaporated. “I enjoyed the company of women,” he says, “but it was just like they were my friends. Even if I had wanted to do anything physical, I couldn’t have.”

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The gynecomastia that eventually developed became deeply humiliating for Price. He stopped wearing T-shirts even on the hottest days, fearing his friends and neighbors might see the telltale bumps beneath the fabric. His breasts by this point resembled the buds of a pubescent girl.

Never once in the subsequent yearlong ordeal of medical testing did it cross his mind that soy milk might be the cause.

“I had no idea,” he says. “I never gave it a second thought.”

The day Dr. Lewi asked him to stop drinking the stuff, he immediately complied. He also began checking the ingredient labels on all other items he regularly consumed. If Dr. Lewi was right, going cold turkey on soy just might begin to reverse the symptoms.

Over the next several months, blood tests revealed Price’s estrogen levels were, indeed, dropping steadily back toward normal.

Even better, the extreme nipple tenderness began abating. Eventually, his breasts stopped hurting completely and he gradually began feeling a little more like his old self.

Dr. Lewi, who had searched the medical literature extensively when trying to solve Price’s case, had come across no papers linking soy to gynecomastia.

Realizing his obligation to warn other doctors about the possibility, he told Price he wanted to follow him for several more months and eventually write up his case for a medical journal.

Price readily agreed, grateful for the chance to spare others from his ordeal.

20s to 40s: Privates in Peril

In a Harvard study published last year in the journal Human Reproduction, Jorge E. Chavarro, M.D., Sc.D., and his colleagues found a strong association between men’s consumption of soy foods and decreased sperm counts.

Related: 4 Ways to Boost Your Fertility

Ninety-nine men reported their intake of 15 different soy-based foods, then underwent semen analysis. Those in the highest category of daily soy intake averaged 32 percent fewer sperm per milliliter of ejaculate than those who went sans soy.

Dr. Chavarro cautions that this doesn’t prove cause and effect, and that it’s too early to counsel men to avoid soy foods in the hope of boosting fertility.

“But clearly, this story is just starting,” he says. “More studies need to be conducted.”

If shooting blanks is worrisome, how about being unable to shoot at all? Two other recently published papers reveal that at least one soy component clearly impairs erectile function in animals—and may do so in men as well.

The studies, published in the Journal of Andrology and Urology respectively, looked at the effect of daidzein on the sexual function of male rats.

Moderate doses of the phyto-estrogen administered either in youth or adulthood significantly affected the quality of their erections. Among other changes, the daidzein-exposed males produced less testosterone, had softer erections, and experienced biochemical changes to their penile tissues that left these tissues less elastic and less capable of complete blood engorgement.

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While acknowledging that rat results do not always directly translate to humans, the authors of the first study suggest that this time there’s reason to believe they will.

They cite, among other things, a 10 percent higher incidence of erectile dysfunction in Chinese men known to consume high amounts of soy compared with Americans who avoid it.

The authors of the Urology study sound a similar warning. They argue that it’s reasonable to believe that men who consume lots of daidzein could experience tissue changes similar to those seen in another mammal.

Yufeng Huang, M.D., a coauthor on both papers, says that the “moderate” dose used in the animal studies leads to approximately the same blood level of daidzein in men who eat soy every day, a common practice in Asia. He believes soy represents a novel and previously overlooked risk factor for ED.

“We are now recommending that soy be avoided by patients with erectile dysfunction,” Dr. Huang says. And because erectile dysfunction increases with age, he also suggests that men ages 40 and above limit their soy intake.

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50s and Beyond: Brain Drain

Last summer, Eef Hogervorst, Ph.D., of England’s Loughborough University, and other researchers published a study on soy products and dementia risk.

The researchers focused their attention on older Indonesians, members of a culture in which tofu has long been a dietary staple. Hogervorst says her team began the study confident of finding a benefit from tofu’s phytoestrogens.

“Almost everything we’d learned from animal and cell-culture work indicated that estrogenlike compounds protect the brain,” she says.

In older men and older women alike, however, they found exactly the opposite indication: Participants over age 68 who were regularly eating the most tofu had double the risk of dementia and memory impairment as those consuming a more moderate amount.

“We were very surprised by this at the time,” says Hogervorst, “but a new consensus is starting to form now. Hormones and hormonelike products are not very good for people over 65.”

Related: 8 Daily Habits That Will Keep Your Brain Young and Sharp

In terms of soy itself, Hogervorst suspects its reputation is changing.

“For a long time now,” she says, “people have been finding only good things about phytoestrogens. Gradually, as some contrasting information accumulates, the paradigm changes 180 degrees and you see people arguing that phytoestrogens are all bad. The truth probably lies somewhere in the middle.”

Dr. Lewi's case report on James Price's condition was published in the May/June 2008 edition of Endocrine Practice, a journal read by many of the nation’s in-the-trenches endocrinologists. Thanks to this, doctors now have a newly documented agent to consider when evaluating gynecomastia.

For his part, Dr. Lewi believes that soy products in moderation can still be a healthy part of a man’s diet.

“The problem,” he says, “is when a thing like soy is touted as this wonderful panacea for health, and people end up going overboard on it.”

A final twist in the Price case, however, shows how difficult it can be to avoid soy. During the follow-up blood testing Price agreed to undergo, his estrogen levels continued to drop, in a virtually linear fashion, back toward normal.

Then, several months later, and seemingly for no reason, the positive trend reversed. As soon as he saw that Price’s estrogen was once again climbing, Dr. Lewi called his patient.

Before Dr. Lewi could even announce the results, Price said, “I already know what you’re going to tell me, Dr. Lewi. You’re going to say my estrogen level is coming up."

Dumbfounded, Dr. Lewi asked Price how he knew that without seeing the test results.

Price explained that after switching from soy milk to lactose-free milk, he was in the grocery store one day and bought some more Ensure. Though he’d followed Dr. Lewi’s advice and checked the labels on virtually every product he purchased, he’d neglected to check Ensure.

“It’s advertised as having vitamins and minerals and all the stuff you need to stay healthy,” he says.

Related: The Best Multivitamins For Men

Only after his breasts started hurting and growing again did it occur to Price that Ensure might also contain the last thing his body needed. He checked the label: Ensure contained soy protein. He told Dr. Lewi that he threw out the rest and was no longer drinking it.

Subsequent blood tests showed that this was enough to send Price’s estrogen back in the healthy direction.

Several months later, his estrogen levels—once higher than those of most women—were in the low-to-normal range for healthy men. They’ve remained in that range ever since, but the physical changes to his penis, his loss of sexual desire, and his heightened emotions have persisted.

Related: The Male Libido Crisis

And while all pain associated with his breasts has disappeared, the tissue unfortunately remains swollen, a consequence of fibrotic tissue changes that take place with long-term gynecomastia.

Although Price remains self-conscious about it, he’s reluctant to try the only cure—cosmetic surgical reduction. There are too many risks, he says—bleeding, infection, problems with anesthesia—to justify going under the knife at this point in his life.

As for other men who might one day develop a similar problem, Price’s advice is unequivocal: Go to your doctor at the first sign of pain or swelling. Symptoms caught and treated early are often reversible.

Price also acknowledges that his body may have an above-average sensitivity to soy’s phytoestrogens.

Still, his experiences have taught him that the foods we eat are not always what we think they are. Soy protein today is an ubiquitous, profitable, and often buried ingredient in a bewildering number of packaged foods. More than most people, Price was doing his best to avoid it. But he was still tripped up.

“In today’s supermarkets,” he says, his voice weary, “you can’t hardly get anything without at least some soy in it.”

Jim Thornton Jim Thornton is a National Magazine Award–winning health writer and champion masters swimmer.

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