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?
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."
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." 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."
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.
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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.
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 levelsonce higher than those of most womenwere 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.
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 curecosmetic surgical reduction. There are too many risks, he saysbleeding, infection, problems with anesthesiato 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."