The pitfalls of soy, daddies' baby blues, and more.

This month, Dr. Sydney Spiesel discusses the pitfalls of a soy-rich diet, dads' baby blues, a new treatment for recurrent urinary tract infections, and the flaws of asthma puffers. Click here and here for the last two columns.

Soybeans: Not entirely good for you?

The bean: One of Henry Ford's better contributions was the soybean. The automaker promoted the bean as a food crop and a material for products as diverse as plastics, printing inks, and fibers—sometimes he wore a necktie made out of soy-derived fabric. Presently, America grows about 83 million tons of soybeans annually, worth about $12 billion. When it comes to food, soy is everywhere. It's inexpensive, a meat substitute, and a high-quality, complete protein. Is there a downside? Maybe. There are at least three potential problems in a soy-rich diet.

The thyroid: Soy proteins themselves seem fine, but other plant-derived ingredients in soy food products may not be. One worrisome bunch are the isoflavones, natural chemicals whose health benefits have been promoted because they are antioxidants. The problem with soy isoflavones is that they can inhibit the production of the thyroid hormone, potentially leading to hypothyroidism, which irreversibly arrests mental development when it occurs in infants. Soy baby formulas are supplemented with a little extra iodine, which solves the problem for babies with normal thyroid glands. But soy-formula-fed babies with inactive glands may need extra thyroid hormone, since the results of hypothyroidism are so disastrous. Soy isoflavones don't pose a problem for adults.

Sex hormones: Another problem is that soy isoflavones act in the body like estrogens—female sex hormones. This effect is small but detectable. No harmful differences were shown in studies comparing post-menopausal women whose diets are rich in soy with similar women whose source of protein is largely dairy. Another retrospective study looked at about 800 adults ages 20 to 34: When they were infants, about one-third of the group had been fed soy formula, and two-thirds had been given cow milk formula. Again, the data suggested little difference in outcome. However, it was surely too early in the reproductive lives of many of the subjects to be certain, and there were not enough subjects to fully answer some of the more subtle questions about reproduction and endocrinology. It would be wonderful if the authors of this paper could go back to their study population in another 10 years to see what the further passage of time revealed.

The heart: The final concern is a subtle one that might not apply to humans at all but nevertheless makes me a little nervous. The FDA and the American Heart Association for some years recommended that a diet should include soy because it's good for the heart. But they've now backed away from that position, because there is little evidence that the modest lowering of cholesterol promoted by a soy-rich diet makes any real difference. On the contrary, there is a recent disquieting study in male mice that were genetically programmed to develop a form of heart disease. (Females are relatively resistant to the effects of the defective gene.) Susceptible mice that were fed a soy-based diet showed heart deterioration and went on to heart failure—while dairy-fed mice did not.

Conclusion: We have no idea if this observation applies to humans or why soy had this effect on the mice, but the study makes me hesitant to recommend a soy-rich diet, especially for people at special risk for heart disease. For myself, I'll stick to the little shreds of tofu in my moo shu beef.

Papa's new baby blues

The condition: Maternal depression following the birth of a baby is estimated to affect between 8 percent and 25 percent of women in the first year after giving birth (the broad estimate reflects the range of criteria for depression applied by different researchers). Now it's becoming clear that postpartum depression affects fathers as well.

The new research: In an interesting study reported in this month's Pediatrics, James Paulson and Sarah Dauber of Eastern Virginia Medical School, and Jenn Leifermann of the University of Colorado's School of Medicine in Denver looked at a national sample of more than 5,000 two-parent families. The research team interviewed mothers and fathers nine months after a baby's birth, using a standard questionnaire to look for symptoms of depression. They found significant symptoms in 14 percent of the mothers they studied—and in 10 percent of the fathers. A similar British study looked at about 25,000 mothers and fathers eight weeks after the birth of a child and identified signs of major depressive illness in 10 percent of mothers and 4 percent of fathers.