After our third son Brennan was born, I noticed that my wife wasn’t eating the tofu that she made for dinner. She commented matter of factly that post-partum women shouldn’t eat tofu or any soy products. This seems to be common knowledge in East Asian cultures, handed down from mothers to daughters.
In retrospect, it makes total sense, medically. During pregnancy, progesterone is very high, but drops significantly after delivery. We know from studies that progesterone, in addition to it’s reproductive functions, acts as a respiratory stimulant and upper airway muscle dilator. It’s been found to stimulate muscle tone in your tongue. Since all humans’ tongues can fall back due to gravity when we lie on our backs, and sometimes obstruct when we’re in deep sleep (due to muscle relaxation), having less progesterone can cause more frequent obstructions and arousals and prevent achieving deep, efficient sleep. This is what also happens during menopause (very slowly) or just before before women’s periods.
We all know that women naturally gain weight as they progress through pregnancy, and this would expect to cause or aggravate sleep-breathing problems due to gradual narrowing in the throat. But progesterone acts to protect the upper airway by increasing muscle tone and respiratory drive. Once you deliver your baby and progesterone drops, you’re left with all the extra weight, but no more progesterone to help you out. This is one good explanation for post-partum depression.
Soy has known estrogenic properties, so if you increase your soy intake just after delivering a baby, along with significantly lowered progesterone levels, the estrogen to progesterone ratio increases, lessening progesterone’s effectiveness. This can lead to worse quality sleep and not feeling refreshed after waking up in the morning.
It seems that the early Chinese medical doctors realized this through astute observation, and this wisdom has been handed down through the centuries.