Thanks for sharing this news article about soy formula.
I read the study and it did not change my opinion on the safety of soy formula. I would be shocked if any of the paediatric associations adjust their position based on this study as it is just one study in a sea of studies that say soy formula is safe.
Given that formula-fed infants represent the maximum amount of phytoestrogen (isoflavone) we might see people consuming per body weight, I actually consider this a very reassuring study both for infants and adults! These infants had, as expected, far more circulating isoflavones (average about 10,000 ng/mL,) yet you had to really go fishing to see any biological differences!
Let me elaborate on why this study’s findings should be taken with a grain of salt:
1.This study was what we call, in science lingo, a “fishing expedition”. The investigators measured a whole slew of “biomarkers” (blood tests, physical measurements) of reproductive maturation. The vast majority of the markers they measured did not differ between cow and formula fed. For those that did differ, the actual magnitude of change was not dramatic. The reality is that if you measure enough markers, some of them will differ, just by chance. For this reason, any legit clinical trial of a drug or supplement will always have just one pre-specified “primary outcome” that will make or break the trial. You can’t just go measuring dozens of things and celebrate the one thing that changed.
Here are some of the biomarkers that did NOT differ between formula and cow milk:
- Estrogen levels
- FSH levels
- Breast bud size
- Growth rate
2. Other studies have looked at this very same question (same biomarkers) and seen no differences, which suggests that “random noise” in these measurements and confounding factors might fully explain their findings. The authors mention these issues in their discussion.
3. What we really care about is long term reproductive health. The link between the markers in this study and this important outcome is extremely tenuous. Furthermore, we have already done MUCH larger trials on this very question. Those trials have shown no reproductive differences in infants fed formula.
Not surprisingly, the media highlighted the provocative message that “some differences were found” and failed to put a balanced picture around the results -including the many other larger, studies more relevant to the actual issue (reproductive health).
I know it’s a lot of work to dig into the studies and separate fact from fiction — I’m always happy to take this on!