New Research Finds Soy Formula Impacts Babies Hormones

New Research Finds Soy Formula Impacts Babies Hormones

Leading health organisations recommend exclusive breastfeeding for the first six months.

They advise breastfeeding should continue alongside suitable solid foods for at least one year.

But what about babies who are mixed fed or formula fed?

What type of formula should parents choose?

New Research Finds Soy Formula Impacts Babies Hormones

Cow’s milk formulas are the most commonly available. Soy formulas are also readily accessible.

Although there are instances when soy formulas might be helpful – for example, if a baby has a rare metabolic condition called galactosemia – some health professionals are reluctant to suggest soy formula, due to its phyto-oestrogen content.

The reason is that the high phyto-oestrogen content might have negative effects on babies, such as posing a long-term reproductive health risk.

In fact, new research has provided further evidence related to this.

What Did The New Study Find?

The new research aimed to investigate the development of estrogen-responsive tissue, along with certain hormone levels, depending on infant feeding practices. The researchers were specifically comparing babies fed with soy formula with babies fed with cow-milk formula and breastfed babies.

Of 410 mother-baby pairs enrolled, 283 pairs completed the study over a three year period. The study was observational rather than randomised, meaning each mother had already decided how she would feed her baby before taking part in the study.

Approximately half of the babies were girls. 102 of the babies were exclusively fed soy formula, 111 babies were fed with cow’s milk formula, and 70 babies were fed breastmilk.

The researchers assessed:

  1. A maturational index, based on epithelial cells from the children’s urogenital tissue (which measures estrogen status)
  2. Ultrasound measurements of uterine, ovarian and testicular volume, as well as breast-buds
  3. Hormone concentrations seen in blood tests.

The results found girls fed with soy formula had developmental trajectories that were consistent with responses to estrogen exposure, compared with girls fed cow’s milk formula.

The vaginal maturation index was higher, and the uterine volume reduced at a slower rate, which suggest responses to estrogen exposure.  The research team found similar differences amongst baby girls who were soy formula fed versus breastfed.

More research is needed to see how these changes might affect health (including reproductive health) over a lifespan.

If you’re unsure about what formula to choose for your formula fed or mixed fed baby, it’s important to seek advice from a medical practitioner.

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Renee Kam IBCLC CONTRIBUTOR

Renee Kam is mother to Jessica and Lara, an International Board Certified Lactation Consultant (IBCLC), a physiotherapist, author of 'The Newborn Baby Manual' and an Australian Breastfeeding Association Counsellor. In her spare time, Renee enjoys spending time with family and friends, horse riding, running and reading.


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