Soy Formulas and the Effects of Isoflavones on the Thyroid
February 13, 2000
Environmental scientist and long-time campaigner against
soy-based infant formulas, Dr Mike Fitzpatrick, has warned about the risk
of thyroid disease in infants fed soy formulas, high soy consumers and
users of isoflavone supplements:
"There is potential for certain individuals to consume
levels of isoflavones in the range that could have goitrogenic effects.
Most at risk appear to be infants fed soy formulas, followed by high soy
users and those using isoflavone supplements".
The report noted that infants fed soy formulas are
exposed to high levels of isoflavones, which are potent anti-thyroid agents,
and that the risks to normal growth and development were significant.
Fitzpatrick stated that thyroid problems due to soy
might not be recognised "due to difficulties in establishing a cause and
effect relationship" and noted that even experienced soy researchers may
be ignorant of the connection between isoflavones and goitre.
Fitzpatrick also rejected claims that there was no
evidence that isoflavones in soy formulas harmed infants citing the reported
cases of goitre that have occurred in infants fed iodine sufficient soy
Fitzpatrick stated his support to the position of
the New Zealand Ministry of Health:
"The Ministry of Health has found that infants with
a history of thyroid dysfunction should avoid soy formulas and soy milks.
Additionally, there is potential for isoflavone exposure to cause chronic
thyroid damage in all infants fed soy formulas" Fitzpatrick stated that
exposing infants to isoflavones was unnecessary and that the risk of harm
could be avoided if manufacturers removed isoflavones from soy formulas.
"In the interim" he stated "it is appropriate for medical practitioners
to monitor the thyroid status of infants fed soy formulas"
Fitzpatrick also claimed that high soy consumers and
users of isoflavone supplements were also at risk of thyroid disorders.
He stated that the subtle effects of anti-thyroid agents on thyroid function
would most likely be evidenced as subclinical, or even overt hypothyroidism.
Fitzpatrick also noted that a sporadic pattern of
soy use may also not be without risk since the resulting thyroid stimulation
parallels the classic method for inducing thyroid tumours in laboratory
animals. He recommended "a more cautionary approach to the use of soy
and isoflavone supplements".
Zealand Medical Journal (Volume 113, Feb 11, 2000)