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Am J Vet Res. 2004 May;65(5):586-91.

Effect of dietary soy on serum thyroid hormone concentrations in healthy adult cats.

Author information

1
Department of Clinical Sciences, School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA.

Abstract

OBJECTIVE:

To compare effects of short-term administration of a soy diet with those of a soy-free diet on serum thyroid hormone concentrations in healthy adult cats.

ANIMALS:

18 healthy adult cats.

PROCEDURE:

Cats were randomly assigned to receive either a soy or soy-free diet for 3 months each in a crossover design. Assays included CBC, serum biochemical profile, thyroid hormone analysis, and measurement of urinary isoflavone concentrations.

RESULTS:

Genistein, a major soy isoflavone, was identified in the urine of 10 of 18 cats prior to dietary intervention. Compared with the soy-free diet, cats that received the soy diet had significantly higher total thyroxine (T4) and free T4 (fT4) concentrations, but unchanged total triiodothyronine (T3) concentrations. The T3/fT4 ratio was also significantly lower in cats that received the soy diet. Although the magnitudes of the increases were small (8% for T4 and 14% for fT4), these changes resulted in an increased proportion of cats (from 1/18 to 4/18) that had fT4 values greater than the upper limit of the laboratory reference range. There was no significant effect of diet on any other measured parameter.

CONCLUSIONS AND CLINICAL RELEVANCE:

Short-term administration of dietary soy has a measurable although modest effect on thyroid hormone homeostasis in cats. Increase in T4 concentration relative to T3 concentration may result from inhibition of 5'-iodothyronine deiodinase or enhanced T3 clearance. Soy is a common dietary component that increases serum T4 concentration in cats.

PMID:
15141877
[Indexed for MEDLINE]

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