Systematic Review and Meta-analysis on the Effect of Soy on Thyroid Function

Area of Science:

• Endocrinology
• Nutritional Science
• Public Health

Background:

• Soy foods are globally popular, especially in Western diets, due to perceived health benefits.
• Concerns exist regarding soy's potential negative impact on thyroid function and hormone levels.

Purpose of the Study:

• To systematically review and meta-analyze the effects of soy consumption on thyroid hormone levels.
• To investigate the relationship between soy intake and thyroid function markers: free triiodothyronine (fT3), free thyroxine (fT4), and thyroid stimulating hormone (TSH).

Main Methods:

• Systematic review and meta-analysis of randomized controlled trials involving soy as an intervention.
• Searched major databases (PubMed, MEDLINE, EMBASE, Cochrane) and grey literature.
• Quantitative synthesis using a random-effects model with standardized mean difference (SMD) and 95% confidence intervals.

Main Results:

• Analysis of 18 studies revealed no significant changes in fT3 or fT4 levels with soy supplementation.
• A statistically significant, albeit modest, elevation in TSH levels was observed (p=0.049).
• No evidence of publication bias was detected.

Conclusions:

• Soy supplementation does not appear to negatively affect thyroid hormones (fT3, fT4).
• A minor increase in TSH levels was noted, but its clinical significance is currently unclear.
• Further research may be needed to fully understand the implications of soy consumption on thyroid health.