Researchers looked at dozens of studies to understand how different foods might affect thyroid cancer risk. They found that eating fish, especially oily fish like salmon, appeared to lower the risk of thyroid cancer. On the flip side, eating lots of refined grains and processed foods with nitrates seemed to increase risk. The study combined traditional research reviews with a special genetic analysis method to strengthen their findings. While these results are promising, experts emphasize that diet is just one factor among many that influence thyroid cancer risk, and more research is needed before making major dietary changes.

The Quick Take

  • What they studied: Whether eating certain foods or following specific eating patterns affects a person’s chances of developing thyroid cancer
  • Who participated: The analysis combined results from 37 different studies (16 long-term follow-up studies and 21 case-control studies) that looked at thousands of people’s eating habits and thyroid cancer outcomes
  • Key finding: Eating fish, particularly oily fish, was linked to a lower risk of thyroid cancer, while eating lots of refined grains and foods with added nitrates was linked to higher risk
  • What it means for you: Adding more fish to your diet might be one small way to support thyroid health, but thyroid cancer risk depends on many factors. Talk to your doctor before making major diet changes, especially if you have thyroid concerns

The Research Details

Researchers conducted a comprehensive review by searching four major medical databases for all studies examining the connection between diet and thyroid cancer through April 2025. They followed strict guidelines (called PRISMA) to ensure they included only high-quality research. The team extracted data from 37 studies total—16 that followed people over time to see who developed thyroid cancer, and 21 that compared people with thyroid cancer to those without it, looking back at their eating habits. They then used a special statistical method called meta-analysis to combine all these studies’ results and look for patterns. Additionally, they performed a genetic analysis method called Mendelian randomization, which uses genetic information to help determine whether diet actually causes changes in thyroid cancer risk, rather than just being associated with it.

By combining so many studies together, researchers can see bigger patterns that might not be obvious in single studies. The genetic analysis method helps answer the important question: does eating certain foods actually cause lower or higher cancer risk, or is it just a coincidence? This two-pronged approach makes the findings more trustworthy and helps separate real cause-and-effect relationships from mere associations.

This study is a systematic review with meta-analysis, which is considered high-quality evidence. The researchers followed strict international guidelines for conducting reviews. They checked for publication bias (the tendency for positive results to get published more often). However, the original studies included were observational (watching what people eat naturally) rather than experiments where people are randomly assigned to eat certain foods, so we can’t be 100% certain about cause-and-effect. The genetic analysis helps strengthen confidence in the findings.

What the Results Show

The combined analysis of all studies showed that people who ate more fish had a lower risk of developing thyroid cancer compared to those who ate less fish. This protective effect was especially strong for oily fish like salmon, mackerel, and sardines. In contrast, people who consumed high amounts of refined cereals (like white bread and processed grains) and foods containing nitrates (like processed meats) had higher thyroid cancer risk. The genetic analysis confirmed that fish consumption, particularly seafood, appeared to genuinely protect against thyroid cancer rather than just being coincidentally associated with lower risk. Alcohol-containing beverages also showed an association with reduced thyroid cancer risk, though researchers noted this finding needs careful interpretation.

The study examined many other dietary factors and food groups, though not all showed clear associations with thyroid cancer risk. The researchers noted that the protective effect of fish was consistent across different types of studies and populations, which strengthens confidence in the finding. The harmful effects of refined grains and nitrates were also relatively consistent across studies. The genetic analysis particularly highlighted seafood as a protective factor, suggesting that specific nutrients in fish—possibly omega-3 fatty acids or other compounds—might be responsible for the protective effect.

This research builds on earlier work showing that diet influences cancer risk. Previous studies had suggested connections between certain foods and thyroid cancer, but results were sometimes mixed or unclear. This comprehensive review synthesizes all available evidence and uses newer genetic analysis methods to clarify which dietary factors have the strongest evidence. The findings align with broader nutrition science showing that fish consumption is associated with various health benefits, and that processed foods and refined grains are linked to increased disease risk.

The original studies included were mostly observational, meaning researchers watched what people naturally ate rather than randomly assigning them to eat specific foods. This makes it harder to prove cause-and-effect. Some studies had small sample sizes or didn’t measure diet the same way. The genetic analysis, while helpful, has its own limitations and can’t account for all factors affecting thyroid cancer risk. Publication bias might exist—studies showing positive results are more likely to be published. Additionally, most studies were conducted in developed countries, so findings might not apply equally to all populations worldwide.

The Bottom Line

Based on this research, eating fish 2-3 times per week, especially oily fish varieties, may be one dietary strategy to support thyroid health (moderate confidence). Reducing refined grains and processed meats with added nitrates appears beneficial (moderate confidence). However, diet is just one factor affecting thyroid cancer risk—genetics, age, gender, and other environmental factors also play important roles. These findings should complement, not replace, medical advice from your doctor.

Anyone interested in cancer prevention and thyroid health should find this relevant. People with family histories of thyroid cancer might particularly benefit from dietary adjustments. However, people with certain health conditions (like those requiring low-iodine diets for thyroid treatment) should consult their doctor before making changes. This research applies to general cancer prevention, not treatment of existing thyroid cancer.

Diet changes typically take months to years to show health benefits. You won’t see immediate changes, but consistent dietary improvements over 6-12 months may contribute to long-term health. Thyroid cancer prevention is a long-term process involving multiple lifestyle factors, not just diet.

Want to Apply This Research?

  • Track weekly fish consumption (aim for 2-3 servings of oily fish per week) and monitor refined grain intake (work toward reducing processed bread, pastries, and cereals). Log these weekly in your nutrition app.
  • Replace one refined grain meal per week with a fish-based meal. For example, swap a white bread sandwich for grilled salmon with vegetables. Gradually increase fish meals as you find recipes you enjoy.
  • Set a weekly reminder to log fish servings and refined grain consumption. Review monthly trends to see if you’re meeting the 2-3 fish servings per week goal. Track how you feel and any digestive changes. Share patterns with your healthcare provider during annual check-ups.

This research suggests associations between diet and thyroid cancer risk but does not provide medical diagnosis or treatment advice. Thyroid cancer risk depends on many factors beyond diet, including genetics, age, gender, and radiation exposure. If you have concerns about thyroid cancer risk or existing thyroid conditions, consult with your healthcare provider or an oncologist before making significant dietary changes. This information is for educational purposes and should not replace professional medical advice. People with thyroid disease requiring specific dietary restrictions should work with their doctor before implementing dietary changes based on this research.