Hi @ingineu, welcome to Connect. I agree with @dorisena. There is more evidence about diet helping to reduce the risk of getting cancer. There is some very early research looking at the anti-cancer abilities of certain foods. This detailed article from Healthline does a great job of outlining foods that help and the availability of research:
- Cancer and Diet 101: How What You Eat Can Influence Cancer https://www.healthline.com/nutrition/cancer-and-diet

In this video Mayo expert, Dr. Dawn Mussallem, talks about cancer-fighting foods.
https://connect.mayoclinic.org/webinar/cancer-fighting-foods/
Bottom line in my opinion is that diet alone cannot be relied on to reduce the mass found in your thyroid. But diet can help keep you healthy and help your recovery from surgery and reduce the risk of cancer.

Has the solid mass been identified as cancerous? Have you asked your doctor about possible alternatives to surgery?