Effects of Dietary Habits on Markers of Oxidative Stress in Subjects with Hashimoto's Thyroiditis: Comparison Between the Mediterranean Diet and a Gluten-Free Diet.

The short version

This single-blind randomised pilot study with 45 people who have Hashimoto's thyroiditis explored whether a Mediterranean diet or a gluten-free diet changes the body's balance between damaging molecules and antioxidants. Hashimoto's thyroiditis is an autoimmune condition in which the immune system attacks the thyroid gland, and patients tend to show higher oxidative stress, meaning an excess of reactive molecules that injure tissue. The Mediterranean diet is a plant-based pattern built on vegetables, legumes, fruit, nuts, whole grains and olive oil, while the gluten-free diet removes wheat, rye, barley and related grains, and the researchers compared both with simply eating as usual. The study ran at a university hospital in Messina, Italy. Participants were adults aged 18 to 65 with newly diagnosed Hashimoto's, normal thyroid function and no thyroid medication, split evenly into three groups of 15: Mediterranean diet, gluten-free diet or free diet. A dietitian explained each regimen individually, and a three-day food record checked adherence. Blood tests at the start and after 12 weeks measured thyroid hormones, thyroid antibodies and four oxidative-stress markers (AGEs, GPx, TRxR and TEAA). Thyroid hormone and antibody levels did not change significantly in any group, including TPO-Ab and Tg-Ab (the antibodies that mark the immune attack on the thyroid). The Mediterranean diet group, however, showed significantly lower AGEs (advanced glycation end products, damaged proteins linked to oxidative stress) and significantly higher GPx, TRxR and TEAA, which are antioxidant enzymes or overall measures of antioxidant defence (p < 0.001 versus baseline and versus the other two groups). The gluten-free and free-diet groups showed no significant change in these markers (p > 0.05). TPO-Ab fell numerically with the gluten-free diet but not significantly, which the authors read as no relevant effect of gluten restriction on thyroid autoimmunity or function after 12 weeks. In other words, the antioxidant signal appeared only with the Mediterranean pattern. The authors conclude that the Mediterranean diet had a strong antioxidant effect and that a gluten-free diet did not improve redox balance in people with Hashimoto's who do not have coeliac disease. The study has clear limits: only 15 people per group, 12 weeks of follow-up, laboratory markers rather than symptoms or quality of life, and no change in thyroid antibodies, so the findings are preliminary and cannot be generalised to all autoimmune thyroid disorders.

Key findings

• In this single-blind pilot trial, 45 euthyroid people with Hashimoto's thyroiditis (an autoimmune disease of the thyroid gland) were randomly assigned to a Mediterranean diet, a gluten-free diet or their usual diet for 12 weeks, with 15 people per group.
• The Mediterranean diet group had lower AGEs (advanced glycation end products, damaged proteins that reflect oxidative stress) and higher antioxidant markers GPx, TRxR and TEAA than at baseline and than the other two groups (p < 0.001).
• The gluten-free diet group showed no significant change in oxidative-stress markers (p > 0.05), and the authors found no relevant impact of gluten restriction on thyroid autoimmunity or function.
• Thyroid hormones (TSH, FT4) and thyroid antibodies (TPO-Ab, Tg-Ab) did not change significantly in any group.
• The study was small and short, measured laboratory markers rather than symptoms or quality of life, and needs confirmation in larger trials.

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