The Paleo Diet is a popular diet that can work well for many chronic diseases, especially autoimmune diseases like Hashimoto’s disease. However, the Paleo Diet can be somewhat restrictive which can result in deficiencies if the dieter doesn’t carefully review their food and micronutrient intake. Iodine is one important micronutrient that may become depleted on a Paleo Diet. The Autoimmune Paleo Diet is an even more restrictive diet so the same deficiency may happen.

Let’s review what the research shows about the Paleo Diet and iodine deficiency.

A paper published in the European Journal of Clinical Nutrition entitled, “A Paleolithic-type diet results in iodine deficiency: a 2-year randomized trial in postmenopausal obese women” sheds some light on this question.Introduction to this study on the Paleo Diet and iodine deficiencyThis study was done in Sweden and the authors begin by stating >50% of iodine intake comes from iodized table salt followed by dairy and seafood. The Paleo Diet is void of dairy, grains, legumes, refined sugar, processed oils, and salt thus removing two important sources of iodine. 150 micrograms of iodine per day is recommended by the Nordic Nutrition Recommendations (NNR) but the thyroid can function at 70 micrograms of iodine per day.

Urinary iodine concentration (UIC) by spot urine is recommended for determining iodine status. Adequate iodine intake is a UIC of 100-199 ug/l. Mild iodine deficiency is a UIC of 50-99 ug/l. Moderate iodine deficiency is 20-49 ug/l. Severe iodine deficiency is <20 ug/l.

However, the authors do state that the best way to measure iodine status is a 24-hour urinary iodine excretion over multiple days.

The authors point out that those at greatest risk for iodine deficiency include pregnant or lactating women and vegans.How was this study done on the Paleo Diet and iodine deficiency?This was a randomized controlled trial consisting of one group following the Paleo Diet and the other following an NNR-based diet for two years. Urine and blood samples were collected at baseline, 6-months, and 24-months. Testing included 24-hour urinary iodine concentration and excretion as well as thyroid hormones.

24-hour urine was collected on three separate days. TSH, Free T4, and Free T3 were the thyroid hormones tested.

70 post-menopausal women were included of which 74% were obese and the rest overweight. 49 subjects completed the study of which 22 followed the NNR diet and 27 followed the Paleo Diet.What were the study results?Women following the Paleo Diet totaled a weight loss of 10.7% compared to 7.7% in the NNR group.

The Paleo Diet group developed iodine deficiency but the NNR group maintained normal iodine status.

TSH, Free T4, and Free T3 levels did not differ between the groups at any time except for Free T3 levels declined after 6 months in the Paleo Diet group.

The author’s conclude that pregnant women should avoid the Paleo Diet because iodine deficiency can cause impaired brain development of the fetus.

The weakness of this study is the 30% drop out rate but the authors state that they don’t believe this affected the results because those most likely to adhere to the diets remained.Dr. Hedberg’s CommentsThis study was done well but a larger group would have provided stronger results. 24 months is an adequate time to assess micronutrient deficiencies from dietary interventions.

The Paleo Diet group did lose more weight but when you look at the NNR recommendations you’ll see a much higher carbohydrate intake of 60% compared to the Paleo Diet group who only consumed 30% carbohydrates. These women were obese or overweight, so they were insulin resistant which means that they won’t do well on higher carbohydrate intake. The Paleo Diet group also consumed 30% protein compared to just 15% in the NNR group.

The decline in Free T3 on the Paleo Diet is due to the lower carbohydrate intake which isn’t necessarily a bad thin...