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Paleolithic ("Paleo") diet causes iodine deficiency



a variety of dairy products, good sources of iodine

In the early part of the 20th Century, the areas around the Great Lakes, the Appalachians, and the Northwestern United States were known as the "goiter belt:" as many as 70% of children had goiter, which is an enlarged thyroid gland. Most of the time a goiter is caused by iodine deficiency, which can cause hypothyroidism (low amounts of circulating thyroid hormone). In turn, that low thyroid can manifest in fatigue, constipation, and most alarmingly for many people, unexplained weight gain. In pregnancy, iodine deficiency can lead to brain damage in the fetus as well as other risks both to the mother and the child.

Around that same time, iodine deficiency was also widespread in Sweden, leading them to begin adding iodine to table salt in 1936. Iodized salt first became available in Michigan in 1924, and although salt is not federally mandated to contain iodine, recent estimates suggest that about 75% of US households use iodized salt. That said, nowadays the major source of dietary iodine here in the US is from dairy products (due to iodine's use in the milking industry), seafoods, and some bread doughs.

The Paleolithic Diet, which is popular nowadays (here's my take on it), purports to reflect the style of eating from before widespread agriculture, excluding grains, legumes, refined sugars, oils, and salt. It's been widely touted as an effective diet for weight loss, and like the Atkins Diet and other such fad diets, in my opinion it mainly works because people stop eating junk. Until recently the Paleo Diet has appeared to be fairly healthy, but a study performed in Sweden and published recently in the European Journal of Clinical Nutrition (doi:10.1038/ejcn.2017.134) suggests otherwise.

The authors recruited 49 postmenopausal and healthy women (average age: 60) who were clinically overweight or obese and randomly assigned them to a 2-year plan of either a Paleolithic Diet (PD) or a diet based on the Swiss government's nutrition recommendations (called the Nordic Nutrition Recommendations diet, or NNR). The women received 12 group training sessions in following their assigned diet and kept dietary records of their food intake, which were collected at the 6-month and 24-month marks. At the start of the study, at 6 months, and at 24 months (the end of the study), the participants provided blood and urine samples so the authors could evaluate their iodine intake (among other markers).

While the NNR did not exclude any foods and sought for a macronutrient ratio of 15% protein, 25-30% fat, and 55-60% carbohydrate intake, the Paleo Diet adherents were instructed to include "lean meat, fish and sea food, fruit, vegetables, root vegetables, eggs and nuts" in their diet and to avoid "dairy products, cereals, beans, refined fats and sugar, added salt, bakery products and soft drinks" as well as "processed, canned and preserved food" and "manufactured and semi-manufactured goods." Their macronutrient goals were 30% protein, 40% fat, and 30% carbohydrate.

The supplied urine samples allowed the researchers to assess the participants' iodine status and their blood tests allowed them to monitor thyroid activity. While at the 6-month point those on the PD had doubled their intake of seafood products (remember, a major source of dietary iodine), they had reduced their intake of dairy products by 98% and their cheese intake by 95%. Breads were reduced by 95% and cereals by 99%+ - and they sustained those similar levels throughout the 24-month study.

After six months the PD group had cut their iodine levels by a little more than half (by 50.7%), although at the end of the study their iodine levels were back up to 80% of their starting point - suggesting that their adherence to the diet was not as good after 24 months as it was at the 6-month point. Those on the NNR diet had about the same iodine levels throughout the study. The good news, if you can call it that, is that thyroid hormones were largely unaffected by the clinically mild iodine deficiency the PD group experienced at 6 months.

What this means for you

The authors state it quite plainly: "...long-term use of a PD [Paleolithic Diet] is associated with the development of mild ID [Iodine Deficiency]" and "we suggest pregnant women avoid PD." Certainly the latter is true: I would contend that the former is true only if we assume that, like many restrictive diets, people can't sustain them for the long term: remember that the PD group's iodine levels increased between 6 and 24 months. While those on PD lost more weight than those on NNR (losing about 3 kilograms more, on average, than the NNR group), I would argue that a restrictive diet and the risk of iodine deficiency isn't worth it: better to eat a variety of foods, lose weight, and remain healthy.

First posted: December 13, 2017