Over the past 5-7 years, more and more people worldwide have become aware of the Paleo Diet, which really is not a diet at all, but rather a lifelong way of eating to reduce the risk of chronic disease and maximize health and wellbeing. One of the fundamental principles of The Paleo Diet is to eliminate or drastically reduce consumption of cereal grains, whether they are refined or whole. Currently, 8 cereal grains (wheat, corn, rice, barley, sorghum, oats, rye, and millet) provide 56% of the food energy and 50% of the protein consumed on earth.3 However, from an evolutionary perspective, these foods were rarely or never consumed by our hunter gatherer ancestors.3
When I first made the suggestion that as a species we would be a lot healthier if we reduced or eliminated cereal consumption in 1999,3 I received, and still receive, criticism by some professionals in the nutritional community because they believe that the elimination of an entire food group (cereals) is nutritionally unsound and “will produce numerous dietary deficiencies.” This statement is not supported by any experimental evidence. In fact, the contrary is true. As I have previously pointed out, elimination of cereal grains actually increases the nutrient density of the 13 vitamins and minerals most lacking in the U.S. diet4, 5 – providing cereals are replaced by fresh fruits, vegetables, meats, poultry, fish, seafood and eggs.
Besides this fundamental lack of knowledge concerning the nutrient density of cereal grains, nearly all classically trained nutritionists have little or no appreciation for the antinutrients present in grains. As the name implies, antinutrients are dietary substances which interfere with our normal metabolism and physiology. Cereal grains are generally concentrated sources of numerous antinutrients and may produce undesirable health effects,3 particularly when consumed as daily staples.
In the U.S. “gluten free” foods have become incredibly popular in recent years as many people recognize that they simply feel better by eliminating the 3 gluten containing grains (wheat, rye and barley). Gluten conscious consumers frequently replace wheat, rye and barley with non-gluten containing grains (rice, corn, oats, sorghum and millet) in the mistaken belief that these 5 non-gluten grains are harmless. However, as I have previously pointed out, even the 5 non-gluten containing grains should be avoided for a variety of reasons.3 Specifically, I’ll detail below how millet adversely affects iodine metabolism and may cause goiter (swelling of the neck) when eaten regularly.
The Culprit: Millet
Unless you are a vegan, a vegetarian or are in search of gluten-free grains, most Americans and westerners have never tasted millet. Nevertheless, you don’t have to look very far to find this cereal grain (grass seed) at most health food stores. If you only dine upon millet dishes once in a blue moon, it will have zero repercussions upon your health, but be aware that millet is a nutrient poor, antinutrient laden food – the regular consumption of which may cause multiple dietary deficiencies and nutrient related diseases,3 including impairment of iodine metabolism and risk for goiter.
Millet is not a single plant species (as are most other cereal grains), but rather interpreted broadly may comprise about 500 species of grass seeds worldwide.13 Only a few species of millet are commonly cultivated as food crops. Worldwide, pearl millet (Pennisetum glaucum) is the most widely produced millet15 and is cultivated extensively in Africa and India. Finger millet (Eleusine coracana, proso millet (Panicum miliaceum), fonio millet (Digitaria exilis), and foxtail millet (Setaria italic) are also important crop species in developing countries.13, 15 Nevertheless millet is a minor cereal grain in terms of global economic importance. Worldwide production of millet is about 1% of either wheat or rice.13
Because millets require little water and are highly drought resistant, they grow well in arid and semi arid regions of the world such as in countries surrounding the Sahara desert in Africa and in dry areas in India and Asia. Further, millet is an attractive agricultural crop for farmers in these regions because under good conditions, it can yield two harvests per year13 and is resistant to pests and pathogens.
In the Sudan region (Darfur Province) of Africa, dietary surveys show that millet consumption in three communities (Kas, Tawaila and Nyala) was the primary source of food calories, respectively yielding 73.6%, 66.7%, and 37.1% of total daily energy.20 In this study, the occurrence of goiter was outrageously high – greater than almost anywhere else in the world. The incidence of goiter for girls in these three communities was 75%, 55%, and 13%, respectively; for boys it was 46%, 35%, and 10%, respectively. Similar high rates of goiter and thyroid disorders have been reported for school children in the Gujarat district of Western India where millet is a staple food.2
Millet Consumption, Iodine Deficiency and Goiter
Wherever and whenever millet becomes a staple food worldwide, the incidence of goiter increases and abnormalities of thyroid function and iodine metabolism occur2,7,16-20 Further, animal studies in rats, pet birds, and goats and tissue (in vitro) studies demonstrate unequivocally that this cereal plays a major role in causing goiter, thyroid abnormalities and impairment of iodine metabolism.1, 8, 10-12, 22
Iodine is an essential nutrient for humans, without which we most conspicuously develop goiter (an enlargement of the thyroid gland about the neck). Additionally, lack of iodine in the diet impairs cognitive development in growing infants and children, miscarriage in pregnant women and brain and nervous system dysfunction in adults.24, 25
Originally, it was thought that goiter occurred primarily from a deficiency of iodine in our food supply and water. Accordingly, in the U.S. and elsewhere most dietary salt (NaCl) has been fortified with iodine. An unappreciated aspect of iodine metabolism is that metabolic deficiencies of this nutrient can still occur even when dietary intake of iodine appears to be sufficient.7 Although virtually unknown to most nutritionists, elements found in millet represent powerful antinutrients that impair iodine metabolism and frequently cause goiter and symptoms of iodine deficiency.
Goitrogens in Millet
Goitrogens are dietary substances which impair thyroid and iodine metabolism and may ultimately cause the development of goiter. As I have previously alluded, a few scientists in the nutritional community early on appreciated that high millet diets promoted goiter. However, it was not completely understood how millet produced its goitrogenic effect. Subsequent discoveries and experiments over the past 35 years now show that compounds known as flavonoids in millets are responsible for causing iodine dysfunction and may in turn produce goiter when consumed as staples.6, 7, 21, 23
All millets are concentrated sources of compounds known as polyphenolics, some of which are referred to as flavonoids. Numerous flavonoids have been found in millets including apigenin, luteolin , kaempferol and vitexin; all of which severely impair thyroid function and iodine metabolism6, 10-12, 21, 23 and cause goiter in animal and tissue models.1, 8, 10-12, 22 Although it is not completely understood, flavonoids from millets appear to inhibit iodine uptake by most cells in the body, impair secretion of thyroid hormones, and reduce organification of Iodine by the enzyme thyroperoxidase.6, 7, 10, 23
Additional Antinutrients in Millets
Although a few scientific articles suggest that millets may possess positive health effects,26, 27 these papers and authors seem to be completely unaware of the numerous antinutrients found in millets and their potential for disrupting nutrition and health.
Let’s begin with the mistaken notion that millets are good sources of calcium.26, 27 Upon chemical analysis on paper, this statement may be true, but in the body (in vivo), nothing could be further from the truth. Calcium, along with iron and zinc that may be present in millets are actually poorly absorbed in our bodies because phytates, tannins and other compounds prevent their assimilation.28-32 Accordingly, high cereal grain diets whether millet derived or not, frequently result in multiple nutrient deficiencies including calcium, iron and zinc.3
In addition to their high phytate, flavonoid and polyphenolic contents, millets are also concentrated sources of other antinutrients including protease inhibitors (trypsin, chymotrypsin, alpha amylase and cysteine)33-35 and steroidal saponins.36, 37 Cereal grain protease inhibitors likely elicit adverse effects upon the pancreas when consumed as staple foods,3 and saponins are known to increase intestinal permeability and may contribute to chronic low level systemic inflammation.
Taken in its entirety, an overwhelming scientific literature demonstrates that millets are second rate foods that when consumed regularly may adversely affect iodine metabolism and elicit goiter. I’m not completely sure where the USDA dietitians derived their recommendations for whole grain consumption, but it certainly could not have come from their familiarity with the millet literature.
Loren Cordain, Ph.D., Professor Emeritus
1. Abel Gadir WS, Adam SE. Development of goitre and enterohepatonephropathy in Nubian Goats fed with pearl millet (Pennisetum typhoides). Vet J. 1999 Mar;157(2):178-85.
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18. [No authors listed] Millet–a possibly goitrogenic cereal. Nutr Rev. 1983 Apr;41(4):113-6.
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