Substances Inhibiting Nutrient Absorption in Food, Namely Goitrogens

Goitrogenic compounds, categorized as antinutritional factors, interfere with the bioavailability of essential micronutrients from dietary sources, with a particular emphasis on iodine uptake disruption. Their bioactive metabolites induce disturbances in iodine metabolism within the organism, potentially culminating in severe metabolic dysregulation and homeostatic imbalance. Due to their established role in the pathogenesis of thyroid enlargement (goiter), these substances are alternatively referred to as goitrogenic agents. This class of antinutritional compounds encompasses thioglycosides (e.g., glucosinolates), cyanogenic glycosides, diverse polyphenolic compounds exhibiting chelating properties, and hemagglutinins—lectin proteins that bind carbohydrate moieties. Their mechanisms of action are multifaceted: certain goitrogens competitively inhibit iodine uptake by thyroid follicular cells, whereas others accelerate renal iodine excretion—both pathways converging toward a net reduction in systemic iodine levels.

The highest concentrations of goitrogenic compounds—commonly referred to as goitrogens—are predominantly found in soybeans and their derived products, including tofu, soy milk, and tempeh. Another significant category comprises cruciferous vegetables, encompassing both tightly headed varieties such as white cabbage and Brussels sprouts, as well as looser-leafed types like kale and Savoy cabbage. Equally noteworthy are broccoli, cauliflower, turnips, rutabagas, mustard greens, and spinach, all of which contain measurable, albeit variable, quantities of these substances. To a lesser but still detectable extent, goitrogens are also present in pine nuts, strawberries, and proso millet (commonly known as "kasza jaglana"). Importantly, these compounds are distributed throughout all plant tissues, with peak concentrations observed in seeds and young shoots. Human exposure occurs not only through the direct consumption of goitrogen-rich foods but also indirectly via dairy products from livestock fed diets high in cruciferous plants (Brassicaceae), which serve as a natural reservoir for these compounds. The table below, compiled by D. Szczukocki and B. Krawczyk, outlines the content of goitrogenic metabolites in selected vegetables, expressed in milligrams per 100 grams of fresh weight: white cabbage (3–6 mg), kale (3–25 mg), Savoy cabbage (18–31 mg), Brussels sprouts (10 mg), cauliflower (4–10 mg), kohlrabi (2–3 mg). Trace or negligible amounts were detected in lettuce, spinach (excluding the aforementioned exceptions), onions, celery, radishes, and tomatoes, indicating a heterogeneous distribution of these compounds across vegetable species.

Goitrogens affect the metabolism of iodine by decreasing its concentration in the body, which in turn leads to a disruption in the economy of this ingredient. Excessive consumption of products that are a source of goitrogen in the first stage causes a decrease in the secretion activity of the thyroid gland.

Thermal food processing—particularly cooking without a lid—facilitates the partial removal of goitrogens, which are antinutritional compounds that interfere with iodine absorption, thereby reducing their concentration by approximately thirty percent. Prior to cooking legumes such as soybeans, a preliminary soaking period of several hours in cold water is advised to further diminish the presence of these undesirable substances. It is equally critical to avoid the concurrent consumption of goitrogen-rich foods (e.g., cruciferous vegetables) alongside iodine sources (marine fish, seafood), as this combination may exacerbate disruptions in iodine metabolism. It is essential to recognize that most food products contain both nutritional and antinutritional components—including goitrogens, which, by impairing iodine utilization, can contribute to the development of goiter and worsen preexisting hypothyroidism. Individuals diagnosed with thyroid dysfunction should exercise particular caution in minimizing dietary goitrogen exposure, employing culinary techniques such as open-lid cooking or presoaking to reduce their concentration in meals.