Seaweed and Soy: Companion Foods in Asian Cuisine and Their Effects on Thyroid Function in American Women

Abstract

Seaweeds and soy are two commonly eaten foods in Asia. Both have been reported to affect thyroid function, seaweed because of its iodine content and soy because of its goitrogenic effect. Twenty-five healthy postmenopausal women (mean age 58 years) completed a double-blinded randomized crossover study. Ten capsules (5 g/day) of placebo or seaweed (Alaria esculenta), providing 475 g of iodine/day, were consumed daily for 7 weeks. A powdered soy protein isolate (Solae Co., St. Louis, MO), providing 2 mg of isoflavones/kg of body weight, was given daily during the last week of each treatment arm. On average, this provided 141.3 mg of isoflavones/day and 67.5 g of protein/day. Blood samples and 48-hour urine samples were collected before and after each intervention period, and urinary I/C (g of iodine/g of creatinine) and serum thyroxine, free thyroxine index, total triiodothyronine, and thyroid stimulating hormone (TSH) were measured. Seaweed ingestion increased I/C concentrations (P Ͻ .0001) and serum TSH (P Ͻ .0001) (1.69 Ϯ 0.22 vs. 2.19 Ϯ 0.22 U/mL, mean Ϯ SE). Soy supplementation did not affect thyroid end points. Seven weeks of 5 g/day seaweed supplementation was associated with a small but statistically significant increase in TSH. Soy protein isolate supplementation was not associated with changes in serum thyroid hormone concentrations.

Managing Terrorism or Accidental Nuclear Errors, Preparing for Iodine-131 Emergencies: A Comprehensive Review

“…Seaweed, especially kelp is the best natural source of iodine [32,33]. Table 3 lists the iodine concentration in various common foodstuffs.…”

Soy protein diet alters expression of hepatic genes regulating fatty acid and thyroid hormone metabolism in the male rat

“…By contrast, mice expressing a mutant TRα1 receptor lacking T 3 binding were hypermetabolic, resistant to diet-induced obesity, and had increased liver fatty acid catabolism, while mice with a different mutation in TRα1 had increased visceral obesity and liver lipid contents [23,24]. Soy proteins and soy isoflavones may, at some dietary inputs, affect serum T 4 and/or T 3 levels in animals [25][26][27], primates [28] and humans [29,30], although not all studies have consistently reported such findings [31]. Interestingly, soy protein isolate, but not soy isoflavones, elevated liver abundance of TRβ1 in male and female Sprague-Dawley rats [26,27].…”

Dietary Seaweed Modifies Estrogen and Phytoestrogen Metabolism in Healthy Postmenopausal Women

“…Fourteen of the participants had significant increases (mean ¼ 2.2 6 1.4 mmol/d; P ¼ 0.0001) during the seaweed period; all 15 women had increases during the SeaSoy supplementation period (2.0 6 1.0 mmol/d; P = 0.0001). A more detailed analysis of changes in iodine and thyroid hormone levels has been presented elsewhere (22).…”

“…It was chosen for its low-iodine (95 mg/g) concentration (22). A 5-g serving of Alaria harvested in the same area contains: 54.6 kJ, 0.9 g protein, 0.18 g fat, 2 g carbohydrate, 1.9 g fiber, 373 mg potassium, and 212 mg sodium (23).…”

“…A 5-g serving of Alaria harvested in the same area contains: 54.6 kJ, 0.9 g protein, 0.18 g fat, 2 g carbohydrate, 1.9 g fiber, 373 mg potassium, and 212 mg sodium (23). The Alaria was collected in June from the Sally Islands by Maine Seaweed Company following standard collection protocols (22).…”