This video may help clarify a few concerns people have about fasting and thyroid function, especially:
-Weight loss does decrease T3 (this is common, expected)
-Low calorie diets in general reduce thyroid hormone levels (T3)
-Why prolonged fasting decreases free T3 and increases reverse T3 (it’s a means to spare muscle from being catabolized)
-Where the idea that “50 grams of carbs” are needed for optimal thyroid function
-Short term VS long-term fasting and thyroid function
obese subjects were studied after 7–18 days of total fasting and while on randomized hypocaloric diets (800 kcal) in which carbohydrate content was varied to provide from 0 to 100% calories. As anticipated, total fasting resulted in a 53% reduction in serum T3 in association with a reciprocal 58% increase in rT3
Key Research Articles Mentioned Herein:
Rosenbaum, M., & Leibel, R. L. (2010). Adaptive thermogenesis in humans. International Journal of Obesity, 34(S1), S47–S55. http://doi.org/10.1038/ijo.2010.184
Serog, P., Apfelbaum, M., Autissier, N., Baigts, F., Brigant, L., & Ktorza, A. (1982). Effects of slimming and composition of diets on VO2 and thyroid hormones in healthy subjects. The American Journal of Clinical Nutrition, 35(1), 24–35.
Spaulding, S. W., Chopra, I. J., Sherwin, R. S., & Lyall, S. S. (1976). Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man. The Journal of Clinical Endocrinology & Metabolism, 42(1), 197–200.