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Special interest in Thyroid Health and Functional Medicine

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Why you struggle to lose weight on a diet

Successful weight loss is doomed to failure unless the reduced intracellular thyroid levels are addressed. Chronic and yo-yo dieting, frequently done by a large percentage of the population, is shown to be associated with reduced cellular T4 uptake of 25%-50% (2-7). Following repeated cycles of dieting, weight loss occurred at half the rate and weight gain occurred at three times the rate compared to controls with the same calorie intake (1). The reduced cellular thyroid level is generally not detected by standard laboratory testing unless a free T3/reverse T3 ratio is done.

Finally a study explained why it is very difficult for obese patients to lose weight; as calories are decreased, thyroid utilisation is reduced and metabolism drops. Additionally, there are increased levels of free fatty acids in the serum with chronic dieting, which further suppresses T4 uptake into the cells and further cellular hypothyroidism (8-12).

In a study published in the American Journal of Physiology-Endocrinology and Metabolism, Van der Heyden et al studied the effect of calorie restriction (dieting) on the transport of T4 and T3 into the cell (13). It was found that dieting obese individuals had a 50% reduction of T4 into the cell and a 25% reduction of T3 into the cell due to the reduced cellular energy stores, demonstrating that in such patients standard thyroid blood tests are not accurate indicators of intracellular thyroid levels.

Many overweight individuals fail to lose weight with dieting. While it is always assumed they are doing a poor job of dieting, it has been shown, however, that chronic dieting in overweight individuals results in increased levels of NEFA, which suppresses T4 uptake into the cells (14). This suppressed T4 uptake results in reduced intracellular T4 levels and subsequent T4 to T3 conversion and a reduced metabolism (14-18).

How you can find out, whether you are affected?

Standard TSH, T4 and T3 testing will not detect this problem. Instead, a free T3/reverse T3 blood test can aid in the diagnosis of reduced uptake of thyroid hormones and intracellular hypothyroidism. It is proving to be the best physiologic marker of intracellular thyroid levels and supplementation with T3 should be considered.

References:

  1. Brownell KD, Greenwood MR, Stellar E, Shrager EE. The effects of repeated cycles of weight loss and regain in rats. Physiol Behav 1986;38(4):459-64.
  2. Lim C-F, Docter R, Krenning EP, et al. Transport of thyroxine into cultured hepatocytes: effects of mild nonthyroidal illness and calorie restriction in obese subjects. Clin Endocrinol (Oxf) 1994;40:79-85.
  3. van der Heyden JT, Docter R, van Toor H, et al. Effects of caloric deprivation on thyroid hormone tissue uptake and generation of low-T3 syndrome. Am J Physiol Endocrinol Metab 1986;251(2):156-E163.
  4. Leibel RL, Jirsch J. Diminshed energy requirements in reduced-obese patients. Metabolism 1984;33(2):164-170.
  5. Elliot DL, Goldberg L, Kuehl KD, Bennett WM. Sustained depression of the resting metabolic rate after massive weight loss. Am J Clin Nutr 1989;49:93-6.
  6. Manore MM, Berry TE, Skinner JS, Carroll SS. Energy expenditure at rest and during exercise in nonobese female cyclical dieters and in nondieting control subjects. Am J Clin Nutr 1991;54:41-6.
  7. Croxson MS, Ibbertson HK, Low serum triiodothyronine (T3) and hypothyroidism in anorexia nervosa. J Clin Endorinol Metab 1977;44:167-174.
  8. Brehm A, Krssak M, Schmid AI, Nowothy P, et al. Increased Lipid Availability Impairs Insulin-Stimulated ATP Synthesis in Human Skeletal Muscle. Diabetes 2006;55:136-140.
  9. DeMarco NM, Beitz DC, Whitehurst GB. Effect of fasting on free fatty acid, glycerol and cholesterol concentrations in blood plasma and lipoprotein lipase activity in adipose tissue of cattle. J Anim Sci 1981;52:75-82.
  10. Lim C-F, Bernard BF, De Jong M, et al. A furan fatty acid and indoxyl sulfate are the putative inhibitors of thyroxine hepatocyte transport in uremia. J Clin Endocrinol Metab 1993;76:318-324.
  11. Lim C-F, Docter R, Visser TJ, Krenning EP, Bernard B, et al. Inhibition of thyroxine transport into cultured rat hepatocytes by serum of non-uremic critically ill patients: Effects of bilirubin and nonesterified fatty acids. J Clin Endocrinol Metab 1993;76:1165-1172.
  12. Elliot DL, Goldberg L, Kuehl KD, Bennett WM. Sustained depression of the resting metabolic rate after massive weight loss. Am J Clin Nutr 1989;49:93-6.
  13. van der Heyden JT, Docter R, van Toor H, et al. Effects of caloric deprivation on thyroid hormone tissue uptake and generation of low-T3 syndrome. Am J Physiol Endocrinol Metab 1986;251(2):156-E163.
  14. Lim C-F, Docter R, Krenning EP, et al. Transport of thyroxine into cultured hepatocytes: effects of mild nonthyroidal illness and calorie restriction in obese subjects. Clin Endocrinol (Oxf) 1994;40:79-85.
  15. Leibel RL, Jirsch J. Diminshed energy requirements in reduced-obese patients. Metabolism 1984;33(2):164-170.
  16. Elliot DL, Goldberg L, Kuehl KD, Bennett WM. Sustained depression of the resting metabolic rate after massive weight loss. Am J Clin Nutr 1989;49:93-6.
  17. Manore MM, Berry TE, Skinner JS, Carroll SS. Energy expenditure at rest and during exercise in nonobese female cyclical dieters and in nondieting control subjects. Am J Clin Nutr 1991;54:41-6.
  18. Croxson MS, Ibbertson HK, Low serum triiodothyronine (T3) and hypothyroidism in anorexia nervosa. J Clin Endorinol Metab 1977;44:167-174.

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