Caloric Restriction But Not Exercise-Induced Reductions in Fat Mass Decrease Plasma Triiodothyronine Concentrations: A Randomized Controlled Trial

Division of Geriatrics and Nutritional Sciences, Department of Internal Medicine, Washington University School of Medicine, St Louis, MO, USA.
Rejuvenation Research (Impact Factor: 3.31). 07/2008; 11(3):605-9. DOI: 10.1089/rej.2007.0622
Source: PubMed


Caloric restriction (CR) decreases circulating triiodothyronine (T(3)) concentration. However, it is not known if this effect is due to body fat mass reductions or due to CR, per se. The purpose of this study was to test the hypothesis that plasma T(3) concentration decreases with CR-induced reductions in fat mass but not in response to similar decreases in fat mass that are induced by exercise. Sedentary, nonobese 50- to 60-year-old men and women with no clinical evidence of cardiovascular or metabolic disease and not taking thyroid medications were randomly assigned to 12 months of caloric restriction (n = 18) or exercise-induced weight loss (n = 17) or to a control group (n = 9). Body weight and composition and plasma concentrations of the thyroid hormones T(3), thyrotropin (TSH), thyroxine (T(4)), and free thyroxine (FT(4)) were measured at baseline and 12 months. Fat mass changed significantly in the CR (-6.3 +/- 1.0 kg) and exercise (-5.5 +/- 1.0 kg) groups but not in the control group (-0.6 +/- 1.4 kg). The changes were not significantly different between the CR and exercise groups. Plasma T(3) concentration decreased in the CR group (-9.8 +/- 2.0 ng/dL, p < 0.0001) but not in the exercise (-3.8 +/- 2.1 ng/dL, p = 0.07) or control (-1.3 +/- 2.8 ng/dL, p = 0.65) groups. TSH, T(4), and FT(4) did not change in any of the study groups. Twelve months of CR decreased circulating T(3) concentrations in middle-aged adults. This effect does not appear to be attributable to changes in body fat mass because a comparable decrease in T(3) concentration was not observed in response to an exercise-induced fat mass reduction.

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Available from: Susan B Racette, Dec 23, 2013
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    • "intake for 12 months decreases visceral fat mass , improves insulin sensitivity , increases plasma adipo - nectin concentration , reduces circulating inflammatory markers , decreases plasma triiodothyronine levels , and reverses some of the age - related deterioration in cardiac diastolic function ( Fontana et al . , 2010a ; Stein et al . , 2012 ; Weiss et al . , 2008 ) . Ongoing studies on human subjects who voluntarily follow a caloric restricted diet will contribute to clarify not only the potential anti - ageing effects of CR ( Mercken et al . , 2013 ) , but also its contribution to the slowdown of age - associated diseases onset ( Stein et al . , 2012 ) ."
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