Caloric restriction but not exercise-induced reductions in fat mass decrease plasma triiodothyronine concentrations: A randomized controlled trial

Edward P. Weiss, Dennis T. Villareal, Susan B. Racette, Karen Steger-May, Bhartur N. Premachandra, Samuel Klein, Luigi Fontana

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

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 T3 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 T3, thyrotropin (TSH), thyroxine (T 4), and free thyroxine (FT4) 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 T3 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, T4, and FT4 did not change in any of the study groups. Twelve months of CR decreased circulating T3 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.

Original languageEnglish
Pages (from-to)605-609
Number of pages5
JournalRejuvenation Research
Volume11
Issue number3
DOIs
StatePublished - Jun 1 2008

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