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Effect of Long-Term Calorie Restriction with Adequate Protein and Micronutrients on Thyroid Hormones

Division of Geriatrics and Nutritional Sciences and Center for Human Nutrition (L.F., S.K., J.O.H.), Washington University School of Medicine, St. Louis, Missouri 63110; Division of Food Science, Human Nutrition and Health (L.F.,), Istituto Superiore di Sanitá, 00161 Rome, Italy; and Thyroid Specialty Laboratory (B.N.P.), St. Louis, Missouri 63125

Address all correspondence and requests for reprints to: Luigi Fontana, M.D., Ph.D., Washington University School of Medicine, 4566 Scott Avenue, Campus Box 8113, St. Louis, Missouri 63110. E-mail: lfontana{at}im.wustl.edu.

Context: Caloric restriction (CR) retards aging in mammals. It has been hypothesized that a reduction in T₃ hormone may increase life span by conserving energy and reducing free-radical production.

Objective: The objective of the study was to assess the relationship between long-term CR with adequate protein and micronutrient intake on thyroid function in healthy lean weight-stable adult men and women.

Design, Setting, and Participants: In this study, serum thyroid hormones were evaluated in 28 men and women (mean age, 52 ± 12 yr) consuming a CR diet for 3–15 yr (6 ± 3 yr), 28 age- and sex-matched sedentary (WD), and 28 body fat-matched exercising (EX) subjects who were eating Western diets.

Main Outcome Measures: Serum total and free T₄, total and free T₃, reverse T₃, and TSH concentrations were the main outcome measures.

Results: Energy intake was lower in the CR group (1779 ± 355 kcal/d) than the WD (2433 ± 502 kcal/d) and EX (2811 ± 711 kcal/d) groups (P < 0.001). Serum T₃ concentration was lower in the CR group than the WD and EX groups (73.6 ± 22 vs. 91.0 ± 13 vs. 94.3 ± 17 ng/dl, respectively) (P 0.001), whereas serum total and free T₄, reverse T₃, and TSH concentrations were similar among groups.

Conclusions: Long-term CR with adequate protein and micronutrient intake in lean and weight-stable healthy humans is associated with a sustained reduction in serum T₃ concentration, similar to that found in CR rodents and monkeys. This effect is likely due to CR itself, rather than to a decrease in body fat mass, and could be involved in slowing the rate of aging.

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				L. Fontana and S. Klein Aging, Adiposity, and Calorie Restriction JAMA, March 7, 2007; 297(9): 986 - 994. [Abstract] [Full Text] [PDF]