Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men

OBJECTIVE Dietary carbohydrate content is a major factor determining endocr ine and metabolic regulation. The aim of this study was to evaluate the rel ation between thyroid hormone levels and metabolic parameters during eucalo ric carbohydrate deprivation. STUDY DESIGN We measured thyroid hormone levels, resting energy expenditure (by indirect calorimetry) and urinary nitrogen excretion in six healthy ma les after 11 days of three isocaloric diets containing 15% of energy equiva lents as protein and 85%, 44% and 2% as carbohydrates. RESULTS In contrast to the high and intermediate carbohydrate diets, carboh ydrate deprivation decreased plasma T-3 values (1.78 +/- 0.09 and 1.71 +/- 0.07 vs. 1.33 +/- 0.05 nmol/l, respectively, P < 0.01), whereas reverse T-3 , T-3 uptake and free T-4 levels increased simultaneously compared to the o ther two diets. TSH values were not different among the three diets. Althou gh dietary carbohydrate content did not influence resting energy expenditur e, carbohydrate deprivation increased urinary nitrogen excretion (10.91 +/- 0.67 and 12.79 +/- 1.14 vs. 15.89 +/- 1.10 g/24 h, respectively, P = 0.03) . CONCLUSIONS Eucaloric carbohydrate deprivation increases protein catabolism despite decreased plasma T-3 levels. Because it has previously been shown that starvation decreases plasma T-3 levels, resting energy expenditure and nitrogen excretion, these discordant endocrine and metabolic changes follo wing carbohydrate deprivation indicate that the effects of starvation on en docrine and metabolic regulation are not merely the result of carbohydrate deprivation.