The influence of caloric deprivation and food composition on TSH, thyroid hormones and nuclear binding of T3 in mononuclear blood cells in obese women

In vivo changes in thyroid-stimulating hormone (TSH), thyroxin (T4), triiodothyronine (T3) and nuclear binding of T3 (NBT3) in mononuclear blood cells were studied in obese women during seven days of caloric deprivation (maximum 1,100 kcal/d). In seven women given a high protein diet (80% protein, 7% carbohydrates, 7% fat) and in two women who fasted (group 1). total T3 (TT3) decreased from 1.66 ± 0.43 nmol/L to 1.11 ± 0.32 nmol/L ( P < .01), free T3 (FT3) decreased from 5.7 ± 1.1 pmol/L to 4.3 ± 1.6 pmol/L ( P < .01), and free T4 (FT4) increased from 17.8 ± 2.3 pmol/L to 21.1 ± 2.0 pmol/L ( P < .01). In five women given a carbohydrate diet (Dextrin-maltose 100%) (group 2), thyroid hormones were unchanged, TT3 was at start 1.66 ± 0.24 nmol/L and after seven days 1.43 ± 0.26 nmol/L (NS), FT3 changed from 6.4 ± 1.8 pmol/L to 6.0 ± 2.1 pmol/L (NS) and FT4 changed from 20.4 ± 5.1 pmol/L to 20.6 ± 3.1 pmol/L (NS). The caloric intake and the weight reduction was the same in the two groups. Basal TSH and TSH after thyrotropin-releasing hormone (TRH) (TSH +30min) declined in both groups. In group 1, basal TSH declined from 1.88 ± 1.07 μU/mL to 1.30 ± 0.91 μU/mL ( P < .03), and TSH +30min declined from 12.44 ± 7.49 μU/mL to 9.38 ± 5.97 μU/mL ( P < .03). In group 2, basal TSH declined from 2.09 ± 0.87 μU/mL to 1.66 ± 0.92 μU/mL ( P < .03), and TSH +30min declined from 15.63 ± 7.90 μU/mL to 11.93 ± 7.20 μU/mL (NS). The NBT3 maximal binding capacity rose from 30.3 ± 7.9 fmol(femtomole)/mg DNA to 42.3 ± 11.3 fmol/mg DNA ( P < .01) in group 1, but was unchanged in group 2, 34.9 ± 7.3 fmol/mg DNA and 32.2 ± 5.8 fmol/mg DNA (NS). The binding affinities at start were, in group 1, 4.7 ± 2.2 × 10 −10 mol/L, and in group 2, 6.4 ± 3.8 × 10 −10 mol/L, and did not change. In vitro incubation of mononuclear blood cells from the same person with increasing T3 (0.5 to 6.3 nmol/L) and constant T4 (96.8 nmol/L) concentrations in human serum for 24 hours at 37°C before measurement of NBT3 showed a dose-dependent reduction in NBT3. We conclude that serum TSH decreased in response to caloric deprivation, independent of changes in T3 and T4, the serum concentration of T3 and T4 were dependent on food composition, and NBT3 seemed to be inversely related to serum T3.