Decreasing serum concentrations of all-trans, 13-cis retinoic acids and retinol during fasting and caloric restriction

Objectives. To investigate the effects of caloric restriction on the serum concentrations of retinoids in man. Design. Samples were drawn before and during caloric restriction by fasting or 4-6 weeks after gastric surgery. Subjects. The fasting group included 17 healthy subjects (11 women and six men) and 16 obese patients (10 women and six men) who underwent bariatric surgery (vertical banded gastroplasty). Main outcome measures. Serum concentrations of all-trans , 13-cis , 4-oxo-13-cis retinoic acids and retinol. Results. The serum concentrations of retinol, all-trans and 13-cis retinoic acids decreased by about 20% after 5 days of fasting. After gastroplasty, the serum concentration of retinol, all-trans , 13-cis retinoic acids, retinol-binding protein and transthyretin also decreased to a similar extent after 1 month. In both groups we found a correlation between the delta values of 13-cis retinoic acid and its metabolite 4-oxo-13-cis retinoic acid. In all subjects there were also correlations between the delta values of the retinoids. However, these correlations were comparatively weak (e.g. r (2) = 0.36 for retinol - all-trans retinoic acid). The change in retinoid concentrations did not correlate to the change of weight or body mass index. Conclusion. Our results support the hypothesis that serum retinol is one of the determinants of serum concentrations of all-trans and 13-cis retinoic acid and that the catabolism of 13-cis retinoic acid is not affected by fasting. However, in the individual case, S-Retinol is a poor predictor of S-All-trans retinoic acid.