Dietary proteins, cholesterol and thyroxine: a proposed mechanism.

The effects of dietary protein sources on plasma cholesterol concentrations are well-documented: animal proteins are hypercholesterolemic relative to plant proteins. While this effect of dietary proteins has been shown in many species, the mechanism is not known. This review will explore the relation between dietary proteins and plasma thyroxine concentrations. Data will be presented showing that feeding dietary animal proteins consistently depresses plasma thyroxine levels. Furthermore, the effects of thyroxine on cholesterol metabolism is consistent with the effects of dietary proteins on cholesterol metabolism. Although evidence is not conclusive, data support the hypothesis that dietary proteins may affect plasma cholesterol levels through changes in plasma thyroxine concentrations. To elucidate the mechanism by which this happens will be the basis for future research.