Weanling rats display bioperiodicity of growth and food intake rates.

Bioperiodicities in biological phenomena have long been studied to gain insight into the dynamics of living organisms. However, apparent periodicities in rates of growth and food intake have often been either ignored or attributed to random error. We have found that such periodicities are not random but take the form of infradian rhythms (period > 28 h), with multiple periods including circasemiseptan (period = 3.5 d). In the reported experiments, we examine the existence of periodic, oscillatory phenomena in growth and eating patterns of rats. The cosinor model of Halberg was used to establish the occurrence of rhythms and quantify rhythm characteristics of components identified in least squares spectra. The four parameters of the rhythm were found to be altered by concentrations of the limiting dietary nutrient in that they had different spectral signatures. Existence of such oscillations in growth rates and food intake rates could have important consequences in designing feeding and growth experiments for achieving optimal physiological responses as well as providing possible insights into eating disorders.