A mathematical model together with data analyses were adapted to describe the effect of variation in dietary energy concentration, achieved by the inclusion of different levels of sawdust, on the growing pig. It was found that the autoregression coefficient of ln (cumulative feed intake) and the slope of the log-linear relationship between body fat and cumulative feed intake (ME) are influenced by energy concentration. In contrast, the slopes of the log-linear relationship of body mass, cumulative heat production, protein and total body energy with cumulative ME do not vary with energy concentration, although all intercepts are again found to vary. The significance of this pattern of growth responses is interpreted in terms of mechanisms controlling growth, and the analytic procedure allows interpolation to sawdust levels not included in the experiment.