A series of processes that forms an integrated mechanism by which a cell or an organism detects the depletion of primary carbohydrate sources,usually glucose, and then activates genes to scavenge the last traces of the primary carbohydrate source and to transport and metabolize alternate carbohydrate sources. The utilization process begins when the cell or organism detects carbohydrate levels, includes the activation of genes whose products detect, transport or metabolize carbohydrates, and ends when the carbohydrate is incorporated into the cell or organism's metabolism.