That's a little bit of a hard read... but if I understand it correctly, they cause decrease efficiency of sugar->ATP conversion, and the indirect effect of that is to cause increase sugar consumption.
Here's a simplified version: energy generation in the mitochondria is based on the energy differential between the intermembrane space and the inner mitochondrial membrane (I may have confused those membranes). Most uncouplers act to reduce that differential, thus causing inefficiency in the system, which is lost as heat.