I think it's not so much the total calories, but the sheer amount of fat. That is, if we send the pill down your GI tract with 1/4 of grease, will it still work?

Presumably their "high-fat" condition has to be fattier than any reasonable person would eat on a regular basis, so that it establishes a useful upper bound. If it was just a couple eggs and hash browns, then finding it's still effective wouldn't be useful because some people eat fattier breakfasts than that.