I'd be sooner to suspect environmental contaminants (changing types of air pollution, microplastics, pesticides on food, stress hormones in factory-farmed meat, et al) as a cause.
Although I suspect there's something to your hypothesis as well. I don't know about a spoonful of oil, but I have gone through phases where food seems less "rewarding" on a physiological level, and as a result I feel more satisfied with less.