Well, not really. Not a conspiracy of the sort you can take to court. A balanced and well researched look back at the nutrition wars and recent talk of a “sugar conspiracy” in this article in Science.
Historical investigations of “merchants of doubt” have been invaluable in showing that scientific uncertainty is sometimes the product of deliberate acts of deception. Such studies underscore the essential insight that the existing evidence base is powerfully shaped by social forces and political choices, and that had decisions unfolded differently, our areas of knowledge (such as genomics) and blind spots (such as obesity prevention or gun violence) would be shifted. But ahistorical accounts thwart our ability to critically evaluate the often long and zigzag process of scientific conjecture and refutation. They provide spurious cover for changes to policy by suggesting that old ideas are illegitimate. And, they advance a false impression that doing the “right” kind of science will somehow avert the messy business of making policy based on incomplete evidence, public values, and democratic politics
The core of the problem is the willingness to jump in and give “expert” advice when the evidence is so limited (for any advice); but then again, demand for advice was so strong, it was bound to be fulfilled, just as demand for finding a “conspiracy” (fat conspiracy, sugar conspiracy, whatever) is so strong. These things probably arise from deep features of human cognition and social interaction.. anyway, I think this is a balanced article, but maybe not harsh enough about the limitations of nutrition advice and the damage done by experts offering advice where the science is not yet settled..