>>509464957 (OP)Corruption.
Congress was freaking out over heart disease way back in the day and some dishonest scientists had a theory it was due to saturated fat but they didnt have any proof so they just made stuff up for congress because congress had a given a deadline for someone to come up with a solution, in order to recieve funding or whatever. When they told congress it was the fat congress subsidized corn in an effort to switch the american diet from a protein and fat based diet to a sugar based diet using corn syrup.
Human testing was banned in the 40s so they do animal testing and also "epidemiological" studies (the study of correlations in data) to try and understand nutrition now but its really just a bunhc of mega corps who pay scientists to basically act like lawyers and interpret the survey data in ways that benefit them.