Archeological records. Grains are only 12K years old. Sugar by itself in quantity only since 1850s.
I really am shocked by this comment. Do you really think humans weren't high fat for virtually all of human history? What do you think they were eating?
And there are still or were until recently many traditional societies thriving on high fat. Great teeth, look up Weston Price, very little heart disease,obesity, super healthy.
Plains Indians basically had bison to eat. And then pemiccan, they were extraordinarily healthy. Their descendants on sugar have deteriorated swiftly.