Every era's advice was presented as the final answer. None of them were.
Modern dieting as a cultural phenomenon is often traced to the 1863 pamphlet "Letter on Corpulence," written by William Banting, a British undertaker who'd lost significant weight avoiding starch and sugar on his doctor's advice — arguably the first mass-market diet book, and the low-carb approach behind it still echoes through diets published 160 years later.
Calorie counting became mainstream as nutrition science formalised energy balance as the dominant weight-management framework.
Following concerns about dietary fat and heart disease, low-fat everything became the dominant public health message — sometimes at the cost of added sugar replacing the removed fat.
Atkins and its successors pushed back hard against the low-fat consensus, reviving Banting's original premise in modern form.
A shift toward food quality and processing level over any single macronutrient — Mediterranean, whole-food and anti-inflammatory framing (including THE FAD) reflect this newer emphasis.
Each era's dominant advice was presented as the final, settled answer, and each was eventually revised or complicated by later research — a useful reminder to hold any single framework, including THE FAD's, with some humility about how the science may keep evolving.