He's probably referring to the food pyramid, in which those food groups were put forth as foundational building blocks of a healthy diet according to the USDA. [1] That saga overlapped with the sugar lobby blaming fats for heart issues [2], and using their weight with the FDA to keep % Daily Values for sugars off food labels until very recently. [3]

[1] https://pubmed.ncbi.nlm.nih.gov/8375951/

[2] https://www.npr.org/sections/thetwo-way/2016/09/13/493739074...

[3] https://www.vox.com/2016/5/20/11719796/new-nutrition-label-a...