There are several remaining questions to the carb diet issue:

1. is the U-curve real? There is a U-curve that usually inflects at 51%. Most people surveyed get 51% of their calories from carbs.

Other dietary recall studies indicate the same - 51%, even the PURE study.

According to the ARIC follow-up published in Lancet Aug 2018, the lifespan decreases as the % of carbs drops. According to the PURE study, higher levels of carbs showed decreasing lifespan. Why?

Is Glycemic Index, or Glycemic Load involved in the explanation? Is it the quality of the carbs?

2. Also, what happened in the ARIC follow-up to the group that "substituted lower carbs with plant protein and fat"? This subgroup, according to the study also lived longer. It was described in the text and there was a separate table. But it didn't show up in the U curve. Why?

https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(18)30135-X/fulltext#seccestitle140

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1989668/