Maybe Mark is more protein centric because of two factors.

As we age, the level of stomach acid drops and that acid is the way proteins break down into absorbable particles, like amino acids. ( Collagen type proteins breakdown into a 3 part amino acid ). Adding an acid like vinegar , lemon juice and HCl tablets brings up the acid level for proper stomach function.

Older folks tend to decrease food consumption, and reduce their effort to prepare food. Ive personally seen this in my mother ,90, an MIL, 88. They do easy. And fewer meals. And both dont eat enough protein. I assume these two are representative of their age group.