Starches would tend to deplete Vitamin C assuming the two carnivore Vitamin C assumptions I pointed out are correct.

The most common complements to verterbate meat are fruit and seeds (eg nuts, grains) as reported in Munoz & Alroy 2014, the article I linked elsewhere in the conversation.

I think humans in particular are primarily scavengers & hunters (especially with self-scavenging by taking large prey to a group site and eating it for an extended period of time) and the main supplemental food for us is fruit. Humans seem to have some seed intolerances (eg to lectin and gluten) so I think that aspect of it is less pronounced or absent in human evolutionary history. We are also distantly descended from browsers (and then scavengers and then hunters and then pastoralists) who probably ate a fair bit of fruit.