Dear Patty,
I googled Greggor's Daily Dozen and watched the video. One thing that strikes me odd is that he never once mentioned any kind of scientific studies about the vegetables he recommends. Why does he always mention them in his other videos demonizing meat? He only briefly mentions potatoes, giving only the obvious example of a “potato only” diet being unbalanced. Also I don't recall him ever mentioning GMO's, wheat intolerance, gluten sensitivity or the differences between organic and conventional farming. Rather than go into any detail he seems to take a Dr. Seuss approach to the subject.
Might I point out that it is virtually impossible to get an adequate amount of either of the two vitamins you mentioned naturally in the diet and that the highest source of b12 is liver and the highest source of vitamin D besides sunlight is fish? Fact is, if they didn't (chemically) add these vitamins to foods virtually everyone would suffer from malnutrition.
Speaking of potatoes which he mentioned in the video I don't recall him ever mentioning nightshade intolerance which I was coincidentally just researching yesterday, wondering if I might have myself. Many believe long term nightshade consumption is the primary cause of arthritis.
Here are highlights of the more interesting nightshade links I was looking at yesterday if anyone is interested:
https://www.westonaprice.org/health-top ... ghtshades/
http://www.greenmedinfo.com/blog/link-b ... flammation
http://blog.arthritis.org/living-with-a ... arthritis/
https://blog.paleohacks.com/nightshades/