I had good idea but it still took me almost 2 minutes to decide on
(D). (D) happens to be the longest version. In order to choose the longest version, we must have really strong reason.
And the reason is parallelism in list: list contains 3 or more items. All the items should be parallel, and there should be "and" or "or" before the last item. (The comma before "and" or "or" is optional, though I would recommend.)
A) this food contains six grams of high-quality protein, all nine essential amino acids, vitamins B12 and D,
and is a source of various other nutrients as well.
The position of and indicates that the list span from " six grams of high-quality protein" to "is a source of various other nutrients as well". They are not parallel.
B) this food contains six grams of high-quality protein, all nine essential amino acids, vitamins B12 and D,
and including various other nutrients.
Similar issue as (A)
C) this food contains six grams of high-quality protein, all nine essential amino acids, vitamins B12 and D,
and various other nutrients are included.
Similar issue as (A) and (B).
D) this food contains six grams of high-quality protein, all nine essential amino acids,
and vitamins B12 and D, and it is a source of various other nutrients.
Note the location of "and" is before "vitamins B12 and D", which parallel with "six grams of high-quality protein" and "all nine essential amino acids".
After that, COMMA + F
ANBOYS is used to construct a coordinating sentence. "it is a source of various other nutrients" is an independent clause.
E) this food contains six grams of high-quality protein, all nine essential amino acids, the vitamins B12 and D,
and provides various other nutrients.
Similar issue as (A), (B), and (C).