That's another one of those food-nazi myths.
Man sheds 80 pounds on McDonald's diet - Health - Diet and nutrition | NBC News
There's a guy who lost eighty pounds by eating "nearly every meal" for six months straight at McDonalds.
Let's for a moment assume that it's so devoid of "XYZ"... then either:
1) McDonalds food contains "XYZ"
or
2) Obviously "XYZ" is unnecessary if you can go without it for six months or more.