Nutritional No-No. Refers to any "unnatural" food item or additive, such as white flour, sugar, table salt, preservatives, food colorings, etc., that nutritionists advise against consuming.
Dude, you're eating coleslaw just plain? Aren't you gonna put some salad dressing on it?
No way, Bud --- that stuff's got a myriad of triple-n's in it --- sugar, salt, hydrogenated oils, preservatives... I wanna stay healthy!