Starch is simply a name for long chains of carbohydrates, with glucose making up the individual elements of these chains. It depends on the bonds that weld the carbs together and whether we can digest them (utilizing the glucose) or not. Those that we can't break up are called resistant starches.

While almost all plants contain starch, the largest suppliers of starch in the human diet are cereals (grains, maize, rice), and root veggies (potatoes), but starches are in nearly every plant food.

The nutritionist recommendations that you mention probably refer to low-carb, or no-carb diets.