Flaked wheat has not been malted, so it cannot convert it's own starches to sugars. Typically, a good North American 2-row malt has enough enzymes to convert about 30-40% additional starches in the mash. You need a higher percentage of 2-row to convert the starches in the flaked wheat. Most wheat beers (Wiessbier, Wiezen, Hefewiezen) use malted wheat. Belgian Wit uses up to 50% flaked wheat.
Reason: Additional info