School Nutrition Flexibility Act - Amends the Richard B. Russell National School Lunch Act to prohibit the Secretary of Agriculture from promulgating rules and regulations applicable to the school lunch and breakfast programs that establish a maximum quantity of grains, meat, or meat alternates that may be served in any meal or during any period of time of any school year.

Makes the formula that school food authorities are required to use to establish the price for a paid lunch (a lunch provided to children who are not eligible for free or reduced price meals) applicable only to school food authorities that had a negative balance in their nonprofit school food service account for the previous school year.