Hope may be on the horizon for the 70% of the adult population that finds cow's milk difficult to stomach. In these individuals, the presence of the sugar lactose leads to clinical symptoms, including abdominal pain, nausea, and diarrhea. To address this problem, dairy manufacturers offer milk in which lactose has been removed enzymatically postcollection. But these methods are often both expensive and time–consuming. An alternative approach is to express a lactase enzyme in the mammary gland that converts lactose to glucose and galactose (pp. 135 and 160). The resultant milk displays all the qualities and appearance of standard milk, but has a significantly reduced lactose content (as low as 15% of control milk).