Barnes & Noble is considering options for its quickly growing but expensive Nook e-book reading business, its latest attempt to regain profitability as the publishing industry adapts to the rising popularity of digital books and magazines. Investors fled as the company also forecast a much bigger loss for the year than originally expected. The stock lost nearly a fifth of its value. Barnes & Noble has been investing heavily in electronic books and its Nook e-book readers as it faces tough competition from online retailers and discount stores. That business is growing as consumers increasingly shift to reading e-books. But it has led to losses for the New York-based bookseller.