When you create a product feed, you can set a popularity setting (the feed type). The currently available product feed types are Best Sellers, New Arrivals and Slow Moving Inventory

Best Seller product feeds will filter out up to 250 products ranked based on quantity sold and gross sales.

New Arrival product feeds will filter out up to 250 products ranked based on date added to your store.

Slow Moving Inventory product feeds will filter out up to 250 products that have been on sale longer than 30 days and inversely ranked based on quantity sold and gross sales.