Seven ups and downs means that men (men) are fat in July and women (women) are fat in August. The beginning of July and the end of August in the lunar calendar are the peak season for crab fishing.

Crab is a migratory crustacean aquatic animal, which breeds in the ocean and grows in rivers, rivers and lakes in fresh water. Mature crabs breed in seawater, which is called reproductive migration, and grow in fresh water, which is called growth migration. Mature crabs must leave the fresh water environment, mate in the seawater environment and give birth to offspring. The time for crabs to migrate to different water systems is different. Among them, the Haihe River system where Baiyangdian is located can generally climb here in July of the lunar calendar. After August, they will embark on a journey back to the sea. So eating crabs is "seven ups and eight downs"