Omega-3 fatty acids in fatty fish protect gums from disease.

Omega-3 fatty acids reduce chronic inflammation, and inflammation in the mouth is a symptom of gum disease. 

In research published in the November 2010 edition of "Nutrition," Masanori Iwasaki of Niigata University reported on a study that showed that consumption of the omega-3 fats in fatty fish protected gums from disease. 

Fish rich in omega-3s include salmon, herring and mackerel.

Info source: http://www.livestrong.com/article/382774-healthy-food-for-healthy-gums/