A mouse study has found that fish oil, which contains high levels of omega-3 polyunsaturated fatty acids, significantly helped clear amyloid-beta peptides (involved in the development of Alzheimer’s) from the brain.
https://www.eurekalert.org/pub_releases/2016-10/foas-abo102616.php
Huixia Ren, Chuanming Luo, Yanqing Feng, Xiaoli Yao, Zhe Shi, Fengyin Liang, Jing X. Kang, Jian-Bo Wan, Zhong Pei, and Huanxing Su. Omega-3 polyunsaturated fatty acids promote amyloid-β clearance from the brain through mediating the function of the glymphatic system. FASEB J. doi:10.1096/fj.201600896 ; http://www.fasebj.org/content/early/2016/10/07/fj.201600896.abstract