olestra
noun
oles·tra ō-ˈle-strə 
: a noncaloric fat substitute consisting of a series of compounds that are sucrose esters of six to eight fatty acids resistant to absorption by the digestive system because of their large size
Example Sentences
Recent Examples on the Web Other exhibits include potato chips made with the fat substitute olestra, which has the benefit of helping weight loss but unfortunate side-effect of diarrhea. 
Alexander Smith, NBC News, 14 June 2017
Alexander Smith, NBC News, 14 June 2017 Word History
Etymology
probably by shortening & alteration from (sucrose) polyester
First Known Use
1987, in the meaning defined above
Medical Definition
olestra
noun
oles·tra ō-ˈles-trə
: a noncaloric fat substitute consisting of a series of compounds that are sucrose esters of six to eight fatty acids resistant to absorption by the digestive system due to their large size