a sanitarium or a resort that specializes in helping people lose weight.
Origin of fat farm
First recorded in 1965–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
slang a health farm or similar establishment to which people go to lose weight
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
A clinic or resort where people go to lose weight, as in She spends all her vacations at a fat farm but it hasn't helped so far. This is a somewhat derisive term for such an establishment. [Colloquial; 1960s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.