The phrase "big fat lie" means a very obvious and significant falsehood or untruth. It emphasizes that the lie is not just a small or harmless deception, but rather a deliberate and substantial fabrication. Full definition
Her first book, Big Fat Lies Women Tell Themselves: Ditch your Inner Critic and Wake Up Your Inner Superstar (New World Library, 2011), shot up to # 1 in several categories on Amazon, including Self - Help, Happiness and Self - Esteem. (findyourcallingnow.com)
(A very enlightening segment in Big Fat Lies is Gillespie's explanation of what exactly makes a fatty acid (the building blocks of fats) saturated, unsaturated or for that matter monounsaturated like olive oil. (novaholisticjournal.com)
Might better have been «A Million Big Fat Lies.» (twliterary.com)