Hello Welcome HCM Regarding your question of rationale of Low fat diet in Cholelitiasis. Cholelithiasis means gall bladder stones. Gall bladder is a small green bag like structure present near liver, it stores bile juice secreted by liver. This bile juice contains bile salts which are produced by degradation Cholesterol in our body and they help in digestion fatty foods we consume. Hence when we take food, gall bladder contracts releasing bile juice into gut, there by aiding digestion fats in our food and this response is more with fatty food. This is the normal physiology and coming to cholelithiasis. Some individuals develop gall bladder stones which are nothing but solidified bile salts in gall bladder due to sluggish flow of gall bladder or increased production of bile salts. When these these stones get dislodged from gall bladder in gut they cause severe pain and this dislodgement is facilitated by fatty foods as fats increse gall bladder contraction. Fatty foods contain high cholesterol which aids in increased bile salts formation and there by increasing chances of stone formation. Hence those patients have cholelithaisis are advised to have low fat diet to dcrese the production of stones and to decrease the incidence of pain episodes precipitated by High fat diet. I hope u find this info helpful. Wish u a speedy recovery and good health.