Stupid question?  People gain weight all the time on seven-day cruises, where news articles have told us that the typical weight gain for passengers on a seven day trip is 1 lb per day.  But what if the macro ingredients of those calories were low carb high fat (LCHF-10% carbohydrates, 50% fat and 40% protein).  Sam Feltham did this last Spring.  He gained about 1 kg but lost 3 cm from his waist.

Fat in the absence of carbohydrate is not the devil.  The devil is in the carbs.