If humans were able to sleep that long at [reported 50 calories per hour](https://www.sleepfoundation.org/how-sleep-works/how-your-bod...), that would give a three months energy expenditure of about 59kg of body fat ([at 7.7kJ/kg](https://www.quora.com/How-many-calories-are-in-1-kg-of-fat)).

However, I am not aware of any confirmation that sleeping so long is possible, and does not harm health. If there was indeed possibility to enter torpor in a controlled manner, that may be up to 88% energy saving, so only ~7kg of body fat would need to be used.