Kinda yes. The problem is utilizing the food energy efficiently. But if we could utilize it at only, say, 20%, that sounds reasonable to me, comparing to heatin

Kinda yes. The problem is utilizing the food energy efficiently. But if we could utilize it at only, say, 20%, that sounds reasonable to me, comparing to heating the house with wood, then 50kg of bananas should be enough. Natural gas is just more convenient, as it doesn't require you to feed the stove/dispose the ashes.