Body fat to energy efficiency

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Just out of curiosity and education I wanted to know how efficient our bodies at using body fat for energy, but cant find anything. In other words, what is the maximum throughput of converting body fat to energy? Is there a maximum, there got to be, of how many calories per hour our bodies can generate from body fat (assuming all needed conditions for this to happen have been met).

I would appreciate any pointers to information. Thanks.

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