Becoming a fat burning beast, being fat adapted, your body preferring fat for fuel. People throw around these terms around here all the time but what does this actually mean? Its it just sceudo/bro-science or is thee actually anything to it?

When i think of being fat adapted, the only thing that it could mean is being in full ketosis. But even if you eat a tiny meal of carbs your body will automatically use those for fuel first. So your body never actually prefers burning fat and you never actually become better at burning it. Only if your starve your body of a carb source will it dip into fat stores more often. Also it will just use dietary protein or lean mass to make up the carbs to balance the carb/fat burning ratio.

So is there actually anything to these sayings or are they just catch phrases used to sell books?