and in modern terms it makes you a social pariah. Really though trimming the fat probably refers to a butcher removing the unwanted flesh from meat, not losing weight.

Spot on. The clue it’s not about evolution is that you don’t “trim” fat from a live animal.

This is a lean period, and the fat that meta had enabled them to cut fat rather than cut muscle or bone, making them now more lean, but still strong. The fat they had served its purpose similar to how fat serves its purpose during famine.