Well from my understanding, if you have an active lifestyle, then your body needs carbs to replenish glycogen stores. And proteins to repair and grow muscles. Fats aren't needed for anything in particular, except in small amounts.

But 2040 kCal is so much that the body will turn the energy into fat even if it didn't start out as fat.

Nothing per se. It's just that fat has 9 calories per gram, so 1250 calories from fat is 138 grams of fat. It's also mostly saturated fat, which is pretty bad for the heart, not to mention that it's nearly half the total daily caloric requirement for an average man.

If you are some combination of older, smaller, less-healthy, and unaccustomed to eating a meal containing that quantity of fat...then your digestive system may be very unhappy, and let you know it.