That's based upon normal metabolism and if you calorie reduce your metabolisim will also slow down, you also need vitamins to help the body work and some will be need to break down fat into energy.

Vitamins and minerals are not something you can reduce without effect/impact. So do factor that into any calorie reduction.

This and body fat only goes so far and as a metric is often flawed in measurement as any rugby or certain sports physics can attest. This is large muscle mass often mess's up those scale calculations and with that, many a fit muscular person will fall into the obese box as muscle weighs more than fat.

Also it's not just fat that gets broken down into energy, muscle is affected as well.

As everything it is a fine balance.

Given all that, eating normal alternate days is a safer approach for many.