That is generally true, minus any plateaus that require assistance like exercise to break through.

For me, I like to eat my calories than drink them if I had to pay attention.

I liked this challenge and think it presented a lot of solid merits.

True, but at 1300 calories you'd also end up in a lower metabolism state (famine mode), undoing any benefits. You'd still lose weight of course but at a cost. I read that kicks in at 1200 calories or lower, but it's close enough.

I'm sure that the calorie intake could be increased without costing too much extra though, by padding things out with rice and/or beans.