The problem is, when you restrict calories significantly over a period of time, you will also lower your body’s set point for calorie intake. This is no longer a temporary situation. If you begin to eat normally, you’ll gain weight.

That's the truth. You can even taste the sweetness in broccoli. 

Hard to do? Not really, if your blood sugar is in balance and your body is able to use stored fat as fuel. But many Americans have some degree of metabolic syndrome, and this would make fasting more difficult.