It's very repetitive, and fairly evangelistic - but if you can look past that, there's a lot of sense behind it. Fasting (voluntarily) as opposed to starvation (outside your control) looks like a useful tool in maintaining good health. In particular it looks to be very helpful when combined with a good LCHF (low carbohydrate, high fat) diet.
Whilst you can live for a surprising amount of time without food (the book cites one medically supervised case of over 380 days!), you don't last long without liquid. I've been restricting myself to water and black coffee, however for longer fasts bone broth is recommended to top up vitamins and minerals. The body becomes remarkably good at recycling so you need far less of a top-up than you may think.
Fasting can be for any period - we all fast multiple times per day starting with the last mouthful of our last meal, but we don't fast for very long. As we're driven to continual snacking (mustn't let those energy levels drop!) the longest period between eating is usually over night.
I tend to eat at around 8pm, and since going (mainly) LCHF I've preferred to get out and run in the morning at the weekend before breakfast - just with a cup of black coffee. Often I wouldn't eat until early afternoon, so that's a voluntary fast of 14 hours. This is good to promote fat burning, but there are greater (and additional) benefits from giving it a bit longer.
Give it a read if you're interested
I went for 24 hours last week, from dinner one evening to dinner the next evening, and found it fairly easy. This week I thought I'd try for a 36-hour fast from dinner Sunday night through to breakfast this morning.
Although my stomach sounded like an Icelandic mud spring when I went to sleep last night, I woke up this morning feeling mighty-fine, and not at all hungry. In fact, I feel very focussed, energetic, and even a little euphoric. I decided not to bother with breakfast and went for a run around the block instead. I'm planning to eat at dinner this evening - I'm going for a longer run tomorrow and would prefer not to pass out and fall in the Thames (low risk, but better safe than sorry). So that will be a 48-hour fast.
I'm probably finding it relatively easy as I've been largely LCHF since the end of 2012. My body is used to being carb-restricted and burning stored fat. I wonder how hard it would be to go a week? The book describes some health benefits of fasting for a week per year which I won't repeat here, but I'm intrigued.