On a low fat but high carbohydrate semi-starvation diet of the type typically used, that drop in metabolism is exactly what happens as the body re-adjusts itself to the amount of fuel coming in so it doesn't starve and die during the perceived famine. Yes, I too wish the authors were familiar with the benefits of a low carbohydrate high fat diet, on which I was able to lose a substantial amount of weight without that drop in metabolism. So it's not inevitable or hopeless, but on the typical fat-shunning low calorie diet it unfortunately likely is.