lowering of metabolism after weight loss

A while ago there was some discussion on if the body adjusts metabolism
after weight loss to maintain the higher weight. Here's an article that
talks about the issue:

Why lost weight returns after dieting
http://www.news-medical.net/?id=2955

The data suggests that weight loss in obese, obesity-prone rats, induced
by caloric restriction, is accompanied by metabolic adaptations that
predispose one to regain the lost weight. In rats that are losing
weight, this is exhibited by a significant reduction in metabolic rate,
measured as both 24-hour energy expenditure and sleeping metabolic rate,
both independent of metabolic mass and energy intake. This adaptation
persists after eight weeks of intake-regulated weight maintenance, but
is no longer present with eight subsequent weeks of feeding at-will
where rats are regaining lost weight. While rats that are regaining
weight may have a shift in appetite that would contribute to their high
rate of weight regain, the drive to increase food intake remains the
most critical factor in the predisposition to regain lost weight. This
adjustment clearly weighs more on the energy balance equation than the
metabolic adjustment on energy expenditure observed in this or any other
study.

Additionally, the effect that energy intake, or more particularly,
carbohydrate intake, has on respiratory quotient [dividing the amount of
CO2 produced (VCO2) by the amount of oxygen uptake (VO2)]. RQ is much
more dramatic than the metabolic adjustment observed from weight
reduction. This drive to increase food intake likely involves
environmental stimuli (diet composition, food palatability, physical
activity) influencing motivational and metabolic components of a
genetically determined set of central systems.

While the data suggest that these metabolic adaptations might hinder
successful weight maintenance, it should not imply that successful
weight maintenance is unachievable. Even with the increased intake of
carbohydrates, regular physical exercise may be the key factor that
counteracts these metabolic adaptations to weight loss.

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I notice that after everyone of these pronouncements saying how hard
weight is to lose they say something like it's not unachievable. How
hard does something have to be before people stop trying to achieve it?
Not very hard.