First, it is my experience that most people do, religiously so, for a short amount of time (a month or so seems common). And then, the 20% for which this advice produces the expected result continues practicing it, and the 80% for which it doesn't work start following less and less religiously, until they don't at all.
That's mostly evidence that dieticians are solving the wrong problem. To borrow from another poster in this thread, if the composition of what you eat was enough to solve obesity, it is likely that saying "don't drink alcohol" would be enough to solve alcoholism. And yet, hundreds of years of experience show that it is wrong for the latter.
A diet that is easy to follow (such as Roberts' Shangri-La and Asprey's RFLP) is what dieticians should be striving for, but instead most of them recommend a regime that their clients are unlikely to follow (and then blame the clients).
I'm not sure I believe that most overweight people have even had the advice of a dietician.
I suppose things like the food pyramid sort of count, but even the old one didn't endorse the empty calories evident in shopping behaviors (i.e, chips and pop).
That's mostly evidence that dieticians are solving the wrong problem. To borrow from another poster in this thread, if the composition of what you eat was enough to solve obesity, it is likely that saying "don't drink alcohol" would be enough to solve alcoholism. And yet, hundreds of years of experience show that it is wrong for the latter.
A diet that is easy to follow (such as Roberts' Shangri-La and Asprey's RFLP) is what dieticians should be striving for, but instead most of them recommend a regime that their clients are unlikely to follow (and then blame the clients).