I do not think that the Government have a choice but to offer such advice, the costs of bad diets is beginning to cripple the NHS.
The bigger problem is around the very poor public understanding of these issues and how to analyse the published information. Add to that the vested interests of food manufacturers "my product is 95% fat free" (and stuffed with too much sugar and salt etc.)
New theories about cause and effects are constantly being investigated and developed in all branches of science and medicine etc. The effects of DNA research and the understanding of genetics has changed massively in the last few decades.
It is not surprising that government information changes over time in the light of new evidence.
The world would still be thought to be flat without these new understandings.
If the government did not issue this advice then inevitably people would start to complain, "well nobody told me this fizzy drink was too full of sugar and would rot my teeth or cause me to develop type 2 diabetes" etc.etc.
It is "contact the injury lawyers" I want to blame someone else for this.
People are notoriously bad at changing eating and other lifestyle habits.
Just look at television adverts. " and now the science bit" shocked tones! All of which implies that this science is too scary and complicated for you to think about. " Just don't worry your pretty little head about it" use our shampoo, deodorant, disinfectant etc, and all will be well.
Rant over!
It is interesting to me that I not think science threads on GN ever seem to get a very big following.