Without wanting to sound like a conspiracy nut, dietary advice is largely based on economic interest. In fact, every decision made politically at any level is first of all a question based on economies.We had the news today of the professor recruited by the government to write recommendations on dietary sugar intake, who has admitted receiving a direct sum from coca cola to advise them on dietary advice. He then, allegedly, also receives money from Mars to help him conduct his university 'research'. This is by no means an isolated incident.
Whilst there are certainly economic interests involved, the food industry likes to increase profit margins, there is also plenty of questionable input from supposed "scientists". (Even where there is no influence from the food or pharrmacutical industries.)
The relationship between economics and politics is complex too. With political dogma often trumping economic issues. (Politics exists wherever you have people, including in scientific research. Which can easily lead to people clinging to "theories" which should long ago have been considered "falsified".)
The very notion of a 'balanced' diet, based on calories, was ingenuously created to allow consumption of nutritiously poor foods into our every day diets.
The whole idea of "calories" having any meaning when it comes to the metabolism of complex organisms is something like a century past it's "use by date"
It's more from the psudo/junk science catagory than anything else.
The idea that 500 calories of cola and chocolate has the same metabolic effects on weight and body composition as 500 calories from vegetables and lean meat is ridiculous; yet this is what most people are brainwashed into thinking.
Actually all four groups of food might be expected to have different effects on people eating them. The only context in which the 500 calories means anything is if you were burning them to heat water. (On the other hand generating electricity using soft drinks might make more sense than using wind.)
Bottom line is that people are getting sicker. Type 2 diabetes is skyrocketing. Diagnosis of type 1 is increasing year on year. Rates of autoimmunity of all conditions are increasing. Our food environment is becoming more and more toxic, and every year food companies are allowed to engage in 'voluntary regulation' to help reduce the very conditions that their products promote.
Or possibly to lobby for more of the same...