There are plenty of reasons why politicians and government bureaucrats have no business telling you what you should eat. The Constitution grants the federal government no authority to do so, for one thing. Even if it did, it is simply wrong to force people to pay taxes so that other people can hand down nutritional advice or -- God forbid -- mandates.
A terrific article by Jane Black in The Washington Post illustrates why, furthermore, the government's advice isn't likely to be very good:
[H]istorically, the government has shied away from offering controversial advice. And with food, everything is controversial: A boost for one type of food in the guidelines can be viewed as a threat by providers of competing products. The result, critics say, is a nutritional education system so politically influenced that it is ineffective.
This year's process appears to be no exception. In public comments, the meat lobby has opposed strict warnings on sodium that could cast a negative light on lunch meats. The milk lobby has expressed concerns about warnings to cut back on added sugars, lest chocolate- and strawberry-flavored milks fall from favor. Several members of the Massachusetts congressional delegation also weighed in against added-sugar restrictions in defense of the cranberry...
In 1977, a Senate select committee led by Sen. George McGovern (D-S.D.) was forced to beat a hasty retreat after it initially recommended that Americans could cut their intake of saturated fat by reducing their consumption of red meat and dairy products. Its revised guidelines suggested choosing "meat, poultry and fish that will reduce saturated-fat intake."
McGovern, whose constituents included many cattle ranchers, lost his seat in 1980. Since then, in case after case, the guidelines have refrained from suggesting that Americans eat less of just about anything.
Public health advocates say that kind of vacuum is precisely the problem: By avoiding blunt messages about what not to eat, the government has spoken in a way that baffles consumers.
"The only time they talk about food is if it's an 'eat more' message," said Marion Nestle, a professor of nutrition at New York University and a longtime critic of the food industry. "If it's a question of eating less, then they talk about nutrients."...
[A]s in the past, translating scientific data into clear and useful recommendations poses political pitfalls. The advisory committee's emphasis on a "plant-based" diet, for example, has caused much consternation among the powerful egg and meat lobbies who say the term might be misunderstood as advocating a vegetarian diet.
This problem trips up all big-government schemes. Right-wing and left-wing statists think they have a terrific idea: give the government power to do this or that, and Experts will use that power to improve mankind. But then the people with a financial stake get involved, and the effort ends up serving them more than mankind. See also health care, national defense, etc..