The federal government's famed "Food Pyramid" is on its way out, to be replaced by something resembling a plate or, somewhat ironically, a pie chart. While the "Food Pyramid" — or "Food Plate" — is a way to educate Americans about healthy eating, some activists want to go further, dictating what's on our plates in the name of public health.

Three examples of nutrition battles in recent years should serve as cautionary tales in the debate over education versus control.

Two leading anti-obesity campaigners, Yale University's Kelly Brownell and Harvard's David Ludwig recently declared: "For some of the most important public health problems today, society does not have the luxury to await scientific certainty."

These academics want to use public policy to make us lose weight — even if the consequences of their proposals aren't fully understood and might even backfire.

One idea sprouting up in state legislatures everywhere is the "soda tax." Advocates reason that raising the price of soda will reduce our consumption of calories, causing widespread weight loss.

A fountain of research, though, shows that taxes won't cause people to lose weight. A Duke study released in December, for example, found that substantial taxes would only result in people consuming 7 fewer calories per day — a trifling amount.

Even Brownell admits that "nobody has been able to see how people will really respond under these conditions." That's hardly a vote of confidence in his pet policy — yet he demands that states adopt it.

And consider the emerging War on Salt. Loved by chefs, salt is derided by public health activists who see it as contributing to hypertension and other health disorders. The Institute of Medicine called for mandatory sodium reductions last year, and New York City started a voluntary (for now) program encouraging food makers to reduce the amount of sodium in their foods.

Ironically, the editor of the American Journal of Hypertension says that sodium reduction is an "experiment on a whole population" because there's not enough scientific research to know what will happen. It's feasible, for instance, that people will simply eat more lower-sodium food to reach the same sodium level they were eating before. This, of course, could cause people to get fatter. Oops.

And while a medical director at the Centers for Disease Control and Prevention claims that it's not prudent to wait for more sodium science before acting, the record speaks differently. Alderman noted recently that nearly half of a set of 9 studies found no association between sodium intake and health.

Nutrition science is always changing, and it's hard to set broad public policy when its underpinnings can fall away with a moment's notice.

Consider the case of trans fats. In the late 1980s, the activist group Center for Science in the Public Interest (CSPI) attacked restaurants' use of beef tallow because it was high in saturated fat. Restaurants switched to using oil containing trans fats.

At the time, CSPI defended trans fats, saying "All told, the charges against trans fat just don't stand up." But just a few years later, CSPI was demonizing trans fats based on new scientific claims, a campaign that ultimately resulted in busy-bee bureaucrats getting involved.

Marion Nestle, a former federal Dietary Guidelines Advisory Committee member, admits that "whether the evidence is good enough to recommend population-based dietary changes comes down to a matter of subjective judgment."

Public health activists want to substitute their judgment for yours and soften evidentiary requirements for making public policy. There's a difference between educating Americans — such as requiring calorie counts on menus — and claiming that said education will be effective when it won't. (Recent research failed to find that menu labeling would reduce the amount of food people ordered, despite activists' predictions.)

There's nothing wrong with teaching Americans about what the latest science says. But it should be up to us to take or leave government recommendations. The last thing Americans should be is puppets of nutrition masters.