Ah, the truth will make you slim. Not.

On Thursday, hundreds of millions of Americans risked obesity, heart disease and indigestion by eating large quantities of food with no precise knowledge of the caloric content. If many of them felt regret on Friday, it was not because they were duped into overeating by the absence of nutritional data.

This may seem odd to the federal government, which has decreed that chain restaurants, convenience stores, vending machines and groceries shall provide information that most people don't care about and won't heed. The Food and Drug Administration (FDA) acted on a provision of the Affordable Care Act mandating more nutritional labeling, and it took an aggressive interpretation of its authority: The mandate also includes movie theaters, vending machines and bars.

Even supporters were stunned by the FDA's ambition. "I'm amazed," New York University nutrition professor Marion Nestle told the New York Times. "It never occurred to me that alcohol would make it in." Now when you start knocking back mojitos during happy hour, you'll be able to calculate the exact impact on your waistline.

The FDA rule rests on a faith that the truth will make you slim. Advocates of this approach, the most notable being former New York Mayor Michael Bloomberg, think unwise eating habits stem from insufficient transparency on the part of food providers, which can be overcome by rules forcing them to lift the veil.

Let the agency speak for itself, in a parody of bureaucratic logic worthy of the Onion. "Consumers can systematically make suboptimal dietary choices because they discount future health consequences relative to immediate benefits more than they would if they chose according to their underlying or true preferences, leading them to regret their choices at a later date," it says.

Interference from Washington is essential, the FDA argues, because "changes in labeling may increase internalization of future costs into current decisionmaking by making the long-term health consequences of consumer food choices more salient and by providing contextual cues of food consumption."

A simpler way to put this is that people often eat and drink things they find appealing and only later wish they hadn't — which doesn't mean they wouldn't do exactly the same thing if they had to do it over again.

Sara Bleich, a professor at the Johns Hopkins Bloomberg School of Public Health — yes, that Bloomberg — says the latest research indicates that most customers at these restaurants don't even notice the calorie counts. Of those who do, she says, "a lot are not changing behavior."

"Some studies show a positive effect" — meaning diners consume fewer calories — "some show no effect, and some show a negative effect," she told me. How does Bleich (who favors the new rule) explain this? "When people make choices about food, they're focusing on price, convenience and taste. Health is a secondary concern."

But more information is always good, right? Not necessarily. Complying with the regulations will cost businesses money. The Food Marketing Institute (FMI), which represents grocery stores, puts the tab at $1 billion in the first year alone. Those costs will eventually be borne by consumers.

It's not the only price they'll pay. "This is going to take away from anything that's freshly made in the store because the costs involved will be so high," the FMI's Robert Rosado told the Wall Street Journal. "You're going to lose fresh choices."

In 2011, opposing the mandate for grocery stores, the Kroger Co. said its chefs often "use different ingredients based on what is seasonal or in stock. It is not unusual for ingredients to change regularly. The restaurant menu labeling rule would render that nearly impossible."

The FDA could confirm their hypothesis is correct by noting that these establishments do, after all, still have customers. Instead, it and Congress have decided to foist information on people who show no desire to acquire it or pay for it.

The agency has fantasies that its rule will curb the appetites of American diners. The appetites of government, meanwhile, will not be restrained.