Portraits of lawmakers in dark suits peered down from the walls as Agriculture Secretary Tom Vilsack and Sylvia Mathews Burwell, the secretary of Heath and Human Services, sat inside a congressional hearing room last October. From behind microphones, they braced for an onslaught of questions. Cameras clicked, papers shuffled, heavy doors opened and closed as lobbyists and journalists slipped into the room. Then, after an opening prayer, the hearing began.

For months, members of Congress had admonished Vilsack and Burwell about how their agencies had handled the Dietary Guidelines for Americans—the government’s sweeping and hugely influential nutrition advice to the public about what to eat, which was due to be released within the year. Now the lawmakers had their chance to chastise the secretaries, face to face.

“You’ve lost credibility with a lot of people,” said Rep. Collin Peterson, D-Minn., jabbing a finger toward them as he blasted them for, in his view, bungling the guidelines.

Peterson’s barb was just one more salvo in a four-decade battle over the guidelines, and only the latest display of how that advice routinely gets hijacked by politics, thanks to a powerful food industry that throws its heft around Congress. The end result, many critics would say, are nutrition recommendations that promote certain sectors of the food industry rather than the health of the American people.

The guidelines have always been as much a political document as a scientific one. The October hearing was ostensibly about a general dissatisfaction with the way the guidelines are generated. But the real flashpoint was a report issued eight months earlier by an advisory panel charged with evaluating the latest nutrition science and making recommendations for what the guidelines should say. Among the panel’s many recommendations was that the guidelines should consider the environmental consequences of food production. More specifically, the report suggested that a diet lower in red meat and processed meat was not only more healthful, but better for the planet.

That report raised hackles in the livestock industry, already under fire for the environmental toll of its operations. Lobbyists, especially those working for cattle producers and meat processors, launched a full-scale offensive on Capitol Hill, with calls and letters to livestock-friendly lawmakers imploring them to quash the sustainability recommendation.

Some members of Congress attacked the work of the panel, officially called the Dietary Guidelines Advisory Committee (DGAC), accusing it of straying beyond its mandate to focus only on nutrition. Mike Conaway, R-Texas, chairman of the House Agriculture Committee, and Peterson, both from livestock-heavy states, asked Vilsack and Burwell to more carefully review the scientific reports. Then, concerned their message still wasn’t getting through, they hauled the secretaries in for a public scolding.

“There has been a strong reaction to the Dietary Guidelines Advisory Committee report,” Peterson said, adding, somewhat ominously, “Maybe we should reconsider why we are doing this.”

In other words, if the government’s nutrition advice threatens the multibillion-dollar livestock industry, maybe that advice should be scrapped altogether.