There are allegations of a conflict of interest between McDonald's and the U.S. government.

A national dairy organization overseen by the federal government played a key role in bumping sales for the fast-food giant last quarter by helping the company use butter instead of margarine in signature menu items, according to a recent report by Quartz.

Are the same people who are advising Americans on their diets also helping McDonald's?

The shift was orchestrated through a relationship between McDonald's and a dairy industry promotional group, funded by U.S. dairy farmers and importers and overseen by the U.S. Department of Agriculture (USDA)—an agency that, with other federal agencies, sets national dietary guidelines. The connection calls up a potential conflict of interest for an agency simultaneously tasked with shaping Americans' diets as well as helping the dairy industry with fast-food deals.

Flickr/Mike Mozart - flic.kr

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Dairy Management Inc. (DMI), the promotional group, staffs product scientists and food researchers as consultants at McDonald's headquarters. The partnership has so far been lucrative for dairy interests: Since 2013, McDonald's has rolled out nearly 30 "dairy-friendly" items, pushing 1.7 billion pounds of milk through subsequent sales. Initiatives carried out by DMI and groups it manages must be approved by the USDA. In other words, those initiatives are effectively controlled by the U.S. government.

McDonald's says that butter has helped its bottom line.

The shift to butter on Egg McMuffin sandwiches, according to McDonald's CEO Steven Easterbrook, drove at least part of the company's recent growth. In a conference call, Easterbrook noted that the switch pleased consumers looking for simpler, natural ingredients in their food. "[W]e saw a double-digit increase in the number of Egg McMuffins sold immediately following the rollout," he said.

Jeepers Media/Mike Mozart, Flickr/Norio Nomura - flic.kr

"We want to give [consumers] more reasons to dine at McDonald's by recommitting to hot fresh food, fast friendly service, and a contemporary restaurant experience," Easterbrook said.

McDonald's did not respond to ATTN:'s request for comment on the initiative.

In addition to Egg McMuffins, McDonald's has added butter to 19 other items.

Along with Egg McMuffins, the so-called "let us butter you up" campaign, which kicked off in September, includes butter in 19 other items, Quartz reported. Additionally, it will increase its annual dairy purchases by more than 500 million pounds of milk.

Other fast-food companies have signed similar deals.

According to Quartz, DMI has had successes in previous efforts to push dairy items at other fast-food restaurants like Papa John's, Domino's, and Taco Bell.

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Though some health advocates have voiced concern with the government's involvement in potentially undermining its own health guidelines by propping up blatantly unhealthy fast-food items, the USDA said that dairy was a part of a well-rounded diet.

"USDA encourages all Americans to eat a healthy, balanced diet—which includes servings of dairy," an agency spokesperson told Quartz.

Head over to Quartz and read the full report.