A federal agency has just been sued for urging Americans to go big on milk, cheese and other dairy.

Three doctors filed a lawsuit Wednesday in federal court against the U.S. Department of Agriculture for its guidance in December suggesting that Americans consume three servings of dairy each day. The doctors allege in the lawsuit filed in the U.S. District Court for the Northern District of California that the dietary guidelines contradict current scientific and medical knowledge, harming the quarter of Americans who are lactose-intolerant. They also suggest that the USDA is looking out for the interests of the meat and dairy industries rather than the health of Americans.

“The USDA’s conflict of interest is perhaps best illustrated in its statement that ‘most individuals would benefit by increasing intake of dairy,’ even though there is no convincing evidence that this is true,” said Donald Forrester, a family practice physician in Sacramento and one of the three doctors who sued along with the Physicians Committee for Responsible Medicine, a nonprofit organization that promotes a plant-based diet.

A spokesman for the USDA said that the Physicians Committee for Responsible Medicine has sued the USDA after the release of the past two dietary guidelines, called the Dietary Guidelines for Americans, which are issued every five years, and that the lawsuits have been dismissed.

“The dietary guidelines are just that — guidelines. They provide guidance based on the best available science and research,” the spokesman said in an email. “Understanding that not all people consume dairy, the Dietary Guidelines for Americans clearly includes information about alternatives. … The dietary guidelines provide a helpful road map with many different routes to get to good health depending on one’s personal preferences.”

The guidelines — the USDA’s CliffsNotes version is now called MyPlate, formerly the food pyramid — are the road map to how the government administers food assistance programs and school lunches. Schools are required to offer milk; students are not required to take it.

But the guidelines influence school lunches in many ways. For example, for a school to offer a plant-based milk alternative, a student must present a doctor’s note about a disability. Water must be offered by schools, but the USDA said schools may not offer it in place of milk and it “must not directly or indirectly restrict the sale or marketing of fluid milk.”

This can be a problem for many schoolchildren who are lactose-intolerant.

“Lactose intolerance is an ethnocentric word if three-quarters of the world’s population cannot digest lactose,” said Ashwani Garg, a family physician in Barrington, Ill., who himself is lactose-intolerant.

He said the inability to digest lactose, the primary carbohydrate in dairy, is prevalent among people of color — 95 percent of Asians, 60 to 80 percent of African Americans and Ashkenazi Jews, 80 to 100 percent of Native Americans and 50 to 80 percent of American Hispanics. For these people, consuming dairy causes diarrhea, pain and other, sometimes serious, digestive symptoms.

Garg said that 8,000 years ago, an enzyme called lactase evolved in humans that allowed them to digest cow’s milk. That enzyme usually diminishes after childhood. In European populations, a single gene mutation allowed lactase to persist through adulthood, and thus the United States’ early European settlers “normalized” the consumption of cow’s milk.

“I was at an American Medical Association meeting a few years ago where they put out guidelines asking that schools make available plant-based options,” Garg said. “We should propose health policy that is congruent with a person’s ethnicity and health-care needs.”

The AMA, which has no regulatory authority, proposed legislation that school lunch programs eliminate requirements that children produce documentation of a disability or a special medical or dietary need to receive an alternative to cow’s milk. They also called for the USDA’s dietary guidelines to indicate that meat and dairy products are optional, based on an individual’s dietary needs.

Current milk consumption in the United States is just about 1.5 servings per person per day, according to Walter Willett, a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health who comes from five generations of dairy farmers. He said the USDA’s recommendation that everyone have three servings of dairy a day — doubling current consumption — is “misleading and irresponsible.”

“The primary rationale for high dairy consumption is the idea that we need a huge amount of calcium for our bones to prevent fractures, and that has just not been shown by research,” Willett said. “Other parts of the world are cutting back on their milk recommendations, because there isn’t evidence that we need that much.”

Willett said a diet high in calcium may reduce the risk for colorectal cancer but increases the risk for prostate cancer. Calcium is essential, he said, as are vitamins A and D — but all of these can be introduced via supplements “to plant-based alternatives or even your Kool-Aid.”

He said the USDA recommends low-fat milk but that since Americans have made a significant pivot from liquid dairy to cheeses in recent years, “low-fat” is harder to achieve. For human health, and because dairy cows are associated with substantial greenhouse gas emissions, Willett said it would be more reasonable for the USDA dietary guidelines to suggest zero to two servings per day.

Mark Kennedy, who as vice president for legal affairs at the Physicians Committee for Responsible Medicine drafted much of the lawsuit, said the USDA has a conflict of interest “overseeing nutrition programs while having a statutory mandate to promote and market agricultural products without regard to whether they are good for consumption. It’s about ‘How can we keep the American farmer in business?’” he said.