There is no potato famine in America. Low-income pregnant women, new moms and their young kids may not eat enough leafy greens, milk, peanut butter or whole grains, but they do eat plenty of white potatoes. Typically in the form of french fries, as it happens. Which is why the federal government does not need to give poor families money to buy even more potatoes.

Potato farmers, and politicians who represent potato-producing states, beg to differ. Big Potato claims Big Brother is practicing anti-tater discrimination.

For 40 years, the Women, Infants and Children supplemental nutrition program — known as WIC — has been giving low-income mothers and young children vouchers to purchase foods with specific nutrients that scientists say this population doesn’t consume sufficiently. Studies have shown that the program improves birth outcomes and may even be helping to curb obesity among low-income preschoolers.

WIC works because it is so targeted to nutritional needs. Unlike with the much larger food-stamp program — now known as the Supplemental Nutrition Assistance Program — which can be used to purchase almost any food (including energy drinks, candy and, yes, even lobster), the foods that qualify for WIC are tightly prescribed based on documented nutritional deficiencies. For example, each month an eligible low-income, breast-feeding woman can get WIC vouchers for 24 quarts of milk and $10 worth to spend on any kind of fruits and vegetables.

Except white potatoes.

That’s because of recommendations from the Institute of Medicine, which was commissioned to study what low-income families eat vs. what nutrients they need. The Institute found that starchy foods such as white potatoes, while nutritious, were already well-represented in poor families’ diets. (Sweet potatoes and yams were not, so they are available through WIC.)

Needless to say, the tuber lobby is unhappy about this. The amount of money at stake through WIC is relatively tiny — small potatoes, you might say, compared with SNAP and the school lunch program, which do pay for potatoes. But spud farmers believe excluding white potatoes from WIC is bad for marketing and therefore gives the entire white potato industry a black eye.

Twenty senators recently sent an angry letter to the Agriculture Department secretary, demanding an immediate end to anti-tater bigotry, and Sen. Susan Collins, R-Maine (where the top agricultural commodity is potatoes), reportedly will soon offer a legislative amendment mandating the inclusion of white potatoes in WIC. Lawmakers from potato-producing states have made similar proposals before, but this one would have a chance of passage both because Collins has become an important political ally and because pressure from the well-heeled potato industry is mounting.

Incidentally, the USDA already has expedited another review of WIC based on nutrition and consumption data released since the last go-round, in the mid-2000s, and will again ask the Institute of Medicine for guidance. But for Big Potato, a scientific review due out in a year seems to offer too much uncertainty. They want a mandate, and they want it now.

A spud earmark is a much bigger deal than it sounds like. To paraphrase Ira Gershwin: You say potato, I say precedent.

“Once the door is open to undermine the program this way, by putting it in the hands of the political machinery rather than scientific recommendations, it will be very hard to reverse it,” Irwin Redlener, a pediatrics professor at Columbia University and president of the Children’s Health Fund, told me.

What’s next? he asked. Will Big Twinkie soon claim underrepresentation in toddlers’ diets, too?

That’s not such a far-fetched question.

Other interest groups have agitated for WIC earmarks in the past. In the 1990s, Sen. Carl Levin, D-Mich. (home state of the Kellogg Co.), fought to allow Kellogg’s Raisin Bran into WIC after the cereal ran afoul of the program’s sugar content restrictions. Sen. Lisa Murkowski of Alaska likewise argued that salmon was unfairly excluded from WIC.

Canned salmon eventually was added to WIC’s food list — but only after the Institute of Medicine’s last comprehensive review concluded that low-income, breast-feeding mothers needed to eat more fish, among other things.

And if the next scientific review finds that poor moms’ and toddlers’ eating habits have become severely white-potato-deficient, then by all means, the USDA should add white potatoes into WIC. But Congress shouldn’t circumvent the process.

This is almost a caricature of an obvious statement, but here goes: Poor kids’ health, not special interests, should always come first. Research has shown, again and again, that inequality begins in utero, and that disparities in earnings and well-being in adulthood are largely determined by disparities in nutrition, education and other conditions during the first few years of a child’s life.

WIC is one of the few federal programs that successfully narrows that early-life disparity. Let’s not mess with it.

Catherine Rampell comments on economics, policy and culture, and anchors The Washington Post’s Rampage blog.