The Supreme Court case that fundamentally reshaped American constitutional law began with a can of fake milk on a Depression-era dinner table. *United States v. Carolene Products Co.* (1938) arose from federal prosecution of a company selling "filled milk" - a dairy substitute that would produce one of the most influential footnotes in legal history.
Milnut, the product at the center of the case, was technically classified as "filled milk" under federal law. The substance looked and tasted like regular milk but had been processed through a centrifuge to remove valuable butterfat, which was then replaced with vegetable or coconut oil. The extracted butterfat was sold separately for profit, allowing Milnut to be priced significantly below traditional dairy products.
During the Great Depression, Milnut's low cost and shelf-stable properties made it an attractive alternative for struggling families. The product was revolutionary within the dairy industry, with one reporter comparing its makers to Thomas Edison and Henry Ford. Despite being safe for consumption, Milnut posed an economic threat to the established dairy industry.
The dairy lobby responded by pushing Congress to enact the Filled Milk Act, which banned interstate shipping of filled milk products. The law bore clear hallmarks of economic protectionism rather than legitimate health regulation. Congressional committee reports claimed filled milk lacked vitamin A and was less suitable for "feeding infants and nursing mothers," but the product was safe and properly labeled to distinguish it from traditional milk.
The legislative process revealed the protectionist nature of the ban. Committee hearings invited affected businesses to testify in favor of the prohibition, suggesting industry influence rather than genuine public health concerns. The law targeted not merely the sale of filled milk, but its interstate transportation, effectively creating a federal barrier to competition.
Carolene Products Company, Milnut's manufacturer, chose to fight the restriction. The company deliberately transported its product across state lines to create a test case challenging the federal ban. This strategy initially succeeded when a district court struck down the law, finding it violated the due process and takings clauses of the Fifth Amendment.
The district court concluded that the Filled Milk Act constituted illegitimate protectionism disguised as health regulation. The ruling recognized that Congress had been pushed to act by dairy industry lobbying rather than discovering legitimate health concerns about filled milk. The court found the law's true purpose was shielding traditional dairy producers from low-cost competition during economic hardship.
When the case reached the Supreme Court, the justices reversed the lower court's decision and upheld the Filled Milk Act. However, the case's lasting impact came not from this holding but from a seemingly minor footnote authored by Justice Harlan Stone. Footnote Four, joined by only four justices and unnecessary to the case's outcome, would transform constitutional jurisprudence.
The footnote established a framework for varying levels of judicial scrutiny based on the type of right or group involved in a case. It suggested that courts should apply heightened scrutiny when reviewing laws that affect fundamental rights, restrict political processes, or target "discrete and insular minorities." This framework moved away from the previously uniform approach to constitutional review.
Before *Carolene Products*, courts generally applied the same level of scrutiny to all constitutional challenges, typically deferring to legislative judgments about economic regulations. Footnote Four created a hierarchy of constitutional protection, with some rights receiving more robust judicial protection than others.
The footnote's three-part framework has become central to modern constitutional analysis. The first category covers laws that violate specific constitutional prohibitions. The second addresses restrictions on political processes, such as voting rights or free speech. The third category involves prejudice against "discrete and insular minorities" who lack political power to protect themselves through the democratic process.
This framework now governs how courts analyze civil rights cases, voting rights disputes, and equal protection claims. Laws affecting fundamental rights or suspect classifications receive "strict scrutiny," requiring the government to demonstrate a compelling interest and narrowly tailored means. Intermediate scrutiny applies to certain classifications like gender, while economic regulations receive minimal "rational basis" review.
The practical impact of Footnote Four extends far beyond the dairy industry dispute that spawned it. The framework has been used to strike down racial segregation, protect voting rights, and safeguard individual liberties against majoritarian oppression. Cases involving marriage equality, reproductive rights, and religious freedom have all been analyzed through the lens of *Carolene Products*' footnote.
The irony of the decision is that a case upholding economic protectionism produced the doctrinal foundation for protecting constitutional rights against government overreach. While Carolene Products lost its challenge to the Filled Milk Act, the company's legal battle created the framework that would later protect countless Americans from discriminatory laws and constitutional violations.
Today, law students across the country study Footnote Four as a cornerstone of constitutional doctrine, while the filled milk industry that sparked the controversy has largely disappeared. The case demonstrates how seemingly minor legal developments can have profound and lasting consequences for American jurisprudence and civil rights protection.