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Monday was a bad day for the food police. A judge in New York City ruled that the city’s board of health exceeded its authority last year when it limited sodas to 16 ounces. The judge gave several reasons, but here’s the one most likely to affect your life: Government can’t control lifestyle diseases the way it controls infectious epidemics.

Communicable diseases, such as smallpox or the flu, travel from person to person through microbes. Most chronic diseases, such as cancer, diabetes, and cardiovascular illness, don’t. They’re driven, as the World Health Organization explains, by “unhealthy lifestyles.” And this radically constrains the government’s ability and authority to control them.

The soda-size limit, which Mayor Michael Bloomberg calls a “portion cap,” never went through the city council. Bloomberg imposed it unilaterally last September through his board of health. The board cited Section 556 of the city charter, which authorizes the city health department to “regulate the food and drug supply” and “supervise the reporting and control of communicable and chronic diseases.” The board noted that “sugary drinks are a leading driver of the obesity epidemic and are associated with dangerous chronic diseases” such as diabetes and heart ailments.

This was an obvious stretch of the charter. When the city council inserted these clauses in 1977, few people saw obesity as a major chronic disease, and nobody saw portion control as part of ordinary food-supply regulation. And while the charter language did include chronic as well as communicable illness, it didn’t say that the department’s power to supervise disease control extended equally to both types.

The health department ignored these distinctions. A week before it approved the portion cap, it released a memo responding to complaints that controlling drink size “is not the government’s role.” The memo, signed by the department’s assistant commissioner for chronic disease prevention, noted that the board of health “has a successful track record of adopting rules that protect the health of New Yorkers, including bans on lead paint, tuberculosis control provisions, and requirements regarding calorie labeling and the elimination of trans fats from restaurants.”

Opponents picked apart these precedents. In an amicus brief filed with the court on Nov. 7, five dissenters on the city council pointed out that calorie counts are just information, that the trans fat ban was ratified by the council, and that lead paint, unlike soda, is inherently toxic. They added:

“Unlike obesity, tuberculosis is a dangerous, communicable disease, and the core function of health departments has long been to control such diseases and prevent extensive person-to-person spreading. … But obesity does not spread in this way. Rather, it develops based on a person’s personal characteristics and environment—including social, behavioral, and cultural factors. … Thus, [the health department’s] ‘control’ powers under the Charter with respect to [communicable] diseases … says nothing about the extent of [its] power to override individual preferences that might contribute to a non-communicable condition like obesity.”

Furthermore, the dissenters argued, the behavioral complexity of today’s chronic diseases meant that any agency fully authorized to control them would become an intrusive nightmare. They conceded that soda might contribute to chronic illness, but “so too does eating fatty foods, exercising too infrequently, or watching too much television.” Unfettered authority to stamp out these maladies, they warned, would empower the health department “to regulate such behaviors with no input from the Council.”

All of this was true. But it wasn’t the whole story. A day after the dissenters filed their brief, health advocates, led by Yale’s Rudd Center for Food Policy and Obesity, issued an amicus brief defending the portion cap. They argued that if health departments couldn’t tackle chronic disease, they couldn’t do their job:

“The most pressing public health problems today are obesity and obesity-related disease, such as diabetes and coronary heart disease. Long gone are the public health problems that historically affected large cities stemming from a lack of sanitation and high incidence of communicable disease. If health departments refused to act on this reality, they would be failing to meet their responsibilities to protect the public’s health.”

City health commissioner Thomas Farley underscored this point. “These chronic conditions now cause a higher toll of preventable human suffering than even the most prevalent communicable diseases,” he testified in a Nov. 9 affidavit. “Their burden also uses more of society’s resources.”

That, too, was true. But the department didn’t stop there. In a brief filed on Nov. 9, it claimed that the complexity of chronic diseases made the task of controlling them a matter of technical expertise. The department argued that state legislators who initially chartered the board of health “could not have foreseen … the specific need for regulations concerning portion caps for sugary beverages to fight obesity and chronic diseases.” Accordingly:

“Because of the complexity and difficulty of the issues involved with supervising the control of chronic disease and supervising and regulating the City's food supply and food service establishments, the Legislature has delegated regulatory authority to the Department and the Board as they have the specialized knowledge and expertise to effectively deal with such matters.”

In other words, obesity, diabetes, and cardiovascular disease are so scientifically convoluted that only the health department is qualified to manage them. Experts, not legislators or citizens, must decide how big a soda can be.

That’s a huge mistake. The factors that make chronic disease trickier than communicable disease involve more than biological science. They involve social science. What you eat, how much exercise you get, and how much stress you endure are matters of lifestyle, economics, and culture. They touch on corporate marketing, mass media, and personal responsibility. To address these problems wisely and within reason, you need a broader perspective. You need to understand people, their values, their foibles, and the limits of what we can or should do for one another.

In his ruling on Monday, the judge rejected the health department’s assertion of sweeping authority over chronic illness. The history of the department’s charter, he wrote, showed that its mandate was to “prevent and protect against communicable, infectious, and pestilent diseases.” The board of health could regulate the food supply, he conceded, but only “when the City is facing eminent [sic] danger due to disease. That has not been demonstrated herein.”

The judge was right about the past. But he’s wrong about the future. The reason chronic disease doesn’t look like an imminent threat, in the old-style sense, is that it doesn’t attack with the same speed as most communicable diseases. The onslaught isn’t imminent. It’s already here. If bureaucrats have no unilateral authority to restrict portion size—and I agree that they don’t—we need to figure out how to promote portion control and other good habits in ways that are effective, legally sound, and socially accepted. Limiting government’s power isn’t the end of the struggle. It’s just the beginning.

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