Cap and trade was a key part of the 1990 Clean Air Act amendments as a way to regulate acid-rain-causing pollutants like sulfur dioxide. Under the program, the overall amount of pollution was limited, and utilities were allowed to trade pollution credits on the open market, so that the lowest-cost reductions got made first. The policy worked well: “Since its implementation, overall levels of sulfur dioxide emissions have been halved, and air and surface-water quality have improved substantially,” Harvard researchers Kristina Lewis and Meredith Rosenthal write.

This leads them to ask: what if a cap-and-trade policy treated unhealthy foods as pollutants, limiting their availability?

The U.S. food supply can also be viewed as a polluted environment. Because of industry’s practices and consumers’ choices, pollutants such as excessive salt, sweeteners, and unhealthful fat end up damaging our health. Setting a cap on the amount of harmful ingredients used in U.S. food production could profoundly affect our diet. This approach could take many forms but would probably work best if applied to entities that supply food products directly to consumers, rather than to the producers of the raw ingredients.

Although food ingredients are components, not by-products, of production, cap and trade may still make sense for several reasons. First, the approach is thought to work best when the capped substance is easy to measure. Ingredients such as salt, sugar, and unhealthy fats are even easier to measure than pollutants like sulfur dioxide. And cap and trade is ideally suited for markets in which many companies use or produce a given substance but it would cost some more than others to decrease that use or production.

This could be one way to combat what former FDA commissioner describes as a “food carnival,” where new combinations of fat, carbohydrates and salt cater to our taste buds. Capping the availability of unhealthy foods could could, in a way, take some air out of our food carnival’s big tent.

But the challenges to such an approach, both politically and practically, may outweigh those potential successes. Food regulation has always been tricky in that eating is a behavior that can be unhealthy but is also necessary to survive. Drawing a line between “unhealthy” and “healthy” is a difficult task; in the past too be sure, some countries have done it - think of Denmark’s new tax on foods with a high fat content - but they’re in the minority. Figuring out what exactly gets capped wouldn’t be so clear cut as it is when you’re dealing in pollutants.

The second, and perhaps more daunting obstacle, is the politics of capping certain foods: it’s a little bit difficult to see Americans getting behind a government cap on saturated fats or sodium. In this way, food is hugely different from pollutants: namely, it’s something we directly interact with everyday. That makes it pretty difficult to see a political path forward for this type of a food policy, whatever beneficial impact it may have.