Obesity is a problem of epidemic proportions in the United States, at least according to many healthcare professionals. But it is not so in America’s prisons, as reported in a recent article published in the Wall Street Journal.

The loved ones of men and women incarcerated in jails around the country complain with good reason that many prisoners experience significant weight loss during the early days and weeks of their confinements. Shedding pounds is so commonplace among inmates that many jailers have seized the main chance by offering their wards opportunities to purchase hamburgers, pizzas and other high-calorie foods to supplement standard prison fare.

How can this be? Individuals who are sentenced to prison for crimes committed against society may or may not deserve jail time as punishment for violating the law. The judicial system, like all institutions designed by human beings, is imperfect. And so, some people who are accused and convicted of the charges against them may be innocent. Should they, on top of their loss of freedom, be nutritionally deprived?

The answer to that question ought to be a resounding “No”, especially so if the goal of incarceration is to rehabilitate the offenders of society’s norms, violent or not. As a matter of fact, America’s jails nowadays are stocked with people convicted of non-violent crimes, especially so the possession or sale of “controlled” substances, such as marijuana, which rarely harms anyone other than the user.

So why do jailers starve their wards? An economist’s answer is question is that incentives matter.

Rewind the tape to the late 17th and early-to-middle 18th centuries. As an alternative to capital punishment, large numbers of convicted felons in Great Britain were sentenced to transportation to Australia. The ship captains who contracted to carry convicts from the United Kingdom to its antipode colony typically were paid a bounty for every condemned prisoner loaded onboard at the port of origin. That upfront payment supplied incentive to cram as many prisoners into the ship’s hold as possible, to skimp on their rations, and, to prevent insurrection, to keep them confined in the vessel’s bowels rather than allowing them fresh air and exercise en route. Not surprisingly, most of the “passengers” ended up as shark bait, not surviving to take up new lives in the prison colony.

The British economist Edwin Chadwick hit on the obvious solution: Compensate ship captains for every prisoner who debarked under his or her own power upon arrival in Australia. Chadwick’s insightful recommendation lowered the death rate to nearly zero because the survival of transportees quickly became a financial priority.

Fast forward to 2010: Many of America’s prisons today enter into contracts with Aramark or other private food service providers to feed their inmates. The contracts usually provide fixed compensation per meal served. So, in order to maximize profits per serving, the private contractor has incentive to supply meals at least cost—to skimp on relatively expensive sources of protein in favor of cheaper carbohydrates and other foods that may fill prisoners’ stomachs but do not nourish them adequately.

The source of the problem here is not with private versus public provision of meals to prison inmates, but rather with contract structure. Assess the performance of private suppliers of food service on the basis of weight maintenance or the nutritional status of those committed to the care of our nation’s jails and the problem of inmates’ weight loss will soon go away.