As a doctor with a strong interest in research and public health policy, I find the current debate over a soda tax in New York disappointing. The state has told us that this tax will reduce obesity. There is simply no authoritative health study to justify this claim; on the contrary, repeated clinical studies tell us that this effort will fail.

Public health policy must be driven by clinical research, not flimsy science used to satisfy a political agenda. The only real conclusion we can draw from the current research is that the cause of the obesity epidemic is unknown.

With obesity in this country affecting approximately 18 percent of adolescents and teenagers and about 33 percent of adults, we should welcome public policy interventions that will mitigate this epidemic. Frustration over the lack of a solution must not be replaced by wishful thinking.

I appreciate that Albany will inevitably need to make some painful decisions to balance the budget. But to date, the results of every clinical trial that assessed if discouraging consumption of sweetened beverages could reduce obesity has ended in failure.

Obesity has been correlated with a vast number of factors, and proponents of soda taxes have pointed to some studies that have drawn a correlation between soda consumption and obesity. Scientists know, however, that correlation itself does not imply causation. As an example, a correlation might be drawn worldwide between the prevalence of flush toilets and heart disease, but such a correlation by itself would not be proof that flush toilets cause heart disease.

The gold standard in medicine to prove causation is the prospective randomized controlled trial, and four such long-term trials done to see if discouraging consumption of sweetened beverages would reduce obesity among school children were unsuccessful.

One trial initially claimed a modicum of success because, although the intervention did not affect the children’s body mass index (the most commonly used scientific measure of obesity), it did show a difference in a more esoteric end-point chosen by the researchers — the number of children whose weight fell into the top 10 percent on a 1990 British growth reference chart. Even this outcome was not to last, as follow-up showed that even this supposed difference in the obesity rate had vanished.

Rarely is there a reason to legislate broad-ranging public health policy such as a new regressive tax solely using epidemiologic data, smoking being a notable exception. But, under no circumstance whatsoever should we institute a new public health policy when it runs directly counter to the findings of every long-term clinical study.

We would be better off intensifying the search for the root cause of the current obesity epidemic instead of wasting our energies and the public’s trust on futile measures such as soda taxes.

Michael G. Kaplan, M. D., is an attending physician at Maimonides Medical Center in Brooklyn.