12/17/2013 01:33 pm ET Updated Feb 16, 2014

The Science Driving a Soda Tax

Last month the American Heart Association (AHA) praised the new Mexican Soda Tax and called on "U.S. states and communities to enact the (soda) tax as well." The reason for the AHA's bold statement: the accumulation of medical evidence implicating sugary drinks as a major cause of obesity, diabetes, heart attacks and strokes.

And while sugar's dominant role in the nation's obesity and diabetes crisis is now well established, science is pointing an even more damning finger at liquid sugar -- the sticky, sweet gulp expressed with every soda, energy drink and a growing line of bottled products. More than 40 percent of the additional calories we have been consuming over the last 30 years have come from sugary drinks. That's enough, all by itself, to explain the obesity epidemic.

Opponents of soda taxes argue that eating cake with sugary frosting is just as bad as drinking a Big Gulp. Science says otherwise.

Our bodies respond differently to sugar, depending on the form it comes in. Cake makes us feel full, and we reduce the amount we subsequently eat. Digestion takes hours, allowing our bodies time to deal with the sugar load. This doesn't happen when we drink a soda.

For eons, human beings have quenched their thirst with water. That's still what our bodies expect. When we add 15 teaspoons of sugar to that glass of water, as we do when we drink a soda or other sugary drinks, we override our finely tuned and long-evolved system.

Unlike solid foods, liquid calories don't trigger our sense of feeling "full." We take in excess liquid calories without being aware of it. These unregistered calories, however, are not just empty calories, they are harmful calories.

Imagine two thirsty people. One has a glass of water, the other a soda. For the water drinker, the liver and pancreas can continue doing the cell repair and other maintenance operations that keep us healthy. For the soda drinker, two sugars (glucose and fructose) are immediately absorbed. The glucose enters the bloodstream, signaling the pancreas to churn out insulin. The fructose -- the sweet part -- goes to the liver, where much of it gets converted into fat.

The overworked pancreas eventually poops out from exhaustion. Diabetes is the result, with its risks of amputations, blindness, kidney dialysis, heart attacks and strokes. Meanwhile, the fructose is converted into fats that infiltrate our organs and clog the heart's arteries, causing heart attacks early in life. The liver itself gets packed with fat. Before reaching the breakdown point, the liver goes deaf to the insulin signal, which, in medical terms, is known as "insulin resistance." The pancreas has no choice but to shout, "make more insulin," thus hastening the pancreatic exhaustion and the onset of diabetes.

Both the developed and the developing worlds are suffering a pandemic of "metabolic syndrome," the medical term for the combination of obesity, high blood pressure, diabetes and high risk of heart attack. The only way to reverse this worldwide calamity will be to kick the liquid sugar habit. How do we change direction?

Taxing soda, as a response to the pandemic of metabolic syndrome, is a smart approach with international support.

We led soda tax campaigns in the California cities of Richmond and El Monte in 2012. We were beaten at the polls, but it was a victory. Never before had people in these blue-collar cities debated the health impacts of sugary drinks. For many, it was the first time they learned about the harm that comes from drinking liquid sugar. Despite the obscene amount of money the beverage industry threw into a counter campaign, they couldn't stop us from planting the seed of knowledge in these largely low-income communities, which are primary markets for soda companies.

Passing taxes is never an easy proposition. Given the preponderance of science and research describing the damage liquid sugar is doing to our health and our communities, soda taxes offer an ideal platform to educate and engage voters in this critical public health issue. The future health of our children may depend on it.