The secret to sugary sodas, at least in America, is high-fructose corn syrup. Beverage bigwigs at Coca-Cola and Pepsico made the switch from cane and beet sugar to HFCS for most of their products sold in the U.S. starting in the mid-1980s, mostly in response to rising costs of sugar. HFCS is made by processing corn syrup with enzymes, and is much cheaper thanks to both U.S. government subsidies of corn and high tariffs on imported sugar.


In the decades since Coke and Pepsi made the switch, HFCS has become nearly ubiquitous in processed foods. Some consumers and nutrition experts have fingered it as the primary suspect in the growing U.S. obesity epidemic, calling for soda giants to switch back to the more familiar sweetener. HFCS makers have worked to counter the bad press, funding sunny advertisements painting the syrup as “natural.”


HFCS is chemically rather similar to table sugar, and is made up of two forms of sugar called glucose and fructose. These two kinds of sugar are called “monosaccharides” or “simple sugars” – the most basic unit of sugar you can get. Cane and beet sugar is nearly 100 percent sucrose, which is a more complex sugar consisting of a glucose molecule and a fructose molecule linked together.


Many concerns about HFCS center on how the body processes fructose differently from sucrose, with some evidence suggesting that fructose is more easily converted to fat than sucrose, and that fructose doesn't provoke the same level of satiety as other sugars, which could lead to overconsumption.


But animal tests showing that fructose leads to increased eating in rodents have been criticized as flawed – in such experiments, the animals had a massive dose of fructose injected directly into their brains, an unrealistic scenario for modeling how people actually process HFCS.


And while fructose is readily converted into fat by the liver, that's equally true whether the fructose comes from HFCS or from the breakdown of sucrose.


“At this time, there's insufficient evidence to say that high-fructose corn syrup is any less healthy than other types of sweeteners,” Mayo Clinic nutritionist Jennifer Nelson writes on the hospital's website.


So scientifically, there's no overwhelming support for one form of sugar over the other. If soda makers swapped HFCS for sucrose, the biggest improvement probably would be in sales of cane and beet sugar. People might prefer the taste of cane sugar-sweetened Mexican coke to HFCS-laden American Coke, but neither is going to do wonders for your health.


There is recent evidence showing that countries with high consumption of HFCS use have higher rates of type 2 diabetes. In a study published in the journal Global Public Health in November 2012, University of Southern California and University of Oxford researchers compared HFCS consumption, sugar consumption, body-mass index averages and obesity and diabetes prevalence rates in 43 different countries. HFCS consumption rates ranged from 0 pounds per person per year, in India and 13 other nations, to nearly 55 pounds per person per year, in the U.S.


They found that type 2 (so-called adult onset) diabetes occurred 20 percent more often in countries with high HFCS consumption rates, compared to countries where it wasn't commonly used.


However, this correlation isn't necessarily causation.


“I think it’s a stretch to say the study shows high-fructose corn syrup has anything special to do with diabetes,” New York University nutrition professor Marion Nestle told the New York Times in November. “Diabetes is a function of development. The more cars, more TVs, more cellphones, more sugar, more meat, more fat, more calories, more obesity, the more diabetes you have.”


Sucrose, glucose, or fructose – it probably doesn't matter. Too much of any sugar is bad for you, causing health problems from tooth decay to diabetes.


The American Heart Association advises that men consume no more than 150 calories of added sugar each day (9 teaspoons) and that women get no more than 100 calories (6 teaspoons). A typical 12-ounce can of soda contains the equivalent of about 10 teaspoons of sugar. Even if Coca-Cola and Pepsi switched out HFCS for table sugar, if you guzzle several cans a day you're still on the road to poor health.


At the moment, the prevailing thinking in nutrition science is that overconsumption of sugar – any sugar – is really to blame for a lot of America's ills.


“High-fructose corn syrup, sugar — no difference,” University of California San Francisco childhood obesity expert Robert Lustig said in one lecture, according to the New York Times. “The point is they’re each bad — equally bad, equally poisonous.”