Tens of thousands of years ago, before two–liter sodas and supersized candy bars, our tongues rarely tasted sweetness.  Sugar was hard to come by.  Honey had it, and fruit contained it, but otherwise sweetness was a sensation few people experienced, and only in certain months of the year.   But because sugar provides safe calories (almost no plant that tastes sweet is poisonous) we evolved to crave it.  Our brains are hard-wired to release a big shot of joy whenever we taste sweetness, by unleashing a chemical called dopamine.

And now, a new chapter in the history of sugar is bursting open.  Dr. Robert Lustig helped to bring the discussion to the forefront with his 2009 lecture, Sugar: The Bitter Truth. Dr. Lustig believes there is a lot more to the health story than simply nutrient-empty calories from sugar making us fat.  Actually, according to Dr. Lustig, the culprit is actually high-fructose corn syrup, a man-made compound that is so cheap it has found its way into nearly every processed food.

High-fructose corn syrup (HFCS), despite its name, and sugar, are both composed of two smaller molecules, glucose and fructose, in roughly equal proportions.  The difference now is that since the mid-1970’s we are consuming HFCS at almost every meal as it is added to nearly all processed foods, from pretzels to ketchup.  This concentrated sweetener not only has given all sugar a bad name, many experts now believe it is at least partly responsible for the dramatic spike in the incidence of type 2 diabetes, obesity, fatty-liver disease and heart disease.   HFCS has been directly linked to elevated triglycerides, and this risk factor is at the center of the aforementioned disorders.  It also causes a much more rapid and dramatic rise in blood glucose levels, increasing the need for insulin.

When high-fructose corn syrup is consumed, the glucose and fructose molecules are not bonded (like regular sugar), so they are readily free for absorption.  Glucose is the fuel of choice for our bodies; our cells use or store it easily when we eat it in high doses in processed food.  Fructose, on the other hand, cannot by its very nature slip into our body’s cells to make energy, so almost all of it slides down the portal vein into the liver, the toxin-processing organ, where it’s dumped (and dumped again, as we eat more foods loaded with concentrated sweeteners).

What does our liver do with all this second-rate fructose fuel?   It can’t store it, so it tries to break it down into energy.  But the cells’ normal energy-generating cycle cannot possibly spin fast enough to process this mountain of fructose, so most of it meanders off into the liver in the form of citrate.

Too much citrate can hurt us.  Citrate is the raw material for fat molecules called triglycerides.  Excess triglycerides in the blood trigger cardiovascular disease and greatly increase the risk for type 2 diabetes.  Some of the citrate also stays as fat droplets in the liver; a fatty liver triggers insulin resistance, which causes type 2 diabetes.  But it’s not just the citrate.  Eating too much fructose can also spark inflammation in the liver, as well as increase blood-pressure-raising byproducts, like uric acid.

The bottom line: read labels for added concentrated sweeteners like HFCS.   Try to choose fresh, whole foods in their unprocessed state.   Sugars found naturally in foods, like fructose (fruit) and lactose (milk and yogurt) are much less likely to cause the metabolic responses described above.   Limit portions of sweetened foods, and mark sweetened sodas and foods with HFCS off your list.

Rachel Moeller Gorman