What’s good? What’s bad? How much sugar is too much? Here’s what the latest science says.
"There is no substitute for whole natural foods, a variety of foods, eaten in season. I read that xylitol, which is marketed as a natural sugar, is actually processed using toxic chemicals. "
But, Lustig says, the genie played a trick on us. Lustig explains the problem with fructose by explaining what happens when you put one of these processed goodies—say, a cracker—into your mouth (the details of this theory were mostly formulated through studies in animals): First, a bite. Then another bite. Sprinkles of cracker descend into your stomach and then to your small intestine, where enzymes dissect sucrose molecules into their constituent parts: glucose and fructose. (HFCS molecules are not bonded, thus the glucose and sucrose are already free.) Remember, glucose is the fuel of choice for our bodies; our cells use it or store it easily even 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 sweetened food).
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, says Lustig. 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. Lustig says that eating too much fructose can also spark inflammation in the liver, as well as increase blood-pressure-raising byproducts like uric acid.
Overall, eating too much fructose from added sugar is like using unleaded gasoline in a diesel engine: it makes bodies sputter and cough till they seize in a puff of smoke.