Fructose is one F-word that should really offend you.
The sweet half of sugar (as opposed to glucose, its more acceptable partner), is one of the biggest causes of “metabolic syndrome,” says Robert H. Lustig, MD, author of the new best-selling book, Fat Chance.
Metabolic syndrome is a cluster of conditions, like obesity, diabetes, and high blood pressure, that essentially leads to most of the diseases that cause early death among Americans—like heart disease, cancer, and dementia. And when it comes to the cause, “fructose is the big kahuna,” Dr. Lustig says.
“Glucose can be metabolized by every cell in the body,” he explains, “but only the liver can metabolize fructose.” So when too much shows up for the party, the liver can’t handle the volume. Here are three reasons that’s bad news for your health:
1. Fructose raises insulin levels. While the liver turns glucose into energy reserves your body can use, it can’t do that with fructose, so the sugar overwhelms the organ. This causes a chain of events that leads to insulin resistance in the liver, which means the pancreas has to release extra insulin. Excess insulin has lots of unwanted effects: it can force extra energy into fat cells, leading to obesity, drive the growth of certain cancers, and more.
2. Fructose creates fat. Since the liver can’t convert fructose into glycogen (the aforementioned energy reserves), it sends it straight to the mitochondria, your cells’ energy-burning factories. “This presents the mitochondria with more energy than they can possibly deal with,” Dr. Lustig says. “They have no choice but to take that excess energy and turn it into fat in the liver.” That fat can then be exported into the blood as triglycerides, which promote heart disease and obesity.
3. Fructose makes you eat more. High insulin levels, caused by the metabolism of fructose, can also block the signaling of hormones that regulate hunger, giving your body a false sense of starvation, causing you to eat more.
So should you shun chocolate cake forever? “Like any poison, the dose determines the lethality. A little sugar is okay, a lot is not,” says Dr. Lustig. Just be sure to read labels, because fructose is lurking in lots of places you wouldn’t expect. —Lisa Elaine Held
For more information, check out Fat Chance.
Want to know where fructose might be hiding out at your house right now? Read 5 sources of fructose you wouldn’t expect.