Is Fructose Bad for You? Here’s Why Fructose May Be Worse Than Sugar

A UCSF researcher answers the question “Why is fructose bad for you?” He asserts that fructose is “alcohol without the buzz.” Learn how fructose drives fat storage, accelerates aging, and makes the brain think it is hungry.

chart comparing glucose and fructose

Is fructose bad for you? Science has the answer.

© Alain Lacroix |

The Atkins diet and a traditional Japanese diet may seem about as far apart as two diets can get: Atkins is low-carb/high-fat while Japanese is high-carb/low-fat. But they both work to promote weight loss and they do have one thing in common: They eliminate the simple sugar known as fructose. But is fructose bad for you?

You may think of fructose (and sugar in general) as empty calories. That’s how nutritionists have been vilifying it for years. But Dr. Robert Lustig from University of California at San Francisco is on a campaign, so to speak, to educate other health professionals and the public about why fructose is actually worse than just empty calories.

Why Is Fructose Bad for You?

Is Fructose Bad for You? Why Fructose is Worse than Sugar

Dr. Lustig, a neuroendocrinologist at UCSF’s Department of Pediatrics and the Philip R. Lee Institute for Health Policy Studies, wants you to know that fructose is very bad news. In published papers, speeches, and interviews over the past several years, he has been spreading the bad news about fructose and explaining how fructose is behind today’s worldwide epidemics of obesity, type 2 diabetes, heart disease, high blood pressure, and abnormal cholesterol.

Fructose is the simple sugar that makes up 50 percent of table sugar (sucrose) which is typically made from sugar cane or beets. The other half of table sugar is glucose. And fructose makes up 55 percent of high-fructose corn syrup (HFCS). Dr. Lustig’s latest paper, recently published in the medical journal Advances in Nutrition, explains why there is nothing empty about the calories in fructose and describes three ways in which fructose harms human health exclusive of its calories.[1]

Even though fructose and glucose are both sugars that make up table sugar, they act very differently in the body. While glucose is so essential for life that your body will manufacture it if needed, there is not even one human biochemical reaction that requires fructose from the diet. The only place in the body that fructose is physiologically necessary is in semen, and the fructose there is made by the body out of glucose.

How Is Fructose Bad for You?

    1. In many ways, says Dr. Lustig, fructose is much more like ethanol (grain alcohol) than glucose. In fact, fructose behaves so much like ethanol inside the body that he has nicknamed it “alcohol without the buzz.” Although fructose does not slow the central nervous system like ethanol, the long-term toxic effects are the same.
      By comparing fructose to both glucose and ethanol, Dr. Lustig points out the three different negative impacts fructose has on your metabolism: First, when you take in more calories than you immediately need, both fructose and ethanol overwhelm the liver and drive the transformation of excess energy into fat. Dr. Lustig illustrates how a can of soda and a can of beer both put a similar load on the liver.

      Not only can you gain excess weight, this process also leads to high triglycerides along with small, dense LDL particles (the really dangerous type of cholesterol), and low HDL cholesterol (the “good” cholesterol). This combination of abnormal cholesterol is called dyslipidemia and causes heart disease and strokes. Excess fructose, like ethanol, also leads to fat accumulation in the liver (resulting in liver dysfunction) and insulin resistance, the precursor to diabetes.

    2. Second, both fructose and ethanol generate excess reactive oxygen species (ROS), which, if not quenched by antioxidants because of nutrient deficiencies, increases the risk of fatty liver disease and liver damage and accelerates aging in general. Glucose does not generate the same load of damaging oxidative stress.


  1. Last, Dr. Lustig explains how fructose affects cellular receptors in the brain’s reward pathway. When the brain is exposed to fructose over and over, dopamine receptors are altered in a way that drives increased food intake and weight gain. You tend to want to take in more food even though you don’t need it for energy. And, with both fructose and ethanol, chronic use causes you to become addicted. You experience symptoms of tolerance (you start to need more and more to feel satisfied) and withdrawal (you get symptoms if you go without it).

Now that you know the answer to the question “Why is fructose bad for you?” it’s time to do something about it! Since common forms of sugar (sucrose) are half fructose, Dr. Lustig believes the key is to dramatically cut down own all common forms of sugar, not just fructose. In doing so, you’ll be improving your metabolism, saving your cardiovascular and liver health, and putting the brakes on the aging process.

For more reasons to cut sugar and ways to do it, see the following articles:

1. Adv Nutr. 2013 Mar 1;4(2):226-35.

Originally published in 2014, this post is regularly updated.

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