What Is Fructose And Is It Bad for Me?

what is fructose?

We all know too much sugar is unhealthy—even dangerous. But is one chemical component worse than another?

By now, everyone agrees: inactivity + extra calories = too much body fat = disease.

Excess calories, whether they’re from protein, fat, or carbohydrate, are stored in the body as fat.

And extra body fat can cause heart problems, type 2 diabetes, kidney damage, and liver damage. And those are just a few of the health risks associated with extra fuel around the middle.

And one of the easiest ways to consume extra calories is from simple carbohydrates, like table sugar, soft drinks, and candy.

How table sugar, fructose, glucose, and high fructose corn syrup differ chemically

Your sugary beverage of choice (unless it’s diet, which opens a whole new can of worms) is likely sweetened with sugar or high fructose corn syrup. Table sugar, or sucrose, is a disaccharide made of glucose and fructose molecules.

How is high fructose corn syrup made?

how is high fructose corn syrup made?

High fructose corn syrup (HFCS) is made from corn starch. All starches are polysaccharides, meaning they are composed of many sugar molecules bonded together to form long chains.

The corn starch is then processed into a syrup and mixed with enzymes, which turn some of the glucose into fructose.

Chemically, HFCS is nearly the same thing as table sugar. HFCS contains 55% fructose, 41% glucose, and 4% other saccharides, and is a liquid rather than a solid.

How are fructose and glucose different?

The major difference between fructose and glucose is how each is processed in the body.

While glucose is metabolized throughout the body, fructose is metabolized in the liver. Once there, fructose is turned into glucose, lactate, and glycogen. (Rippe)

This difference in metabolic pathways is where we find the root of the whole fructose vs. glucose showdown.

It’s theorized that because of its metabolic pathway, fructose causes inflammation. And chronic inflammation has been linked to just about every disease that comes with excess calories, including heart disease and type 2 diabetes, as well as dementia and depression.

Could limiting fructose lessen the negative effects of excess body fat? Many researchers have asked some form of that question.

Does fructose cause inflammation?

fructose and inflammation

A limited amount of research suggests fructose is more harmful than glucose because it increases inflammation. Let’s look at studies that suggest fructose causes inflammation.

  • Liver inflammation and damage

A study of mice with free access to a solution containing 30% glucose, fructose, sucrose, artificial sweetener, or plain water.

Although the mice with access to glucose experienced the most weight gain, those with access to fructose experienced “significantly higher” accumulation of hepatic lipids.

This makes sense, as fructose is turned into glucose via the liver. Researchers concluded that high fructose consumption could lead to liver damage. (Bergheim)

  • Systemic inflammation via intestinal permeability

The same mice study from above also found that the fructose mice showed an increase in endotoxin levels in their blood.

Researchers theorized that the high levels of fructose increased the permeability of the mice’s intestines. By decreasing the gut-barrier function, fructose acted as a sort of vehicle for endotoxins in the intestines to enter the circulatory system.

Once in the circulatory system, these endotoxins caused systemic inflammation. (Bergheim)

  • Adipose tissue inflammation

A human study found that increased consumption of fructose led to an increase of a protein secreted by the liver and adipose tissue, which caused an increase in the inflammatory response of adipose tissue. (Schwarz)

However, despite this research, the body of scientific literature shows that fructose doesn’t have a negative effect on the body.

Most research suggests that fructose is safe

fructose is safe

Kuzma and the rest of the team set out to learn whether fructose actually causes inflammation.

They designed a study to look at the metabolic effects of soft drinks sweetened with glucose, fructose, or high fructose corn syrup. This double-blind, randomized, crossover study evaluated 24 participants that were separated into two groups: overweight and normal weight.

Researchers designed the study to examine systemic inflammation, but also looked for adipose tissue inflammation, intestinal permeability, and the mechanism by which fructose could increase inflammation. (Kuzma, et al.)

Participants were screened for smoking, drug and alcohol abuse, chronic inflammatory diseases, and fructose malabsorption, a surprisingly common GI problem that warrants more research. (Choi, et al.)

Because weight gain causes inflammation, the duration of the study was intentionally short. Participants drank the beverage during three eight-day periods, which consisted of 25% of their estimated calorie requirements. (Kuzma)


Researchers found no changes in markers of systemic inflammation between groups.

They also didn’t observe increased intestinal permeability or abnormal adipose tissue inflammation.

Unsurprisingly, participants increased their total calorie intake while consuming each sweetened beverage by 15% over their estimated daily calorie needs. This observation reaffirms the commonly agreed-upon idea that it’s easy to over-consume when drinking sugary drinks.

Is fructose bad for me?

is fructose bad for me?

Three other studies found results similar to the study above, with no markers of inflammation evident, although one study did observe extra visceral fat in the fructose group.

The bulk of research with human subjects suggests that fructose is no more dangerous than glucose. (Silbernagel, et al.) (Aeberli, et al.) (Cox, et al.)

But just because high levels of fructose aren’t necessarily worse than high levels of glucose, extra sugar is dangerous. And this research reaffirms how easy it is to over-consume when drinking daily sugar.

Of course, there is emphasis on the word extra. In the right amount and at the right time, sugar is necessary for performance.

Glucose is essential to your metabolic process, and athletes need lots of it.

Carbs, sugar, glucose, fructose, sucrose, monosaccharides, disaccharides, and polysaccharides—sugars in all of the many forms—have a place in a healthy diet.

From a nutritional standpoint, there is even a time and place for an athlete to chug a Coke.

However, studies like this help remind us that while your favorite soda might give you a needed boost during hour 5 of an ultra-endurance event, that same soda is also one of the fastest and least nutritious ways to ingest excess calories. It’s a tool—use it wisely.

About the author:

Matt Mosman (MS, CISSN, CSCS) is a research scientist, endurance athlete, and the founder and Chief Endurance Officer at EndurElite. Matt holds his B.S. in Exercise Science from Creighton University and his M.S. in Exercise Physiology from the University of California. Matt and his family reside in Spearfish South Dakota, where they enjoy running, mountain biking, camping, and all the outdoor adventures Spearfish has to offer.


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