Fructose has, surprisingly, become a controversial ingredient in health and fitness-minded circles. Some say it’s categorically bad for you, while other simply say to stick to the unrefined varieties and that surely a natural food can’t hurt us.

While the ultimate decision may differ depending on your health and nutritional needs, making the decision requires a good look at what exactly fructose is and how it affects our bodies.

What Is It?

Fructose is a monosaccharide, or simple sugar. It can be found by itself in nature as part of them makeup the many types of plants. It can also be molecularly linked with glucose, another monosaccharide, to produce sucrose--this is the molecule we know as table sugar.

What Is Its Biological Role?

When we eat foods containing fructose [1], it goes through several stages during the digestion process before it can be absorbed by our body and put to any kind of use. In the stomach, the bonds it has with other sugars are separated, such as reducing table sugar into glucose and fructose isolates.

These now-partner less mono-saccharides travel into the small intestine, where fructose can be absorbed into the bloodstream. From there, fructose is carried to the liver, which does a lot of work to make fructose useable by the body. The liver utilizes an enzyme called aldolase B, which assists in several biochemical transformations of the fructose molecule.

After these transformations are complete, the structure of fructose will have been changed to appear nearly identical to glucose. This means that fructose can now use the same cellular pathways as glucose, to allow the body to make proper use of this sugar. These pathways are referred to as aerobic or anaerobic respiration.

In aerobic respiration, the body burns oxygen and fructose together to help produce ATP, the body’s essential energy unit. Fructose and glucose present in the bloodstream that is not immediately needed to produce ATP undergoes yet another biochemical change to transform into glycogen.

Glycogen is a long-term storage version of these energy supplies. Glycogen is stored in the body as fat until needed at later time, when the body needs ATP for energy but has no immediately available sources of sugars with which to make it. Some individuals do not absorb all of the fructose they consume, typically because they consume so much more than they need that the liver cannot keep up with metabolic demands.

When this happens, fructose passes through the small intestine and continues further into the digestive tract. The large intestine contains a micro-biome of bacteria that balances itself to keep you healthy. Fructose disrupts this systems by selectively feeding the negative bacteria.

This can result in digestion disrupting conditions like SIBO [2], or small intestinal bacterial overgrowth. In cases like this fructose becomes an enemy rather than an ally, because it is overwhelming the body’s ability to process it into something useful.

How Does It Help Bodybuilders and People Who Work Out?

Fructose’s status as a mono-saccharide allows it to be absorbed quickly by the body and turned into energy. This makes it a useful booster for endurance athletes such as marathon runners, who need to supplement their body’s energy stores throughout their athletic event to maintain peak performance.

What Foods Contain It?

Natural, unrefined fructose is found in fresh fruits and some root vegetables, as well as honey. Fructose can also be refined and used as an additive in processed foods. In processed foods, a refined version called high fructose corn syrup is frequently used to add sweetness to foods.

How Much Of It Do You Need?

Fructose is only one of many sources of sugars and carbohydrates. There is no officially recommended daily allowance for fructose [3] alone, though there are general guidelines for sugar consumption which are dependent on your caloric intake. If you suffer from a condition such as fructose malabsorption, however it is best to limit your fructose intake.

Are There Risks Associated With Consuming Too Much Of It?

If you consume more fructose than your body can process at one time, it can cause damage to the liver, as well as additional digestive distress as your body passes un-absorbed fructose into the large intestine. This can cause a swell in intestinal bacteria levels that results in increased gas, bloating, cramping, and diarrhea.

Are There Risks Associated With Consuming Too Little Of It?

There is no danger associated with specifically avoiding fructose, as long as you are sure to get your carbohydrates somewhere in your diet so that your body has enough material to work with when producing important energy sources like ATP.

When you look at the positive functions of fructose alongside the possible less positive ones, it seems that perhaps the best advice is to treat this part of your nutrition plan holistically. Consuming in moderation with an eye on how your body handles fructose can help you put it to good use.


[1] Wikipedia. Fructose., 2017.

[2] Dr. Axe, Josh. Do You Have SIBO? Here Is All You Need To Know., 2015.

[3] American Heart Association. Added Sugars., 2017.