Fructose and Its Impact on Our Bodies

High-Fructose Corn Syrup is not an Innocent Chemical.
While fructose would appear to be a better alternative to dietary glucose because of its insulin sparing properties – research is beginning to pour in associating HFCS consumption with a myriad of problems, linking it to sky-rocketing numbers of: degenerative diseases, metabolic syndrome, obesity, increased triglycerides (dyslipidemia), high blood pressure, and Type 2 diabetes. HFCS has further been implicated in dysregulation of the immune system with an over-expression of inflammation in the body (oxidative stress and inflammatory cytokines).


Other research has also linked fructose maldigestion to elevated serum amylase (a digestive enzyme secreted by the pancreas), reduced serum folate levels (folate is one of the “B” vitamins. It is vital for proper neural growth in a developing fetus), and metal depression, especially in women.

Fructose is a valuable and needed nutrient. It is not the fructose that is the problem but the overly generous supply found in our manufactured foods. Fructose found in fruits and vegetables is slowly absorbed into the blood stream, its absorption blunted by the soluble fibre naturally found in these foods. In contrast, HFCS and crystalline fructose disrupt liver metabolism, which, along with excess glucose, spikes blood sugar levels and exhausts our pancreas. It is the overwhelming amounts of fructose and ensuing spike in blood sugar levels that are derailing our body’s metabolism and immune system in ways we don’t fully understand.

Our modern diets are proving to be one large, uncontrolled experiment on our nation’s health. Manufactured sugars are not our body’s friend. To learn more about the dangers of manufactured sugars, we recommend a book by Nancy Appleton PhD (nutrition) entitled Suicide by Sugar. And for further on-line reading from a very reputable source.

How is Fructose Absorbed by the Digestive Tract and How is it Metabolized in the Body?
Fructose is a simple sugar – or what is called a monosaccharide. It is found in 3 main forms: in fruits and some vegetables, as a component of sucrose (a disaccharide made up of glucose + fructose), and as a naturally occurring fructose polymer (a string of fructose molecules) called fructans (found in wheat and some vegetables).

While glucose readily passes through the gut membrane barrier, fructose needs the assistance of a transporter system – the main one is called GLUT5.

Fructose absorption across the gut membrane is further facilitated by glucose. When glucose and fructose are present within the gut in a one-to-one ratio, then fructose absorption is at its maximum efficiency. Sucrose (table sugar), which is chemically structured with equal amounts of glucose and fructose, is usually absorbed completely by the small intestine.

However, with products like crystalline fructose or HFCS, two factors pose problems with fructose absorption. First, the low glucose-to-fructose ratio in these products means a good deal of the ingested fructose will remain unabsorbed and continue its journey down the digestive tract. Second, GLUT5 is quickly swamped when presented with an abundance of fructose, thus limiting the rate of fructose passage into the blood stream. As you will learn, unabsorbed fructose can be an explosive problem.

The upper portion of the small intestine has the largest concentration of GLUT5 and therefore, is the site for most of our fructose absorption. The number of GLUT5 units varies from individual to individual depending upon one’s genetic inheritance – a fact that explains the variation among individuals in their absorptive capacity for similar amounts of fructose.

And regardless of one’s genetic GLUT5 allotment, each individual can, to a certain degree, upregulate their GLUT5 – that is, as one eats more fructose, the body has the ability to compensate by producing more GLUT5 – or conversely, as one cuts back on fructose consumption, the body will rid itself of extra, needless GLUT5 units. Think of it like a bodybuilder who can increase muscle mass by lifting heavy weights – he may not be the strongest guy (that depends upon genetics) – but he can add muscle mass to his body and conversely, will lose extra muscle after quitting regular gym workouts.

An important note to make: recent scientific evidence has shown that people with Type 2 diabetes develop a significant upregulation of their GLUT5 expression, giving their intestines an increased ability to absorb monosaccharaides (glucose and fructose). This brings into sharp focus the importance of dietary modifications for controlling diabetes.

Another published paper found gender differences in the ability of absorb fructose. Women were found to exhibit a higher prevalence of fructose maldigestion versus men.

While glucose can be utilized (metabolized) by just about every cell in the human body, fructose cannot. Fructose needs to be processed and stored in the liver as a back-up energy source called glycogen. Once the liver’s storage capacity is filled, then excess fructose is converted by the liver into various products; one main product is triglycerides. Triglycerides are further converted by the liver into very low-density lipoproteins (VLDL), which are released for storage in fat cells and muscle.

The processing of excess fructose by the liver is not an energy-free task. There are consequences to be paid for making the liver work harder – one of which is a subtle shift in the acid/base balance of the body – tilting things towards an acidic environment. A diet low in fruits and vegetables also adds to the problem. A net acid shift in our body’s chemistry may have numerous consequences that negatively impact our health – one particular consequence is related to bone health and the development of osteoporosis.

For more information.

Excess Fructose in the Bowel: What are the Consequences?
As you can see, the rate of fructose absorption is limited by the number of GLUT5 units we are born with and/or also by the amount of glucose (or rather, the ratio of glucose to fructose) we consume.

The malabsorption of fructose is dose-related (and glucose-dependent) – meaning that you may be able to get away with eating small amounts of fructose but as you increase the concentration of fructose ingestion, you will increase the malabsorption.

Furthermore, many manufactured foods may actually contain a high ratio of fructose and little or no glucose. When the glucose molecule is not present at the same time as the fructose molecule, little, if any, fructose, will be absorbed, and will, therefore, pass to the large bowel.

Finally, just the sheer volume of fructose consumed is a problem. Remember, the average American is eating 80 grams of fructose each day – it is impossible for all of that to get absorbed from the gut into the blood stream (and perhaps that’s a good thing for our livers!). All that excess fructose then continues its journey and finds its way down the digestive tract.

There are other organisms living inside of us that are thrilled to find extra fructose – the bacteria in our large bowel! There are billions of bacteria residing in our bowels. Half of our stool weight is made up of discarded bacteria. And, there are around 400 species of bowel bacteria – each one of us carries a unique ratio of these bacteria. The preferred nutrient for gut bacteria is sugar molecules.

When fructose meets bacteria, a feast begins! Bacteria rapidly ferment the fructose in varying proportions of a variety of gases such as hydrogen, methane, carbon dioxide, hydrogen sulfide and short-chain fatty acids. Each species of bacteria gives off one of these gases and, depending upon which species is overabundant in your colon, dictates the nature of your excess gas. Most people are primarily hydrogen-producers, while smaller numbers of people mainly give off methane. The fermenting gases build up quickly to create feelings of bloating, distention, bowel discomfort or abdominal pain.

Excess fructose that finds its way to the bowel does more than just feed the bacteria – it also draws along with it excess water (an osmotic effect), which has a laxative action on the bowel, causing diarrhea. Added to this is another by-product of the gut bacteria metabolism, the short-chain fatty acids, which also serve to attract more water to the bowel.

Methane gas is not inert. Henry Lin MD and Mark Pimentel MD at Cedars Sinai Hospital in Los Angeles have performed a number of experiments that show that excess methane gas in the large bowel is biologically active and capable of disrupting the motor action (motility) of the colon – creating cramping and bowel spasms and slowing the stool transit – all of which add up to abdominal pain and constipation.

It is tempting to speculate that the reason some people can handle excess dietary fructose without suffering its ill effects on their bowels may be due to the nature of their colon bacteria. Their predominating crop of bugs may prove to be protective, providing less stress on their lower digestive tract – regardless of dietary indiscretions. That they may also be super – absorbers of fructose may mean that they are presenting less fructose to their bowel bacterial buddies. Research into the use of certain strains of “good bacteria” for the treatment of IBS symptoms helps confirm this speculation.