Humans have ingested more than 16–24 g of fructose daily for thousands of years now without any issues. The fructose was sourced primarily from natural whole fruits, certain vegetables, and honey. In the last century, however, modern food processing methods were instituted in Europe and North America and things changed drastically. By the 1950’s high fructose corn syrup (HFCS) was invented. HFCS is derived from mostly TOXIC GMO corn starch that has been synthetically processed by glucose isomerase to convert part of its glucose into often disproportionate levels of fructose.
In recent decades, the average US consumption of fructose SKYROCKETED to 80g per day, mostly in the form of refined HFCS, used extensively as a sweetener in juices, soft drinks, and processed foods! Most of the increase in consumption is derived from refined or processed (HFCS). This equates to 330–380 kcal/day, or 17–20% of daily energy intake sourced from fructose, which is far greater than our ancestors consumed!
Along with the extreme increase of fructose, mostly in the form of processed HFCS, came the rise of fructose malabsorption or fructose intolerance.
Fructose malabsorption is the result of incomplete digestion of fructose. Fructose intolerance, ranging from mild to severe, is a condition associated with increasing levels of gastrointestinal (GI) distress. It occurs more frequently in individuals with compromised gut function when compared with healthy individuals, as expected. Individuals with IBS and other digestive disorders have to be especially careful until the issue is resolved. Besides IBS, other inflammatory conditions like Crohn’s disease, gastroenteritis, or celiac disease, can also lead to, and even be caused by fructose intolerance.
DID YOU KNOW: It is estimated that 70% of IBS patients have some form of fructose intolerance, with processed HFCS undeniably linked to increased symptoms!
Glucose is absorbed in the lumen of the small intestines via transporter proteins GLUT2 and GLUT5. However, fructose is absorbed mainly through GLUT5 transporters by a facilitated energy-dependent process. This transport-mediated process can ONLY withstand around 15g of fructose at one time. Consequently, when GLUT5 transporters become overwhelmed by EXCESSIVE fructose ingestion (like with HFCS and maybe fruit juices), incomplete absorption in the colon can result, causing bloating, gas, inflammation-pH imbalances, and pain.
There are also other substances that may institute fructose malabsorption and create gastrointestinal distress, such as artificial sugar substitute sorbitol (sugar alcohol), processed mostly from corn and certain fruits. Sorbitol can be found in many food products, especially candy and dessert products labeled as “containing no sugar” or “lite”.
Genetic fructose intolerance is not as common and is found mostly in children when sugars are first being introduced in their diets.
Nonetheless, it is mostly the added refined sugars and HFCS that instigate the majority of the damage. Elevated HFCS consumption ALONE has been highly implicated in increasing rates of fructose intolerance!
FRUCTOSE INTOLERANCE IS ALSO DOSE DEPENDENT
Breath tests are the most common way to identify fructose intolerances. An elevation in the breath concentrations of hydrogen and/or methane above a certain level, along with increased symptoms post fructose ingestion, is usually sufficient proof of an intolerance or malabsorption issue.
Positive breath test results are not common when pure fructose is provided in a dose of less than 25 g. Although, “In a clinical setting, the absorption of pure fructose has been shown to range between < 5 to > 50 g, indicating wide individual variability and the possibility of very low absorptive capacity in some individuals.” (1)
It is said to be uncommon (however, certainly possible on a standard American diet), to consume 25g of free fructose in one sitting free from glucose or other nutrients (glucose, fiber, starch, fat, protein). For instance, one would have to consume 26 oz. (769 mL) of apple juice or more than 50 oz. (1,500 mL) of cola sweetened with HFCS-55 to imbibe 25g of fructose in absence of glucose. Besides, processed foods and beverages have little to no fiber which can increase intestinal malabsorption issues.
DID YOU KNOW: A super big gulp alone is 40oz., so it is not so uncommon for the average American to reach MORE than 25g of fructose in ONE processed fast food meal!
“It has been estimated that up to 50% of the U.S. population is unable to absorb 25g of pure fructose as evaluated in clinical studies. In clinical trials, it was shown that up to 80% of healthy controls were unable to absorb a 50g fructose load.” (2)
Once fructose malabsorption materializes, certain higher fructose fruits and all fruits in even moderate quantities can be problematic. So besides HFCS and sorbitol, fruits that contain more fructose than glucose like agave, apples, pears, and watermelon, and of course all concentrated juices, especially apple, pear, and even grape juice can lead to or increase fructose intolerance levels. Dry figs, dates, prunes, and raisins are also high in fructose. Remember, most juices also lack fiber, so the fructose is available immediately potentially overwhelming fructose receptors!
Interestingly, many people claim that consuming glucose after high fructose foods provides immediate relief from the pain and bloating associated with fructose intolerance, confirming the theory that fructose needs adequate glucose to be absorbed. However, this should only be a temporary remedy until the digestive issue is resolved or under control.
If you experience any type of fructose malabsorption or intolerance you should limit your intake of fructose for a period of time, while AVOIDING any products containing sorbitol or HFCS. As stated it is much more common for individuals with intestinal issues to experience intolerances. So, in addition it would be wise to do a colon cleanse, balance intestinal pH, and begin healing the GI tract before reinstituting regular consumption of fructose for lasting results.
Studies show that reducing fructose intake to 5 grams for one month showed significant relief of symptoms in all subjects as well as in IBS patients. (3)
After 1 month it is recommended to begin re-introducing small quantities of higher fructose-containing fruits, one at a time, in order to establish how much fructose you can tolerate, while at the same time continuing to correct any digestive complications that would cause recurrences. Keep in mind that many people with digestive issues accumulate pathogenic bacteria which feed on sugar, so it may not be the fructose per say, but imbalances in gut ecology. High sugar diets, which includes fructose, can also be the cause of the gut imbalances.
WHAT ARE FRUCTANS?
Fructans can also be problematic for people with fructose intolerances. Fructans are short chains of fructose molecules that end in a glucose molecule and can also be problematic for someone with fructose intolerance complications. Fructans are found in certain grains like wheat, spelt, and kamut, which are otherwise healthy foods if you are not gluten sensitive or intolerant, when non-refined, and prepared properly. Fructans can also be found in brown rice and some vegetables including asparagus, artichokes, green beans, and tomato paste. All of these foods are extremely healthy, alkaline forming, and very beneficial to the colon, feeding beneficial bacteria under normal balanced conditions. Again, people with digestive conditions like IBS would be more likely to experience intolerances, and these foods can and should be reinstituted after issues are resolved.
Small intestinal bacterial overgrowth (SIBO) can also be at the root of your GI symptoms, and particularly when breath tests for hydrogen and methane are positive with glucose and fructose, particularly in the diabetic population.
Keeping fructose levels at or below 25g a day like our ancestors is not at all difficult if you avoid toxic processed foods and beverages, and you can eat ALOT more fruit than you think to do that! Based on a 100-gram serving, or 1 cup of both high and low fructose fruits you can consume 1 banana, 1 apple, 1 tomato, 1 lemon, 1 cup blueberries, and 1 cup of strawberries. That is a hell of a lot of fruit if you ask me!
1- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3471321/
2- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3471321/
3- https://www.ncbi.nlm.nih.gov/pubmed/17000196/
http://foodintolerances.org/intolerances/fructose-intolerance/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3934501/
http://www.medscape.com/viewarticle/756266_4
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2652499/
https://en.wikipedia.org/wiki/High_fructose_corn_syrup