Sugar has been attracting a lot of press over the past few years—and little of it good! A lot of people have ‘quit sugar’ and seen the enormous benefits of doing so. Giving up the sugar, and more importantly fructose, will benefit pretty much everyone however for some it may mean the difference between life and death.
Fructose intolerance

Mixed fruits

Clinical intolerance to fructose was initially described in 1956. The following year, researchers reported a familial coincidence of the disorder occurring in other family members, postulating that the defect was a deficiency of a liver enzyme they called hepatic fructose 1-aldolase (aldolase-B isoenzyme). They called this Hereditary Fructose Intolerance. Within the next 4-5 years, the symptoms associated with Hereditary Fructose Intolerance were documented in infants, including vomiting, hypoglycemia, failure to thrive, cachexia, hepatomegaly, jaundice, coagulopathy, hemorrhage, renal Fanconi syndrome, severe metabolic acidosis (in part due to lactic acidosis) and in many cases, liver failure, coma and death. Hereditary Fructose Intolerance is an inherited disorder. Both the mother and father have the gene that causes the condition but may not have symptoms of fructose intolerance themselves. This is called an autosomal recessive pattern of inheritance.

Fructose is one of the simple sugars we eat—others include glucose (the form in which sugar circulates in the blood) and galactose (produced by the digestion of milk). These simple sugars can be absorbed by the small intestine. Fructose is found naturally in table sugar, fruits, vegetables, and honey. Synthetic fructose (in the form of corn syrup) is used as a sweetener in most commercial foods, including baby foods and sweetened beverages.
The digestion of food begins in the mouth, moves to the stomach, and then into the small intestine. Along the way, specific enzymes are needed to process the different types of sugars in the foods we eat. An enzyme is a substance that acts as a catalyst to produce chemical changes without being changed itself. Absorption of fructose requires two steps of enzymatic activity (phosphorelation). The first occurs in the small intestine while the second principally occurs in the liver. People with Hereditary Fructose Intolerance have a liver that is genetically unable to produce adequate amounts of the aldolase-B isoenzyme to complete the phosphorelation process of even small amounts of fructose in the diet. People who develop dysfunctioning livers which are unable to produce this enzyme for small to moderate amounts of fructose in the diet, will also experience similar symptoms. This illness is called Partial Fructose Intolerance.
When people with the genetic limitations, or through their dysfunctioning liver, ingest fructose or sucrose (cane or beet sugar, table sugar), there is incomplete digestion of fructose which then circulates in the blood, accumulates in the liver, kidneys and brain. Accumulation progressively causes damage that can lead to further liver-kidney dysfunction as well as mental dysfunction. The mental dysfunction is compounded by oscillating states of hypoglycaemia (accumulated fructose interferes with the conversion of glycogen, the body’s energy storage material, into glucose, which results in abnormally low oscillating levels of blood glucose) where parts of the brain close down.
An interesting observation of many of the infants that eventually become diagnosed with Hereditary Fructose Intolerance is their powerful protective aversion (feeling of intense dislike) to sweet-tasting foods and beverages when they are first introduced to them. They continually spit them out when their parents attempt to place them into their mouth. Eventually through persistent exposure to sweet foods, the infant accepts them and often develops an addictive response to fructose, demanding sweet foods from then on.

Symptoms of Fructose Intolerance

The disorder will not be apparent until an infant is fed formula, juice, fruits, or baby foods that contain fructose. Many soy-based formulas contain considerable amounts of sucrose as a carbohydrate source. Initial symptoms include abdominal pain, bloating, sometimes vomiting and unexplained fever, thirst, increased urination and sweating. The infant often rejects all foods within which they detect fructose. Tremors and seizures caused by low blood sugar can also occur. The liver becomes swollen, and induces darkening below the eyes, and in later stages the infants become jaundiced with yellowing of the eyes and skin. If fructose is continued to be given to the infant/child, they can succumb to coma and death. Most infants survive, but go on to demonstrate the same symptoms as those people who develop Partial Fructose Intolerance.One of the main challenges of either of the states of fructose intolerance in children is their challenging behaviours that emulate the symptoms of ADHD—bouts of uncontrollable inattention, hyperactivity, impulsiveness, loud crying, and demanding nature—particularly for sweet foods (addiction response). When the child attends preschool and later primary school they do poorly in exams, have difficulty with short-term memory, have poor concentration, have heightened confusion, and have general socialisation difficulties while fructose is part of their diet. In later life they are inclined to develop addictive responses to smoking, drugs, alcohol, difficulties succeeding (or even fitting-in) in society, and in extreme cases show bipolar symptoms and other serious psychological illnesses. In older age with continued ingestion of fructose throughout their life, they are prone to dementia and the other age-related mental diseases.


The diagnosis of Hereditary Fructose Intolerance includes genetic testing with DNA analysis to identify one of the common gene mutations that lead to this disorder. However, negative results are not a guarantee that the person does not have Hereditary Fructose Intolerance. Urine tests can be used to detect fructose sugar in the urine while blood tests can also be used to detect hyperbilirubinemia, and uric acid in the blood. A liver biopsy may be performed to test for levels of enzymes present (aldolase assay) and to evaluate the extent of damage to the liver.For an assessment of Lifestyle Fructose Intolerance, the best way to do this is through personal food trials. A Fructose Free Trial involves removing all starchy vegetables, table sugar, fruits, fast foods and sorbitol, from your diet while keeping short-term memory graphs and long-term memory controls to record changes to individual symptoms. The trial needs to be conducted over a three week period to cover variations in the reduction of symptoms. In most trials that I have conducted, individuals with Lifestyle Fructose Intolerance who undertake the trials, will quite clearly recognise the difference in mental clarity, reduced emotional stress, increased motivation and fulfilment in their everyday lives as well as a reduction in liver symptoms. Clearly seeing these results helps them to make choices around their fructose consumption. When their liver function is challenged they remove fructose from their diet and when it is functioning normally they determine how much fructose they can safely consume while maintaining normal health, this includes in drinks such as beer and wine.

Weaning infants

If, when your infant begins eating formula or is introduced to solid vegetables/fruits, and within a few weeks they develop any of the symptoms mentioned in this article, then you are advised to undertake a Fructose Free Trial to determine fructose intolerance. Early identification of a fructose intolerance will allow you to manage it and start to understand how sensitive your child is to fructose. It will also allow you to better identify behavioural problems that may occur (that may be similar to ADHD) and manage them without medication. Knowing if your child has a fructose intolerance will also aid you in helping them to avoid it as they go through life. If they haven’t developed a ‘sweet tooth’ at an early age they will be able to more easily refuse treats and sweets which they will undoubtedly be bombarded with as they grow up!

Our Clear Main, Free Mind workshop is on this weekend in Canberra where you can learn all you need to know about fructose and how to conduct your own Fructose Free Trials. So come along and find out how you can determine if fructose is causing you health problems! Or if you can’t come along you can find more information here or contact us to make an appointment today. Also check out Blog: Why is Fructose Satan’s Sugar?