Hereditary Fructose Intolerance: Reasons for Inability to Metabolize Fructose

Nutritional Biochemistry 1
NUTRITIONAL BIOCHEMISTRY
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Nutritional Biochemistry 2
Reasons why a person suffering from Hereditary Fructose Intolerance is not able to
metabolize fructose
Hereditary fructose intolerance is a disease caused by the deficiency of aldolase B
enzyme. A person suffering from HFI should not ingest fructose nor sucrose as this may lead to a
severe disease called hypoglycemia and also the build-up of other dangerous substances in the
liver. According to Bouteldia & Timson1, Mutations in the ALDOB gene cause this condition.
These genes are inherited in a recessive manner. The gene also provides the directives for
making the aldolase B enzyme. The enzyme is located in the liver and helps in fructose
breakdown into energy. The alterations of ALDOB gene then reduce the capability of aldolase B
enzyme to metabolize fructose.
Fructose digestion starts in the small intestines and because the body cannot absorb solid
molecules then it is broken down into fructose and sucrose particles by sucrose enzyme. Fructose
molecules then enter the small intestines lining through a channel into the bloodstream.
Bouteldia & Timson1 also explained that after fructose enters the bloodstream, it then travels
with all the other absorbed nutrients for metabolism in the liber. Metabolism then occurs in the
liver. The process of metabolism of fructose in the liver is called fructolysis.
Fructose metabolism is started by its phosphorylation in the liver to D-fructose 1-
phosphate. This is characterized via an enzyme called fructokinase. According to
Goudsmit2 ,when there is the deficiency aldolase, D-fructose 1-phosphate accumulates in the
liver and therefore inhibiting a kinase reaction. This results in a slower removal of fructose in the
bloodstream. Goudsmit2 also explained that fructose may be phosphorylated in the muscle or as
adipose tissue when their concentration goes high.2 This is done by an enzyme called

Nutritional Biochemistry 3
hexokinase. D-fructose 6-phosphate produced then enters the catabolic pathways or can be
changed to glycogen. To avoid hypoglycemia, it’s therefore released into the blood.
Human liver aldolase works together with D-fructose 1-phosphate and D-fructose 1, 6-
biphosphate substrates. Patients with hereditary fructose intolerance indicate a significant
functioning of fructose 1,6-biphosphate than the fructose 1-phosphate in the liver tissues. There
is also the increase in enzyme elevation due to ingestion of D-fructose. Liver cirrhosis and
fibrosis are some of the chronic diseases that are accompanied by hereditary fructose disorder.
There are histologic changes from 1 to 1.5h in the liver hepatocytes after fructose ingestion. The
amount of AST and GPT released then increases.
Parents of individuals with hereditary fructose intolerance disease carry a copy of the
mutated gene. According to Lenaspa et al3, there are several symptoms of HFI disorder, for
example, poor feeding in case the patient is a baby, vomiting, convulsions, excessive sleepiness,
avoidance of fruits, irritability, and prolonged jaundice. Continuous ingestion of fructose-
containing fruits may lead to the damage of the kidney and liver. When the infants are affected,
they fail to gain weight and grow. It also may lead to low blood sugar. The liver of the affected
may also enlarge. Lenaspa et al3 reported that continuous exposure to fructose may lead to coma
and death due to kidney and liver failures. Symptoms vary from one person to another.
According to coffee4, eliminating fructose and sucrose from the diet helps in the treatment of the
disease though when severe it may not intestines in treating the liver disease. Therefore, a person
suffering from hereditary fructose intolerance is not able to metabolize fructose.
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