Fructose
is fruit sugar. In the limited quantities of fruit we recommend for our patients
(see Page Fundamental Food Plan II), fructose is rarely a problem. However, in
a marketing scheme to convince the public that fruit sugar is somehow better
than table sugar (dextrose), large quantities of fructose are being consumed,
typically as high fructose corn sweetener. The consequences of fructose
consumption in a concentrated form may have significant effect on the
metabolism of carbohydrates, uric acid, etc.
Function:
Humans
have a limited ability to metabolize fructose (fruit sugar). Fructose is
metabolized differently from other sugars. A fructose load leads to
accumulation of fructose-1-phosphate in cells, which may partially deplete
intracellular ATP levels in susceptible individuals. Decreased cellular ATP
causes disturbances in protein, DNA and RNA synthesis, interferes with cyclic
AMP formation, and reduced ammonia detoxification. Elevations of lactate, uric
acid, and triglycerides may result with implications for gout and
cardiovascular disease. Several forms of hereditary fructose intolerance have
been described.
Fructose Intolerance
Symptoms:
Since
fructose intolerance is a cellular event, rather than a single nutrient
deficiency, symptoms may vary widely among persons. Preliminary evidence
suggests clinical symptoms of fructose intolerance may include fatigue,
headaches, weakness, dizziness, behavioral changes, and depressed immune
function. Medical literature suggests that certain individuals with fructose
intolerance may show hypertriglyceridemia, elevation
of uric acid, and interference with copper metabolism.
Fructose Overload:
Dietary
sources of fructose are numerous; however, an excess intake of fructose should
be avoided. It is usually not necessary to have an absolute removal of dietary
fructose. In this manner, whole foods containing fructose (fruits and some
vegetables) may be consumed in modest quantities in order to benefit from their
overall nutritional value. Foods very rich in fructose include table sugar
(sucrose), high fructose corn syrup, corn syrup, fruit juice concentrates, and
a large list of prepared foods containing sucrose and/or corn syrup.
Fructose Overload
effects on biochemical pathways:
The
metabolism of glucose and fructose is similar. However, fructose can induce
numerous abnormalities that include fatty liver, which in turn could eventually
lead to impaired liver function, cell damage, and fibrosis. Fructose metabolism
has the ability to induce generation of reactive oxygen species due to
increased activity of xanthine oxidase and generation
of glyceraldehyde, which is an inducer of free
radicals. The liver may be exposed to oxidative stress following the
consumption of fructose.
"Nutritional Factors Adversely
Influencing the Glucose/Insulin System"
Fields, M. J Am Coll
Nutrition, 1998;17(4):317-321.
In
another scientific article from the American Journal of Clinical Nutrition (Nov
2002;76(5):911-22), the metabolism of fructose was
again discussed. The report indicated
that fructose, compared with glucose, is preferentially metabolized to fat in
your liver. In animal models fructose
produced:
- Insulin
resistance
- Impaired
glucose tolerance
- High
insulin levels
- High
triglycerides
- Hypertension
Americans' consumption of fructose, as a
combination of sucrose and high-fructose corn syrup, has increased by 26
percent from 1970 to 1997. Dietary fructose has increased markedly in part due
to the notion that fructose was considered to be beneficial to diabetes
mellitus and insulin resistance because ingesting it results in smaller rises
in glucose and insulin after consumption compared to glucose and complex
carbohydrates. However, when hormonal factors are considered, fructose not only
seems to actually promote disease more than even glucose, but fructose in
contrast to glucose is metabolized to fat in your liver.
Small amounts of fructose are probably acceptable
and may even have some favorable metabolic effects. However, on the basis of
the available data regarding the endocrine and metabolic effects of consuming
large quantities of fructose such as in high fructose corn syrup, and the
potential to exacerbate components of insulin resistance syndrome, there is no
advantage of fructose compared to glucose (free glucose and starch). This is
particularly important for those with high cholesterol levels or insulin
resistance who may be more susceptible to the negative metabolic effects of
fructose.
