Near-Sightedness
Appears Linked to Excess Sugar in Diet
Diets
high in refined starches such as breads and cereals increase
insulin levels. This affects the development of the eyeball.
Myopia
or near-sightedness is extremely prevalent. It affects more than 25
- 35% of European descent populations and up to 50% or more of
Asian descent populations.
If
we did not have compensatory mechanisms for myopia and were left
to mere Paleolithic resources, it is likely myopic individuals
would not survive very long as clear distance vision is required
for escape from predators, location of food, recognition of other
species members and awareness of environmental dangers and
benefits.
Studies
carried out in hunter-gatherer societies and in recently
westernized hunter-gatherer groups indicate that the prevalence of
myopia normally occurs in 0-2% of the population, and most
refractive errors are less than minor. Moderate to high myopia is
either non-existent or occurs in about one person out of a
thousand.
Diets
high in refined starches such as breads and cereals increase
insulin levels. This affects the development of the eyeball,
making it abnormally long and causing short-sightedness, suggests
a team led by Loren Cordain, an evolutionary biologist at Colorado
State University in Fort Collins.
When
these hunter-gatherer societies change their lifestyles and
introduce grains and carbohydrates, they rapidly
develop (within a single generation)
myopia rates that equal or exceed those in western societies.
In
Dr. Cordain’s study of 229 hunter-gatherer societies, he found
that although refined cereals and sugars were rarely if ever
consumed by groups living in their traditional manner, these foods
quickly became dietary staples following western contact.
Hunter-gatherer
diets are typically characterized by high levels of protein,
moderate levels of fat and low levels of carbohydrate when
compared to modern western diets.
The
carbohydrates present in hunter-gatherer diets are of a low
glycemic index: they are slowly absorbed and produce a gradual and
minimal rise in plasma glucose and insulin levels when compared to
the sugars and refined starches in western diets.
Studies
of recently acculturated hunter-gatherer populations that have
adopted western dietary patterns frequently show high levels of
hyperglycemia, insulin resistance, hyperinsulinemia and type 2
diabetes. Conversely, hunter-gatherer populations in their native
environments rarely exhibit these symptoms.
In
industrialized countries, this dietary shift from hunter-gatherers
occurred more slowly over the 200 or so years since the advent of
the industrial revolution as more and more refined sugars were
gradually included in the diet along with increasingly greater
levels of refined cereals.
Although
highly refined sugars and cereals are common elements of the
modern urban diet, these carbohydrates were eaten sparingly or not
at all by the average citizen in 17th and 18th century Europe and
only started to become available to the masses after the
industrial revolution.
Only
with the widespread introduction of steel roller mills in the late
19th century did fiber-depleted wheat flour of a low extraction
become widely available.
Hence,
over the last 200-250 years the average glycemic load of foods in
urban areas of industrialized countries has risen steadily,
primarily because of increasing consumption of refined cereals and
sugars. This increase in sugars is clearly related to increased
levels of insulin.
"Overnight
Epidemics"
While
fewer than one per cent of the Inuit and Pacific islanders had
myopia early in the last century, these rates have since
skyrocketed to as high as 50 per cent. These "overnight
epidemics" have usually been blamed on the increase in
reading following the sudden advent of literacy and compulsory
schooling in these societies.
But
while reading may play a role, it does not explain why the
incidence of myopia has remained low in societies that have
adopted Western lifestyles but not Western diets, says Cordain.
"In
the islands of Vanuatu they have eight hours of compulsory
schooling a day," he says, "yet the rate of myopia in
these children is only two per cent." The difference is that
Vanuatuans eat fish, yam and coconut rather than white bread and
cereals.
The
theory is also consistent with observations that people are more
likely to develop myopia if they are overweight or have
adult-onset diabetes, both of which involve elevated insulin
levels. The progression of myopia has also been shown to be slower
in children whose protein consumption is increased.
High
Carbohydrate Intake Increase Insulin Levels.
This
elevated level of insulin from consumption of excess grains and
sugars will serve to increase free insulin like growth factor
(IGF-1) which can then accelerate scleral tissue growth during
critical developmental stages thus leading to myopia.
A
variety of studies also suggest that high carbohydrate diets may
cause permanent changes in the development and progression of
refractive errors, particularly during periods of early growth and
development.
High
insulin levels from the carbohydrate loads could disturb the
delicate choreography that normally coordinates eyeball
lengthening and lens growth. And if the eyeball grows too long,
the lens can no longer flatten itself enough to focus a sharp
image on the retina,
Population
studies have demonstrated that people of Asian and Chinese descent
tend to be more insulin resistant than people of European descent.
The prevalence of myopia is also higher in Asian populations than
it is in European populations; it is possible that the higher
rates of myopia in Asian populations may, in part, be due to their
increased genetic susceptibility to insulin resistance. Acta
Ophthalmologica Scandinavica March 2002 vol 80, p 125
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