Text 18063, 117 rader
Skriven 2007-07-20 08:48:00 av FRED A BALL (1:123/140)
Ärende: Fructose
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Is fructose bad for you?
From Harvard Health Publications
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It doesn’t cause spikes in insulin and blood sugar,but large amounts of
fructose may contribute to overeating.

Most of the sugar we eat gets broken down and absorbed in the small
intestine. Swarms of specialized enzymes attack larger molecules and
convert them into three simpler sugars: mainly glucose, but also
galactose (a part of lactose, the sugar in milk) and fructose. There are
a few more steps involved in breaking down the starches in bread,
potatoes, and the like, but ultimately starch shares a similar digestive
fate.

Our livers prudently stow away some of the absorbed glucose as glycogen,
a molecule that can be turned back into glucose when we haven’t eaten
for a while. But most of the sugary stuff is distributed right away.
Glucose levels in the blood shoot up, and the pancreas gets busy,
pumping out the insulin that cells throughout the body need in order to
take in glucose and use it for energy.

Post-meal glucose and insulin spikes are perfectly normaland entirely
unavoidable. But if they’re too big, or come too often, they’re harmful.
Canadian researchers devised the glycemic index (GI) to make it easier
to compare how different foods affect blood sugar levels: the higher the
GI number, the bigger the increase in blood sugar. A number of studies
have found that people who eat a lot of high-GI foods — cookies, candy,
bread made with refined flour, potatoes — have higher rates of diabetes
and heart disease.

Specialized metabolism

Pretty much all of the body’s cells come equipped with enzymes that
allow them to harness glucose. But the enzyme that metabolizes fructose,
called fructokinase, is found exclusively in liver cells. So although
fructose is involved in glucose metabolism indirectly, fructose
metabolism is pretty specialized. As a result, if you eat fructose, your
blood glucose and insulin levels stay fairly level.

If, as the GI-index research indicates, glucose and insulin increases
are a problem, then substituting fructose for other sugars in the food
supply looks like it might be a solution.

But, alas, it’s more complicated than that. For all the mischief that
glucose and insulin cause, they do trigger some helpful hormonal
changes. Levels of leptin, the satiety hormone that gives us a full
feeling, go up when insulin surges, and levels of ghrelin, the “hunger
hormone,ö go down. There’s fairly good evidence that fructose has just
the opposite effect, reducing leptin, so we don’t necessarily feel full
after a fructose-filled meal, and not lowering ghrelin as much as
glucose does, so we stay hungry. For this reason, some experts see
high-fructose diets as contributing to overeating.

Another problem: Oversupply the metabolic pathway for fructose with the
sugar, and the liver ends up churning out triglycerides fat that
circulates in the blood. The same is true of glucose and its metabolic
pathway, but it takes larger amounts.

That floozy is she to blame?

Fructose is a naturally occurring sugar. You’ll find it in honey,
vegetables (in small amounts), and, of course, fruit. Not all the sugar
in fruit is fructose, which is one of the reasons (lack of fiber is
another) that some fruits, such as watermelon, have a high glycemic
index.

But most people’s intake of fructose from fruits and vegetables is
dwarfed by what they get from sucrose — better known as table sugar, or
just sugar — and high-fructose corn syrup. Sucrose is a two-sugar
molecule (a disaccharide) consisting of fructose and glucose. High-
fructose corn syrup is corn syrup that has been processed to increase
the fructose level, which makes it taste sweeter. The most common
variety is 55% fructose and 45% glucose. In the United States,
high-fructose corn syrup has replaced sucrose as a sweetener, especially
in soft drinks, but in many other foods too. Sally Squires, the
Washington Post nutrition columnist, has called it “the floozy of the
sugar world: sweeter and cheaper than sucrose, but viewed with distrust
by some consumers.

Experts debate how responsible high-fructose corn syrup is for the
American obesity epidemic and the soaring type 2 diabetes rate. Those
who see a connection note that the great American weight problem and the
sweetening of the food supply with the suspect syrup happened at about
the same time. They also point to fructose metabolism and its
triglyceride output.

Doubters counter with several arguments. Sucrose and high- fructose corn
syrup contain about the same amount of fructose and glucose (a 50-50
split versus a 55-45 one), so it’s questionable w different. Many of the
damning metabolic studies have used all-fructose solutions, not
high-fructose corn syrup. And the trouble is all the nutritionally
empty, added sugar in our diets, not any particular form of that sugar.

Eat fruit

Where does this leave us? Certainly no one should stop eating fruit out
of some misguided fear of fructose. Most varieties of fruit are brimming
with nutritional virtue vitamins, minerals, fiber and have
relatively little fructose and other sugar.

Is high-fructose corn syrup especially harmful? Hard to say. At this
point, the case against soft drinks sweetened with the stuff is pretty
persuasive, although even that might be just a matter of the added
calories.

Happy Cooking
Fred

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