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How fructose might destroy your liver and more

Kathleen Blanchard's picture
Fructose linked to liver disease.

Researchers are taking a closer look at fructose that is pervasive in foods most of us consume daily. A new study conducted on animals suggests fructose that is a simple sugar found in fruits and added to others in the form of high fructose corn syrup, might be eating at your liver faster than you’re eating your food.

The investigation that comes from Wake Forest Baptist Medical Center showed that fructose quickly caused liver damage, even in the absence of weight gain in animal models.

The study, published in the June 19 online edition of the American Journal of Clinical Nutrition, showed animals given a high fructose diet had double the amount of liver damage as animals used controls.

Kylie Kavanagh, D.V.M., assistant professor of pathology-comparative medicine at Wake Forest Baptist and lead author of the study said the finding suggests not all calories are created equal.

Kavanagh and colleagues previously studied monkeys given a high fructose, low fat diet for 7 years. The monkeys were allowed to eat as much as they wanted. They compared the monkeys to a control group fed a low-fructose, low-fat diet for the same amount of time.

As anticipated, the animals got fat eating all they wanted and with the added fructose. They also developed type 2 diabetes at 3 times the rate as the control group; in addition to liver damage known as hepatic steatosis, or non-alcoholic fatty liver disease (NAFLD).

The researchers wanted to know if it was calorie intake or something else causing the animals to develop liver damage, leading to the new study designed to ensure the animals would not gain weight.

Liver damage from fructose without weigh gain found

For the new study, the researchers divided 10 monkeys into 2 groups. None had ever eaten fructose before.

One group was fed a calorie-controlled diet comprised of 24 percent fructose. The control group was also given a specific amount of calories that contained just 0.5 percent fructose.

Each week the researchers weighed the animals and measured waist circumference, adjust their diet to prevent weight gain.

They also performed liver function tests measurable in blood samples.

They discovered that even in the absence of any weight gain, a high fructose diet caused bacteria to lea from the intestines to the liver at a high rate; causing liver damage.

How fructose affects intestinal bacteria discovered

Intestinal bacteria normally have a protective effect on overall health. Something about fructose seems to cause bacteria to leak from the gut into the bloodstream

Practically speaking, the finding could mean it is not fat in and around the body organs that cause liver damage and fatty liver disease as suspected by most clinicians.

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“The liver damage began even in the absence of weight gain. This could have clinical implications because most doctors and scientists have thought that it was the fat in and around tissues in the body that caused the health problems,” Kavanagh said in a press release.

The researchers say the study is limited because they did not test for dextrose, another simple sugar found in plants. Kavanagh says they studied fructose because it is the most common sugar in the American diet. Though they can’t say for certain it is fructose that damages the liver, they can say a diet high in added sugars does cause liver damage from leakage of intestinal bacteria.

The study is certainly not the first to suggest fructose may not be metabolized efficiently. Our body needs sugar as a quick source of energy. Small amounts are necessary and easily tolerated. The way fructose added to foods behaves in the body has been the target of some research.

One study, published in the Journal of the American Medical Association (JAMA) suggested fructose could contribute to obesity because it makes us feel hungry. Obesity is also linked to higher rates of liver disease.

In this instance, the researchers found sugar, not weight gain, might be the culprit for the health problems found in the animals studied.

High fructose corn syrup has been linked to a variety of health problems, including gout, high blood pressure and kidney problems that have recently begun to surface.

Last year, a finding published in the journal PNAS found fructose is metabolized by two different enzymes – one makes us more prone to type 2 diabetes, weight gain and fatty liver disease, while pathway that breaks the sugar down in the body can protect us from the ill health effects of too much sugar.

Richard Johnson, MD, the senior author of the study and Chief of the Division of Renal Diseases and Hypertension at the University of Colorado School of Medicine suggested some people may just be more vulnerable to the ill health effects of too much fructose.

Liver disease is on the rise and has been affecting people at a younger age. The condition can eventually lead to cirrhosis and is a growing public health issue.

The condition is estimated to affect one-third of the U.S. population and is also associated with increased waist circumference that is also becoming more prevalent.

What researchers know about liver disease that is not brought about by excessive alcohol intake is that it stems from insult to the liver that in turn leads to inflammation. Genes are thought to play a role, but here is no clear-cut explanation as to why some people are susceptible to the disease, according to the Cleveland Clinic.

How much fructose do we need?

Experts believe a balanced diet is the best option for optimal health and that fructose is dispensable in the diet. The amount we get from fruits is beneficial because we’re also getting fiber and other nutrients.

Sedentary and overweight individuals who are already at risk for disease especially should focus on eating fruits, whole grains and low saturated fat. Consuming fewer sugary drinks like sodas, cereals with extra sugar and sweet snacks is also important.

It isn't time to say we need to ditch fructose altogether. But evidence is mounting that too much sugar could have negative consequences for health, beyond just too many calories and now supported by the newer study, published in the Journal of Clinical Nutrition.

It may be that too much fructose that is typical of a Western diet is a contributor to liver damage that can lead to liver disease, based on the preliminary finding. The highest levels of fructose are found in sodas, sports drinks, honey, flavored water and table sugar.

BMC Biology