02 January 2013

Study Finds Eating Fructose May Stimulate Overeating

Supports Chapter 8: Why ‘five portions’?

Scientists have used imaging tests to show for the first time that fructose, a sugar that saturates the American diet, can trigger brain changes that may lead to overeating.

After drinking a fructose beverage, the brain doesn't register the feeling of being full as it does when simple glucose is consumed, researchers found.

It's a small study and does not prove that fructose or its relative, high-fructose corn syrup, can cause obesity, but experts say it adds evidence they may play a role.

The sugars often are added to processed foods and beverages and consumption has risen dramatically since the 1970s along with obesity.

A third of US children and teens and more than two-thirds of adults are obese or overweight.

All sugars are not equal
even though they contain the same amount of calories — because they are metabolised differently in the body.

Table sugar is sucrose, which is half fructose, half glucose, while high-fructose corn syrup is 55% fructose and 45% glucose. Some nutrition experts say this sweetener may pose special risks, but others and the industry reject that claim.

Doctors say we eat too much sugar in all forms.

For the study, scientists used magnetic resonance imaging, or MRI, scans to track blood flow in the brain in 20 young, normal-weight people before and after they had drinks containing glucose or fructose in two sessions several weeks apart.

Scans showed that drinking glucose "turns off or suppresses the activity of areas of the brain that are critical for reward and desire for food", said one study leader, Yale University endocrinologist Dr Robert Sherwin.

With fructose, "we don't see those changes," he said.

"As a result, the desire to eat continues - it isn't turned off."

What's convincing, said Dr. Jonathan Purnell, an endocrinologist at Oregon Health and Science University, is that the imaging results mirrored how hungry the people said they felt, as well as what earlier studies found in animals.

"It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose," said Purnell.

He wrote a commentary that appears with the federally funded study in Wednesday's Journal of the American Medical Association.

Researchers are now testing obese people to determine if they react the same way to fructose and glucose as the normal-weight people in the study.

But there is one other source of fructose which the study neglected fruit. While many already know that high-fructose corn syrup is not healthy, we are told by the 'experts' that fruit is healthy. Yet the sugar that makes fruit sweet is pure fructose! Go figure, as our American cousins say.

Page KA et al. Effects of Fructose vs Glucose on Regional Cerebral Blood Flow in Brain Regions Involved With Appetite and Reward Pathways. JAMA. 2013;309(1):63-70


Anonymous said...

You're right about the confusion regarding fructose.
I know four children (different families)that are obese to morbidly obese who eat 6+ fruits a day and very little vegetables.
Their parents believe that they are eating healthily and say they're having more than their "5 a day".
All the kids have behavioural problems too.
I've tried to explain about fructose but they won't listen.

The 5 a day should include a maximum of 1 fruit, preferably none when there are obesity issues, and this should be made explicitly clear.
I'm not holding my breath on this though.....

George Henderson said...

You might like this recent review of Fructose and CVD:


Ed Terry said...

While high-fructose corn syrup may be biochemically similar to sucrose, the "food-like" substances manufacturers fail to mention that due to its physical properties, HFCS can be added to many more foods than granulated sugar can. It's very difficult to find any processed food that does not have HFCS as an ingredient.

Anonymous said...

Whilst I can imagine too much fruit and sweet vegetables can lead to obesity the question is , how much is too much? I'm a great believer in going right back to basics before I formulate any personal theories about food and the fact remains we DO have a natural sweet tooth. There must be some evolutionary benefit for a liking for sweetness. All I can think of is that, like the lobster in the slowly boiling water, we have been getting heavier and heavier doses of ' sweet' over the centuries and
like a drug a 'normal' amount is simply not enough now .

Anonymous said...

I think the question is more, how sweet is sweet? The amount of sugar that I eat is negligible and my children cannot understand how I can find things like cabbage, carrots and parsnips TOO sweet for my liking. I believe it's just down to conditioning ( what we get used to ) and the fruit we eat today bears no relation in terms of sweetness to uncultivated natural fruit.

Lorraine said...

Very true. It is also surprising to know that whole wheat bread increases blood sugar to a higher level than sucrose. Eating 2 slices of whole wheat bread can often be worse on blood sugar than drinking a sugar sweetened fizzy drink or eating a chocolate bar.

Joe said...

With billions of neurons in the mouth,stomach,gut, maybe the stomach can 'learn' habits. One of which could be to recognize fructose and then send a message to the brain to release insulin via the pancreas, which will not happen possibly of low Glut5. Every time the neurons detect fructose (which is very often nowadays) they will get more experienced in doing so. Maybe,when becoming more sensitive to fructose, they will send the same signals to the brain with less fructose. These neurons will also make sure Ghrelin levels are high: leaving the (fructose) eater with a feeling of never being full and wanting to eat more. Would it even be possible that the neurons getting 'fructosised' continuously sending the wrong message to the brain? Maybe this can explain the low level of hormones and the feeling of starvation of someone who has lost a lot of weight.... Avoiding regaining weight quickly is only possible when the neurons in the mouth, stomach and gut are 'de-fructosised'.

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