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Is fructose really an obesity culprit?

Kathleen Blanchard's picture
Brain imaging suggests fructose makes us want to eat more, leading to obesity.

Research published in the Journal of the American Medical Association (JAMA) suggests fructose might be contributing to obesity because it makes us hungry. The study has also been met with some criticism.

High fructose corn syrup can be found in more foods and drinks that you might imagine and could be sabotaging American’s battle of the bulge. Scientists used brain imaging to make the discovery. They wanted to find out if there was a link between fructose consumption and weight gain.

Kathleen A. Page, M.D., of Yale University School of Medicine, New Haven, Conn., and colleagues decided to take a look into the brain using MRI. They wanted to see how fructose compared to glucose ingestion. Fructose is a natural sweetener found in honey, tree and vine fruits, berries, and most root vegetables. But it’s also added to food and beverages because it’s inexpensive and sweeter than glucose. Commercially, fructose usually comes from corn, sugar cane or sometimes sugar beets.

The American diet is laden with fructose. Compared to glucose, they are both simple sugars with the same molecular structure – but they act differently in the brain. Glucose is found in table sugar, starch and all major carbohydrates.

A study published in April 2009 by Johns Hopkins researchers found fructose metabolism in the brain increases hunger. The authors stated the sugar is a health concern that contributes to obesity.The Hopkins researchers noted fructose bypasses a key process in the brain known as glycolysis, unlike glucose.

What that means is that the body produces lower levels of ATP that is needed for energy than glucose. The result is our body thinks we need more energy, so the brain receives signals telling us to eat. We get hungry. You can watch a video here.

The new study reveals even more. Researchers gave 20 healthy volunteers glucose and a fructose drink at two separate times. The study participants underwent MRI before and after ingesting the sugars. The goal was to observe what happens in the hypothalamus of the brain that controls appetite and satiety.

What they found builds on past studies that fructose can confuse the body, leading to overeating. Yale University endocrinologist Dr. Robert Sherwin explained the images showed glucose switches off areas of the brain related to reward and desire for food.

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Specifically, there was less cerebral blood flow (CBF) to the hypothalamus of the brain after drinking glucose, compared to fructose. Another goal of the study was to see how fructose affects hormones. The authors write: “Fructose vs glucose ingestion resulted in lower peak levels of serum, insulin (mean difference, 49 and glucagon-like polypeptide 1.”

What does the study mean for consumers?
There is still going to be debate about whether fructose – especially high fructose corn syrup – is bad for health. James Rippe, MD, professor of biomedical sciences at the University of Central Florida and a paid consultant for the Corn Refiners Association is already defending corn sweetener. He claims if you consume fructose and glucose together there wouldn’t be any effect on the brain because they balance each other out.

Rippe wrote in 2010, “Most of the studies being cited to support the proposed linkages between fructose consumption and obesity and other metabolic conditions employ epidemiologic data that establishes associations rather than cause and effect.” He says Americans are simply consuming more calories from all sources and that’s what’s making us obese, noting that fructose consumption has actually declined since 1999.

Most people consume fructose and glucose – table sugar is an equal combination of both. High-fructose corn syrup is about 55% fructose and 45% glucose. One of the problems with the study is that it was small. In an editorial to the study, Jonathan Purnell, MD, an endocrinologist at Oregon Health & Science University in Portland wrote: “This study didn’t prove that fructose causes weight gain. It doesn’t reflect real-world conditions.”

Instead of avoiding fructose altogether – especially fruits – Purnell says more studies to test sugar mixtures found in food and comparing them to water and artificial sweeteners would give us more information. Fruit contains fructose, but Purnell explains there is also water and fiber present that alter properties of straight fructose like that used in the study. Most experts agree Americans are consuming too much sugar in any form – and that means calories.

If you want to find out if fructose is adding pounds and making you hungry, start reading food labels and cutting back. You’ll reduce your calorie intake and it’s possible you won’t have food cravings. Keep eating your fruits and vegetables and focus on foods known to promote good health. If you drink soda – even diet soda - consider cutting back or eliminating the drinks altogether. Check your favorite bottled green tea too because it probably contains high fructose corn syrup. You might just want to brew your own and consider unsweetened tea a better choice.

JAMA. 2013;309(1):63-70. doi:10.1001/jama.2012.116975

Updated 12/6/2014

Image credit: Wikimedia commons



Very true! Good article. It is not only fructose, though. Here is an example. If our system needs sodium the brain instigates hunger pangs until it gets what it needs at that time, sodium. This scenario is the same with all chemical compounds the system works on. If the compound is not in the food we eat, the need for that compound becomes more desperate, and hunger pangs become more profound. Sugar is easily and quickly digested but does not contain many nutritional benefits. As a matter of fact, the calories in sugar are called empty calories. Sugar is needed because it supplies the energy to digest more nutritious foods. But that energy needs to be sustained by vitamins, minerals, and trace elements. Even the most powerful car still needs petrol to move. And vitamins, minerals and trace elements are the fuel allowing sugar to provide energy. This is why a variety of vegetables is so important because they contain protein, simple and complex carbohydrates in the right proportions to supply all nutrients the human system needs, with the right amount of energy for digestion.
Yep! It's a synergistic effect no doubt.
You missed the part of the study where they actually surveyed the people on satiety, fullness and hunger - here is the quote from the study (have removed the numbers to make it easier to read, emphasis mine) - "There was NO significant difference between glucose vs fructose ingestion on predrink-postdrink changes in hunger, fullness or satiety". Considering that HFCS and sucrose actually contain (almost) equal amounts of glucose and fructose - it is a little hard to extrapolate this study, even if there was differences in the actual physical outcomes. Also consider the serving sizes used, 75g of glucose would require drinking 150g of sucrose or slightly less HFCS (we also don't know if there would be any effect in solid vs liquid food) A little early to take anything from a study that really only showed changes in blood flow but NOT in actual measures of hunger, fullness and satiety!
Yes, except in previous studies done on animals. When rodents are fed fructose they increase their food seeking behaviors, which is part of what has led to more investigation. Another quote: . "Fructose ingestion produces smaller increases in circulating satiety hormones compared with glucose ingestion, and central administration of fructose provokes feeding in rodents, whereas centrally administered glucose promotes satiety." One reason I mention to readers that they could try to eliminate fructose and glucose at the same time is because I've done that and it makes a difference. I don't buy anything with corn syrup in it anymore. My cholesterol levels are better; weight is on an even keel too. It's everywhere. We're consuming too many calories period. It's a cheap way to 'push' food and drinks. I think there's more to come.