Is fructose really an obesity culprit?
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.
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
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