By Dr. Mercola
People everywhere are finally waking up to the indisputable fact that all sugars are not created equal when it comes to the physical end results they create.
Scientists using newer functional magnetic resonance imaging (fMRI) tests have now shown that fructose, a sugar found in most processed foods (typically in the form of high fructose corn syrup), can in fact trigger changes in your brain that may lead to overeating and weight gain.1
The researchers discovered that when you drink a beverage containing fructose, your brain does not register the feeling of being satiated, as it does when you consume simple glucose. As reported by Yahoo! Health:2
“All sugars are not equal — even though they contain the same amount of calories — because they are metabolized differently in the body.
Table sugar is sucrose, which is half fructose, half glucose. High-fructose corn syrup is 55 percent fructose and 45 percent glucose. Some nutrition experts say this sweetener may pose special risks, but others and the industry reject that claim. And doctors say we eat too much sugar in all forms.”
Beware: Fructose Can Make You Hungry, Study Finds
Twenty healthy adults were included in the featured study, published in the journal JAMA on January 2.3 fMRI was used to measure the hypothalamus response when the volunteers consumed a beverage containing identical amounts of either fructose or glucose (75 grams). The two drinks were given in random order to all participants during testing sessions spaced eight months apart.
Your hypothalamus helps regulate hunger-related signals involving a number of hormones, including insulin, leptin, and ghrelin. The scans revealed that when drinking glucose, within 15 minutes the activity in the area of the brain involved with reward and desire for food was suppressed, which leads to a feeling of fullness or satiety. According to co-author Dr. Robert Sherwin:4
“With fructose, we don’t see those changes. As a result, the desire to eat continues — it isn’t turned off.”
In fact, fructose not only did not suppress hypothalamic activity, it actually caused a small spike instead. Furthermore, glucose boosted the links between the hypothalamus, thalamus, and striatum, while fructose strengthened the connectivity between the hypothalamus and thalamus, but not the striatum. This is important, as the striatum also deactivates once your body senses it has eaten enough… According to the authors:
“These findings suggest that ingestion of glucose, but not fructose, initiates a coordinated response between the homeostatic-striatal network that regulates feeding behavior.”
What all this means in everyday terms is that when you consume fructose, you may actually be “programming” your body to consume more calories, as fructose fails to trigger that feeling of fullness, and may even trigger continued hunger pangs. Dr. Jonathan Purnell, an endocrinologist at Oregon Health & Science University, told Yahoo! Health:
“It implies that fructose, at least with regards to promoting food intake and weight gain, is a bad actor compared to glucose.”
How Your Body Metabolizes Fructose Versus Glucose
Part of what makes fructose so unhealthy is that it is metabolized by your liver to fat in far more rapidly than any other sugar. The entire burden of metabolizing fructose falls on your liver, and it promotes visceral fat.5 This is the type of fat that collects around your organs and in your abdominal region and is associated with a greater risk of heart disease.
Without getting into the complex biochemistry of carbohydrate metabolism, it is important to understand how your body processes fructose versus glucose. Dr. Robert Lustig, Professor of Pediatrics in the Division of Endocrinology at the University of California, has been a pioneer in decoding sugar metabolism. His work has highlighted some major differences in how different sugars are broken down and used. Here’s a summary of the main points:
- After eating fructose, 100 percent of the metabolic burden rests on your liver. With glucose, your liver has to break down only 20 percent. The metabolism of fructose by your liver creates a long list of waste products and toxins, including a large amount of uric acid, which drives up blood pressure and causes gout.
- Every cell in your body, including your brain, utilizes glucose. Therefore, much of it is “burned up” immediately after you consume it. By contrast, fructose is turned into free fatty acids (FFAs), VLDL (the damaging form of cholesterol), and triglycerides, which get stored as fat.
- The fatty acids created during fructose metabolism accumulate as fat droplets in your liver and skeletal muscle tissues, causing insulin resistance and non-alcoholic fatty liver disease (NAFLD).6 Insulin resistance progresses to metabolic syndrome and type II diabetes.
- Fructose is the most lipophilic carbohydrate. In other words, fructose converts to glycerol 3 phosphate (g-3-p), which is directly used to turn FFAs into triglycerides. The more g-3-p you have, the more fat you store. Glucose does not do this.
- When you eat 120 calories of glucose, less than one calorie is stored as fat. 120 calories of fructose results in 40 calories being stored as fat.
- Glucose suppresses your hunger hormone ghrelin and stimulates leptin, which suppresses your appetite. Fructose has no effect on ghrelin and interferes with your brain’s communication with leptin, resulting in overeating.