A new study found that fructose makes you hungrier because the simple sugar doesn’t trigger the brain’s receptors that signal fullness.
High fructose corn syrup has been singled out as a direct cause of obesity because the nation’s collective waistline exploded in lockstep with the use of HFCS in our food supply. Now, a new groundbreaking study shows that pure fructose turns down areas of your brain that help you feel full and satisfied.
Anything that turns down your body’s ability to feel satisfied increases the odds that you’ll gain weight.
High fructose corn syrup is a blend of glucose and fructose in roughly the same amounts. Table sugar is also a blend of fructose and sucrose in roughly equal amounts. Honey is also a blend of sucrose and fructose, but also has antioxidants and water. Fructose is the main sugar in fruit, but the major source of fructose in the US diet comes from HFCS and table sugar, not fruit. The major contributors of fructose in the US diet are sweetened beverages and baked goods.
All sweetened beverages and virtually all packaged baked goods and desserts contain fructose. Although fructose is a simple sugar, it’s digested more like a fat, which makes it metabolically different and more unhealthy than other simple sugars. Research has linked fructose to increased risk for heart disease, type 2 diabetes, fatty liver, overweight and obesity. Now, a new study shows that fructose behaves differently in the brain compared to glucose, the other main simple sugar in the diet.
Researchers from Yale University School of Medicine evaluated the differences between glucose and fructose ingestion in 20 normal weight adults. The study, published in the Journal of the American Medical Association, compared whole brain MRI images of subjects before and after consuming 75-gram solutions of pure glucose or fructose as a liquid on two separate occasions.
How Fructose Makes You Hungrier
The results showed that glucose affects the brain in ways that helps to suppress hunger and appetite while fructose has the opposite effect and may drive us to consume more calories than we need. When subjects received the glucose solution, areas of the brain that control fullness and turn down cravings were triggered. In addition, glucose also caused a significant decrease in post-drink fullness and satiety whereas fructose did not. Fructose was found to activate areas of the brain that increase desire and cravings for food.
As dietitians, we always recommend to “eat your calories, don’t drink them,” because so many studies show that liquid calories are not as satisfying as solids. This study provides some insight into why beverages lack the ability to trigger satiety. Since high fructose corn syrup is most often used in beverages—from sodas and energy drinks to flavored teas and waters—maybe the fructose in these products is the real problem? However, pure fructose is generally never used alone in foods and beverages as a sweetener; it’s almost always used in conjunction with other sugars, so the implications of this single study are unclear.
What should you do? While some experts are advising that consumer avoid eating and drinking products that contain added fructose, corn syrup or high fructose corn syrup, I suggest the same recommendations that I’ve been giving for several years: Limit all added sugars and sweeteners to levels recommended by the American Heart Association (100 calories for women; 150 for men). In addition, start reading food labels and avoiding products that list sugars as one of the main ingredients. Keep liquid calories to a minimum and save those calories for beverages that actually provide some nutrition to your diet, like 100% fruit juice of nonfat milk.