Fructose Metabolism By The Brain Increases Food Intake And Obesity, Review Suggests

ScienceDaily (Mar. 26, 2009) — M. Daniel Lane and colleagues at Johns Hopkins have built on the suggested link between the consumption of fructose and increased food intake, which may contribute to a high incidence of obesity, and Type 2 diabetes.

Over the past four decades life-styles have gravitated toward the excessive consumption of 'high energy' foods and sedentary behavior that has resulted in a high incidence of obesity and its pathological consequences. This scenario has led to the increased occurrence of insulin resistance and Type 2 diabetes. At present, approximately thirty percent of adult Americans can be classified as obese. Moreover, these changes now extend into the younger age group.

M. Daniel Lane and co-workers at The Johns Hopkins University School of Medicine in Baltimore have now pulled together work, largely in their laboratory (many papers beginning in 2000), dealing with the role of malonyl-CoA in the signaling system in the brain (specifically the hypothalamus) that has inputs into the higher brain centers that determine feeding behavior, most notably appetite. Two papers in the journal PNAS in 2007 and 2008 showed that glucose and fructose act quite differently in the brain (hypothalamus) - glucose decreasing food intake and fructose increasing food intake. Both of these sugars signal in the brain through the malonyl-CoA signaling pathway and have inverse effects on food intake.

Lane commented: "We feel that these findings may have particular relevance to the massive increase in the use of high fructose sweeteners (both high fructose corn syrup and table sugar) in virtually all sweetened foods, most notably soft drinks. The per capita consumption of these sweeteners in the USA is about 145 lbs/year and is probably much higher in teenagers/youth that have a high level of consumption of soft drinks. There is a large literature now that correlates, but does not prove that a culprit in the rise of teenage obesity may be fructose."

The fact that fructose metabolism by the brain increases food intake and obesity risk raises health concerns in view of the large and increasing per capita consumption of high fructose sweeteners, especially by youth.
Journal Reference:

1.Lane et al. Effect of glucose and fructose on food intake via malonyl-CoA signaling in the brain. Biochemical and Biophysical Research Communications, 2009; DOI: 10.1016/j.bbrc.2009.02.145

What Makes Fructose Fattening? Some Answers Found in the Brain
ScienceDaily (Feb. 9, 2011) — The dietary concerns of too much fructose is well documented. High-fructose corn syrup has become the sweetener most commonly added to processed foods. Many dietary experts believe this increase directly correlates to the nation's growing obesity epidemic. Now, new research at Oregon Health & Science University demonstrates that the brain -- which serves as a master control for body weight -- reacts differently to fructose compared with another common sweetener, glucose.
The research is published in the online edition of the journal Diabetes, Obesity and Metabolism and will appear in the March print edition.

"We know from animal models that the brain responds uniquely to different nutrients and that these responses can determine how much they eat," said Jonathan Purnell, M.D., an associate professor of medicine (endocrinology, diabetes and clinical nutrition) in the OHSU School of Medicine.

"With newer technologies such as functional MRI, we can examine how brain activity in humans reacts when exposed to, say, carbohydrates or fats. What we've found in this case is that the brain's response to fructose is very different to the response to glucose, which is less likely to promote weight gain."

Functional MRI allows researchers to watch brain activity in real time. To conduct the research, nine normal-weight human study subjects were imaged as they received an infusion of fructose, glucose or a saline solution. When the resulting brain scans from these three groups were compared, the scientists observed distinct differences.

Brain activity in the hypothalamus, one brain area involved in regulating food intake, was not affected by either fructose or glucose. However, activity in the cortical brain control areas showed the opposite response during infusions of the sugars. Activity in these areas was inhibited when fructose was given but activated during glucose infusion.

This is an important finding because these control brain areas included sites that are thought to be important in determining how we respond to food taste, smells, and pictures, which the American public is bombarded with daily.

"This study provides evidence in humans that fructose and glucose elicits opposite responses in the brain. It supports the animal research that shows similar findings and links fructose with obesity," added Purnell.

"For consumers, our findings support current recommendations that people be conscious of sweeteners added to their drinks and meals and not overindulge on high-fructose, processed foods."

Journal Reference:

1.J. Q. Purnell, B. A. Klopfenstein, A. A. Stevens, P. J. Havel, S. H. Adams, T. N. Dunn, C. Krisky, W. D. Rooney. Brain functional magnetic resonance imaging response to glucose and fructose infusions in humans. Diabetes, Obesity and Metabolism, 2011; 13 (3): 229 DOI: 10.1111/j.1463-1326.2010.01340.x