Scientists from the University of Colorado have found a link between fructose and Alzheimer's disease. They say the sugar shuts down parts of the brain that deal with memory and attention to time and causes people to focus on finding food. In ancient times fructose was rare and the effects were reversible. Today fructose is plentiful and its effects on the brain are irreversible.
When threatened with the possibility of starvation, early humans developed a survival response that sent them foraging for food. Yet foraging is effective only if metabolism is inhibited in various parts of the brain. Foraging requires focus, rapid assessment, impulsivity, exploratory behavior and risk taking. It is enhanced by blocking whatever gets in the way, like recent memories and attention to time. Fructose, a kind of sugar, helps damp down these centers, allowing more focus on food gathering.
In fact, the researchers found the entire foraging response was set in motion by the metabolism of fructose whether it was eaten or produced in the body. Metabolizing fructose and its byproduct, intracellular uric acid, was critical to the survival of both humans and animals.
The researchers noted that fructose reduces blood flow to the brain's cerebral cortex involved in self-control, as well as the hippocampus and thalamus. Meanwhile, blood flow increased around the visual cortex associated with food reward. All of this stimulated the foraging response.
"We believe that initially the fructose-dependent reduction in cerebral metabolism in these regions was reversible and meant to be beneficial," [the study's lead author Richard Johnson, MD, a professor at the University of Colorado School of Medicine] said. "But chronic and persistent reduction in cerebral metabolism driven by recurrent fructose metabolism leads to progressive brain atrophy and neuron loss with all of the features of AD."
Johnson said this could explain why some AD patients wander off. They are actually foraging.