An evolutionary human foraging instinct, which was fueled by fructose production in the brain, may give possible clues to the development and possible treatment of Alzheimer’s Disease (AD), according to researchers at the University of Colorado Anschutz Medical Campus.
The study which was published recently in The American Journal of Clinical Nutrition, offers a new way of looking at the fatal disease characterized by abnormal accumulation of certain proteins in brain. These protein stores( tau and amyloid beta proteins) tend to slowly erode memory and cognition.
Does fructose cause Alzheimer’s Disease?
“We make the case that Alzheimer’s Disease is driven by diet,” said the study’s lead author Richard Johnson, MD, professor at the University of Colorado School of Medicine specializing in renal disease and hypertension.
Johnson and his team suggest that Alzheimer’s disease is basically a harmful adaptation of an evolutionary survival pathway. The said pathway was used in animals and our distant ancestors during the times of food scarcity.
“A basic tenet of life is of course to assure enough food, water and oxygen for survival,” the study said. “Much research has focused on the acute survival responses to hypoxia and starvation. However, nature has developed a smart way to protect animals before the crisis actually occurs.”
When threatened with the possibility of starvation, early humans developed a survival response which immediately sent them foraging for food. However, foraging is only effective if metabolism is inhibited in various parts of the brain. Foraging requires keen focus, rapid assessment, impulsivity, exploratory behavior and risk taking. It is enhanced by blocking whatever gets in the way, like recent memories, distractions and attention to time. The fruit sugar fructose, helps to damp down these centers, allowing more focus on food gathering.
In fact, the researchers found the entire foraging response was set in motion by fructose metabolism. This is equally functional whether fructose is eaten or produced in body. Metabolizing fructose and its byproduct, intracellular uric acid, was critical to the survival of both humans and animals in these conditions.
The researchers noted that fructose reduces blood flow to the brain’s cerebral cortex which is involved in self-control, as well as the hippocampus and thalamus. Meanwhile, the blood flow increases around the visual cortex associated with food reward. All of this together stimulated the foraging response.
“We believe that initially the fructose initiated reduction in cerebral metabolism in these regions was reversible and meant to be beneficial,” Johnson said. “But chronic and persistent reduction in cerebral metabolism driven by the recurrent fructose metabolism leads to progressive brain atrophy and neuron loss with all of the features of AD.”
Johnson suspects the survival response or the survival switch that helped ancient humans get through periods of scarcity, is now still stuck in the `on’ position in a time of relative food abundance & scarcity is rarest of the rare case. This leads to the overeating of high fat, high sugar and high salt food prompting excess fructose production.
Fructose produced in the brain has the tendency to lead to inflammation and ultimately Alzheimer’s disease, the study said. Animals given fructose show memory lapses, a loss in ability to navigate a maze and inflammation of neurons.
“A study found that laboratory rats long kept on fructose develop tau & amyloid beta proteins in brain. These are the same proteins which are seen in Alzheimer’s disease,” Johnson said. The patients of Alzheimer’s disease have high fructose levels in their brain.
Johnson suspects that the tendency of some AD patients to wander off could possibly be a vestige of ancient foraging response.
The study said more research is highly needed on the role of fructose and uric acid metabolism in AD.
“We suggest that both dietary and pharmacologic trials to reduce fructose exposure or block fructose metabolism should be performed. This can help to determine if this could be a potential benefit in prevention, management or treatment of this disease,” Johnson said.
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