Hunger is a powerful motivator — a signal from our body that we need sustenance to survive.

So how is it that people with anorexia and bulimia nervosa can ignore those hunger pains?

The answer is in their brains, according to new research.

Scientists at the University of Colorado Anschutz Medical Campus recently discovered that normal patterns of appetite stimulation in the brain are reversed in those with eating disorders.

Rather than the hypothalamus, a brain region that regulates appetite, driving our motivation to eat, signals from other parts of the brain can override the hypothalamus in people with eating disorders.

We are born with a propensity to like sweets, but this gets overridden in the brains of people with anorexia. (Photo courtesy FreeImages.com/Ronny Satzke)

We are born with a propensity to like sweets, but this gets overridden in the brains of people with anorexia. (Photo courtesy FreeImages.com/Ronny Satzke)

“In the clinical world we call this mind over matter,” said Guido Frank, MD, lead author of the study and associate professor of psychiatry and neuroscience at the University of Colorado School of Medicine. “Now we have physiological evidence to back up that idea.”

An expert on eating disorders, Frank set out to discover the hierarchies of the brain that govern appetite and food intake. He wanted to understand the neurological reasons behind why some people eat when they were hungry and others don’t.

Using brain scans, the researchers examined how 26 healthy women and 26 women with anorexia or bulimia nervosa reacted to tasting a sugary drink.

They discovered that those with eating disorders had widespread alterations in the structure of brain pathways governing taste-reward and appetite regulation. The alterations were found in the white matter, which coordinates communication between different parts of the brain.

There were also major differences in the role the hypothalamus played in each group, according to the scientists.

Among those without an eating disorder, brain regions that drive eating took their cues from the hypothalamus.

But in the women with an eating disorder, the pathways to the hypothalamus were significantly weaker and the direction of information went in the opposite direction.

As a result, their brain may be able to override the hypothalamus and fight off the signals to eat.

“The appetite region of the brain should drive you off your chair to get something to eat,” said Frank. “But in patients with anorexia or bulimia nervosa that is not the case.”

While we are programmed to like sweet tastes from birth, that programming gets rewritten in those with eating disorders who begin to avoid sweets out of the fear of gaining weight.

According to the study, humans are programmed at birth to like sweet tastes. But those with eating disorders begin to avoid eating

“One could see such avoidance as a form of learned behavior and, more specifically, operant conditioning, with weight gain as the feared `punishment,”’ the researchers said.

This behavior eventually alters the brain circuits governing appetite and food intake, according to the researchers.

The scientists suggest that being afraid to eat certain foods could impact the taste-reward processing mechanisms in the brain, which then reduces the influence of the hypothalamus. The end result: The ability to ignore hunger pains even as a patient is starving themselves to death.

“We now understand better on the biological level how those with an eating disorder may be able to override the drive to eat,” said Frank. “Next we need to begin looking at children to see when all of this starts to come into play.”