Moreover, the tendency to eat in response to negative emotions is found to be particularly prevalent among the obese. Emotional states induce fight-or-flight responses, and in these states blood goes to areas other than the brain to prepare surges of energy to fight or flee. This in turns leaves the area in the brain responsible for self-regulation deficient in blood and oxygen supply.
Even positive emotions can lead people to overeat. “When people are happy and binge it is because they have associated celebrating with eating, because of having had experiences in childhood where they go out for ice cream or other fun food to celebrate an occasion,” says Carole Lieberman, assistant clinical professor of psychiatry, University of California, Los Angeles. Over time, the neuronal paths are strengthened by sensory cues.
A study published in Nature Neuroscience reported that levels of ghrelin increase during stress, and this could explain why stress prompts us to eat when we are not hungry. “Ghrelin [produced by the stomach] rises in response to stress and sleep deprivation — which tells the brain ‘I’m hungry,’ ” says Shawn Talbott, nutritional biochemist and author of “The Cortisol Connection: Why Stress Makes You Fat and Ruins Your Health.” And cortisol (produced by adrenal glands) also rises in response to stress, which tells the brain to refuel. “The end result is that the brain gets two signals that are slightly different, but result in us eating more.”
When it comes to understanding overeating, neurobiology has just detected the tip of the iceberg. But insights are pouring in every day, and in the future we may be able to devise possible ways to curb the monster.
Hunger or Craving?
It’s tricky to distinguish cravings from real hunger. “There is not too much real difference metabolically; cravings do create some of the same metabolic hunger signals as real hunger,” says Susan Roberts, professor at the Friedman School of Nutrition Science and Policy at Tufts University. “If your desire to eat is only for this food, and another healthier food is not worth eating instead, that is a good sign this is a craving rather than pure hunger,” Roberts says.
Real hunger is always in response to the body’s need for nutrients, and cravings — or, as some call it, “psychological hunger” — is almost always in response to sensory cues, such as
the sight or smell of food, or emotions like stress.
Real hunger will increase gradually: You’re a little hungry one moment, 10 minutes later you’re quite hungry, and after half an hour you know you must rush to the cafeteria. Cravings are just instantaneous. You could be reading relationship advice on a website, just when an ad with crepes filled with cheese and green beans and topped with a chive-cream sauce suddenly crops up and you’re hungry.
When you eat in response to real hunger, it is always followed by a feeling of satiety. You
can go on binging as a result of a craving and not ever feel full.
Overeating and Eating Disorders
Overeating is a prominent characteristic of such eating disorders as bulimia nervosa and binge eating, but it’s true that normal people will give in to temptation at times. But if your overeating sessions are quite frequent, maybe it’s not normal.
“When people overeat on more than an occasional basis, it is reflective of emotional problems, some more serious than others,” Carole Lieberman says. There might be underlying psychological issues that one may be trying to deal with. “With overeating and eating disorders, people are trying to fill up an emptiness inside of them that was created in childhood from lack of love and attention.”
Brain imaging researchers have shown that reward circuitry is often not working properly in the obese. One research found that leptin pathways did not work normally in overeating individuals as compared to normal “non-overeating” individuals.
It’s hard to say if the circuitry was tweaked before overeating started, or if the overeating spoiled it. It’s probably a bit of both — one big vicious cycle.
This article is updated from its initial publication in Brain World Magazine’s Fall 2010 issue.
More From Brain World
- An Appetite for Wonder: How Eating Better Boosts Your Brain
- Eating for Brainpower: How Eating Better Can Fight Memory Loss
- Know Your Brain: The Gustatory Cortex — How Taste Works
- Night Eating Syndrome: Causes and Concerns
- Thanksgiving: What You Ate and How You Did It!
- Why Do We Crave? The Science Behind Food Cravings
