Obesity levels are at all-time highs in the United States and also in places like Mexico, an ominous development for a world awash in calories.
Gradually, scientists are making incremental gains in understanding how brain hormones are related to dysfunctional appetite. The identification of hunger-regulating hormones like leptin and ghrelin are expanding the science of expanding waistlines.
Yet hunger and overeating are not simple functions of body chemistry. They involve behavior, genes, attitudes, upbringing, socialization, emotions and environmental stimuli as well.
Intense life changes can wreak havoc with our desire for food. The bereaved may lose any interest in eating, while the anxious may overeat habitually. Being around certain sights and smells triggers craving.
Healthy and unhealthy appetites involve a number of amazingly intricate bodily signaling systems that are the focus of research in neuroscience, psychology and medicine.
"Binge Eating Disorder" may be included in the 2013 publication of the Diagnostic and Statistical Manual of Mental Disorders. A committee of specialists is reviewing studies to determine whether the Fifth Edition of the rulebook that doctors and other clinicians use to diagnose psychological, emotional and behavioral conditions should have a new entry to reflect this problem.
Overeating is not just about physiology, it is also a way of feeling and behaving
Many people struggle with overeating. Body image issues influence people's sense of worth and personal dignity. There is a great popular interest in understanding why it can be so difficult to get this aspect of our lives right. Scientists and doctors try to educate the public about the state of the current science, and about what is known.
Modern scientific medicine has developed a way of thinking about disease and health that is holistic, inclusive, and integrative. There is a growing recognition that in the case of overeating, the list of causes are long, including attitudes about food coming from one's childhood and upbringing, levels of energy expenditures, genes and hormones that regulate metabolism, neural networks in the brain activated when food is smelled, and so forth.
Rather than emphasize any one cause, many scientists look at overeating in terms of a network of interacting systems affecting and affected by physiology, thinking, emotions, feelings, and behavior.
This counters a historical tendency among hunger scientists to try to isolate a few particular hormones and signaling systems as the cause of overeating. This approach of reducing the complex to the simple has an amazing track record in the history of science, responsible for much of the modern world's technical achievements. Scientific medicine attempts to understand illness and disease using this powerful "reductionistic" approach, which has produced countless innovations and therapies.
Yet some systems in nature defy an overly mechanical understanding. The human body is not a car with faulty parts that can be identified as the cause of performance failures.
Hunger can be understood as a bio-psycho-social product of body chemistry, psychological states and environmental context. Overeating involves a person's experience of craving and not being sated as much as the physiological signaling of brain chemicals like dopamine or hormones such as ghrelin and leptin. Overeating is not just a system for science to investigate, it is a feeling involving thoughts and emotions and attitudes, as well as a behavior.
Overeating involves disordered chemical signaling systems in the brain and body
There does appear to be a fantastically intricate series of feedback loops and chemical signaling occurring when people get hungry and then eat but are not sated. Feeling "full" or satisfied is actually a complicated business where glucose (blood sugar) levels, brain chemicals such as dopamine, and a suite of hormones produce a network of changes that register in the mind as the feeling of wanting more food, or not.
Blood glucose levels are regulated by insulin, but some people have a disorder in which the pancreas fails to produce sufficient insulin (Type 1 diabetes). Or, the cells may not take up the blood insulin correctly (Type 2 diabetes).
Failure to metabolize blood sugar properly can influence the formation of adipose tissue (fat). The "metabolic syndrome" of disordered levels of blood sugar and hormones secreted by fat contribute to a person who has eaten plenty to still have cravings or not to feel satisfied.
Fat cells secrete a protein known as leptin that acts as a signaling molecule. In healthy people, this hormone acts to inhibit appetite. One of the causes of obesity is from a failure to produce the right amounts of leptin, but sometimes the problem is more a failure to respond to proper leptin levels.
In the healthy, leptin works in concert with another hormone named ghrelin, which is secreted as a person becomes hungry. After eating, ghrelin levels decline in a person with an appetite, metabolism, and levels of fat tissue that are regulated normally.
Evidently it does not take much to knock these signaling systems out of balance. Obesity, diabetes and overeating disorders are at record levels.
Stress, problems with work, romance and family life, the experience of loss and grieving, as well as aging change our metabolisms and leave us vulnerable to craving more than we need. Humans did not evolve in environments with triple bacon cheeseburgers and Super Big Gulps easily available, and the presence of such energy-intense, calorie-rich stimuli in our modern settings triggers our minds to crave what very few of us need.
Treatments for overeating and binge-eating disorder
Many people coping with eating disorders may alternate between periods of fad diets and binging, or intermittently exercising and then being sedentary. Over time, such sporadic efforts can easily lead to more weight gain. There are other options available, however.
There is some evidence that the drug topiramate, also known for it's anticonvulsant properties, can work as a treatment for overeating and binge-eating disorders. It's mechanism of action is to dilate blood vessels and reduce activity levels of central nervous system nerve cells. Some people seem to be able to manage their unhealthy cravings for food better after this substance is administered.
Denise Wilfley, PhD, is quoted in Psychiatry Online as reporting that "ample research has demonstrated that cognitive-behavioral therapy and interpersonal therapy can counter binge eating and lead to long-term weight loss", though the benefits are modest.
Empowered consumers and patients should not expect topiramate, a talk therapy, counseling or other potential remedies to be a "magic bullet" that cures the desire to binge eat. These therapies will typically deliver marginal improvements for most, though some may benefit more. A cost-benefit analysis is appropriate before trying any potential remedy.
There is a complex relationship between the experience of hunger and it's physiological basis. Science is still establishing some of the core principles that govern how genes, upbringing, diet, stress, attitudes, choices, brain hormones, blood sugar and environmental variables interact to affect the urge to keep eating.
There are therapeutic options available for those who poorly manage the urge to overeat. Medication and/or talk-therapies may provide benefits, though individuals coping with the urge to binge eat should expect modest benefits in most cases.
People managing this problem have considerably more resources than even ten years ago. While basic science moves forward slowly, there is ever more information available on how to recognize, understand and manage this problem than ever. The neuroscience of perceiving internal body states is proceeding incrementally. The genes that regulate metabolic chemical pathways and the networks of signaling molecules that activate and deactivate those genes are being discovered. Fat may be eventually understood as something like an organ that secretes molecules to regulate it's own state.
For now, hunger and the feeling of being satisfied are still mysterious from the point of view of reductionistic science. We may anticipate all the basic research paying off in the not too distant future, perhaps helping empower us to understand why we want what we do not need.