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Brain Hormones, Body Weight, and Physical Activity: Can Rewiring the Brain Lead to Lasting Weight Loss?

Mar 4, 2011
 

Sheri_Colberg

By Sheri Colberg, PhD

 

For decades, people blamed excess body fat on a lack of willpower, evidenced by the fact that 90-95 percent of dieters regain all the weight they lose. More recently, hormones like leptin that are released from fat cells have taken more of the rap, along with the inheritance of "bad" genes, increased food intake, and decreased energy expenditure.

None of these can fully explain the worldwide expansion of our collective waistline, though, or our apparent powerlessness to sustain positive changes in lifestyle despite the health benefits of doing so. What we’re finally starting to understand is that weight gain and obesity are actually related to physical alterations that impair the brain’s ability to allow sustained behavioral changes. Altered brain circuitry and function, i.e., the formation of neural circuits in the brain involved in energy homeostasis, underlie weight gain and weight regain. Once established, this "metabolic imprinting" overrides willpower and drives unhealthy behaviors.  

Obese individuals apparently have fewer brain dopamine receptors, a critical finding since dopamine modulates motivation and reward circuits. This deficiency likely perpetuates pathological eating as a means to compensate for decreased activation of these neural, pleasure-seeking circuits in the brain. In fact, studies done in animals have shown that sugar — which releases dopamine in the brain — is likely as addictive as heroin, making withdrawal from sugar mentally and often physically painful. Per capita sugar intake among Americans has never been higher despite our obsession with diets and dieting. Each time the synaptic connections link, intake of sugar (or other behavior) becomes more strongly imprinted. Normally, connections stabilize and dopamine levels drop off over time, but with addictions, dopamine floods the system with each use, reinforcing the memory and pushing other stimuli into the background. Addicts don’t make bad choices as much as they fail to inhibit behavior that has become reflexive. If the brain is continually subjected to an overload of dopamine, the number of receptors will dwindle over time and more is needed to get the same effect. 

What is causing this brain dysfunction that is so pervasive today? A poor diet is likely involved since a brain lacking essential nutrients cannot function optimally. For example, a deficiency of omega-3 fats in the diet negatively impacts brain architecture and chemistry, given that these fatty acids support synaptic plasticity and positively affect the expression of several molecules related to learning and memory. Surprisingly, mental stress itself apparently causes deleterious changes in the brain, such as decreased activity in certain areas (e.g., amygdala, prefrontal cortex, and dentate gyrus) and smaller hippocampal volumes (a region associated with cognitive and metabolic regulation). When daily life stressors prevent new neuronal connections from forming in the brain — as evidence now suggests they can — the result is structural changes in the brain that often lead to overeating and weight gain, as well as cravings, addictions, depression, and more. In fact, it is likely that people who achieve and maintain weight loss long-term likely have "rewired" their brains for easier weight management.  

Emerging research on brain neuroplasticity proves that the release of neurotransmitters can be altered in response to both positive and negative stimuli. In one study, use of a dopamine reuptake inhibitor to overstimulate the production of dopamine in the brain led to down-regulation of the dopaminergic system, decreased dopamine synthesis, and rebound gains in body weight. Conversely, chronic caloric restriction stimulates the production of new neurons in the brain and release of brain-derived neurotrophic factor (a well-established regulator of synaptic plasticity), both of which modulate responses to food intake; and in humans, a mutation in a BDNF receptor that prevents its binding has been linked to obesity and impairments in learning and memory.  

What can be done to overcome such imprinting on the brain? It almost always comes back to using exercise as medicine. All physical activity modulates synaptic plasticity in the dentate gyrus, the part of the brain critical for controlling stress and depression and forming memories, and may lead to alternate, positive brain adaptations. Stress ties in with addiction in that withdrawal puts the body in survival mode. Exercise is one way to rebalance the system caused by withdrawal because being physically active causes the release not only of endorphins, but also of endocannabinoids, a class of neurotransmitters that dull pain. Marijuana, exercise and chocolate all activate the same receptors in the brain, and two endocannabinoids are produced during exercise. 

In summary, the brain is in a continual state of flux and can be rewired with small, but targeted, changes in food and nutrient intake, physical activity levels, and daily stress management. A focus on brain rewiring should replace "willpower," detailed dietary prescriptions, and other tired and unsuccessful methods as the means to lasting weight loss!

Sign up for the newly-launched DIABETES "Fit Brain, Fit Body!" fitness/lifestyle programs or for 5 free Healthy Living Reports at www.lifelongexercise.com, and access more articles and information at www.shericolberg.com. If you need tips for getting safely started on an exercise program, check out The 7 Step Diabetes Fitness Plan. For people with any Type of diabetes who are already more active, consult the Diabetic Athlete’s Handbook.

Click here for a full list of all of Sheri Colberg’s articles on fitness and diabetes.

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