I am a bit of an ice cream addict. I have had brief periods of abstinence but usually its only a matter of time before the Edy’s creeps its way back into my freezer. Falling off the wagon doesn’t happen quickly, but rather a little bit here and a little bit there. I will usually go through periods where my will power is fortified but usually it’s only a matter of time before I begin to have symptoms of withdrawal on those lonely nights when there was nothing in the freezer. My wife, always concerned that I will suffer from lack of what to eat, is more than happy to enable me and will gladly keep the fridge stocked with half gallons of my favorite flavors. . On my most recent breakdown I was a daily user. As my waistline began to expand and soften, I realized that something had to be done. Unfortunately, cutting down was more difficult than I thought it would be. I tried skipping a day or two. I tried using a smaller dish. No matter what, I couldn’t resist. I finally recognized that having it in the house was too great a temptation. My wife and I sat down and after a long intervention agreed that we must go cold turkey. And by ‘we’ I meant ‘me’.
While this all may be a tongue in cheek, overly melodramatic representation, I wanted to bring a personal anecdote to segue into a very important topic in the area of weight loss. Have you ever felt like you were addicted to certain foods? Ever felt like you couldn’t get off of sugar? Ever felt like the potato chips were a drug? Or the french fries? Or the cheesecake? You may not be far off from reality.
It turns out that the same part of the brain that is stimulated by cocaine, tobacco, and alcohol is also stimulated by sugar, fat, and salt. Understanding the mechanisms of how this works will be of great help in conquering the cravings that lead to weight gain.
What follows is a bit technical, but the message is important so bear with me. There is an important part of the brain called the “dopaminergic reward pathway”. If that’s too much of a mouthful, just call it the reward pathway. This pathway is responsible for making you feel pleasure in response to a variety of stimuli (e.g. sex, drugs, and rock and roll). Stimulating this part of the brain will:
1. Increase your sense of pleasure and well being.
2. Lead to a desire to repeat the stimulating behaviors even if there are other things distracting you.
3. Lead to strong positive memories.
4. Lead to enhanced attentiveness, which will allow you to better learn and store memories of your environment.
Addictive drugs ‘hijack’ this part of the brain leading to intense pleasure in response to the drug.
How does the reward system work? All nerves in the brain create extremely complicated networks. Connected nerves don’t actually directly touch one another. There is a sliver of space between them called a synapse. The first nerve is called the pre-synaptic neuron. I’ll call this nerve one. It will release chemicals (neurotransmitters) that are sensed by receptors on the second nerve wich is called the post-synaptic neuron. I’ll call this nerve two. This never then transmits the signal down the circuit. Nerve two is sensitive to the quantity of neurotransmitter it receives and will adjust the number of receptors it has in response to the strength of the signal. This is a crucial point to understand. If nerver two is hit with a large barrage of neurotransmitters, the signal in the will be too intense. In response to over stimulation, nerve two will compensate by decreasing the number of receptors for that neurotransmitter. So now you have a scenario where, if the number of neurotransmitters released into the synapse were to drop to their original levels, nerve two will not have as many receptors as it did originally. The end result will be a very diminished signal. These are the mechanisms behind tolerance, i.e. needing more of a substance for the same effect, and withdrawal.
Drugs create a high by stimulating an overload of the neurotransmitter dopamine into the synapse, which creates a super strong signal in nerve two. Over time, with repeated highs, nerve two adapts and decreases its dopamine receptors to tone down the signal back to normal.
The result is that the same dose of drug only maintains a normal signal, not a high. Then more drugs are needed to achieve the same high. This is referred to as “tolerance”. Tolerance’s evil twin is withdrawal. Withdrawal is the constellation of very uncomfortable and sometimes fatal biological responses that result upon removal of substance to which someone has been chronically exposed. Why this happens should be clear to us now. After long-term exposure, nerve two adapts to the stimulus by decreasing the number of receptors it has. When the drug is taken away, the synapse is left with a normal amount of neurotransmitter but a severe deficit in the number of receptors. This will lead to profoundly diminished stimulation. This leads to the physiological and psychological changes that characterize withdrawal.
So now you know how addictive drugs work. But what does this have to do with food and obesity? Stay tuned for part two of the series well we’ll connect drugs and food. It’s a cliffhanger!References: Wilson G. Eating disorders, obesity, and addiction. European Eating Disorders Review 2010;18:341-51. Davis C, Carter J. Compulsive overeating as an addiction disorder: A review of theory and evidence. Appetite 2009;53:1-8. Yanovski S. Sugar and fat: cravings and aversions. Journal of Nutrition 2003;133. Avena N, Rada P, Hoebel B. Evidence fo sugar addiction: Behavioral and neurochemical effects of intermittent, excessive sugar intake. Neuroscience and Biobehavioral Reviews 2008;32.