Junk food desensitizes the reward centers of the brain
Posted Apr 26 2010 7:43am
Dr. Fuhrman’s concept of toxic hunger states that the unhealthy foods at the center of the standard American diet are addictive. Like all other drugs, addictive substances involve both pleasure and pain. By definition, an addictive substance is toxic and therefore produces uncomfortable withdrawal symptoms when the body attempts to detoxify the waste products left behind. When we feel this discomfort, eating relieves the symptoms – when the body begins digestion it stops detoxification. So we mistakenly believe that these feelings are hunger, and we are then almost forced to eat too frequently in order to lessen the withdrawal symptoms from our low nutrient diets. This leads us to progressively eat more and more of the addictive food, and makes becoming overweight inevitable. Dr. Fuhrman further asserts that foods, lacking sufficient micronutrients, lead to a buildup of oxidative stress, free radicals and other inflammatory substances that are mobilized during catabolism causing distressful symptoms curtailed by overeating.
Scientists studying addiction are now confirming Dr. Fuhrman’s assertion that unhealthy food is indeed addictive. Scientists following up their preliminary data on the subject
have published a new study in Nature Neuroscience showing that drug addiction and compulsive eating have the same effects on the brain – they desensitize brain reward circuits.1 In the brain, eating is motivated by pleasure and reward.
The researchers studied three groups of rats – all three groups were allowed access to their standard (healthy) chow at all times. In addition, rats had either no access, restricted access (1 hour per day), or extended access (18-23 hours per day) to palatable energy dense food for 40 days. This palatable energy dense food consisted of nutrient deficient processed foods readily available to humans – things like sausage, bacon, and cheesecake.2
Extended access rats gained weight rapidly, and were significantly heavier than chow only or restricted access rats. Their calorie intake was almost double that of the chow only rats. Even the restricted access rats developed binge-like eating behaviors, getting about 66% of their daily calories during their 1 hour of access to the unhealthy food.
The scientists used electrodes to measure the rats’ reward thresholds. The reward threshold is the minimum amount of stimulation that produces feelings of satisfaction. As the experiment continued, extended access rats had progressively higher reward thresholds. This means that their reward circuitry became less and less responsive, and a greater amount of unhealthy food was therefore required to satisfy their appetites. Even when the rats were taught to anticipate an electric shock, they kept eating, not even trying to avoid the shocks. This compulsive behavior in the face of negative consequences is a hallmark of addiction.
The scientists traced these effects to a decrease in levels of specific dopamine receptors in the striatum region of the brain. These exact neurobiological changes have been shown to occur in rats that are given extended access to heroin or cocaine. In fact, after access to the unhealthy food was no longer permitted, withdrawal (measured by continued elevation of the reward threshold) persisted in these rats for a full 14 days - rats in withdrawal from cocaine have been reported to experience withdrawal for only 48 hours. These results demonstrate how powerfully addictive – and powerfully toxic – unhealthy food is.
In the Western world, we have extended access to unhealthy food – nutrient-deficient processed food seems to be everywhere we turn. In such an environment, it is almost inevitable that we will become addicted, progressively gain weight, and suffer the health consequences. Only by removing the toxic, addictive foods from our diets and replacing them with health promoting foods can we break the cycle of toxic hunger and achieve excellent health.
1. Johnson PM, Kenny PJ. Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats. Nat Neurosci. 2010 Mar 28. [Epub ahead of print]