Food addiction
Dopamine is a neurotransmitter that plays a key role in addictive diseases. Among the various dopaminergic neurotransmission systems, the mesolimbic mescortical pathway is involved in motivation and reward behavior. It is now known that addictive substances/behaviors increase dopamine secretion, and when this stimulation is repeated, changes occur in the mesolimbic pathway, causing addictive behavior (Proc. Natl. Acad. Sci. 1988).
Food addiction has been discussed for decades since T. Randolph first mentioned it in 1956 (Q J Stud Alcohol 1956), but there has been little progress. It was only when obesity and binge eating were found to be related to dopamine signaling (Lancet. 2001) and activation of reward-related brain regions that it began to receive attention (Biol Psychiatry. 2009).
In fact, food addiction shows very similar symptoms to drug addiction, such as loss of control and inability to stop despite knowing negative consequences (Psychiat Ann. 2003). It also largely matches the diagnostic criteria for substance dependence in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) (Appetite 2011).
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| Food addiciton |
Addictive foods exist separately
In fact, addictive substances rarely exist in nature. Most addictive substances are processed. For example, opium is made by refining poppies. Natural foods include sweet foods (e.g., fruits) and foods containing fat (e.g., nuts), but it is difficult to find natural foods that contain a lot of both sugar and fat. However, in the modern food industry, there are highly processed foods that are artificially increased in sugar and fat to make them more delicious. These processed foods are very likely to cause addiction by stimulating the brain's reward area by being stimulatingly delicious or by rapidly increasing blood sugar levels.
In one study, rats fed a high-sugar, high-fat, energy-dense diet (containing bacon, sausage, cheesecake, sugar frosting, and chocolate) for a long period of time had a persistent increase in the threshold for the brain stimulation reward response (BSR), similar to heroin and cocaine. This means that the brain’s reward system was malfunctioning. This persisted much longer than opioids even after the diet was discontinued.
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| (a) Energy-dense foods raise the threshold of the brain's reward system like drugs, and (b) this effect lasts longer than drugs after food withdrawal. (Nat Neurosci. 2010) |
The researchers also found that eating delicious, high-fat foods decreased the expression level of D2R. This result is consistent with reports that drug addicts and obese people have very low D2R density (Benton & Young, 2016; Science. 2008).
Dopamine binds to dopamine receptors on the cell membrane and acts through intracellular signaling, and the dopamine D2 receptor (D2R) plays a central role in regulating dopaminergic neurotransmission. This means that when repeated consumption of delicious foods causes neural adaptation responses such as a decrease in D2R, reward deprivation occurs and addictive behaviors such as compulsive eating are induced. The general hedonic mechanism is the basis of obesity and drug addiction (Nat Neurosci 2010).
Reward hypersensitivity also occurs when you go on a starvation diet for a long time. The longer you starve, the stronger the pleasure circuit that recognizes food as pleasure develops, making it easier to engage in addictive behaviors such as overeating and binge eating. Many people experience rapid weight gain after taking a body profile. Moderation is necessary, but dieting that is too extreme affects the brain and inevitably leads to compulsive eating (overeating and binge eating).
Why You Want to Eat Pizza
Glycemic load (GL) is closely related to the activation of brain regions associated with addiction (Am J Clin Nutr 2013). That’s why processed foods, which are high in refined carbohydrates (sugar, white flour) and fat, and have fiber, protein, and water removed so that sugar and fat are absorbed quickly into the body, are generally considered to be foods that are prone to addiction. Pizza is one such example.
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| Ranking of most addictive foods. Pizza is number one. (PLOS ONE 2015) |
And there's one more scientific reason why you keep wanting to eat pizza. It's cheese, and pizza is a typical food that uses a lot of cheese.
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| I love pizza |
80% of milk protein is casein, and casein protein is concentrated during the cheese processing process, increasing its content by 7 to 10 times. Casein is broken down into various types of casomorphins through the digestive process, which act on the brain's reward system to make you feel good and cause addiction. This is called opioid activity, and these compounds are called opioids. Neal Barnard, an American vegetarian doctor, even claimed that dairy products, including cheese, are "dairy crack" (crack = a type of new drug). Casein is also found in human breast milk. Of course, the ratio is different from cow's milk. This makes me wonder why babies look happy when they drink milk.
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| I love cheese |
But there are other foods that contain opioids. Exorphins and gliadorphins (or gluteomorphins) that are produced by the digestion of wheat gluten, soymorphins from soybeans, rubiscolins from spinach, and orizatensin from rice. So, should we not eat all of these foods?
I don’t think so. I think cheese is addictive not because of casomorphins, but because it is a high-protein, high-fat, energy-dense food. Humans have been able to survive times of famine by craving energy-rich foods, and that’s how they evolved.
Rather than disparaging certain foods as "crack" or "junk food," I think we need to be thankful for all foods, even processed foods. The pleasure of eating is one of the important pleasures in life, so there's no need to give up the foods you like. However, just as overeating no matter how healthy a food is, you need to eat everything in moderation.