FAT FIX: Is food addiction predisposed or does overeating high-fat fare alter the brain? A mouse study sheds light on some of the dynamics that are also likely at work in the brains of humans.
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Like many people, rats are happy to gorge themselves on tasty, high-fat treats. Bacon, sausage, chocolate and even cheesecake quickly became favorites of laboratory rats that recently were given access to these human indulgences—so much so that the animals came to depend on high quantities to feel good, like drug users who need to up their intake to get high.
A new study, published online March 28 in Nature Neuroscience, describes these rats' indulgent tribulations, adding to research literature on the how excess food intake can trigger changes in the brain, alterations that seem to create a neurochemical dependency in the eater—or user. (Scientific American is part of Nature Publishing Group.) Preliminary findings from the work were presented at the Society for Neuroscience meeting in October 2009.
Like many pleasurable behaviors—including sex and drug use—eating can trigger the release of dopamine, a feel-good neurotransmitter in the brain. This internal chemical reward, in turn, increases the likelihood that the associated action will eventually become habitual through positive reinforcement conditioning. If activated by overeating, these neurochemical patterns can make the behavior tough to shake—a result seen in many human cases, notes Paul Kenny, an associate professor in the Department of Molecular Therapeutics at The Scripps Research Institute in Jupiter, Fla., and co-author of the new study. "Most people who are overweight would say, 'I would like to control my weight and my eating,' but they find it very hard to control their feeding behavior," he says.
Despite a growing body of research, it has been unclear whether extreme overeating was initiated by a chemical irregularity in the brain or if the behavior itself was changing the brain's biochemical makeup. The new research by Kenny and his colleague Paul Johnson, a graduate student, shows that both conditions are possible.
Bigger waists, higher thresholds
To see just how overeating and obesity alters the brain's reward circuitry, the researchers implanted stimulating electrodes in rats' brains to monitor their changing reward threshold levels. Some rats were given only one hour a day to feast on tasty, high-fat foodstuffs, whereas others had almost unlimited access (18 to 23 hours a day). All the rats, including a control group that was given no human food, had open access to water and standard, healthful lab rat chow.
Unsurprisingly, the rats with extended access to the high-fat foods ate little to none of their comparatively bland lab fare and quickly grew obese—consuming about twice the amount of calories as the control, chow-only group. The researchers also found that even the rats with limited access to the unhealthful food were doing their best to keep up. These subjects managed, on average, to consume 66 percent of their daily calories over the course of the single hour per day in which they could eat the junk food, developing a pattern of compulsive binge eating. Only the obese rats with extended access to the bad food, however, had sharply increasing thresholds for reward levels.
"This research by Kenny's group is a great contribution," says Nicole Avena, a visiting research associate at Princeton University's Department of Psychology who was not involved in the new study but has completed similar research on addiction and high-sugar diets. Many studies have drawn the connection between excessive food intake and addiction in both animal models and humans. A 2001 study in The Lancet observed a similar dearth of dopamine receptors in the brains of many obese people as in those hooked on cocaine or alcohol. The new research adds a more nuanced understanding of just how food can modify the brain—and shows that differences in the brain from the outset can predispose an individual for overeating.
Engineering an overeater
To start an addictive cycle, dopamine must be felt, and for that the brain must have ample dopamine receptors. In many substance abusers a low level of dopamine receptors, either from the outset or caused by the behavior, means they increasingly have to seek more dopamine-inducing substances to reach a level of neurochemical reward they can enjoy. After someone dependent on a substance stops using it, however, it often takes time for depleted dopamine receptors to return to baseline levels. For mice addicted to cocaine, it can take two days to regain normalized levels. The obese rats in the new study took two weeks to regain their baseline density of receptors.
To gauge just how much the quantity of dopamine receptors had affected the rats' eating behavior, Kenny and Johnson inserted a virus into the brains of a test group of the animals to knock out their striatal dopamine D2 receptors, which are known in humans to be at low levels in many substance abusers. They found that rather than gradually increasing rat brain reward thresholds and accompanying overeating behavior these rats almost immediately had higher thresholds and took to overeating immediately when given access to a high-fat diet. This connection, Kenny says, shows that for people who have lower levels of D2 receptors, "it could predispose you to developing this kind of habitual behavior."
Genetics likely play a role in an individual's likelihood of becoming obese—in both metabolic and neurochemical systems. In humans, for example, one genetic flag known as the TaqIA A1 allele has been linked to fewer D2 receptors as well as drug addiction and obesity. And in the rats there were "occasionally one or two animals per study that didn't overeat," Kenny says. He and his colleagues are currently investigating possible genetic underpinnings of this phenomenon to see if there is a similar genetic marker that could be useful in helping humans avoid obesity. Further findings in this field might help in developing new prevention and treatment possibilities. Counseling techniques, therapy and even pharmaceutical treatments that have shown success for substance abuse might show promise for those who struggle with overeating, Kenny notes.
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26 Comments
Add CommentI see two significant factors that these studies have not addressed or corrected for:
Reply | Report Abuse | Link to this1. Taste buds predispose mammals to choose tasty foods. No healthy tasty foods were offered. Bland rat chow?! Healthy tasty food may be a fairly recent development in food choices.
2. Food choices either acidify or alkalize the blood, as taught by Dr. Robert O. Young. Since animal proteins & sugars & high glycemic foods acidify the blood, and less commonly eaten green vegetables alkalize the blood, these macro chemical blood chemistry factors should be part of any study.
You're crazy if you think something written by Robert O. Young should be mentioned in any study.
Reply | Report Abuse | Link to thisNevermind your taste argument.
You're crazy if you think Robert O. Young , who doesn't seem to be a doctor by any account, should be a part of any study.
Reply | Report Abuse | Link to thisNevermind your taste argument.
Here is the link, that highlights the Robert O. Young scam.
Reply | Report Abuse | Link to thishttp://www.phmiracle-scam.com/
@ EdieFrederick if you are taking any of these products I recommend you stop before it kills you. Seriously!
My father is diabetic and he seems to eat for pleasure, he has sleep apnea and bad pessimistic/anger problems.
Reply | Report Abuse | Link to thisI think he fits well into the category of "food addicts" his excesive intake of cheese, butter, sugar and sour cream is killing him.
Is there anyway i can help him? he dosent listen, he even says he hates his life but still dosent seem to have the will power to stop eating like those lab rats. Its causing problems in the family and shortening his life. All he does is sleep, eat and go to the restroom and he cant even breathe well. He even falls asleep while taking a crap for like 2 hours every day. His feet always hurt and his legs are purple and his skin is dry, he is in a very severe condition and he dosent seem to understand it. Im guessing the drug-like food in combination with his suffering and pessimism are making him lose his mind.
How can I stop this!?!?! I know many people out there have this problem!
Is there a scientist out there that will pay my father to use him for some kind of diet plan experiment? Its an emergency!
he dosent even want to do the bypass surgery or the stomach staple surgery its just sad.
Princeton Neuroscience Institute have been studying signs of sugar addiction in rats for years.
Reply | Report Abuse | Link to thisThey found that rats displayed all of the 3 classic symptoms of addiction...to sugar
http://www.healthhabits.ca/2008/12/15/is-sugar-addictive/
In addition to the effect of brain chemicals, researchers have also been looking on the effect insulin plays on junk food addiction
http://www.healthhabits.ca/2008/11/13/why-do-i-crave-carbs/
Princeton Neuroscience Institute have been studying signs of sugar addiction in rats for years.
Reply | Report Abuse | Link to thisThey found that rats displayed all of the 3 classic symptoms of addiction...to sugar
http://www.healthhabits.ca/2008/12/15/is-sugar-addictive/
In addition to the effect of brain chemicals, researchers have also been looking on the effect insulin plays on junk food addiction
http://www.healthhabits.ca/2008/11/13/why-do-i-crave-carbs/
Agree with Aaron. Sugars are not considered in the article and the terms "fattening" and "high-fat" are seemingly used interchangeably. The hormonal derangement from massive sugar intake and subsequent insulin response is probably a better predictor of this addictive behavior than fat composition alone.
Reply | Report Abuse | Link to thisThis article is another sad display of fat phobic lipid hypothesis confirmation bias. Overeating does cause obesity. But you don't have to overeat carbohydrates to cause obesity. Just eat them in sufficient quantity to keep insulin levels high. Basic biochemistry. Dietary fats do not raise blood sugar levels or fat metabolism in the absence of enabling concomitant dietary carbohydrates. So what was the amount of carbohydrates in the rats diet? Fat consumption is mostly self limiting unless mixed with carbohydrates. When was the last time you consumed say two ounces of corn oil? Easy to do when it is in the form of bag of corn chips but not by itself. At least make your hypothesis agree with biochemistry and physiology.
Reply | Report Abuse | Link to thisThis article is another sad display of fat phobic lipid hypothesis confirmation bias. Overeating does cause obesity. But you don't have to overeat carbohydrates to cause obesity. Just eat them in sufficient quantity to keep insulin levels high. Basic biochemistry. Dietary fats do not raise blood sugar levels or fat metabolism in the absence of enabling concomitant dietary carbohydrates. So what was the amount of carbohydrates in the rats diet? Fat consumption is mostly self limiting unless mixed with carbohydrates. When was the last time you consumed say two ounces of corn oil? Easy to do when it is in the form of bag of corn chips but not by itself. At least make your hypothesis agree with biochemistry and physiology.
Reply | Report Abuse | Link to thisWild salmon contains up to 40% fat, some of it saturated fat, yet the omega-3 fats in wild salmon are the healthiest form of fat found in nature.
Reply | Report Abuse | Link to thisIn one study, eatting wild salmon actually causes the body to burn 25% more fat.
It's not the quanity of fat that is important, but the quality of the fat that's important, too.
Relating this study to anything clinically relevant regarding obesity is such a stretch I cannot even begin to see how they got here (oh wait, I do, there is food and through tremendous manipulation of environment eventually fat rats). How they can study multiple variables and claim anything valid out of this is mind boggling, but not surprising. The sugar industry depends on garbage science like this to further its agenda as a low fat and therefore healthy food and continue to blame fats as the culprit (even though fats and sugar were both variables in this study, look at the headline to see which was blamed for the bad results) . The sad thing is that SA has decided to present this as something of significance.
Reply | Report Abuse | Link to thisYes! Thank you for mentioning the lipid hypothesis lie!
Reply | Report Abuse | Link to thisThank you for mentioning the lipid hypothesis lie. I am only just now learning how this lie has caused considerable harm to the health of people who fall for it.
Reply | Report Abuse | Link to thisFat is not the problem, carbohydrates are. All of the credible scientific research in this area has shown that healthy fats (not the polyunsaturated poisons pushed by the food industry) are an essential component of a healthy human diet. We've been eating animal fats for 2&1/2 million years. What we have NOT been eating are refined carbohydrates and grains (a phenomenon peculiar to the last 10, years of human existence, a mere blink of the eye). Sugar (and most grain based carbohydrates are the culprit NOT FAT).
Reply | Report Abuse | Link to thisShould have read 10,000 years... the period in which humans changed from hunter gatherers to agriculturalists.
Reply | Report Abuse | Link to thisWhat outraged me about this pathetically flawed study (leading me to suspect it was sponsored by the Corn, high fructose corn syrup, industry) was the inclusion of CHEESECAKE. The major portion of calories in cheesecake is from the SUGAR (Duhhhhhhh!)
Reply | Report Abuse | Link to thisIt seems to me that obesity is the culprit no matter how you get there. If you lay on the couch and stuff yourself with celery I suppose you will develop obesity related problems. It is true that fat is often blamed because it has a higher calorie/gram. So, if you are trying to lose weight, reducing fat calories adds up faster. But, carbohydrates have a much higher glycemic index and are much more of a problem for diabetics. Maybe it is time we stop trying to analyze the behaviour causing obesity. A better strategy might be to stop supporting excuses for self destructive behaviour. Simple physics: use more calories than you eat=problem solved.
Reply | Report Abuse | Link to thisDo rats show addictive behaviour if given brussel sprout flavored lard?
jbairddo, I am largely in agreement with your sentiments, but don't know exactly what you mean by the "sugar industry," or why it would want to sponsor this.
Reply | Report Abuse | Link to thisabyssalmystery: "Simple physics: use more calories than you eat=problem solved."
Reply | Report Abuse | Link to thisabyssalmystery and a large number of well meaning people who are obviously not physicists seem to think this statement holds true for humans. You are in great need of understanding our physiology and biochemistry. The role of insulin in regulating blood sugar trumps this simple statement. The first and second laws of thermodynamics cannot be used here. We are not closed systems.
Ummmmmm, doughnuts
Reply | Report Abuse | Link to thisJust great, first they eliminate normal healthy food and try to stuff us full of aspartame and high fructose corn syrup then when people get fat and unhealthy they want to develop a pill for it which will probably turn out to be worse than the disease.
Yes food is addictive, I've been on it myself for quite some time.
There’s an interesting post over at the Health Journal Club that makes the case that people should just not eat anything that wasn’t a food 100 years ago. Gets rid of the aspartame, bleached GM flour, high fructose corn syrup garbage they try to pass off as food these days. If interested you can read on it here,
http://healthjournalclub.blogspot.com/2010/01/100-year-diet.html
Let's give credit to David Kessler here in THE END OF OVEREATING. In this book we are presented with this very concentrated focus on the manipulation of our reward systems by the major corporations. However try and get through to the cynics and undereducated...trying to drive the analogy based upon the theme of a biological reward center is like telling them that dinosaurs ruled the earth. But once you recognize that your schemas for reward are in control, then some sort of action can be taken. I'm reminded here of the tick on Animal Planets most extreme dieters...Americans weighing in at 600 times their natural weight. Add the SUV to a 250lb. woman and you come pretty close.
Reply | Report Abuse | Link to thiswfcloud
Reply | Report Abuse | Link to thisI am aware that the situation is more complex than how I described it. However, how could you possibly disagree that if you control your caloric intake you can control your body weight? You don't need to be a physicist to comprehend that. By the way, I may not be a physicist but I am in the process of getting a degree in Physics and more importantly I am a type I diabetic. When you start weighing every gram of food you ingest and have to compensate with injections of insulin, you learn more about metabolism than your doctors ever will.
http://thedegree.net/?p=25&cpage=1#comment-219
Reply | Report Abuse | Link to thisThe best weight control is the most natural one: eating raw fruits and vegetables before anything cooked! I have lost over 20 kilograms over the past years , just by following the West Australian health initiative: "Eat 2 & 5", and written a book called " Colour Eating Without Heating", based on the same principle.
Reply | Report Abuse | Link to thisSee youthevity.com
Yes good point guys let's remember that fats and sugars may both cause obesity-see the Liver fed state vs fasting state (however fatty acids inhibit glycolisis),on the other hand fatty acid synthesis occurs in the cytosol,where they entry via citrate shuttle-then via carnitin right into the mitochondria..those details should be kept in mind in the study design ,I mean the study even though quite serious may be somhow biased..
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