A couple decades ago it was hardly an issue, but now obesity affects 1 of every 3 adults in the United States. There are multiple camps within the obesity world. Some believe obesity is simply an issue of too many calories. If obese people were to simply eat less they would no longer have a weight problem. There’s another camp that believes it’s not quite that black and white. There are various things that could mediate the relationship such as viruses and environmental chemicals. Or the brain.
Photo credit: Suboxoneassistedtreatment.org
Some people may be more susceptible to obesity than others due to the way their brain processes food. The brain has what can be described as a “reward circuit”. Think of it as an electrical circuit, that when completed triggers a sense of satisfaction. Remember that piece of black forest chocolate cake with the shaved chocolate ganache topping? Did you feel a sense of happiness or satisfaction from the taste? That’s your reward system talking.
So think about this for a minute…
How loudly does your reward system speak to you?
Some people don’t seem to have as strong of a voice in their reward system. Sure, they like chocolate cake but it’s nothing special. It tastes good and it’s filling, but that’s as far as it goes. Others seem to have a reward system that can wail like a colicky infant. This system plays a major role in one’s appetite.
Research has shown that exposure to our favorite foods through pictures or smells can be enough to override our feelings of satiety. Despite feeling stuffed after dinner, the thought of dessert is still appetizing. To counter this desire, we rely on a system of “brakes” to tell us we don’t need that dessert because we’re not hungry. What’s interesting is that in obese people, it appears this reward circuit is overactive. The brakes are unable to tone down the reward circuit, so the brain constantly seeks activation. This may lead to overeating.
Researchers in Finland conducted an experiment to determine what exactly was going on in the brain and body when the reward system was activated. The study involved 35 people (16 of normal weight and 19 who were morbidly obese) and took photos of their brain activity through functional magnetic resonance imaging (fMRI), a machine that detects changes in blood flow between areas of the brain. These changes in blood flow indicate which areas are currently being used. While the people were in the fMRI, researchers showed them images of highly palatable food, bland food, cars (chosen as a non-food stimulus), as well as image-free periods to see how their brains responded. They also measured the amount of glucose (the body’s energy currency) used by each area of the brain with positron emission tomography (PET).
The results were quite interesting. Obese subjects’ brains used more energy than normal weight subjects when both appetizing and bland foods were shown. Also, obese subjects’ brains had higher blood flow than normal weight subjects when seeing the appetizing foods as opposed to the bland foods. Therefore the reward circuit was not being adequately inhibited. This tells us that people in the study who were obese had more activity in their reward circuit than those of normal weight. Additionally, that activity was stronger when the obese person saw photos of appetizing foods as opposed to bland foods. In other words, obese people seem to be not only more sensitive to the prospect of food, but they also experience a greater reward from the experience than people of normal weight. This sense of reward can be inhibited due to external and physiological cues (i.e. feeling full) in normal weight people, but this is not so in those who are obese.
These findings have significant implications for weight management. When working with obese individuals, a multi-factor approach may be necessary. It’s not enough to simply educate about calories. The physiological and cognitive changes that occur during obesity need to be addressed as well.
Reference:
Nummenmaa L, Hirvonen J, Hannukainen JC, Immonen H, Lindroos MM, et al. (2012) Dorsal Striatum and Its Limbic Connectivity Mediate Abnormal
Anticipatory Reward Processing in Obesity. PLoS ONE 7(2): e31089. doi:10.1371/journal.pone.0031089
The title of this blog entry is so great!
Thanks!
I enjoyed reading your post. It is very clear, and its conclusion has very pertinent and practical implications. Wonder how these things would actually look in practice – how the brain would be ‘retrained’. Sounds very hard, especially as so many stimulants (advertising, smells, how foods are ‘designed’ etc) are around in everyday life that seem to be directed at triggering these kinds of overresponses.
You pose a great question! The interesting thing about this finding is that the reward system in obese individuals functions similarly to the reward system in those with drug addiction. If drug addiction therapy progress is any indication of how we’ll progress with a cognitive component of obesity treatment, the future is not looking too bright. However, funding seems to be more plentiful for obesity research than for drug addiction. With several years of well-funded intense study, we may see options for brain “retraining” medication. It may also involve a counseling or group therapy component. We’ll just have to watch and see how the treatment arm develops.
I enjoyed reading this post, Alysia, but even more important I feel I could share it with a teenager. And s/he would have NO PROBLEM WHATSOEVER understanding the language and science here. You have done a great job using short sentences and simple but lively language. You tell a story. This is really a high point at the midpoint of this whole 100-blog endeavor. Scientists might tell you the sample size in the study you quote is pretty darn small. But I’m thrilled that a young person could rethink their approach to binge-eating based on what you’ve shared, and HOW you’ve shared it.
Best,
MB
Thank you for those kind words! Glad you enjoyed the post.
Very intriguing research. I wonder if the same is for obese children, and if this reward circuit is genetic or trained by our environments (or both). Maybe advertising or life experiences lead to a change in how our “brake systems” work!
Those are great questions, and I would love to know the answers too. There may be research out there, but I haven’t come across any. Thanks for reading!
Great post Alysia. I agree that the language is quite clear and understandable. I did find it a little repetitive, but nothing alarming. It would have been nice to see more links to relevant other information and definitions. The first three paragraphs speak to the reader in an engaging style, but then it does seem to lose that human engagement. You stop talking to the reader and start talking about ‘obese subjects’ and ‘normal weight subjects’. It would have been better to refer to ‘people’ and to try to keep that personal link. I also didn’t find the picture very informative or engaging – perhaps a picture of a chocolate cake might have been more interesting and telling for the reader who may have been stimulated by it!
Thanks for your suggestions, Michelle!
Fascinating post! I was hoping for a bit more of a discussion at the end about the implications of this knowledge. How could physiological and cognitive issues be addressed? For instance, could consistent use of cognitive behavioral techniques change the way our brains respond to stimuli? Or should those of us whose brains respond most actively to food cues be focusing on avoiding those cues? There may not be an answer to this question yet, but even describing potential avenues for further research would help readers get a better sense of how the health field might be able to use this knowledge.
Great question, Liz. The short answer is that we don’t really know much about the implications yet. Part of the problem is that we don’t have enough conclusive research with large sample sizes to change how we approach the issue. Another part is that those who work in the field of obesity disagree as to how it is best treated (e.g. diet and exercise, weight-loss surgery, medication, cognitive therapy, etc). What this study does tell us is that practitioners who are approaching obesity with a black and white “cut calories and that’s all that you need to know” approach are not acknowledging all aspects of the condition. The way obese people are drawn to food is different than normal weight people and needs to be considered. The study’s author stated these findings are similar to what is seen cognitively in drug addiction, another area we don’t really know how to treat effectively…at least not yet.
Great post and very interesting topic. I wonder how the fMRI and PET data changes as someone transitions between weight categories (gains weight to get to obese, or starts losing weight, or has a surgical procedure done).
Do taste buds play a role in the reward system?
That would be really interesting further research. I’m afraid I don’t have an answer for you at this point.
Terrific post! The writing was clear and concise. The flow was terrific and the reward/brakes analogy was really easy to understand. I also really want to highlight how great it is to read about emerging research that relies on fMRI data. I recently read a report about its use in market research too. When you use the reward/brake analogy, the fMRI for market research makes a lot more sense!
Market research. What a cool application for fMRI. Thanks for sharing this!
Wow great post!! I think the title was awesome. You did a wonderful job of posing some interesting topics that take us below the mere surface. As someone who is in the process of losing 300 pounds, I can relate!! So far I’ve lost 128 pounds and one of the major ways I’m doing this is by educating myself on these very issues. So thank you!!
Congrats, Holly! 128 lbs is quite impressive. Keep up the good work and thanks for reading!
UGH. I’m so sick of eliminationism. Obesity (read: obese PEOPLE) need eliminating and removal from the planet because they are flawed for their biology. Obese people need to be “fixed.”
Obesity is not a diagnosis, or a disease. Obesity is a physical descriptor for bodies. Obesity should be changed just as much as we try to change people’s heights. (Hint: we don’t try to change people’s heights.) It’s a real shame research can’t be focused on HEALTH, rather than aesthetics (body size). Why not study eating behaviors independent of size? Why not study how to make thin people gain weight? The assumption is always that fat people are overeaters, have unhealthy habits, or are somehow flawed (even if it’s thinly veiled concern for flawed biology like in this study), rather than studying REAL health markers independent of weight.
Here’s a great starting point if you’re curious about fat and health, and I highly recommend looking into the concept of separating weight from health:
http://kateharding.net/faq/but-dont-you-realize-fat-is-unhealthy/
Considering we can’t even define who is “obese” (because BMI is the only real ruler to measure fatness we have right now, and BMI is complete and total bunk), studies like this are total junk science to me because they’re founded on a measure that’s meaningless. http://www.npr.org/templates/story/story.php?storyId=106268439 Also, check out the BMI project: http://kateharding.net/bmi-illustrated/
Another good post on fat bodies as “evidence” for an “epidemic” http://danceswithfat.wordpress.com/2012/01/28/fat-bodies-are-not-evidence/
Thank you for your comments, Jennifer. It sounds like you are a passionate proponent of a healthy body image, for which I applaud your efforts. I agree, that a focus on health rather than aesthetics is crucial. What’s important to understand is that obesity is receiving attention because it affects one’s health.
Obesity is at the center of a complicated interaction that increases one’s risk for heart disease, type 2 diabetes, high blood pressure, etc. Those diseases then increase your risk for other diseases and complication (i.e. kidney failure, systemic inflammation, infections, etc). The links between obesity and poor health outcomes go beyond just an association. For example, losing as little as 10% of one’s body weight has shown to improve the severity of type 2 diabetes. That’s a cause and effect demonstration. The fact that obesity is related to poor health outcomes has been well established.
I’m a bit perplexed by your claims regarding the lack of study of eating behaviors and weight gain in those who are underweight. These are actually major fields in nutrition and play a large part in the treatment of people with diseases such as AIDS and cancer where wasting of the body becomes a concern. If you’re interested in learning more about this area of research, I’d start with a google search on Ancel Keys.
In reference to BMI as the only measure of fatness, this just isn’t true. There are numerous measures of fatness: total body fat, body fat percentage (skin folds), waist circumference, and waist-hip ratio to name a few. All of which have been validated for use in research. BMI is often used because it’s less expensive and requires little equipment. There are concerns with BMI such as the assumptions it makes regarding body composition and leg height. For that reason an individual should use BMI as a screening tool and confirm any weight concerns with another measure (waist circumference is an easy one to do). However, in studies of the general population and at the population (as opposed to the individual) level these differences in body type balance out.
Many of your comments here seem to center on the stigma of obesity. The Yale Rudd Center for Food Policy & Obesity does a lot of work with reducing obesity stigma and focusing on health not size. If this is an area that interests you, you may want to check out their site: http://www.yaleruddcenter.org/
Thanks again for your comments.
I’m definitely concerned about fat stigma. Mostly I’m concerned that fat stigma is biasing science and research, which feeds into the stigma feedback loop that allows the funding of junk science studies about how to eliminate people of size, rather than how to eliminate health problems like heart disease, diabetes, and high blood pressure (incidentally, in the case of kidney failure, studies have show that heavier patients survive longer on dialysis than thinner patients). Studies (and comments) like these imply that thin people don’t get heart disease, diabetes, or high blood pressure (or cancer, or asthma, or arthritis, or any of the numerous other illnesses the media loves to attribute to a large body habitus). I think what would really do the science world AND the public a good service would be to remove weight from the equation and discuss the health issues themselves. as a scientist, it’s hard for me to take studies that focus on body size seriously without looking deeper into the situation. On a personal note, as a person of size, I have a hard time thinking I would have responded as their “typical” fat person because as a junk food-hating wholesome foods-loving eating vegan, most of what the Standard American Diet calls “appetizing” I would call “disgusting” (and it would actually make me physically ill). Did they cherry pick their participants to only use thin health food nuts and obese SAD-eaters? Did they make sure their thin participants weren’t overeaters to begin with and exclude, say, bulimics with a history of overeating but who may actually be thin? Why not focus on over-eaters versus non-over-eaters independent of size? (Probably because it’d be too difficult to determine who is an over eater and how to define over eating, whereas it’s very easy to define who is fat and who is not fat, even by flawed measures.)
What I’m getting from your response here is this: “don’t you know obesity is unhealthy??” But remember: correlation does not equal causation.
Again, my problem is with equating weight with health. Main Stream Media (and the diet industry-funded research) can definitely make us believe that only fat people have heart attacks, high blood pressure, or diabetes (even type 2 diabetes is not limited to people of size), but that’s simply not true. (As for weight loss “improving” diabetes, I’d argue that if someone makes efforts to improve their diet and activity level, the odds are definitely in their favor that their diabetes will be better managed, regardless of their size.)
Other useful posts on separating weight from health are on the Junk Food Science (now retired) blog:
http://junkfoodscience.blogspot.com/2006/11/obesity-paradox-1.html
http://junkfoodscience.blogspot.com/2006/12/obesity-paradox-2-how-can-it-be.html
http://junkfoodscience.blogspot.com/2007/01/obesity-paradox-3.html
http://junkfoodscience.blogspot.com/2007/03/obesity-paradox-4.html
http://junkfoodscience.blogspot.com/2008/05/epidemic-that-wasnt.html
And about BMI and other ways to “measure” obesity: http://junkfoodscience.blogspot.com/2009/04/does-it-really-matter-how-your-numbers.html
Great post, thanks for discussing this topic. I agree that stigma regarding heavier people in the medical/research community is problematic and leads to unmerited assumptions about those individuals. Body size is a complex issue that arises from the interaction of genetic , psychological, social, and environmental factors and is not something anyone should suffer feelings of guilt or embaressment from. I also think that the types of food we intake are and extremely important part of the equation for understaind human disease.
However, ignoring excess weight as a risk factor for chronic disease would require rejecting a mountain of evidence accumulated over the last 5-6 decades (most of which is NOT junk science). Because excess weight has consistently shown strong associations with chronic disease, precedes the events in question, exhibits a dose-response relationship, has biologically plausible relationships to pathology, shows nearly identical findings in well controlled animal models, and reduces the risk of disease when weight is removed, I think it’s safe to say that possessing excess body fat CAUSES a number of chronic diseases over time (yes….including certain cancers).
While BMI is not the best measure of body fat, it’s a decent proxy for the majority of the population and is extremely easy to measure. I think in the future it would be nice if we could be more accurate about these measurements as we use them in nearly every study of metabolic diseases.
Great article. Very well written. I also think Jennifer has highlighted some very important points about fat stigma. I personally feel that it is a problem to divide people into ‘obese’ and ‘non obese’ subjects. I understand we have various measures like the BMI to define what this means but again even if we are saying a person is overweight it doesn’t imply everyone who is falling in this category is somehow the same – even within those categories there is a lot of discrepancy in terms of how overweight is this person, what are his eating habits like? I feel a lot of people who are not infact overweight but have very unhealthy eating habits need to be studied as well. I haven’t looked into it much but it might be interesting to see how the reward system works in such individuals, i.e. in those individuals who are not obese but who have unhealthy eating habits.
Thanks for commenting.
Like many readers, I’m keenly interested in what the “multi-factor approach” you mention might consist of. I hope you get the chance to address the topic again, short though the remaining time on the project is.
“obesity effects 1 of every 3 adults” I think should be “obesity affects 1 of every 3 adults”
Thanks for pointing out the affect/effect error. The multi-factor approach would consist of addressing more than just calorie counting and nutrition education. We know that knowledge plays only a small role in obesity. There are just too many other factors involved for weight management to be that straight forward. Relating to this article, the multi-factor approach would acknowledge the cognitive as well as physiological differences (e.g. reward system activation) seen in those who are obese. Some programs are already addressing this need for a more comprehensive approach. There are currently weight management programs that incorporate a psychological approach, such as cognitive behavior theory, into their education component. This can be effective in situations of binge eating, stress/emotional/boredom eating, etc that can be unacknowledged underlying factors in some obesity cases.