Saturday, February 22, 2014

Why Do We Overeat? A Neurobiological Perspective

I just posted a narrated Powerpoint version of my talk "Why Do We Overeat? A Neurobiological Perspective" to YouTube.  Here's the abstract:
In the United States, the "obesity epidemic" has paralleled a gradual increase in daily calorie intake.  Why do we eat more than we used to, and more than we need to remain lean-- despite negative consequences?  This talk reviews the neurobiology of eating behavior, recent changes in the US food system, and why the brain's hardware may not be up to the task of constructively navigating the modern food environment.
This is the same talk I gave at the University of Virginia this January.  I had a number of people request it, so here it is:
 
 
This is one of my favorite talks, and it was very well received at UVA.  If you find it informative, please share it!
 
 

17 comments:

Keith Hansen said...

Stephan,
Thank you for sharing so much knowledge and shaping the way I view nutrition. I am a personal trainer and your work helps me every day. I give dietary advice to clients without giving them strict diets and after I educate clients they feel confident in making healthy choices conducive to reaching their goals.
Keith

Gretchen said...

I listened to your talk (which I can do now that I have DSL), and I have a couple of comments.

1. On graph of cost of food vs disposable income, you said this showed that food is cheaper today. Not necessarily true, as the results are a ratio. Maybe people (on average) have higher disposable incomes. I've kept track of food expenditures, and they've just about doubled from 1991 through 2011. My income has also increased, so maybe the ratio has gone down, but the income of a freelancer varies widely from year to year, so I can't easily compute that change.

2. Instead of researching the obvious (people eat more when the food tastes good) I wish someone would research why rich people (especially women) tend to be thinner than poor people. A rich person wouldn't mind paying $6 for a brownie and would probably have a secretary or other assistant who could go across the street to buy it for him/her.

I suspect the answer here would turn out to be the obvious guess, that cheap food is starchier and cheap restaurants try to attract customers with huge starchy meals while upscale restaurants serve tiny portions of food with more protein and other expensive ingredients.

But maybe studying the eating habits of rich people would inspire the nonrich to emulate those habits.

Stephan Guyenet said...

Hi Keith,

Thanks-- glad you find it helpful.

Hi Gretchen,

The graph shows food spending as a percentage of disposable income. Absolute food prices have greatly increased since 1930, but disposable income has increased even more. This has resulted in a large decline in the proportion of disposable income spent on food.

However, the change since 1991 has been small (from 11 to 10%). Food spending was 13% in 1980, 14% in 1970, 18% in 1960. So while the longer-term trends are substantial, in the last two decades there hasn't been much change.

Regarding your second question, I think it's useful to note that the obesity prevalence is high among rich people too in the US-- just not as high as it is among poor people. Rich people can afford better food, a gym membership, and they probably tend to care more about appearance and fitness.

By the way, I think it can be very useful to "research the obvious" such as the hypothesis that people eat more of food that tastes good. Sometimes common sense turns out to be wrong, or an oversimplification.

Gretchen said...

"Absolute food prices have greatly increased since 1930, but disposable income has increased even more. This has resulted in a large decline in the proportion of disposable income spent on food."

That was my point. You said, "The cost of food has plummeted." I agree the *relative* cost has gone down.

Re researching obvious, maybe studying the eating habits of the rich might reveal something beyond being able to afford better food.

I suspect food security would play a part. When I was in grad school, I'd eat everything in sight at a free buffet because my food budget was miniscule. Had I been rich, I would have eaten only what I wanted. Do rich people at restaurants leave half the meal on their plate?

But as you said, there might be unexpected factors too.

Jin said...

There must be studies on the social pressure to be thin. Or perhaps, social pressure to avoid being the fattest person in one's peer group/social circle.

This blog has discussed how protein satiates. Wealthier people can afford to dine out or take out at restaurants that offer simpler yet satisfying fare. Grilled fish, simple steaks, roasted meats with nary a french fry in sight.

For the rest of us, we might be living in a sea of highly rewarding calorie dense dining out & take out choices, unless we cook simpler fare at home.

Anecdotally, I would guess stress levels play a role as well.

Methinks said...

Gretchen,

The price of anything (including food) in real dollars is all that matters. The other way to look at it is that you can consume a higher quantity of food for the same amount you spent on a smaller quantity of food 30 years ago.

As for why very rich people and celebrities (which is the group I'm assuming you're actually referring to) are slim despite being able to afford more food, I think the answer might include that:

a.) There are diminishing marginal returns to food consumption. Once you're satiated, more food does not increase your utility and because eating non-stop can make you feel pretty sick, eating beyond the point of diminishing marginal returns may decrease utility (note that one's perceived utility is likely at a level of more food than may be required by the body to meet energy needs).

b.) Particularly women in that socioeconomic group are under intense social pressure to remain thin. And I do mean intense!


Gretchen said...

@Jin. I agree about social pressures. Studies have shown that you're more apt to be fat if your friends are fat.

And the pressure is greater for women, I think. A "portly" man may be seen as successful, but not a fat woman.

@Methinks, I was referring to rich people, not necessarily celebrities.

But these are all just unproven opinions. As Stephan noted, sometimes studies show that common sense was wrong.

Sanjeev said...

> very rich people and celebrities (which is the group I'm assuming you're actually referring to) are slim

Relative to the resources they can devote to the issue, and some of the factors you actually mention (economic incentives, peer pressure), IMHO their results are abysmal.

> very rich people and celebrities (which is the group I'm assuming you're actually referring to) are slim

what, like Oprah?

http://en.wikipedia.org/wiki/Spit-take

(spit take or maybe "keyboard warning" ... just expressing surprise)

Sanjeev said...

> Or perhaps, social pressure to avoid being the fattest person in one's peer group/social circle.

contagion theory,
https://www.google.ca/search?q=christakis+fowler+contagion+theory&ie=utf-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&channel=sb&gfe_rd=ctrl&ei=ldgLU7yyEKeC8QeSuIGwBg&gws_rd=cr

this is related to the "broken window theory" of policing.

and Japanese cultural studies ... listen to a bunch of Westerners living in Japan and you'll hear this stuff fall out occasionally (this little tidbit's all anecdote - good for ideas, NOT for results),

and a discussion of some real data on Japan

carbsanity.blogspot.com/2013/06/eating-less.htm

Eric said...

Stephan,

That was informative and thought-provoking. Thanks.

Some parts that were more stat and science-heavy went by me somewhat. Not your fault - you simplified the content reasonably for lay people like me. I'll search your website for more explanation on those areas.

Regarding higher obesity among the poor, based on observation, I blame it more on personal choice than funds.

I buy my food in city supermarkets where a majority of my fellow shoppers pay for their groceries with state-provided EBT cards.

I pay out of pocket and I'm not rich. Thus, I'm cost-conscious and shop exclusively from the cheaper items on store sales flyers. I'm not especially careful about what I eat, but I try to make relatively healthy food choices.

So it's striking that, from what I see, the people who pay for their groceries with EBT cards consistently buy cartfuls of full-price, brand-name junk food and otherwise factory-prepared food.

We have the same food options and they have larger budgets due to EBT, yet their greater spending power pays for an unhealthier diet by their choice.

Sam said...

Great talk Stephan, but I have to say that I keep hearing about how protein is more satiating than the other macros, but I just don't buy it! In my personal experience that is not the case, and I never reach satiety, no matter what the macro ratio, unless a meal contains 500-600 calories, which is about what it takes to refill liver glycogen. Coincidence? Maybe the brain is more sensitive to the calorie count than we think?
I tried to bypass this using the "stretch detectors" by consuming water, soup or broth with a meal, and/or with mega helpings of non starchy veg., but if I didn't hit 500-600 calories, I would just feel uncomfortably stuffed, but still hungry.
Since you always look at the evolutionary angle, why would we evolve to be especially satiated by meat/protein? I can't see why. Also, maybe the studies that 'proved' protein improved satiety is because the people got sick of eating bland meat? (and no, im not vegan). It would be great if you did a post revisiting this protein satiety claim, and see if its myth or true.

JBG said...

The situation with respect to engineered food is bad almost beyond belief. See:

http://www.consumerreports.org/cro/magazine/2014/01/food-fake-out/index.htm

(Skip the video and the material on the right side of the display.)

A couple indicative examples of what is to be found at the link: "blueberry" cereal with NO blueberries, and coffee "creamer" with NO cream. Lotsa detail.

Gretchen said...

@Sanjeev:

> very rich people and celebrities (which is the group I'm assuming you're actually referring to) are slim

>what, like Oprah?

Citing the example of one person is meaningless. It's like finding a thin person and using that as proof there's no obesity problem in Americ.

Methinks said...

Gretchen,

Note my use of the word "might". I thought that it was obvious that my comment was mostly opinion. Although, I don't think that it's "unproven opinion" that in the absence of a disorder like Prader-Willis Syndrome gorging eventually makes people feel pretty disgusting and feeling disgusting is pretty much the definition of reduced utility.

Also, while I have no idea exactly what role social pressure plays in keeping wealthy people's weight down, I can tell you the pressure is intense. Live on the Upper East Side of Manhattan for a while and you'll see what I mean. Of course, part of the reason especially the women are comparatively thin is that rich men tend to choose naturally thin women to marry. Or maybe it's because wealthy people are better educated and engage in activities that result in better health. I don't know. I'm just throwing ideas your way.

BTW, when I was very poor I tried that eat-until-you're-sick thing at the all-you-can-eat buffet because you won't have to eat again and I found myself completely sick and unable to function. I have no idea how you managed that. You must be blessed with a stronger constitution than I am.

biwerfever said...

Hi Stephen, I attended your talk at UVA (I'm a PhD student studying regulation of vascular tone) and loved it. I'm also an avid cross fitter/paleo/"clean" eating fan (not the annoying kind, i swear) and both have really changed my life. I feel really great (which as you know, is hard to do in grad school). Everyone else thinks i'm crazy, but the way you presented this information was so articulate and made perfect sense.

I have been kicking myself for not hanging around to meet you. Although i've never been interested in neuroscience, i found your presentation fascinating. I haven't read your blog for very long, but I was just curious as to what you're doing now: post doc? faculty? What are your professional plans?

Thanks & keep up the good work!
Lauren

Stephan Guyenet said...

Hi Lauren,

Awesome, sorry we didn't have a chance to catch up.

I'm currently taking some time off and I'm probably going to write a book. Still thinking through the book and what I want my life to be. I'll probably return to research (possibly industry) at some point.

Actually, I say I'm taking time off, but what I mean is I'm not working a regular job. I'm still putting a lot of time into finishing up papers and developing the Ideal Weight Program. Good luck with your studies.

Jane said...

Stephan, I really hope you return to research. Your blog is invaluable for communicating what researchers are doing and thinking. The first thing I do when I get into the science library is read your blog, and I've done it every day for 5 years. I would be lost without it.