New hypothesis proposes a link between obesity and carbon dioxide

Let me preface anything else in this post by clarifying something important. What we are talking about here is a hypothesis—it's not been proven. In fact, it's not even really been tested yet. The studies that will put the hypothesis to the test are currently underway. So please (please, please, please) do not walk away assuming this is a given. It's not. It could very well be completely and utterly wrong. But it's interesting. And it will be in the news. And I want you guys to hear about it in the proper context.

Make sense? Okay, then ...

There are scientists who think that there could, possibly be a connection between air pollution and obesity.

This idea is (for now) based on "what if" extrapolation rather than data. But it's not totally crazy. We know air pollution affects health in ways would not have been obvious just a few decades ago. For instance, there is a strong, well-documented connection between air pollution and heart disease. In 2009, Aruni Bhatnagar, professor of medicine at the University of Louisville, told me that studies from 250 different metropolitan areas in the United States showed that a spike in air pollution was reliably followed by a spike in cardiac deaths within next 24-48 hours. The people primarily at risk are those who already have underlying heart health problems, but it's not always clear who those people are. We don't yet know exactly how pollution affects the heart—it could well be a cascade of effects that actually starts in the lungs—but we can see that the affect is there.

This new hypothesis, proposed by Arne Astrup, head of the department of obesity and nutrition at the University of Copenhagen, does not come with that kind of supporting evidence. Instead, it's more of an extrapolation.

At Discovery News, Emily Sohn explains why this hypothesis could make sense—and why it's way too early to say whether or not it's actually right.

The idea proposes that breathing in extra CO2 makes blood more acidic, which in turn causes neurons that regulate appetite, sleep and metabolism to fire more frequently. As a result, we might be eating more, sleeping less and gaining more weight, partly as a result of the air we breathe.

...Obesity and its associated health risks have escalated dramatically in the last few decades. And even though just about everyone thinks the reason is obvious -- we are eating too many calories and exercising too little -- research has revealed that obesity is far more complex than that, with multiple genes, metabolic pathways and even gut microbes involved, said obesity researcher David Allison, director of the Nutrition Obesity Research Center at the University of Alabama at Birmingham.

Read the full story at Discovery News

Image: Pollution, a Creative Commons Attribution Share-Alike (2.0) image from akeg's photostream


  1. So I think what Maggie is saying here is that we can go ahead and eat all the fatty, sugar-filled crap we want because it’s now been definitively proven that obesity is caused by the air we breathe. Got it!

    1. I really hope a group of conservative, fat, people decide this is the explanation they’ve been waiting for – and try to blame their obesity on higher CO2 levels (using global warming data they’ve earlier called fake).

        1. Or at least a fat joke. I mean, as a fat reader, my day isn’t complete unless you squeeze one in. 

          1. It’s not a fat joke; it’s a joke about someone profiting from the misery that they helped cause.

  2. Based on my experience living in two non-US countries whose residents are significantly thinner than Americans and yet who breath the same air, I will pass on this theory.

    1. Why? You haven’t studied the phenomenon in any meaningful way, so rejecting the possibility just because it doesn’t fit your anecdotal evidence is ridiculous.

      They aren’t saying it’s the cause of obesity either. They’re making a hypothesis that it could be a contributing factor, in addition to all the other diet related issues Americans are putting themselves through.

      It’s certainly worth studying. 

    2. Dunno, the CO2 near ground in a traffic jam may well be higher than the average level globally.

  3. Wouldn’t that mean living around a lot of people and other animals would also make people fat? Then why would population dense areas, and especially population dense areas where there is a lot of pollution, not be obese? 

    1. Good point.  I’ve noticed that small towns and rural areas have more fat people than urban areas, where people seem to try harder to stay thin, be trendy, etc.  I have no stats to back this up, it’s just something I’ve noticed in N America.  On the other hand, about a decade ago, my sister and I went to Europe, to visit the tiny town we grew up in, as well as small nearby city, and my sister was the second fattest person we saw; it was her observation.  She was right, and by no means was she fat by health standards, I’d say she was a size 8 and about 21 yo.  I think food/ diet is the #1 reason people are getting fat.  There are other causes, like stress, not enough sleep, in some cases genetics including disorders, lack of physical activity, self hate, etc.  Maybe CO2 falls in there as well, but if we focused on what we already know, people could prevent becoming obese and stop coming up with new excuses. 

  4. I actually laughed reading the first paragraph.  Thanks for putting it there Maggie- I doubt it will be 100% effective, but maybe it will help.

  5. I totally agree with his findings. I believe that CO2 also makes you lazy and older. 

    I stay thin, active and younger by breathing out as much CO2 as possible. Sometimes, when I notice I’m not breathing out enough CO2, I have to go out and jog or do some other exercise such as cycling or swimming to get my breathing faster and rid of that nasty CO2. I try and breath out as much as possible in order prevent the CO2 from making me fat, lazy and old.
    Did I mention that CO2 also gives you disease and forms disease causing agents, such as diabetes, heart problems, high cholesterol and high pressure? 

  6. I was just getting used to blaming my gut on stress, a virus, bad genetics, a hormonal imbalance, and horizontal stripes.  Now my belly band will need to include an oxygen tank if I go that route.  But at least I know its not because of my diet or lack of activity.

  7. The possibility of free will exists absolutely. The objective conditions in which each can exercise free will do not. I think more than air pollution needs changing. Who is trying to fool who here? Maybe obesity is a cause of air pollution.

  8. My fried went into space to do a ‘CO2 Cleanse’ and lost weight incredibly fast after a week of not breathing any CO2 (or breathing anything at all). And lately, I think I am putting on a ton of weight due to all the residual CO2 pockets trapped in these delicious glazed donuts I’ve been eating by the dozen…

  9. This seems to be extremely unlikely: the article referred to suggests that CO2 levels in the order of 7000 ppm are necessary to increase the firing rate of appetite regulating neurons via blood pH change. Current CO2 levels are 15 times lower than this. Further, a study in which a group of subjects breathed CO2 at 8000 ppm demonstrated no statistically significant change in appetite. Seems like pseudo-science to me.

    1. Not only that, but the difference in atmospheric CO2 level change over the last century can easily be swamped by the difference between outdoor and indoor levels of CO2. E.g., a well-insulated house in the winter will very possibly have higher CO2 levels than what the Earth might have 100 years from now. So it would be interesting to compare blood pH and weight of people who work in indoor locations vs. outdoor, people who sleep with windows open or closed, etc.

    1. Conversely, the two things I always notice when I go to LA is how skinny everyone is, and how bad the air quality is.

      1. Every time I go to LA I’m struck by how many doughnut shops there are (and the other random businesses they’re combo’d with) and how I never see a skinny latino child. I hypothesize that at quinceanera they emerge from a baby fat cocoon. 

  10. We must not lose sight of the most important thing here, folks. Obesity is an epidemic and fat bodies are pathological. No matter what the cause, we must never forget that we are fighting a war on fat people. I mean, on obesity. 

  11. William Broad’s new book, The Science of Yoga, puts forth that “traditional” yoga, not the modern exercise fad, consisted of deliberately manipulating one’s CO2 levels by slowing down the breath and holding the breath. This allowed various metabolic adjustments that permitted one to go into a near-hibernation state that appeared something like death to observers. Yogis used little caves sealed off with grass and beeswax to prevent outside air from coming in, creating an even greater increase in CO2 levels. Broad says that even the slowed breathing people are encouraged to do in their yoga exercise class could be enough to slow metabolism and make them more likely to put on the pounds, even though they think they are doing something that will help with weight loss.

    All of that seems to support CO2 as being a factor in metabolism. 

    But still, the increase in atmospheric CO2 seems insignificant compared to the other factors at play. I thought lung CO2 was determined by breathing rate. Am I wrong about this? If ambient CO2 has any chance of affecting blood CO2, it really seems like it would have to do with interior, sealed environments, and with people just not spending as much time outdoors. 

    The other thing I wonder about is if sedentary people just breathe differently. Perhaps they engage in shallower breathing. 

  12. The carbon mongers have just jumped the shark with this one.
    Perhaps you could try something sensible like exploring our nation’s chemical laden factory farmed cheap carb diet??? No, I must be nuts, thinking diet might be related to obesity…

    1.  No, I’m what you would call a carbon monger and I’m not jumping this shark. 
      This new idea seems a couple of weeks too early.  It’s foolish. 

      But it sure makes a strong link between carbonated drinks and obesity. 
      Finally an explanation.    =]

      1. Carbonated drinks make you fat because of all the sugar content.  Even diet soda is bad, for obvious reasons, but also, because fake sugars – used for diet soda – are up to 800 times as sweet as plain white sugar.  So you have a diet soda, and your body ends up craving even more sugar/ sweets, chances are you cave in to that craving.

        1.  Oh yea, you are right, I was just being facetious. 
          I drink about three gallons of whole milk per week. 
          I have no adipose tissue. 

  13. Then rural residents should be thinner since they’re surrounded by O2-producing plants and trees.  And evidence to support that?

    1. I think what the issue is with rural residents, and anyone really, is the lack of cooking/ food prep knowledge.  Many people have lost that through the generations.  At least in the city, people have healthy options for eating out.  Also, I know someone who married a farmer, and she makes dinner for around 9pm, when her husband finally gets in.  That’s way too late to be eating a full dinner.  I grew up on a farm, no one in my family was fat, my gran did start to get puffy at one point in her 60s, but then lost the weight and was slim again until she passed away in her late 80s.  We never ate dinner late.  There was supper around 7pm, but that was a light meal, like a sandwich, or some yogurt with fruit and tea; we always had tea throughout the day.  I always have a substantial breakfast, a good lunch, dinner is usually lighter, and depending on how late I stay up, I may have a snack in the evening.  Another thing is, that people who think they are being healthy, because of the latest fad or “findings”, such as diet versions, low fat items, etc.  I remember not that long ago, margarine was the healthy option, then olive oil to use for stir frys, now margarine isn’t good any more, and olive oil shouldn’t be over heated, because it has a very low smoking point and breaks down easily.  I’m finding articles which are highlighting butter and lard as healthy option, and it makes me happy.  Finally someone in the media is realizing this.  Apparently until something gets media coverage, people just don’t buy into it.  Another issue is the long work week, people working 50-80 hour weeks.  It’s ridiculous, how can anyone have the energy to make smart choices at that point. 

      1. I agree. The CO2 theory may have some merit, but it’s like blaming your neighbor’s sprinkler when your cellar floods from a dam break. I think obesity is due to lousy food, lousy habits, and lousy living conditions even among the middle class. I’m referring to families where both parents work so dinner comes from the microwave instead of the stove top. I’d like to see a study of obesity in families where the mother or father stays home and cooks from the produce, meat, and seafood aisles instead of the frozen food and cookie aisles.

  14. Sleep apnea, which does cause a buildup of CO2 in the body due to the obstruction of the airway during sleep, is associated with increased blood pressure and weight gain. One’s appetite is increased which causes more calories to be consumed, and the sleep apnea sufferer also is sleepy during the day which results in a decrease in physical activity. 

  15. I thought obesity caused global warming. After all, if you’re too fat to walk anywhere or fit behind the wheel of a compact car, then you might have a higher carbon footprint.

    In related news, the fact that people who live in in the western U.S. (where “the scenery’s attractive and the air is radioactive”) have low cancer mortality rates can mean only one thing: Radioactivity makes people stop smoking.

  16. I have doubts about this for the following reasons.

    1) We all breathe the same air yet obesity rates are significantly different across the states in the US and  countries of the world.

    2) It’s the wealthy countries with growing obesity problems and it started in the wealthiest country.  Oddly, it’s the poorer US states with the greatest problem, which suggests the problem isn’t just access to food (otherwise the richest people in the rich countries would be fattest).

    3) In a previous post Maggie had a chart showing obesity rates for the past 50 years and the rate accelerated dramatically starting in the late 70’s.  If the number of obese people had continued to grow at the same rate as it did from 1960-1975 only about 18% of the population would be obese today instead of 35%.

    Item 3) above suggests that the problem was triggered on a national scale almost all at once, so it’s probably tied to federal policies, and number 2) suggests that the problem involves cheap, low quality food (poorer people eat more of it out of necessity). 

    My hypothesis is that the problem is changes in government farm subsidies in the early 70’s that resulted in huge amounts of corn, soybeans, wheat, etc. being grown – far more than we used to consume.  Result: dramatic price drops and efforts by processors and food companies to figure out how to sell it to us.  So the calories we consume increase, but it’s starches and fats: corn starch (breading), corn sweetener, corn oil, soybean oil, soy lecithin, corn chips, sweetened breakfast cereals, soda, buns, breads, bagels, muffins, etc.  The program changes were made in the early to mid 70’s they trickled through the agricultural system and a few years later we’re being sold a mountain of food we don’t need.

    1. Also, because of the top 4 crops being over produced in the US, there isn’t enough rotation going on, and the soil becomes depleted, so fertilizers are over used – fertilizers have been linked to hormone changes, which affect weight gain.  If farmers rotated crops, like they should be, there wouldn’t be as much need for fertilizers or pesticides.  A lot of non GMO crops have their own abilities to fight off predators and disease, but the GMO produce requires more pesticides, which also contribute to poor health, and less natural nutrients in the crops.

    2. To add to your last paragraph, note that it was in the 70s that the government nutrition experts started recommending that everyone eat less meat and fat and more carbohydrates.

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