I have long thought that there is more to the obesity epidemic than merely a change in diet, although I do believe that the large increase in the consumption of carbs in general and fructose specifically are exacerbating forces. I’m always on the lookout for something that happened around the late 1970s/early 1980s that might be a major driving force behind the explosion of obesity that we’ve experienced since then.
The epidemiology of the sudden increase in fat deposition in so many people looks like an infectious disease, but I have a problem in buying into that idea whole hog. If it were an infectious disease, I don’t see how the switch to a low-carb diet would make it go away. I suspect that it is probably some sort of environmental contaminant that underlies the situation. The difficulty is in discovering what the factors are and how they work to make us all struggle to keep our weights in check. I doubt that there is one specific catalyst for the entire obesity problem; I would think that a combination of ingredients are probably at fault. But what are they?
I’ve posted on a few previously. In addition to those, a paper recently published online in the journal Environmental Health Perspectives implicates phthalates as another possible agent.
Phthalates are a class of chemicals that are plasticizers. In other words, they turn hard plastics – particularly PVC – into softer, more flexible, ones. Phthalates are also used in cosmetics, shampoos, soaps, lubricants, pesticides, paints, and, strangely enough, rubberized sex toys. (Due to the phthalates in this last, some manufacturers of these objects recommend the use of a condom on the device prior to use.)
Although phthalates are oil soluble like PCBs and dioxins and the other pollutants I’ve posted about before, they are also apparently fairly quickly metabolized and their metabolic by products are excreted in the urine. But while they hang around – and they do hang around because most of us are constantly being exposed – they cause some problems. More than 75 percent of Americans have measurable detectable levels of phthalate metabolites.
One of the actions of phthalates is to act as an anti-testosterone.

Phthalates are known antiandrogens in experimental animal models, with consistent results dating back several decades. Testicular steroid hormone synthesis and reproductive system development in males have been adversely affected by exposure, especially neonatal exposure, to certain phthalates…

And, in males at least, since a lack of testosterone or low testosterone levels have been associated with obesity and insulin resistance, anything that reduces testosterone or negates its effects should cause insulin resistance and/or obesity. The authors of this paper looked for such a correlation.
The researchers used 1999–2002 data from the CDC National Health and Nutrition Examination Survey (NHANES) to look for a correlation between phthalate exposure and obesity and/or insulin resistance in adult men. They compared urine concentrations of six phthalate metabolites to the participants’ waist circumference and measures of insulin resistance while controlling for a variety of potential confounders, including age, ethnicity, fat and calorie consumption, physical activity, and smoking status.
The data show a significant correlation between four of the phthalate metabolites and a larger waist circumference and three metabolites and increased insulin resistance. When subjected to more rigorous statistical analysis taking into consideration liver and kidney function, the researchers found that the associations decreased a little but were still significant for all the metabolites but one.
The paper is available in free full text if you would like to read it in its entirety and look at the graphs showing a dose-response curve effect for these metabolites.
I want to add that this paper in no way ‘proves’ that phthalates cause obesity and/or insulin resistance. What it does show is that there is a correlation between large levels of phthalate metabolites (and presumably phthalites) and an increased waist circumference and insulin resistance. But it is axiomatic that correlation does not imply causation. Actually it does imply causation, but there is really no proof that the one causes the other.
If you look outside and you see a lot of umbrellas you can be pretty sure it’s raining. You look out a little later and see no umbrellas and it’s not raining. After you make these observations a number of times, it would be reasonable to say that umbrellas cause rain because every time you see an umbrella it’s raining. In this case there is a correlation but there is no causation. In fact, there is causation, but it works the other way: the rain causes people to pop out their umbrellas.
The next step to see if there is causation is to give lab animals phthalates to see what happens. In the case of rodents, the effect is smaller than that found in humans. As the authors point out

Associations between certain phthalate metabolites and antiandrogenic effects have also been found in humans at much lower exposure levels than those used in rodent experiments. Suspected metabolites include mono-benzyl phthalate (MBzP), mono-ethyl phthalate (MEP), mono-isononyl phthalate (MiNP), mono-methyl phthalate, and mono-butyl phthalate (MBP). Urinary phthalate metabolites in pregnant women have been found to correlate with subtle genital changes in their infant males, and breast-milk phthalate metabolites have been correlated with shifts in reproductive hormones in infant males.

Although there is no absolute proof that phthalates are a driving force, much less THE driving force, in the development of insulin and obesity, there is enough correlative evidence for me to make me avoid them as much as possible. There are way too many natural products out there that are cosmetics, soaps, shampoos, and even sex toys for all I know to keep me from having to use those products containing phthalates. I would encourage readers of this blog to do the same. Here is a Wikipedia entry on phthalates along with a list of the most common ones so that you can identify them on the labels of products you may be considering. All have phthalate on the end – dimethyl phthalate, for example – so they’re not tough to identify.


  1. On a completely unrelated note, I’m hoping for more thoughts from you on the question of whether fibre is good, or bad, for you.
    You may recall commenting on the insanely backward reasoning of “well, lots of fibre injures the cilia in your colon, so I guess injuring it must be good for you, because we all KNOW fibre is good for you”.
    So, I’ve always preferred complex grain breads, and figured it’s better for me…but now (aside from your inevitable abhorrence for glutens) I’m wondering if maybe whole grain bread might sometimes be too much of a good thing. Or eating oatmeal every day for breakfast.
    For that matter, I’ve always sorta thought that it was easier to wipe when I wasn’t getting so much fibre.
    Another topic you actually said you were going to expound upon is the popularity of doctors giving hysterical releases to their female patients…making me wish I were born a century earlier.
    Hi Kaz–
    The short answer is that I don’t think fiber is particularly good for you.  It certainly not all it’s cracked up to be.

    I’m working on the blog you’re awaiting on the hysterical paroxisms of a hundred years ago.

  2. I recently saved an article from BBC titled “Did microwaves’spark’ obesity?” Professor Jane Wardle is quoted as saying that since the obesity epidemic (in the UK)started in the mid ’80s, it could be linked to the popularity of microwave ovens. The article suggests some silly reasons that this might be so, but one that is not mentioned is that a lot of what went into those ovens was nuked in plastic containers or covered with plastic film. I remember when plastic baby bottles were introduced to replace “dangerous” glass bottles; perhaps the infant formula that was microwaved in plastic bottles also contributed to our current problem.
    The article can be found here: http://newsvote.bbc.co.uk/mpapps/pagetools/print/news.bbc.co.uk/1/hi/health/6725775.stm
    Hi Judy–
    You may be right on the money.  Most stuff is nuked with a plastic film, and phthalates are what makes the plastic flexible.  I don’t know if the nuking makes the stuff leach out into the food, but I wouldn’t be surprised if it did. 

  3. The data you present makes it pretty clear that there is a strong correlation in males, but I did not see any indication that the same could be said for females; yet females are just as much at risk for obesity as males. Thanks for the article.
    Hi Pam–
    Thanks for reminding me.  I intended to put that in the post, but slipped up.  The paper points out that the anti-testosterone effects would not apply to females.
    I’m not contending that this is the only cause of obesity, just that there is a correlation.

  4. Actually, the leaking of phtalates in microwave ovens is a relativly well known phenomenon in Germany. It’s been warned about in mainstream media for some years now.

  5. Few things:
    1- Men’s Health had a question from a reader a month or two ago about plastic water bottle in the ice box and phthalates. Answer was: Freezing, fine. Heating, bad. Apparently, someone they get advice from thinks heating releases the phthalates.
    2- Correlation is not causation. It is present in causal relationship, but just because you’re correlated doesn’t mean you have causation. Famous examples: the man in England who gets more pigeon poop on his window sill when the DJIA goes up and less when it goes down. This had, for a ten year run, a 78% correlation. I suppose we could come up with a causal story to explain it, but, no one’s buying that bridge to Brooklyn either. DJIA & hem lines too. I think that’s 85% correlated. Hrm, what else can we link here… all the correlations between heart health and fiber intake.
    3- Was wondering about something off this topic. In both PP books, you advocate drinking “until you float”. I’ve read a lot recently about the 8 cups a day thing not having any base in anything, and no one is sure where it came from. Personally, I feel better when I’m “floating” (though makes me feel like I have a small bladder sometimes). So, do you have insight into where it came from? Or why do you and MD recommend it? Curious.
    Hi Max–
    The main reason we recommend a lot of water is that it makes a lot of urine.  A lot of urine gets rid of a lot of ketones.  Ketones contain calories, so it’s a free way to ditch calories.  And, we think, it probably reduces the amount of ketones released in the breath so people don’t go around with as much ketone-breath.
    Aside from that reason, there isn’t a real reason to drink copious amounts of liquid.  I’m sure our Paleolithic ancestors drank when they were thirsty and when water was available.  One of the main components of meat, fruits, and vegetables is water, so even when you’re eating, you’re drinking.

  6. Are phthalates in the plastic bottles that soda and bottled water come in?
    Yes, they are in soft plastic bottles.  Plastic is hard.  Phthalates make it soft, so if you’ve got soft plastic, odds are you’ve got phthalates.

  7. Aren’t testosterone levels lower than the used to be 100 years ago? As well as average sperm count?

  8. If ketones are got rid of in the urine, and the brain runs better on ketones, should brain-intensive workers not drink so much water?
    Hi fish–
    If one is following a ketogenic diet the liver makes plenty of ketones to replace those lost in the urine, so drinking water isn’t really a problem.

  9. I like your umbrella analogy, I think I’ll steal it and replace it with mine. The one I’ve been using goes like this. There are usually skid marks at the scene of an automobile accident. Where there are no skid marks there are no automobile accidents. Therefore skid marks cause automobile accidents. I try to avoid skid marks at all costs. However it’s difficult to find skid marks when it rains so it must be that most accidents are caused by umbrellas. The logic is undeniable.
    Great blog,
    Hey Dan–
    Here is a fun little video about a town called Allopath that cleverly uses the skid-marks-as-the-cause-of-automobile-accidents analogy.

  10. Sweden banned pthalates in cosmetics due to the connection between high pthalates in pregnant women and problems of genital development in boys. interestingly( and unrelated), Sweden also banned iron fortification of foods in 1995 due to the well-established link between too-much iron and just about every serious degenerative disease. socialism may be the pits, but sometimes the Swedes get it right on the money!
    Hi gareth–
    They are very right on these issues.

  11. Dr. Eades I’m so glad to see you posting about this issues with phthalates. I’ve been lecturing worldwide on the subject and imagine that many more problems will surface regarding this toxin. One area I think needs more research is the link between phthalates and autism, especially in males. It is something I have thought about and wonder what you think.
    Hi Mark–
    I haven’t read anything specifically linking pthalates to autism, but I’m not all that well read in that subject.  If you’ve got any specific papers, I would appreciate the references.

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