Addicted to novelty since 2001

Expanding Waists, Decreasing Populations?

I listened to the second half of that BBC documentary on obesity that I mentioned. It was equally fascinating, and it got me thinking about the converging problems of increasing global obesity and declining birth rates (the program didn’t cover this particular ground).

Obesity rates are predicted to increase dramatically in the developing world, and certainly aren’t declining in the developed world. As nations develop, their birth rates plummet. Many Western nations are struggling to maintain a replacement birth rate.

Fatter People, Fewer Kids

Overweight and obese women have a harder time conceiving. I went looking for a nice graph that charted increasing weight or BMI (body mass index) to declining fertility, but I came up empty. I was surprised how little hard data on this issue I could find. Either my search skills failed me or there isn’t a ton of useful studies out there to cite. I did find a 2006 article from the University of Adelaide:

“We know that obese women are 2.7 times more likely to be infertile compared to normal women. Obesity rates have doubled in Australia in the last two decades and that is the reason why a lot of women are having trouble falling pregnant or carrying babies to full term.”

Everybody agrees that obesity leads to reduced fertility, but this was the only data point I could find. Maybe Dr. Beth can help?

Compounding the issue, men who are overweight or obese have lower sperm counts and concentrations (focus, spermatozoa, focus!)–their fertility (or should that be virility?) decreases by 20 to 25%.

I wonder how an overweight and obese human race impacts longterm population projections? If we don’t live as long, have a harder time procreating and procreate less as more nations become ‘developed’, maybe we’ll reach that population peak sooner than we think?

And then start a long, slow decline? Wouldn’t that be cool if, by 3007, there were only, say, a billion people on the planet again?

4 Responses to “Expanding Waists, Decreasing Populations?”

  1. Charity Froggenhall

    If obesity keeps happening, by 3007 we’ll only be able to FIT a billion people on the planet.

    But seriously, thanks for pointing to this series. Rethinking obesity in poor countries as another form of malnutrition is key. And just because someone is fat, it doesn’t mean they’re nourished.

  2. Gregg

    I not trying to be insulting here, as I’ve certainly fought my own battles with the bulge and would have been considered obese a year ago; but is it maybe a good thing that obese people are less fertile? The debate rages as to how much is in our genes and how much is lack of self-control; but most agree some portion is genetically pre-determined. Could this be nature’s attempt to reduce the amount of obesity by reducing the likelihood that contributing genes will be passed on?

    If being obese was something that lead to higher health and longer lives, it would have been bred into us long ago. Well that might lead some to argue that maybe it is now getting bred in, it has come up on us too fast for it to be just genetics. Check out this post by Duane Storey to see the speed it came upon us.

  3. Duane Storey

    I read tons of research in this area. The infertility in women is generally related to something called PCOS. It is caused by excess insulin levels, which in turn causes women to produce more androgens (male hormones) than usual. The #1 treatment (after diet and exercise) is a diabetic drug called Metformin which reduces insulin levels.

    There’s also some evidence that the genetic problems (or the thrifty gene if you will) was in part responsible for the sudden rash of women using formula instead of breast feeding years ago (since formula was almost all carbohydrates, while breast milk contains a lot of protein and fat). That causes the young body to have high insulin levels during it’s first few months of it’s life, which seems to cause some changes in the genetics.

    I’ve read lots of research recently on how bad caffeine is for people, and how it might be contributing to obesity (even in diet pop), since it also leads to elevated insulin levels. I have been unable to locate a soft-drink consumption chart though, even though I’ve looked quite hard.

  4. Beth

    Decreased fertility in obese women isn’t just limited to those with polycystic ovary syndrome (PCOS).

    “Obesity independent of polycystic ovary syndrome (PCOS) is associated with anovulation [i.e., not ovulating], and minimal weight loss alone is an effective therapy for induction of ovulation in both obese women and obese PCOS women.”[1]

    To address your request, Darren, I did a quick search of the medical literature and found many references to the relationship between obesity and infertility/decreased fertility.

    A few examples:

    A review of data from 7327 pregnant women found decreased fecundity (measured as time it took to get pregnant) in overweight/obese women compared with optimal weight women, even when those women had normal menstrual periods. [2]

    A review of data from the US National Survey of Family Growth (NSFG) found that obesity (among other factors) was associated with infertility. [3]

    A literature review providing evidence of the link between obesity and infertility (as well as associations between obesity and miscarriage & stillbirths) [4]

    I could go on, but I’m pretty sure no one is still reading this comment. Suffice it to say there seems to be quite a bit of medical literature to this back up.

    Dr. Beth


    [1]Nelson & Fleming. (2007). The preconceptual contraception paradigm: obesity and infertility. Human Reproduction. 22(4):912-5.

    [2] Gesink Law et al. (2007) Obesity and time to pregnancy. Human Reproduction. 22(2):414.

    [3] Kelly Weeder & Cox. (2006)Women & Health. The impact of lifestyle risk factors on female infertility. 44(4):1-23.

    [4] Davies. (2006). Evidence for effects of weight on reproduction in women. Reproductive BioMedicine Online 12(5): 552-56.

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