Most of the time I can’t stand the way the media, the general public, and women themselves talk about weight. Fat shaming is everywhere. We shame others. We shame ourselves. We are taught that higher body weight stems from personality flaws, lack of willpower, or other nonsense judgements. For example, I recently started reading Harry Potter to my kids and, although I’m excited for them to join this magical world, the fat shaming in the first two chapters is outrageous. Et tu J.K. Rowlings?
On the other extreme is the oft-criticized Health at Every Size Movement that promotes bad science in an effort to overlook the health consequences of excess body fat.
Frankly, we need to stop fat shaming AND we need to have evidence based discussions about the way weight intersects with health. Threading this needle is hard. And, I’ll be honest, sometimes I avoid the subject just to avoid sounding daft. Nonetheless, avoiding the topic is foolhardy, especially because the evidence on weight and the pelvic floor is surprisingly clear (I say “surprising” because very little in the postpartum world is clear).
BMI and Your Pelvic Floor
Having a higher BMI increases your risk of pelvic floor disorder, specifically stress urinary incontinence. The relationship has been extremely well-documented. Therefore, let’s throw out the taboo and talk about weight (I.e. “a body’s relative mass or the quantity of matter contained by it, giving rise to a downward force; the heaviness of a person or thing”).
Isn’t BMI Stupid or Something?
A lot of online sources will tell you to ignore BMI, but this directive is misguided. BMI, or body mass index, often gets a bad rap because it looks at the relationship between height and weight without taking into account muscle mass. Someone could have a lot of muscle and an “inflated” BMI, whereas a skinny person could have a perfectly fine BMI, but very little muscle (muscle is good). Sidenote: Read this post to learn more about the epidemiology of BMI.
BMI is NOT a measure of fatness. It is an imperfect proxy for it. Therefore, the cut-offs of “overweight” or “obese” become loaded and not totally useful from an individual perspective, but can tell us a lot about populations. As Dr. Chung explains on Evidence Based Fitness, “If you are able to measure body fat, then using BMI is not useful because you already directly measured the variable of interest. BMI is only useful when you cannot measure body fat.”
In other words, BMI is a flag. If your BMI flags you into the overweight (BMI > 25) or obese (BMI > 30) categories, it means you should do more testing, not hold up BMI as the last word. That said, Dr. Chung also notes, “…having a high BMI, regardless of your body fat percentage, may still be a risk factor for bad things.”
This is a roundabout way of saying that studies using BMI to establish risk factors for pelvic floor disorder aren’t to be dismissed simply because we don’t like or fully understand Body Mass Index. BMI is an easy measurement and helpful when examining population wide risk factors. If anything, BMI under-selects at risk populations rather than over-selects. This means the bigger problem is not miscounting those with a lot of muscle mass, but rather overlooking those who are at risk of disease but not technically overweight.
In terms of pelvic floor disorder, BMI plays a clear role.
Having a high BMI increases your risk of pelvic floor disorder. Below is just a sampling of some studies.
A 2008 study looking at the prevalence of pelvic floor disorder showed that increased age, parity (number of children), and BMI were “significantly associated” with at least one disorder. Specifically, 15.1% of women considered underweight/normal weight reported at least one pelvic floor disorder, whereas 30.4% of women with a BMI considered obese reported at least one pelvic floor disorder, which is a rate comparable to women who had three plus vaginal deliveries and more than the rate of women who had one or two vaginal deliveries. This makes BMI a pretty significant risk factor.
Clearly, observational studies will have limitations and this is why we can only make statements like “Higher BMI is associated with higher rates of pelvic floor disorder.” We can’t say greater weight causes it. However, once a preponderance of the evidence shows a robust association, a causative link becomes more likely.
Another 2008 study, this time a review of the evidence thus far on obesity and pelvic floor disorder, showed that weight loss associated with gastric bypass, as well as more modest weight reductions from lifestyle interventions, improved symptoms of pelvic floor disorders. Conversely, the literature on obesity as a risk factor for recurrence of PFD after surgery was mixed, but “one study with an eleven year follow-up after hysterectomy showed a 4.4% rate of vaginal vault prolapse and obesity as the strongest risk factor for its occurrence.”
A 2015 study looked at the effect of body mass index on postpartum pelvic floor support and concluded, “Our finding suggests that postpartum BMI influences pelvic floor laxity 1 year after delivery. Postpartum weight reduction may serve as a strategy for POP prevention in some women.”
And, a 2017 study found that “[i]ncreased body mass index (BMI), WHTR and waist circumference (WC) showed highly significant associations with an increased risk of stress and mixed urinary incontinence.”
What does this mean? Will a higher BMI doom someone to pelvic floor disorder? Well, no. That’s not how risk factors work. For example, I’ve never had a high BMI and I have (manageable) pelvic floor disorder. BMI is clearly not the only component and no study has shown that. I had other risk factors, including bad genes, long labors, giant babies, etc… That said, if I had a higher BMI, my pelvic floor disorder might be less manageable. The goal is reduction of risk factors. I can’t change my genes or my labors, but I can strive to keep my BMI under control as I age. Conversely, plenty of women with higher BMIs don’t have PFD.
Therefore, we must be clear that we know nothing about someone’s pelvic floor simply by assessing her BMI. But we do know that someone with PFD and a high BMI might benefit from strategies to mitigate this particular risk factor.
Why Would BMI Affect Pelvic Floor Disorder?
The literature shows an association between BMI and pelvic floor disorder. But why? What is going on?
Quick answer: Probably pressure.
Most clinicians hypothesize that increased abdominal pressure can lead to “structural damage and neurologic dysfunction,” which makes sense if you consider the pelvic floor’s location and the increase in stress incontinence during pregnancy, a time of greater pressure on the pelvic floor. However, there’s probably more than just pressure going on. A 2014 study looking at different subgroups of incontinence and BMI again showed a strong association between BMI and PFD, but suggested the association is probably not only attributed to mechanical pressure.
Similarly, reductions in BMI often reduce the rate of PFD, but this is probably due to a combination of factors, the weight loss itself and the lifestyle changes that would accompany this weight loss (e.g. Increased physical activity).
Again, parsing out risk factors is notoriously difficult, which is why so many studies showing that BMI is a clear risk factor for pelvic floor disorder should make us take note of the consistency in the literature. Many risk factors for pelvic floor disorder are not modifiable. We can’t stop ourselves from aging (but we can be active as we age). We can’t go back in time and alter childbirth (but we can make decisions for any future births). However, we can make lifestyle changes that may result in reductions in BMI.
That said, pelvic floor disorder is complicated and risk factors are aplenty, so put individual BMI into context and don’t go on a crash diet thinking rapid weight loss will cure a pelvic floor disorder. The evidence does NOT support this conclusion.
Rather, I’d suggest small, incremental steps to a healthier lifestyle that might also improve any pelvic floor symptoms. A healthy lifestyle, one that includes reasonable eating patterns and moving your body on a regular basis, benefits pretty much everything ever. But, leave the fat shaming at home because that has not benefited anyone ever (not even Harry Potter).