body image · fat · health · Science

Does my life depend on my body shape?

CW: discussion of body shapes and body weight, primarily with respect to a recent study assessing those variations in relationship to mortality risk. Lots of critique, too– you can count on that.

I have wide hips, large thighs and a large butt. Always have, always will. Regardless of my age, height, weight, fitness, that’s what my physical outline has looked like. My sister has always had slimmer thighs and butt, carrying more weight in her midsection. We are both in our 50s now, heavier and both carrying more weight in our midsections. We’re both doing what we do, happy to hang out when one of us can travel to the other.

My sister Elizabeth (left) and me, on the beach in South Carolina.
My sister Elizabeth (left) and me, on the beach in South Carolina.

All this is to say: we have the bodies we have, in the shapes they are. And even though the internet will offer you plenty of opportunities to spend your hard-earned cash on pills, supplements, gadgets and programs to try to change your body shape, I recommend saving it. It’s a waste of money.

So why do people worry about their body shapes and want to change them? In addition to all the messaging we get about what the “perfect” body shape is, medical science warns us of the dangers supposedly hidden in those shapes.

A new study came out in the past 10 days, looking at associations between body shape and mortality risk. Naturally, the press was on the scene, ready to inform us in the most provocative ways they could think of. Here’s a sample of the (inaccurate) headlines:

Headlines, the best of which is "thick thighs save lives". I wish this were the case.
Headlines, the best of which is “thick thighs save lives”. I wish this were the case.

What’s inaccurate about them? It’s not the case that having (or working to acquire) thick or chunky or wide hips and thighs will itself cause increased longevity; of course we know that. What these news outlets are saying is that people who carry their weight more centrally are at higher mortality risk than those who carry their weight less centrally. But is this true? Let’s see what the article is saying.

In a recent meta-analysis (study of a lot of studies) a team of Iranian and Canadian researchers set out to identify and quantify mortality risk factors specifically related to body dimensions and ratios Waist circumference, waist-to-hip ratio are commonly studied measures for this type of research. In addition, this group studied thigh circumference, hip circumference, something called “body adiposity index” (roughly, a function of the ration of hip circumference to height) and another fancy biometric called “A body shape index”.

In case you’re still reading (one can hope), here’s what the researchers concluded:

Indices of central fatness … were positively and significantly associated with a higher all cause mortality risk.

Larger hip circumference and thigh circumference were associated with a lower risk.

The results suggest that measures of central adiposity could be used with body mass index as a supplementary approach to determine the risk of premature death.

What do I make of this? Well, glad you asked. Here are a few takeaways:

One thing: They definitely found lower mortality risk associated with larger hip circumference. But there’s more– look at this pair of graphs:

Two graphs measuring changes in mortality risk as hip circumference increases.

What’s interesting to me here is that the top graph, which controls for BMI and waist circumference, shows the risk dropping well below 1 (which is set as the standard, so less than 1 is better). But in addition, the bottom graph, which doesn’t control for BMI/waist circumference, still shows a dip in the mortality risk below 1 up to about 112 cm, and a very small increased risk up to 120 cm.

Why is this interesting? Because the second graph shows that people with larger hips have a lower relative mortality risk, even apart from body weight.

Another thing: Here’s another set of interesting-to-me graphs:

Two graphs with mortality risk based on waist-to-height ratio for men (on left) and women (on right).

What we see here that caught my eye was how the waist-to-height ratio increase is fairly straightforwardly associated with increased mortality risk for men, but for women this is not so. As waist-to-height ratio increases, there is a dip in mortality risk for women before increased starting at around .52.

Which leads me to yet-another-thing: the researchers mention (which other researchers know but sadly, not reporters) that many of these associations disappear with age. That is, for people older than 60, these body dimension metrics and ratios don’t tell us much of anything about mortality risk.

Last thing: all through the text of this article, the authors either cite other studies or give results which suggest that body weight itself is not positively associated with increased mortality risk. They point out the need for studying different populations, including those who are healthy (vs. those with underlying medical conditions), smokers, ex-smokers, and never-smokers, and subcategories of those with men vs. women. What does this tell us?

Science is complicated.

A woman looking at the contents of a beaker; photo by the National Cancer Institute, via Unsplash.

So, does my life depend on my body shape? No.We have the shapes we do. Hundreds of features of both our bodies and the world our bodies inhabit influence how we live and how long that will be.

But I still kind of want this T shirt:

Thick thighs save lives.
Thick thighs save lives.

Readers: does this sort of body-shape research bother you? Do you ignore it? I’m curious about how these murky medical messages translate in the public. If you have any thoughts, I’d love to hear them.