I’m not a horror fan at all. The blood and gore just gross me out, even if they’re comically unrealistic. But the worst part for me (which I know is the best part for others) is the surprise twists, especially at the end. I get confused, distracted, scared if it’s scary, and really grossed out to the point of nightmares sometimes. And this includes experiences even after the age of 10. So I don’t watch them.
We know to steel ourselves for surprise twists at the end of movies. But who prepares themself for an out-of-the-blue and contrary-to-the-plot twist in an article on the connections between physical activity and health in kids? Not me, and probably not you.
So imagine my surprise when, while reading an article reporting results of a study finding a correlation between more time spent being physically active and better metabolic health among adolescents, it switches gears completely at the end, saying this:
Professor Bell explains: “This suggests that it’s never too late to benefit from physical activity, but also that we need to remove barriers that make activity hard to maintain. Keeping it up is key. This includes making weight loss via diet a priority, since higher weight is itself a barrier to moving.”
Here is what the study itself said:
A group about 1800 girls and boys born around 1991-92 were studied on three different occasions from 2003 to 2008. The researchers were looking for connections between levels of physical activity and biological markers of their overall metabolic health (e.g. cholesterol types, triglycerides, etc.– 230 in total). What they found was this:
- Better metabolic health was associated with recent moderate-to-vigorous physical activity, regardless of previous activity patterns (this is a bit more complex, but basically correct).
- Worse metabolic health was associated with more sedentary activity patterns.
- The correlation between moderate-to-vigorous activity and metabolic health wasn’t weaker for subgroups with higher body fat (which could mean those who have a history of less physical activity, or also those with higher BMI).
They conclude here:
Our results support associations of physical activity with metabolic traits that are small in magnitude and more robust for higher MVPA [moderate to vigorous physical activity] than lower sedentary time. Activity fluctuates over time, but associations of current activity with most metabolic traits do not differ by previous activity. This suggests that the metabolic effects of physical activity, if causal, depend on most recent engagement.
There’s nothing here about losing weight as a causal factor or salient feature in their analysis. So why did the main author say that in the article? I decided to dig a little deeper, which means going to the original full article. I’m doing it, so you don’t have to– it’s part of the service we provide at Fit is a Feminist Issue.
Here’s what’s going on: in their discussion of where their study fits in the literature on metabolic health, physical activity, body weight, and risks for e.g. type 2 diabetes in youth, they say this:
much of the association of higher activity with lower subsequent adiposity is driven by reverse causation in this data… [there appears to be] a lowering effect of total activity on fat mass and blood pressure… The standardised effect size was 6 times larger in the reverse direction, however—from fat mass to inactivity—suggesting that adiposity affects activity levels more than activity levels affect adiposity.
Effect sizes matter a great deal for public health messaging since the existence of an association, or indeed a causal effect, does not alone describe its importance. Future work should compare magnitudes of effect size between common risk factors as the rate of discovery and the need to prioritise limited public health resources both increase.
The researchers say their results (and literature) support the idea that (in adolescents), body weight affects physical activity levels up to 6 times as much as activity level affects body weight. This part is no surprise, as loads of studies support the view that exercise doesn’t result in much of any weight loss.
Here’s a surprise, though (and this one isn’t scary, so it’s okay to keep reading): saying that body weight influences physical activity (that is, kids with higher body weights tend to be less active) means to the researchers that we need to work on our public health messaging, as this is very important.
YES! Of course we need to work on this. Movement at every size and shape and ability (and age, too, of course) helps us in just about every way.
But then (now the scary part is coming, be warned), the main researcher, Joshua Bell (not the violinist, I assume) has to go and say that, because higher weights are a barrier to increased physical activity, that kids should “make weight loss via diet a priority.”
Why no? Because 1) no one knows how to bring about and maintain weight loss via diet in kids (or anyone else); 2) we do know how to remove barriers to increased physical activity for kids with higher body weights. How do we do this?
- attack fat shaming and weight stigmatization of kids everywhere we find it;
- create opportunities for fun, non-competitive, easy-to-do movement for kids, done at their own pace and for reasonable time lengths, with no measuring, and lots of assistance and support;
- work on ways to incorporate those conditions for movement into the everyday lives of kids and the people around them;
- never use the word diet again around them (or anyone, for that matter).
This kind of public health messaging and programming is something we can all agree to. And that’s no surprise.