Every gram is dangerous, or the newest scary BMI news

A paper clip, which weighs one gram

Sorry to interrupt your holiday weekend (if you’re in Canada or the US) or just your placid Sunday/busy Monday (if you’re somewhere else), but I have to let y’all know that, according to the latest childhood obesity research from the journal Pediatrics, we have to watch out for risks of gaining even a few grams of potential weight gain (much less pounds or kilos).

What am I talking about here?  This headline:

Headline from CNN news story: WIll 100% fruit juice make your child gain weight?

Spoiler:  the answer is no, or at most hardly at all.

But that of course does not sell newspapers, or as they say now, result in lots of click-throughs (actually, I’m not sure what they say now.  Anyone know?  Please tell me).

This research article is about the potential weight gain risks for children of drinking 6–8 ounces (18–23 cl) of 100% fruit juice a day.  When I posted this article on Facebook, a friend commented that fruit juice is bad for kids because it’s bad for their teeth.  There’s evidence for that claim and it seems reasonable.  It’s also included in this research article on recommendations on fruit juice intake for children and adolescents.

So what does the BMI article say?

First, a few numbers, from the article:

1 daily 6- to 8-oz serving increment of 100% fruit juice was associated with a 0.003 (95% CI: 0.001 to 0.004) unit increase in BMI z score over 1 year in children of all ages (0% increase in BMI percentile). In children ages 1 to 6 years, 1 serving increment was associated with a 0.087 (95% confidence interval: 0.008 to 0.167) unit increase in BMI z score (4% increase in BMI percentile). 100% fruit juice consumption was not associated with BMI z score increase in children ages 7 to 18 years.

That is, for children 7–18 years, drinking fruit juice every day had no effect on weight gain.  None.  Zero.  Zilch. Nada.  Bupkes.

The word "zero" in white, surrounded by a numeric zero on a black background.

The word “zero” in white, surrounded by a numeric zero on a black background.

But:  for children ages 1–6, daily fruit juice intake was associated with a 4% increase in BMI percentile.  Please note, that’s not a four-point BMI increase, or 4 pounds, or 4 kilos.  What is it?  This (from the article, p.8):

As an example, consider a 5-year-old girl at the 50th percentile for weight (18.0 kg) and BMI (15.2 kg/m2). An increase of 0.046 to 0.087 BMI z–score U over 1 year translates into an increase in this child’s BMI percentile to the 52nd to 54th percentile: a weight gain of 0.08 kg to 0.15 kg over 1 year. A small amount of weight gain that is not clinically significant at the individual level may gain significance when considered at the population level.

 

Okay, let’s translate some of this.  This study would predict that for say, some 5-year-old girl in the 50th percentile for weight (for her age), could gain .08 to .15 kilos in one year (0r 2.28–5.29 ounces).  That’s the weight of about 2–2.5 Clif bars. The researchers also graciously add that this amount of weight gain is not clinically significant at the individual level.  You bet it’s not!

This amount of potential weight gain, even for small children, is tiny enough to be within the normal variance of weight over time.  That is, IT DOESN’T MATTER.  AT ALL.

Why am I bringing this up to y’all?  After all, this is a study about children, not adults.  I bring it up because it’s another example where we are directed to pay attention to minute changes in body metrics and imbue them with all sorts of alarmist meaning.  The changes that are documented here are admittedly irrelevant to the health and well-being of children.  They are statistically significant (for very small children only), but that doesn’t mean that they mean anything at all for how we should behave or act or respond or live.

Not that I’m advocating for rampant fruit juice drinking on the part of children and adults everywhere.  As I said earlier, there’s other evidence about the effects of fruit juice intake on cavities.  If you’re interested, check it out and do what you will.

Science is a big tent.  People do all kinds of research searching for connections among lots of features of our bodies, our behaviors, our environment, etc.  Sometimes they find big connections, sometimes small ones, sometimes they find nothing.  As consumers of science, especially body weight science, I think it’s important to notice when the results of scientific study are NOT alarming or NOT relevant, even when they feature dazzling metrics (and ominous headlines).

In short, sometimes we need to take our science with a grain of salt.  Which weighs 0.00067 grams (if it’s table salt).

A spoon inscribed with "take it with a grain of salt".

A spoon inscribed with “take it with a grain of salt”.

 

 

About catherine w

I'm an analytic philosopher, retooled as a public health ethicist. I'm interested in heath behavior change, particularly around eating and activity, and how things other than knowledge affect our health decisions.I'm also a cyclist (road, off-road, commuter), squash player, x skier, occasional yoga-doer, hiker, swimmer and leisurely walker.

3 thoughts on “Every gram is dangerous, or the newest scary BMI news

  1. Jean says:

    People do have to read food labels and ensure there is no sugar added to the fruit juice. One of the rules my parents had (they had 6 children) and my sisters who have children, is not to give fruit juice in a baby bottle for child to mindlessly suck on just to keep them quiet. Instead to give it to child as a small amount of healthy drink that is consumed consciously ie. at breakfast. Not as a pacifier drink.
    What amazes me is people allowing children to drink Gatoraid and other energy drinks. Seriously?? I never grew up while running around on school playgrounds and playing softball in high heat with any energy drink…around. We just drank water from school water fountain.

    Like

  2. Kim Solga says:

    Catherine, thanks for this as always. Your work on this blog is a public service indeed!!

    For me the key story here is the absolute due diligence fail at the journo level. I appreciate news desk staff can’t always have advanced science training, but surely to do their basic jobs – report the facts – they need to have a way to interpret what they are reading accurately. I’m among those academics who is often at risk of having my research badly mishandled by news outlets or scaremongering columnists, so I think about this a lot. My question is: how do we better help media staff understand complex research so they can at least not get it seriously wrong?

    I know there’s also the click through issue but I suspect that’s only part of the story.

    Liked by 3 people

    • where we are says:

      I completely agree! This is irresponsible journalism and another reason that people end up denouncing media and even science. I hope a link to this blog was posted in the comments of that article.

      Like

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