Obesity – How the Media Misleads You

Here are some news headlines reporting on a study published earlier this week:

“Can you be obese and ‘healthy’? Study says no” – FOX News

“Healthy and overweight is a myth, study suggests” – BBC News

“No ‘healthy pattern of obesity,’ review finds” – CBC News

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Those headlines are certainly compelling, but as a scientist I have learned to take health and science stories in the media with a significantly oversized cube of sodium chloride.

Most journalists do not have the training or experience to critically analyze scientific research papers. Often they don’t even read the paper before they report on it, they just quote from a press release!

I think that sucks, so let’s go through the study in more detail and see what it says. Then we can decide for ourselves whether the headlines are truthful.

Here is the full reference for the paper: Kramer, C. K. et al. 2013. Are metabolically healthy overweight and obesity benign conditions? A systematic review and meta-analysis. Annals of Internal Medicine 159: 758-769 and here is a link to the abstract: http://annals.org/article.aspx?articleid=1784291

Strap yourselves in.

1. What did this study look like?

This paper is a meta-analysis, which means it borrows data from many previous studies and runs statistical tests on all of them simultaneously.

In this meta-analysis the authors are looking at the difference in health outcomes in people of varying body mass index (BMI) and metabolic health status. The authors want to know if either of these variables can predict the risk of a cardiovascular event (= heart attack or stroke) or all-cause mortality (= dying).

Participants in all of the previous studies were sorted into 3 BMI categories and 2 metabolic health categories. The BMI categories are:

– normal-weight (BMI 18.5 – 25)

– overweight (BMI >25 – 30)

– obese (BMI >30)

The metabolic health categories, determined by an assessment of waist circumference, blood pressure, fasting glucose level, and other parameters that indicate metabolic syndrome, are simply:

– metabolically healthy

– metabolically unhealthy

So there are 6 groups of people overall:

– Metabolically healthy normal-weight (MH-NW)

– Metabolically healthy overweight (MH-OW)

– Metabolically healthy obese (MH-OB)

– Metabolically unhealthy normal weight (MU-NW)

– Metabolically unhealthy overweight (MU-OW)

– Metabolically unhealthy obese (MU-OB)

On to the results!

2. What did this study find?

To assess the differences in health outcomes among the different groups, the authors calculated a number called “relative risk” (RR). In these RR estimates, the MH-NW group is assigned a “risk” of 1.0 as a standard to compare everyone else to. Individuals in any groups with RR > 1 have a higher chance of death or cardiovascular events (CVE) than the MH-NW, while individuals in any groups with RR < 1 have a lower chance of death or CVE than the MH-NW.

Furthermore, the authors divided the previous studies into two groups: those that followed people for short periods of time (< 10 years) vs. long periods of time (> 10 years) after the initial assessment of BMI and metabolic health. Note: people were not allowed to change categories over their lives. If they started the study labelled MH-OW, then that was the category their death or CVE was attributed to.

a) Metabolically unhealthy people: The meta-analysis found that all of the MU people had the same increase in mortality and CV risk, regardless of their BMI, in both the short- and long-term follow-ups. There was no difference in RR among the MU-NW, MU-OW, or MU-OB groups.

So for these groups it’s being metabolically unhealthy that was the issue, not being overweight or obese. Pretty straightforward.

b) Metabolically healthy people: As long as a person was metabolically healthy, being overweight (BMI >25 – 30) did not increase their RR, even when the follow-up period was extended to >10 years. Only individuals in the MH-OB category (BMI > 30) had an increase in RR. This increased risk only appeared when the shorter <10-year studies were excluded from the analysis.

This is where the study is adding to our knowledge, because the meta-analysis was able to differentiate between short- and long-term follow-ups in the MH-OB (remember, overweight had no effect). In short-term studies the MH-OB were NOT at elevated risk of death or CV events relative to the MH-NW control group. However, when looking only at long-term studies that followed individuals for 10 years, the MH-OB were at slightly elevated risk.

3. Let’s look a little deeper

Here are the numbers in the Results for the >10 year studies only, presented as mean (lower 95% confidence interval, upper 95% confidence interval):

MH-NW: 1

MH-OW: 1.21 (0.91 – 1.61)

MH-OB: 1.24 (1.02 – 1.55)

MU-OB: 2.65 (2.18 – 3.12)

MU-OW: 2.70 (2.08 – 3.30)

MU-NW: 3.14 (2.36 – 3.93)

I presented the groups in order of lowest risk to highest risk. Do you notice something surprising?

The increased risk for metabolically unhealthy people of all BMIs was much larger than the increased risk for MH-OB in the >10-year follow-ups.

Being normal-weight does not protect you from the health consequences of being metabolically-unhealthy.

So what’s actually happening? To me it sounds like the major finding here is that being metabolically unhealthy is bad, regardless of your weight.

4. Time to re-write the headlines

Unfortunately, the media coverage of this study has been, in my opinion, misleading. Let’s look at those headlines again:

“Can you be obese and ‘healthy’? Study says no” – FOX News, via ScienceLive

“Healthy and overweight is a myth, study suggests” – BBC News

“No ‘healthy pattern of obesity,’ review finds” – CBC News

Are those statements true? Do they communicate the major findings of this study? Are journalists, editors, and media outlets providing factual health and science information?

By letting the finding that MH-OB are at slightly elevated risk relative to MH-NW dominate the headlines, the media is ignoring the fact that the metabolically unhealthy at any BMI had far worse health outcomes than the metabolically healthy obese. Presenting the narrative in this way does nothing to encourage improved metabolic health in the people at the highest risk of all: the metabolically unhealthy normal-weight individuals.

If what we care about is improving health outcomes, shouldn’t we focus on keeping people of all weights in the “metabolically healthy” category, and less on getting people to change their BMI category? This means promoting habits that we know improve metabolic health, such as regular physical activity, reducing stress, and getting more sleep – not fixating on the number on the scale.

Read the original source when you can. Use your critical thinking skills. Don’t take media health claims at face value. Refuse to click on substandard journalism.

We can do better than this.

This was a guest post by my friend Sarah Lord. Sarah is a PhD candidate in biological sciences at the University of Alberta in Edmonton, Canada.

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