Does Overweight Really Decrease the Risk of Death?

by Lindsey Smith, PhD Student in Nutrition Epidemiology at UNC

Every year on January 1st, millions of Americans toss out their sweets, join the gym, and shell out big bucks on fancy workout gear with the resolution to lose weight. This year, however, dieters got a welcome reprieve from those pesky resolutions to shed excess fat when a recent scientific report made headlines nationwide, with bold titles claiming “Overweight Americans face lower mortality risk” and “Best to be overweight?” The study, which was published in JAMA (the premier medical journal), is a systematic review and meta-analysis. The results of this meta-analysis showed that, relative to normal weight, grade 1 obesity (the mildest type of obesity) was not associated with higher all-cause mortality. What’s more, overweight was associated actually associated with lower all-cause mortality.

So does this mean we should all toss our weight-loss efforts out the window and tear into that bag of Oreos?

Not so fast.

Unfortunately, most news articles are forced by their brevity and readership to skim over key details, which caution against a strict interpretation of these results and suggest we might reconsider before abandoning obesity-prevention efforts. Here’s why:

(1)    The nature of the study design: meta-analyses are a type of study which combine results from previously published articles to draw conclusions. However, publication bias presents a serious problem to the validity of this methodology. In layman’s terms, studies that present significant findings are often more likely to be published than studies that find no differences. This means that meta-analyses are often only able to take into account one piece of the whole picture.  Although there are ways to test whether publication bias influences results, there is no way to truly know whether publication bias came into play.

(2)    Age/period/cohort: It is very difficult to disentangle the effects of age, period, and cohort when examining these types of studies. Typically, meta-analyses pool results from studies that may span decades as long as the studies meet certain inclusion criteria. But, as US adults have become increasingly overweight in the last 50 years, the fundamental meaning of overweight and obesity has changed. In 1970, someone who was obese might have been considered very ill. In 2010, when obesity is the norm, an obese person might actually represent the normal state. Being normal weight or underweight could be the result of pre-existing or latent illness, which would explain why lower weights are linked to increased risk of death.

(3)    Treatment effects: treatments for obesity and co-related morbidities (such as diabetes and hypertension) have dramatically improved in recent decades, extending the life of those who might otherwise died earlier due to these complications. In this case, it would be wrong to interpret these results as meaning that obesity isn’t associated with increased death—it simply means that we have come a long way in keeping sick people alive longer.

(4)    Biologic plausibility: the authors, and most epidemiologists, use cut-points to define overweight and obesity. Yet, intuitively, one might question whether there is much biologic difference between someone with a BMI of 24.5 (“normal weight”) and a BMI of 25.5 (“overweight”). In many cases, how a variable is classified can make a difference in the outcome. While this type of categorization is often necessary in epidemiological analysis, it is important to draw a distinction between what is statistically true and biologically meaningful.  It is possible that if BMI were constructed differently, the observed associations in this study might disappear or even reverse.

The key here is to read the literature with a discerning eye. Although this study used rigorous epidemiological methods, distilling the results into a single bullet or headline can be misleading. It is also dangerous to draw conclusions from one study without considering others. For example, a recent study from Columbia University found the exact opposite results: that obesity increase risk of mortality, and this effect gets stronger with age. More research is required—ideally through randomized controlled trials—to truly understand the complex relationship between overweight/obesity and mortality.



Flegal KM, Kit BK, Orpana H, Graubard BI. Association of All-Cause Mortality with Overweight and Obesity Using Standard Body Mass Index Categories. JAMA2013; 309(1):71-82.

Masters RK, Powers DA, Link BG. Obesity and US Mortality Risk over the Adult Life Course.  American Journal of Epidemiology 2013;177(5):431-42.

Print Friendly, PDF & Email

20 thoughts on “Does Overweight Really Decrease the Risk of Death?

  1. This is really interesting! It’s really easy to forget how the media has a tendency to sensationalize a single study’s finding without mentioning other studies that have conflicting results.

    There seems to be a gap between complex epidemiological journal articles and overly-general news articles. One may be too difficult to interpret for the average person, and the other is so simplified it can be misleading. I wonder if there’s anything in between?

  2. Greetings from Los angeles! I’m bored to death at work so I decided to check out your site on my iphone during lunch break. I really like the knowledge you provide here and can’t wait
    to take a look when I get home. I’m amazed at how fast your blog loaded on my mobile .. I’m not even using
    WIFI, just 3G .. Anyways, awesome blog!

    Take a look at my homepage … Coy

  3. I’m really loving the theme/design of your website. Do you ever run into any web browser compatibility problems? A couple of my blog readers have complained about my blog not operating correctly in Explorer but looks great in Opera. Do you have any recommendations to help fix this problem?

  4. Pingback: Does Overweight Really Decrease Risk of Death? | Lindsey P. Smith

  5. Howdy I am so grateful I found your blog, I really
    found you by error, while I was researching on Yahoo for something else, Anyhow I
    am here now and would just like to say thanks for a marvelous post and a all round
    emtertaining blog (I also love the theme/design), I don’t have time to browse
    it all at the moment but I havbe saved it aand also included
    your RSS feeds, so when I have time I will be back to read a lot more, Please do keep up the superb

  6. It is actually a great and useful piece off information.
    I am satisfied that you just shared this useful information with us.
    Please keep us informed like this. Thank you for sharing.

  7. Hello! I realize this iis somewhat off-topic but I had tto ask.
    Does building a well-established blog like yours require a large amont of work?
    I’mbrand new tto running a blog but I do write in my diary
    every day. I’d like to star a blog so I can share my own exdperience and thoughts online.
    Please leet me know if you have any kind of ideas or tips for new aspiring bloggers.
    Appreciate it!

    Feel free to surf to my blog post – rapid weight loss

  8. Having read this I thought it was extremely informative.
    I appreciate youu taking the time and energy to put this short article together.

    I once again find myself personally spending a lot of time both reading and leaving comments.
    But so what, it was stipl worth it!

    Here is my webpage; garcinia|garcinia cambogia (

  9. Thajk you, I’ve just been looking for information approximately
    this tppic for a long time and yours is the greatest I’ve came upon so far.
    But, what in rgards to the conclusion? Are you positive abouut the source?

    Feel free to visit my page; garcinia cambogia
    extract reviews (

  10. I’m not certain where you’re getting your information, but great topic.
    I must spend some time studying much more or understanding more.

    Thanks for wonderful info I waas on the lookout for
    this information for my mission.

    Feel free to visit my web page :: Dr oz diet (

  11. Hey there! Someone in my Myspace group shared this site with us so I came to look it over.
    I’m definitely enjoying the information. I’m bookmarking and will be tweeting this to my followers!

    Fantastic blog and superb design.

Comments are closed.