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Overweight Kids Are More Sensitive to Obesogenic Environment



One of the common misconceptions around the obesity epidemic is that obese kids have lifestyles that are so much worse than those of their non-obese peers.

This assumption, as noted in a recent post, was not really borne out by the findings in the Canadian Health Measures Survey, which did not find marked differences in physical activity between overweight and lean kids (at least not when corrected for the increased effort it takes to move larger bodies).

Indeed, the survey showed that virtually ALL Canadians (young and old, lean and overweight, male and female) do not get even the rather modest amounts of recommended physical activity a day.

So if overweight kids are not moving less (nor, as I suspect, are eating more), then why are some kids overweight and others are not?

If the environmental effects are pretty much the same for everyone, why do we even have lean and obese kids?

This question was addressed by Andreas Beyerlein and colleagues from the Ludwig-Maximilians University of Munich, Germany, in a study just publshed in PLoS One.

The researchers analysed data on over 7,000 3-10 year-old and almost 6,000 11-17 year-old children from a representative cross-sectional German health survey conducted between 2003 and 2006 to look at the impact of maternal BMI, maternal smoking in pregnancy, low parental socioeconomic status, exclusive formula-feeding, and high TV viewing time on BMI.

It turns out that in both age groups, the estimated effects of all risk factors (except formula-feeding) on BMI were greatest for children with the highest BMI. Thus, for example, increased time spent watching TV was associated with a much greater impact on BMI in the overweight and obese kids than in the normal weight kids.

Or as the researchers point out:

“…risk factors for childhood overweight are associated with greater shifts in the upper parts of the children’s BMI distribution than in the middle and lower parts.”

In other words, it is not that lean kids don’t also watch a lot of TV or have mothers who smoked during pregnancy – it is just that kids at the higher end of the BMI distribution appear far more sensitive to these factors than their leaner counterparts.

By way of explanation, the authors suggest:

“…genetic variants with a possibly increased susceptibility of carriers to certain risk factors might offer an explanation for differences in the effect magnitude of risk factors by BMI percentiles”.

Thus, kids who are genetically predisposed to obesity are far more likely to pack on the pounds when spending hours in front of the TV than kids who are genetically less obesity prone. The same could probably be said for overeating or any of the other environmental drivers of obesity, which have much greater effects in terms of promoting weight gain in some kids than in others.

From a prevention and treatment perspective, this means that overweight and obese kids will have to work much harder at changing their lifestyles or avoiding obesogenic stimuli than thin kids, who can “luckily” get away with their similarly “lazy and gluttonous” lifestyles.

Readers will see how this relates back to the whole topic of weight-bias and discrimination, where we so easily fall into the mode of blaming obesity largely on unhealthy lifestyles and will power, when thin people may just turn out to be genetically more fortunate.

What this means for obesity prone kids is that they may not be able to eat as much ice cream or spend as much time in front of their TVs and computers as their skinny friends – but then again, who said life had to be fair?

This should of course not be used as an excuse to do nothing but rather seen as a good reason to fully appreciate and empathize with kids who carry extra weight – some will need to work very hard at controlling their weight – others seem to have simply drawn the “get out of jail free” card.

AMS
Toronto, Ontario

Beyerlein A, Toschke AM, Schaffrath Rosario A, & von Kries R (2011). Risk factors for obesity: further evidence for stronger effects on overweight children and adolescents compared to normal-weight subjects. PloS one, 6 (1) PMID: 21283747

6 Comments

  1. Hi Dr. Sharma,

    thanks again for a great post. It’s nice to have someone simplify some of the key articles that come out from the Halls of Academia.

    There is some really interesting work coming out from Caroline Davis’ lab indicating some support for the idea that overweight or obese individuals are actually generally more reward sensitive in general. Do you have any thoughts about this?

    Cheers,

    MYL

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  2. To add to the mix:

    THURSDAY, Feb. 3 (HealthDay News) — Poor eating and activity habits, not genetics, are the underlying causes for most cases of adolescent obesity, new research suggests.

    The finding stems from an analysis involving more than 1,000 Michigan sixth-grade students who participated in the Project Healthy Schools program, which is in place in 13 middle schools across the state.

    “For the extremely overweight child, genetic screening may be a consideration,” study senior author Dr. Kim A. Eagle, a cardiologist and a director of the University of Michigan Cardiovascular Center in Ann Arbor, said in a center news release.

    “For the rest, increasing physical activity, reducing recreational screen time and improving the nutritional value of school lunches offers great promise to begin a reversal of current childhood obesity trends.”

    The study findings were published in a recent issue of the American Heart Journal.

    The authors noted that, in 1980, just 6.5 percent of U.S. children aged 6 to 11 years were considered obese, but that percentage rose to nearly 20 percent by 2008.

    The recent study found that 15 percent of the participants were obese. And almost all had poor eating habits.

    Nearly one-third of all the students said they drank a soda the day before, while fewer than half said they could recall having eaten two portions of fruits and vegetables in the same time frame.

    And while 34 percent of non-obese kids consumed lunches provided by their school, that figure rose to 45 percent among obese students.

    Only one-third of all the kids reported exercising a half hour for five days during the previous week. Obese children were much less likely than non-obese kids to participate in regular exercise and/or physical education classes, and less likely to be a part of a sports team.

    Among obese children, 58 percent reported watching two hours of TV in the past day. That compared with 41 percent of non-obese kids.

    The finding comes against the backdrop of the recent enactment of the federal government’s new “Healthy, Hunger-Free Kids Act of 2010,” which is designed to foster healthier school menus for the nation’s 31 million children currently receiving lunch through school-based programs.

    SOURCE: University of Michigan Cardiovascular Center, news release, Jan. 31, 2011

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  3. Interesting study. I don’t think the results will come as a surprise to anyone who was obese as a child and watched their friends (and siblings!)gobble candy and McDonalds food and stay as skinny as a stick!

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  4. Thanks Arya, The next interesting question is: How do genetic factors exert their vulnerability to these kids? An intriguing answer may be that genetic risk factors may shape these kid’s susceptibility by altering the functional properties of brain reward circuitry. Overeating is more and more accepted as disease of reward and motivation. Caroline Davis, as you have mentioned in a recent post, is showing intriguing results showing differences in Opioid and Dopamine functioning in the brain reward circuitry of “normal” eaters and “overeaters” And I agree wholeheartedly, that those who have the misfortune of inheriting a more vulnerable reward circuit genotype should not be subject to stigmatization. Let’s figure out ways (genetic screening of dopamine and opioid machinery??) of identifying these individuals early and intervening…. Can’t wait!

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  5. Part of what makes this difficult, is that in a population that is exposed to a “healthy” environment, there will still be children who are to the right of the center on the curve in terms of BMI. How do we differentiate between those who are “naturally fat” and those who are made fat (or fatter) because of the environment? Children who are exposed to weight loss diets may end up starting lifelong weight cycling which ends up making them less healthy in the long run than if they had been provided instead with the tools to have a healthy life at whatever weight they ended up at “naturally.” The bias and stigma make it all the harder to live a healthy, supported life.
    My wish would be that children with a genetic predisposition to weight gain would be treated well — they need even higher self-confidence than a child who isn’t likely to become fat. They also would benefit from opportunities to find joyful movement, and to eat in ways that lead to good health.

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