Thursday, September 13, 2012

Study Reveals Overweight Teens Have Fewer Arms Than Healthy-Weight Ones


A truly shocking study published today ahead of print in the journal Pediatrics revealed that overweight teens reported having one fewer arm than their healthy weight counterparts.

Sigh.

(I'm sighing a lot these days).

No, overweight teens don't have fewer arms than their healthy weight counterparts, and I'm equally doubtful that overweight teens eat fewer calories than so-called healthy weight teens either, yet that's what's been trumpeted all over the media and blogosphere for the past few days.

The reporting stems from a paper entitled, "Self-Reported Energy Intake by Age in Overweight and Healthy Weight Children in NHANES, 2001-2008". In it researchers detailed the "surprising" finding that overweight and obese girls over age 7, and overweight and obese boys over age 10 reported consuming fewer calories than their healthy weight peers.

What I find rather amazing though is that the researchers, rather than focus on the story being overweight girls as young as 7 and boys as young as 10 may have already suffered sufficient societal stigma to under report their dietary intake when asked how much they're eating, instead decided to conclude that contrary to what the laws of thermodynamics require, overweight kids and teens either have created for themselves a, "self-perpetuating" state of obesity, or that they're significantly less active.

Now to be fair they also mention a third possibility, that perhaps overweight kids under report their dietary intakes, but then they explain why they think that isn't the case.

So is there evidence out there suggesting that overweight teens are in fact the world's worst dietary historians?

Why yes there is.

In February of last year there was a review paper published in the International Journal of Pediatric Obesity titled, Assessing dietary intake in children and adolescents: Considerations and recommendations for obesity research. Regarding under-estimation, here's what the review paper's authors had to say,
"One of the most robust findings in dietary studies of children and adolescents is the positive association between under reporting and increased body fatness, particularly in adolescents (4,14,15). This is consistent with studies in overweight and obese adults (16). The extent of mis-reporting irrespective of weight status increases with age and has been reported as 14% of energy intake in 6-year-olds (17), 25% in 10-year-olds (18) and 40% (4,19) to 50% (14) in obese adolescents.."
The authors further report that the type of study most likely to suffer from under-reporting is the very type performed here,
"Studies characterising under-reporting have focused on total diet assessment methods and in particular, energy intake"
So let me ask you a question.

If we knew that when polled obese teens under-reported their number of limbs by 50% do you think it'd be wise to take their reporting at face value and come up with theories as to why one of their arms fell off, or would it be more useful and important to try to understand the drivers that led those teens to misrepresent their limb status'?

Sir William Osler one of the founders of modern medicine once said,
"When you hear hoof-beats think horses, not zebras"
The horse is under-reported calories. Moreover it's a horse that's been spotted many times. To ignore that horse and instead focus on one-armed teen zebras? The only explanations for that behaviour I can come up with are ignorance, or willful misrepresentation in the name of publication or publicity - and neither are pretty.

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21 comments:

  1. Rather than assuming that the kids are lying, why not consider the possibility that food intake and physical activity are not the most important variables affecting body size?

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    1. Perhaps you should re-read the post to find the answer to your question Dee.

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    2. Anonymous8:51 am

      I don't see anything about lying in the post. Under reporting does not mean lying.

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  2. What makes you think that I didn't read the post?

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  3. Are the study's conclusions also supported by any studies that actually observe children eating?

    In my experience serving lunches at elementary schools, the overweight kids have heartier appetites, whereas not all of the normal weight kids do. This is especially when we serve pasta, but I do recognize that my observations don't constitute a statistically relevant study.

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  4. The first time I went on a "not crazy" diet (eat fewer calories, more fruits, and veggies, like that) the thing that shocked me was HOW MUCH food I was expected to eat! It was a revelation that I could eat so much food when it involved eating cantaloupe and strawberries and green beans, etc. I definitely was eating much less food by volume, but the caloric content was the key. (How many cups of spinach equal a slice of pizza?) I'm sure that's what's going on with the kids who "self-report" (which is inane when you're talking 7-year-olds).

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  5. Anonymous8:58 am

    Being overweight or obese indicates that at least at some point calorie intake was higher than what the body required. It doesn't mean calorie intake is significantly higher than the average on a daily basis.

    Also as Yoni says, if you've been teased or bullied about weight and are ashamed of it, why would you want to report your eating habits in great detail? This has been proven in adult studies, the higher the body weight the more likely a person is to undereport their weight and food intake. It's reflection on the cripling social stigma. Men who are the shortest are the most likely to over-report their height as well, another area where there is discrimination.

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  6. Yoni, could you please comment about the thermic effect of feeding and/or the increased caloric expenditure involved in eating non-processed foods? Could these affect one's weight in isocaloric diets? For example if an individual was eating once per day, all processed, easily digested calories vs. eating fibrous, foods requiring "work" to digest multiple times per day could this in theory account for some of the wieght differences?

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    1. Hi Laurel,

      Could be a player in part, though I'm not sure there's evidence to suggest that overweight kids eat demonstrably more processed than non-overweight kids. That said, there was a study I blogged about a ways back that suggested processed food was in a sense pre-digested and provided roughly 10% greater energy calorie per calorie when thermic effect of food was measured.

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    2. Anonymous11:56 am

      Yoni, could you link to that study if you have it handy? Would love to read it!

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  7. Anonymous9:50 am

    The assumption that obese children are under reporting their food intake is damaging and shortsighted. I was an overweight child and was constantly dieting - as a teen I ate so few calories I passed out at school at times. I lived on diet coke and salad. But i was 40 pounds overweight. If someone asked me to report my calories they would have been shocked to see how few I was eating and yet staying fat. I am surprised and saddened that someone with so much experience with overweight and obese people would simplify the matter so much. There are many factors at play, like a lack of energy expenditure due to years of deprivation, that need to be considered. My nephew is overweight and eats like a bird - the pickiest, tiny bites eater. My son, same age, eats voraciously (seriously, man sized portions) and is slim. There are millions of anecdotes like this.....maybe this study is just supporting what many obese people already know.

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    1. John U8:42 pm

      I totally understand and agree with you. The issue that is not being discussed in these blogs is the relationship between insulin in the circulation and fat storage. When insulin in present in the circulation, whatever nutrients are also present will be stored into your fat cells if not used for your immediate energy needs. So any excess of calories, no matter how small will be stored. When all the nutrients in the circulation have been consumed for energy requirements, your body would normally receive it needs from your you fat cells, but if insulin is still present, you fat cells will not mobilize fat to feed your body and you will feel hungry and might even eat some food. If that food is carbohydrate, the cycle will repeat itself and you will store more fat and feel hungry again.

      Why is this not being addressed in these blogs?

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  8. Anonymous10:04 am

    Hard to say it's an unreasonable assumption when there are studies that clearly identify under reporting as an issue. On the other hand perhaps it's somewhat short-sighted to identify your anecdotal n of 3 as the norm vs the well designed studies that state otherwise.

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  9. And I am sighing that you trotted out the "law of thermodynamics." The human body is not a closed chemical reaction in a sealed glass jar. It adjusts -- you may have seen the BBC series where thin people as an experiment ate twice their caloric requirements, but did not gain weight at the expected 3500 calories = one pound pace? The thermodynamics argument is incredibly flawed, and you discredit yourself by using it.

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    1. The laws still apply. Pace definitely varies. The body is indeed a black box, but it isn't a perpetual motion machine.

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    2. The thermodynamics argument is far from flawed. Not everybody burns calories at the same rate, true. Dr. Freedhoff has pointed to studies that show he understands people can have varying metabolic rates -- such as his post about how the "Biggest Loser" show/diet ruins its participants' metabolisms.

      BUT....

      There is a simply limit to how conservative the human body can be with calories. Maybe human metabolism can vary by as much as a few hundred kCal per use per day, yes. But nobody can stay fat on a reduced intake. The whole "No fat people in concentration camps" thing.

      It's simply not reasonable or logical to believe that people who eat way fewer calories than average are really going to sustain an obese body mass on that type of intake. When non-self-reported studies are conducted using doubly-labeled water to discern people's actual metabolic rates, they have shown that the obese actually have increased metabolic rates and burn more calories compared to normal-weight controls (presumably because of the extra muscle tissue needed to move around all the fat).

      And the tendency of obese people to underreport intake -- by as much as 50% of calories -- is well-known. Whenever obese people ARE put in a closed environment and are underfed, they do lose weight.

      So yes, metabolism can adjust up or down, but there still are limits to how much it can adjust. Thermodynamics as pertaining to human body weight is still quite relevant.

      I'm curious as to how many calories fewer the overweight and obese kids were claiming to eat compared to normal-weight peers. The study abstract doesn't say.

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  10. Anonymous12:32 pm

    In counselling it is important to determine what someone's eating habits are at present. If someone is having just diet coke and salad of course the recomendations should not be to decrease further regardless of a person's current weight. A thorough weight and dietary history should be obtained before any one gives diet change recommendations.

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  11. Yikes. Let's all go back and read the original. There is no value judgement made in obese teens under-reporting, the point is the folly of making absurd conclusions based on the evidence that obese teens were under-reporting. Sheesh. One not so absurd conclusion that one might make from the information is that obese teens have trouble regulating and calculating their intake of food- that the natural mechanisms that keep some people at normal weight effortlessly are not working effectively in obese teens.

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  12. I think that almost everyone will underreport how much they are eating if they are not used to tracking their food and calories. Having done so for two years, I am amazed at some the calorie counts that people post on tweetwhatyoueat. A burrito eaten in a restaurant has 500 calories? In your dreams. Make it at least 750, maybe more. It is also easy to get the size of a portion completely wrong if you don't measure it. So, if inexperienced teens are underreporting food intake, they are far from alone, even they are not under pressure to lose weight and eat less, which many of these teens no doubt experience.

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  13. Yes! When I first read the popular reports about this study, my eyebrows went up. As soon as I investigated for myself and saw the words "self-reported," the mystery was solved.

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