header image
Apr 21
Film poster for An Inconvenient Truth
Image via Wikipedia

Thankfully the current generation of young people are far more aware of the environmental issues and willing to do something about it. They have taught their parents to recycle, use reusable grocery bags, to buy carbon credits (though controversial), etc, etc.  However, this same young generation is the fattest in our history (and potentially the least fit).

Does being overweight really coincide with the principles of trying to keep the planet healthy?

I have wanted to write a piece about this issue for awhile but didn’t have a nice published journal arguing what I thought were various obvious points, but now one has come out.

In a study published in the International Journal of Epidemiology by Edward and Roberts (2009) argues that food production is one of the main contributors (20%) to greenhouse gas emissions (H/T to esciencenews). If you have a population of people in the developed nations that are overweight (ranging from 20-65+ % of the population) this would have a number of implications. It costs more to transport the heavier people but also they are eating more than someone of normal weight and hence use up a greater amount of the valuable and dwindling energy resources and a greater amount of food producing land. This is not exactly rocket science to realize this.

Being overweight is equivalent to deciding to drive around in a SUV (or any other gas guzzler).

If people slimmed down (via escience news):

Transport-related emissions will also be lower because it takes less energy to transport slim people. The researchers estimate that a lean population of 1 billion people would emit 1.0 GT (1,000 million tonnes) less carbon dioxide equivalents per year compared with a fat one.

Really the comparison here was between a population of ‘lean’ with a mean body mass index (BMI) of 24.5 vs a more typical ‘developed’ country with a BMI of 29 (to give you a frame of reference normal weight is 18.5 -24.9, overweight is 25-29.9m and obese is 30+). The heavier population would consume 19% more food than the lean population.

I really don’t have to give you a bunch of numbers and facts I think all of you intuitively know that it only make sense that an overweight population consumes more energy and contributes a greater amount to environmental issues (including global warming).

I think the authors give a pretty clear statement in their discussion (GHG = global green house gases):

We argue that increased population adiposity, because of its contribution to climate change from additional food and transport GHG emissions, should be recognized as an environmental problem.

So if you care about the environment, be it you are young or old, then do your part and stay (or become) slim (meaning normal weight) - which will also contribute to your own health.

If you care about the planet’s health, then do something about it by taking care of your own health - by maintaining a healthy weight. Something for all of us to think about, but maybe this message has the best chance in taking hold in the current young generation who as a whole do care about the planet’s health.

Are you a gaz guzzler, a hybrid, an all electric, or even a highly efficient bicycle?

Apr 15

Is the likelihood of you currently having or developing depression related to your body mass index?

Body mass index (BMI) is simply a comparison of a person’s body weight and height. Formerly, it is your weight in kg divided by the square of your height (kg/m2). You can go here to find out what your BMI is, using either imperial or metric measurements.

A BMI of under 18.5 is considered underweight, 18.5 - 25 is normal, above 25 to 30 is overweight, and over 30 is obese. With this knowledge what BMI do you think would be correlated with longest lifespan? And how much is lifespan reduced if you are overweight or obese?

Which of these groups do you think are more likely to develop depression? Before you guess you might want to refer back to my U shape curve blog piece.

Zhao et al., 2009 looked at data from 177,047 participants 18 years or older (American citizens) in which they were able to obtain self reported height and weight, along with current level of depression (diagnostic questionnaire) and life time self report. Take a look at their main figure.

a) is current depression, b) lifetime depression, c) anxiety.

As you can see there is a U shape curve, with those having a BMI of less than 18.5 and females with a BMI above 25 prone to depression. For males an increase in depression is not really noticeable until you get to the very high end of the BMI scale (35+). For females the lowest level of depression is for the BMI 18.5-25 group (normal weight). For males the range appears larger: 18.5 - 35. In c) the bottom graph we can see roughly the same story for anxiety. So it appears you can be too thin, but also too heavy.

I could show you more graphs of relative risks after taking into account confounding variables, but I think you get the idea. Even after adjusting for various confounding variable the authors conclude:

After adjusting for demographics, ORCs, lifestyle or psychosocial factors, compared with men with a normal BMI, men with a BMI >40 kg/m2 were significantly more likely to have current depression or lifetime diagnosed depression and anxiety; men with a BMI <18.5 kg/m2 were also significantly more likely to have lifetime diagnosed depression. Women who were either overweight or obese were significantly more likely than women with a normal BMI to have all the three psychiatric disorders.

The only thing that is surprising to me in the authors conclusion is that they don’t find females who are underweight (BMI < 18.5) also have higher levels of depression.

Other than showing you what body size/shape is correlated with increased depression, I wanted you to observe an example of the U shape curve in biology. I will be providing more of these in the future.

Take home message: As in many things, too much or too little might not be the best. Either end of the extreme in body mass index is correlated with higher levels of depression. For women there appears to be a narrower range of BMI that is correlated with lower level of depression as compared to men (this could be partially cultural).

Mar 19
Summer Fountain shows Obesety in Children as s...
Image by hyperscholar via Flickr

Yesterday, I told you that children who are overweight perform worse than their normal weighted counterparts on certain cognitive tasks related to planning. This piece was a follow-up to all the very similar results in adults.

With parents always wanting the best for their children then obviously they would be on the watch for obvious to the eyes bodily changes in their children.

But us humans don’t always see reality (or we tend to put on the rose tinted glasses). A series of research paper have found that parents do not judge their children weight/chubbiness correctly. Akerman et al., 2007 observed that when parents estimated weight and had normal weighted children they roughly equally underestimated (43.1%) or overestimated (49.3%) the child’s weight (with 7.6% being accurate). But things changed with the kids were either underweight or overweight. For the underweight children 70% of these parents overestimated the children’s weight (16% accurate, and 14% underestimated). For the overweight children 61.6% underestimated, 7.9% were accurate and 30.5 overestimated.

In another study the researchers found that not only did parents underestimate children measured weight but so did the children and their physicians (Chaimovitz et al., 2008). The conclusion of this paper was:

Many children underestimated their degree of
overweight. Their parents and even their attending physicians
shared this misperception. This study demonstrates the need to
further educate physicians to recognize obesity and overweight
so that they can counsel children and their families.

I find this very interesting because how are you going to fix a problem if you can’t see it staring you in the face. Parents and apparently doctors need to take off the rose tinted glasses and face reality. I wonder if the doctors (and parents) version of ‘normal’ has changed over the years because the average weight of children have increased over these years. The overweight silhouette is the new average ?

This is not only an American phenomena, as a Canadian study found very similar results with 63% of the parents with overweight children judging them as in the normal weight category (He and Evans, 2007). The title of this study was interesting: ‘Are parents aware their children are overweight or obese? Do they care?’

If you have a child maybe you want to accurately measure your child’s height and weight - and compare it to what is normal for the appropriate age range (see here). Your inability to see the reality of your child’s weight could lead to your child’s reduced cognitive ability. For if you don’t recognize the problem you can not fix it. And we naturally want the best for our kids - but then we have to view the situation correctly. While you are at it you might want to check you own body mass index (BMI) and calculate your number. Are you wearing rose tinted glasses?

caveat: BMI is not the be all measurement of appropriate body size - and can be innacurate in terms of ‘fatness’ so you might want to look into getting a proper body fat measurement (there are several options, from cheap and ‘reasonably’ accurate, to more expensive and subsequently more accurate).

Mar 16
Silhouettes representing healthy, overweight, ...
Image via Wikipedia

What is your body mass index (BMI) - you can check it here or here (metric): normal weight = 18.5 - 24.9, overweight = 25.0 - 29.9, obese = 30.0 +)

Do you want a properly working brain - then don’t become overweight (now you don’t have to read the rest of the piece). You are your brain, or at least it is the one thing you can not afford to lose. New research indicates that being overweight is related to reduced cognitive ability.

While some recent papers I have been reading indicates to me that being overweight (BMI 25-29.9) or even obese (BMI 30+) does not cost you that much in terms of earlier death (Fontaine et al., 2003, Pischon et al., 2008) (I will try to cover this more fully in another post) however, you may forfeit a fully functional mind.

High BMI related with lower prefrontal cortex activity and worse mental ability in healthy subjects:

Volkow et al., 2009 studied 21 healthy subjects who had BMIs in the range of 19-37, with 3 subjects in the obese range (BMI 30+). The researchers found that a significant negative correlation (relationship) between BMI and reduced activity (as measured by metabolism) in the prefrontal cortex, when the brain was at rest (baseline). What this means is the higher your BMI the less active the prefrontal cortex is. The prefrontal cortex is the part of your brain responsible for controlling higher cognitive function (planning - thinking).

But more interesting is that the baseline metabolic activity level associated positively with a number of mental performance measurements (memory as measured by the California Verbal Learning task, and executive function via the Stroop interference task, and Symbol Digital Modality test).  Therefore, the subjects with a high baseline prefrontal cortex metabolism (smaller BMI) performed the best on these mental tasks. At the opposite end of the spectrum, the high BMI individuals with low prefrontal baseline activity performed the worse on excutive function and memory tests.

Interestingly, during the cognitive tasks there was no correlation between prefrontal brain metabolism and BMI or performance on the mental tasks.

Healthy overweight individuals have lower ‘thinking’ ability: more papers finding the same trend (with larger number of subjects):

While one of the short comings of the above paper is the small number of subjects, several other papers with large number of HEALTHY subjects have found similar trends of high BMI related with reduced cognitive ability (Sabia et al., 2009 n = 5,131, Gunstad et al., 2007 n= 408). Interestingly, Sabia et al., 2009 not only found overweight individuals (BMI 25+) but also underweight people (18.5 or less) had reduced cognitive ability in late middle age compared to ‘normal’ weighted individuals.

The consistent finding among these three studies is the executive function is reduced as the BMI increases, even in otherwise healthy individuals. Executive function (thought to mainly be controlled by the prefrontal cortex) measures your general cognitive ability - planning, cognitive flexibility, abstract thinking, initiating appropriate actions and inhibiting inappropriate actions - or you could executive function just call this plain old thinking. This reduced executive ability in the overweight individual could play into my theory of American’s weight gain could be tied into the rise of debt (I will follow up on this theme in the future).

Increase BMI related to reduced gray matter in the brain:

Adding to the overall gloomy picture is a study of 1,428 healthy individuals in which the researchers found high BMI correlated with reduced brain gray matter in men (Taki et al., 2008). They found no relationship between BMI and gray matter in women, and go onto to speculate the higher levels of visceral fat in men (compared to women with similar BMI) could be the mediator of the reduced gray matter in high BMI men.

Take home message:

If you want to keep your brain’s gray matter (if you are a man), and your ability to plan and think at your best level then don’t become overweight (men and women). The general finding is not just for obese people (BMI 30+) but also for overweight people (BMI 25 - 29.9). Also being underweight (less than 18.5) is related to reduced cognitive ability. And all of these results are based on otherwise healthy individuals.

What is your BMI? go check it out here or here (metric).

You might not lose too many years of life due to being overweight (because of medical advances keeping your heart pumping) but you won’t be playing with a full deck upstairs - ouch!