On due dates (Or: why confidence intervals are often better than means)

A very pregnant woman (not my wife). Image by Nina Matthews.

A very pregnant woman (not my wife). Image by Nina Matthews.

As regular readers will know, my wife is pregnant.  In fact, today is the due date.  As of this writing (2:30 EST), labour has yet to commence.

Throughout the pregnancy, my wife and I have constantly reminded ourselves that the due date is a gross over-simplification.  It’s pretty obvious that it’s a ball-park estimate at best.  And yet, providing a precise date creates some weird psychological tension, even when you know that it shouldn’t be taken too seriously.

For example:

  • If today is the “due date”, does that mean that tomorrow the baby is “over due”?
  • Can the baby spoil, like over due milk?
  • Does it mean there is something wrong with the baby?
  • Seriously: when is this baby going to come out??!?!
  • Etc.

These are all questions that are naturally raised by pronouncing a specific due date, and by repeating it at every appointment over a 9 month period (and by being asked about the due date every time you pass someone in the street).

due dates

Image via spacefem.

This is especially annoying given than only ~10% of women give birth on their actual due date (which is actually quite impressive, given that it’s calculated 6+ months in advance). For a visual representation of what this looks like, check out the above figure compiled from a survey by spacefem (the original figure is interactive, so it’s worth clicking through). While births are most likely right around the due date, that is in no way guaranteed (another very cool interactive figure at spacefem shows that roughly 60% of women give birth within a week of their due date, yet only ~10% give birth on the due date itself)   So everyone knows that the due date is a radical oversimplification, and yet we stick with it.

There is another way

Consider if instead of providing a specific date, a pregnant woman was provided instead with a range of dates.  So rather than giving us a due date of August 19, the doctor could have instead said that there is a 60% chance that the baby will be born between August 12 and 26th.  Or that there is a 95% chance the baby will be born between July 19 and September 19.  You could easily create a figure like the one above, with the actual dates plugged in.

The nerds among us will recognize that I’m suggesting that instead of providing women with a due date in the form of a mean (e.g. one specific date), I’m suggesting they be provided with a 60% or 95% confidence interval.  I personally think it would be much more useful (and more accurate) information, while being arguably more intuitive than the due date, which always seems a bit random and arbitrary to  me.

So if there are any healthcare providers out there, I strongly urge you to try presenting the due date in a different way.  You could even do some A/B testing to see which format women prefer.

And seriously, when is this baby going to come out!??!?

Travis

Category: News | 5 Comments

You should workout in jeans (I do)

Appropriate workout clothes (image by Per Ljung)

Appropriate workout clothes (image by Per Ljung)

At various points over the past few years, I have been fortunate to basically have a gym as my office.  I’ve worked near treadmills, exercise bikes, light free weights, and a bunch of machines (bench press, leg press, a chin-up bar, etc).  The gyms have always been for research and data collection, but there were plenty of opportunities for those of us working in the lab to pop out and do a quick set almost anytime we liked.  And it was awesome.

During my time in the lab I would often take a short break to do a set of bench press, chin-ups, or leg press.  And when I had to do some reading (which, as a researcher, is pretty often), I would do it while riding one of the exercise bikes. Most of the time I did all these exercises while wearing my work clothes (typically jeans and a dress shirt or polo shirt).   It felt a bit strange to do bench press while wearing a dress shirt, but it saved soooooo much time.  By the end of the day it was great to know that I didn’t have to spend another 45 minutes working out, as I’d already done a full workout spread throughout the day.  And after an hour or two staring at a computer screen, it feels really good to do something physical for a change.

Why can’t every workplace be like this?  Aside from the obvious fact that most of us don’t work in a gym.  But it wouldn’t be that hard to place a few weight machines within an office building.  Like one of those outdoor gyms you sometime see in parks, but in the break room.  I now work in a traditional office, which is conveniently located in a building beside a gym.  And yet I already do WAY less weight training than I have done in other work environments where workout equipment was never more than a few feet away.

Wouldn’t it be great to walk down the hall and see someone riding a bike while wearing high heels, or doing bench press in a polo shirt?  Wouldn’t you feel better if you could workout during the day, rather than sitting the whole time?  And think of the time it would save (or the extra workouts you would get in).

I realize this is a bit of a pipe dream.  So, for now, I’m saving up all my reading so that I can do it all in batches while I ride the bike at the gym.  And I will close my office door to do push-ups every once in a while without people thinking I’m a weirdo.  Maybe I can fit a chin-up bar behind the door?  Next time you’re bored at work consider trying a little resistance training (assuming it’s safe, of course). I bet you will be glad you did.

Travis

Category: Miscellaneous, News | 12 Comments

Time to watch my weight?

After reading Peter’s post from earlier this week on the problems with BMI, I thought I should repost the below article from a couple years ago.  

Image by Magnus D

I had an interesting experience at my last physical exam, and I thought it would be worth sharing here on the blog.  Before the physical a nurse put me through an eye test, then took my blood pressure, height and weight.  She then calculated my BMI, and told me that I was in the “normal range” (it was around 24.5).  But, she continued, I was pretty close to the overweight cut-off of 25.0, so I should “watch my weight” moving forward.

I said “un-huh” and sort of laughed inside my head, given that I’m an obesity researcher and we have written the odd post about BMI here on Obesity Panacea.  But the more I talked about the episode with other people, the more ridiculous it seemed.  Here’s why.

BMI is only one aspect of health

As we have said before, weight ≠ health. BMI is moderately useful at estimating body fat, and therefore health risk (especially at the population level).  However, as Peter and I have argued many times, your behaviour matters as much (or more) than your weight when it comes to health.  If you are physically active and eat a healthy diet, you’re likely to be relatively healthy whether your BMI is 22 or 32.  It’s not that weight doesn’t matter at all, but it’s far from the only thing that matters.

(For more on the relationship between BMI and health, I suggest this excellent post by Peter from earlier this week.  Or, for a review paper on the health-benefits of exercise regardless of body weight, click here.)

Context matters

My weight has been stable for several years.  I am (extremely) physically active. I try to limit the amount of time I spend sitting.  And thanks to my wife’s positive influence, I eat a reasonably healthy diet (mostly homemade vegetarian food for breakfast and supper, with leftovers and/or pizza for lunch).  My metabolic health is also fine although, ironically, I had to specifically ask before I was be told my HDL and triglyceride levels.

Why would you counsel a weight stable person with a BMI in the healthy range about their weight (as opposed to their behaviour) anyway?  I’m certainly not the only person to have this experience – here’s what colleague and fellow PLOS blogger Atif Kukaswadia had to say on twitter:

My BMI is around 24.9. My doc told me to “not gain any more weight” for the same reason.

Yet, as our science blogging friend DrugMonkey pointed out on twitter, none of that means that we’re going to be weight stable forever. I’m in my late 20′s, cutting back on my participation in competitive sports, recently married, and nearing the end of grad school.  It wouldn’t be at all surprising if someone in my position were to begin putting on a few pounds over the next few years. In that context, the nurse’s advice seems to make perfect sense.

Except for one (very big) oversight.

How do you “watch your weight”, anyway?

This is really the crux of the problem.  Weight is an outcome, not a behaviour. When someone tells you to watch your weight, what do they really mean?

Obviously one would assume that the nurse meant that I should be physically active and eat a healthy diet.  Except she didn’t say anything about either of those things.  She didn’t ask about my level of activity or my diet (although it had been recorded during an earlier visit), nor did she give me any counseling on what a healthy diet should look like.

What if someone in my position were to take the nurse’s advice and begin dieting to reduce their weight or prevent weight gain (despite being weight stable and already healthy)?  As our colleague Dr Arya Sharma has argued, trying to lose weight is actually a pretty good way to gain weight over the long term.

as I have said before, all weight loss attempts should be medically indicated and anyone attempting to lose weight needs to be warned that they may in fact be increasing their long term risk of becoming (even more) overweight or obese.

I don’t want to be too harsh on the nurse because she clearly meant well.  But a clinical strategy that focuses exclusively on body weight, with no information or counselling related to healthy behaviours, and completely ignoring all context, is almost certainly going to fail (and possibly make things worse than they were at the beginning).

As always, I’m curious to hear what others think.  Has anyone had a similar experience? Have a different perspective on the nurse’s advice?  You can also check out Dr Freedhoff’s thoughts on the issue over at Weighty Matters.

Travis

Category: Miscellaneous, News, nutrition, Obesity Research | 8 Comments

The Body Mass Index (BMI) Says Nothing About Your Health

obesity ratesIf you go to your physician’s office and inquire about your weight status, he or she will measure your height and weight to derive your BMI (weight in kg divided by height in m squared). Then they will compare your BMI to that of established criteria to decide whether you are underweight (30 kg/m2) . Often times, this measure alone determines whether or not you receive lifestyle treatment.

But how useful is this measure anyways? What does it tell you about your health? And finally, how helpful is it to measure when assessing the effect of a lifestyle (diet/exercise) intervention?

Before I get into the various limitations of BMI, I must point out that the measure is quite useful across large populations, as it is well correlated with the degree of adiposity, and of course it is extremely simple to measure in clinical practice.

Nevertheless, here are some of the key issues with BMI, particularly when used on an individual basis.

1. BMI does not differentiate between the Michelin Man and The Terminator

Ok, we might as well just get this abundantly obvious problem out of the way. I have heard countless times how one buff celebrity or another (e.g. Tom Cruise, Arnold Schwarzenegger, The Rock etc.) would be classified as overweight or obese according to their BMI due to their excess amount of muscle. Yes, this is absolutely true. BMI is a measure of relative weight; fat mass and muscle mass are not distinguished. Here’s what is equally true: the large majority of the general population with a BMI in the overweight or obese range does not look like Jerry Maguire or the Terminator. Also, if you seek advice from your physician about your “excess weight”, in case you have body dysmorphia and cannot yourself decide, they will quickly be able to assess whether your excess weight is due to your bulging muscles or your rolls of adipose tissue. So while this is an obvious problem, I would argue not the main issue.

2. BMI does not differentiate between apples and pears

For over 60 years, we have known that independent of how heavy a person is, the distribution of their body weight, or more generally the shape of their body is a key predictor of health risk. It is now well established that individuals who deposit much of their body weight around their midsection, the so called apple-shaped, are at much greater risk of disease and early mortality in contrast to the so called pear-shaped, who carry their weight more peripherally, particularly in the lower body. Thus, two individuals with a BMI of 32 kg/m2 could have drastically different body shapes, and thus varying risk of disease and early mortality.

Fortunately, a very simple measure allows you or your physician to decide whether your elevated BMI is of the apple or pear variety: waist circumference. Current thresholds suggest that a waist circumference above 88 cm in women and 102cm in men denotes abdominal obesity. Interestingly, for the same BMI level, those individuals with an elevated waist circumference have a greater risk of diabetes, cardiovascular disease, mortality, and numerous other health outcomes. Thus, as studies from our laboratory have consistently suggested, waist circumference may be a more important measure of obesity and health risk than BMI. Currently, most researchers would agree that waist circumference should be measured along with BMI to adequately classify obesity-related health risk.

You can measure your own waist circumference by using a tape measure and wrapping it around your abdomen, at the level of the top of your hip bones. Make sure you measure at the end of exhalation, without sucking in your gut – you’re only fooling yourself!

3. BMI does not always budge in response to lifestyle change

Given the number of papers my supervisor, Dr. Ross, and I have published on the topic, I would argue this is the biggest drawback of using BMI: it doesn’t always change even though you may be getting healthier. This is particularly so if you adopt a physically active lifestyle, along with a balanced diet, but are not necessarily cutting a whole lot of calories. This lack of change in BMI or body weight is all too often interpreted as a failure, resulting in the disappointed individual resuming their inactive lifestyle and unhealthy eating patterns.

However, as we have argued most recently in a paper in the Canadian Journal of Cardiology, several lines of evidence suggest that weight loss or changes in BMI are not absolutely necessary to observe substantial health benefit from a healthy lifestyle. Thus, an apparent resistance to weight-loss should never be a reason for stopping your healthy behaviours.

First, it is well established that increasing physical activity and associated improvement in cardiorespiratory fitness are associated with profound reductions in coronary heart disease and related mortality independent of weight or BMI. Second, exercise (even a single session) is associated with substantial reduction in several cardiometabolic risk factors (such as blood pressure, glucose tolerance, blood lipids, etc.) despite minimal or no change in body weight. Third, waist circumference and abdominal fat (arguably, the most dangerous fat) can be substantively reduced (10-20%) in response to exercise with minimal or no weight loss. In fact, significant reductions in fat mass often occur concurrent with equal increases in muscle mass in response to physical activity – equal but opposite (and beneficial!) changes which are not detected by alterations in body weight on the bathroom scale, and thus BMI.

So in the end, while BMI surely has its strengths in ease of use and pretty good reliability in large populations, on an individual basis, the greater focus should be on healthy behaviors: physical activity and a healthy diet. And if you must measure something, check your waist circumference.

Enjoyed this post? Please sign up for future updates on similar topics to be delivered to your email inbox or RSS reader.

Peter

Reference:

Ross R, & Janiszewski PM (2008). Is weight loss the optimal target for obesity-related cardiovascular disease risk reduction? The Canadian journal of cardiology, 24 Suppl D PMID: 18787733

Category: News | 12 Comments

This picture captures why “no sugar added” is a meaningless concept

It seems that every time I go to the grocery store I see more products proudly announcing that they have “no sugar added”.  Typically these claims are seen on juice and other products that contain a high sugar content.

As Yoni Freedhoff has pointed out in the past (emphasis mine):

[These claims are] there to make you feel that the product inside the box is a healthy one.

A quick peek at the back of the box is probably in order.

Take Mott’s Fruitsations Unsweetened Strawberry Fruit Rockets for instance. Reading the ingredients you’ll find that they include both, “Concentrated Strawberry Puree“, and, “Concentrated Fruit Juices“.

And what are concentrated purees and juices?

Sugar.  Plain old sugar.

I know that some people will say that sugar in juice is different from table sugar or high fructose corn syrup because it is “natural”.   I disagree.  But let’s say that we accept that the sugars found in juice are somehow “better” than added sugars, and that “no sugar added” is a term that has value.  What then to make of the below picture, courtesy of freelance science writer David Despain:
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Category: Miscellaneous, News, nutrition, Obesity Research | Tagged | 6 Comments

Juice is not natural (!!!)

orange juice

The health-impact of juice is a contentious issue. Yes, it’s full of vitamins and minerals. But it’s also full of sugar.  How much sugar?  The below graph compares the calories and sugar content in a 12-ounce can of Coca-Cola, Pepsi, and Tropicana Orange Juice.  I’ve hidden the names.  Which one is the “healthy” orange juice?

Calories and Sugar Content in 12 ounces of Tropicana, Pepsi, and Coca-Cola


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Category: News | 22 Comments