“Exercise not helpful for weight loss!” – so read the headlines on a recent newsflash that just surfaced in my inbox.

As you can imagine, I received a flurry of emails asking me to speak to the article.  It took a little bit of sleuthing, but a persistent search turned up the pdf of the research article in question.

Here are some factoids and bits of analysis for you to consider.

You can’t out train a bad diet

When it comes to weight loss, we know this is absolutely true:

The energy balance equation suggests that energy intake and energy expenditure occupy equivalent roles in determining energy balance, when in fact the factors governing energy intakes influence the energy balance far more powerfully than the factors determining resting energy expenditure.

Flatt JP. Issues and misconceptions about obesity. Obesity (Silver Spring). 2011 Apr;19(4):676-86. 

Yet the conclusions of the study reported upon in the “Exercise not helpful for weight loss” alert actually read thus:

Our study showed that increased physical activity alone has a small impact on obesity prevalence at the county level in the US. Indeed, the rise in physical activity levels will have a positive independent impact on the health of Americans as it will reduce the burden of cardiovascular diseases and diabetes. Other changes such as reduction in caloric intake are likely needed to curb the obesity epidemic and its burden.

Dwyer-Lindgren L, Freedman G, Engell RE, et al. Prevalence of physical activity and obesity in US counties, 2001-2011: a road map for action. Popul Health Metr. 2013;11:7.

This is not the same as saying ‘exercise is not helpful for weight loss’.

It simply means you can’t out train a bad diet.

Read the fine print

Research always needs to be examined for what possible interpretations of the data.  Especially when it comes to self-reported data.  Apparently, the researchers suspect the self-reporting element may have important bearing on the results of this study.

In this study, subjects were asked to self-report on 1)  height and weight, from which body mass index was calculated, 2)  activity levels, and 3) calorie consumption.  To assess the  leisure time physical activity, the respondents were asked, “During the past month, other than your regular job, did you participate in any physical activities or exercises such as running, calisthenics, golf, gardening, or walking for exercise?”

“Sufficient activity” was defined as 150 minutes of moderate activity a week – again, self-reported.  Amount of activity reported varied widely between responding counties across the U.S.  Covariates – other factors were taken into consideration to help evaluate the data – were considered, such as access of specific populations to health care,  assuming that those with access may be in the care of health care providers that may influence their decisions about healthier diet and exercise habits.  Other covariates included level of education, racial composition, pollution, and employment.

About 3.7 million adults aged 20 years or older participated in the study from 2000 to 2011, and 30,000 adults aged 20 or older participated from 1999 to 2010.

Study limitations

When you read the fine print, all kinds of red flags pop up – all connected to human behaviors.

Self-reported declines of mean adult caloric intake dropped from 2,269 kcal/day in 2003–2004 to 2,195 kcal/day in 2009-2010.  These self-reported figures for caloric consumption are “markedly lower than average caloric availability in the US, which exceeds 3,750 kcal/day.”

In other words, the subjects have some ‘splainen to do:  The increases in obesity, decreases in caloric intake, and increases in physical activity seen here don’t add up and raised the eyebrows of the research team.  As noted in the report, obese individuals are more likely to under report their calorie intake.  Thus it is quite possible that as obesity levels increased, calorie reporting may have been further underestimated.  If calorie intake is greater than that needed to remain in energy balance, then it can easily offset the energy consumed by increased activity.

In addition, the increasing social pressure to be more active can lead to fudging on self-reporting:

The increase in self-reported physical activity could also be due to increased positivity bias. Given increased public awareness campaigns for physical activity, it is possible that individuals have become more likely to report positive behaviors even if they have not increased their physical activity. Our sensitivity analyses of different ways of constructing sufficient physical activity show that the national trend may be leveling rather than increasing.

It makes a difference how you read the data

Remember the covariates I mentioned above?  Though there was overall a low correlation between change in the level of physical activity and obesity in from 2001 to 2009, for every 1 percentage point increase in physical activity, obesity prevalence was actually 0.11 percentage points lower. This result is considered significant when controlling the data for a number of other covariates: percent rural, change in poverty level, change in unemployment, and an increase in the number of doctors in the given population.  In other words, the decrease in obesity correlated positively with increased physical activity in counties where education, health care, and economy showed an improvement.

Exercise does a lot more than burn calories

While noting the flaws of this study – some of which I’ve explained above – in Conclusions, the team says that the rise in physical activity levels will have  a positive independent impact on the health of Americans by reducing the burden of cardiovascular diseases and diabetes. At the same time, other changes – such as reduction in caloric intake – are likely needed to curb the obesity epidemic.

Exercise builds brain power, enhances self-esteem – in those of any size – and builds physical confidence.  We know that people engaged in regular exercise programs feel more in control of their dietary choices.  And people with better means, and increased access to health care – an improved standard of living and better education – shows up in improvements in health.  This powerfully underscores the need for ongoing community education and the importance of improved standards of living.

And it tells us – and I’ll say it again – that you can’t out train a bad diet.

Bottom line?  Keep moving – there’s a lot more at stake here than just weight loss – and remember that you carve your figure with your fork.

P.S.  To help illustrate the point, watch this short video by Brad Pilon and Craig Ballantyne.  Watch while during this 2 minute segment, Brad consumes 1,000 calories of pizza and root beer while Craig, running at an 11-mile-per-hour pace, “runs off” under 50 calories in the same amount of time.


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