Do physical activity interventions also decrease sedentary time ?

Image Source 1 & 2.

Image Source 1 & 2.

Today’s post comes from friend and colleague Dr Stephanie Prince, discussing her important new paper published in Obesity Reviews (available free here).  More on Stephanie can be found at the bottom of this post.  And if you happen to be attending the Canadian Association of Cardiovascular Prevention and Rehabilitation (CACPR) conference in Vancouver this week, swing by to hear Stephanie present on Saturday in the Scientific Abstract Presentations session (details here).


Physical activity has long been established as a strong predictor of cardiometabolic health, disease and mortality.  For decades now researchers have been trying to develop interventions that will increase our physical activity levels, most notably at higher intensities – think moderate-to-vigorous physical activity (otherwise known as MVPA).  In Canada, we have physical activity guidelines which promote that adults (18-64 years) aspire to achieve a minimum of 150 minutes of MVPA per week in bouts of 10 minutes or more, with the idea that more physical activity is always better.  Canadians also have sedentary behaviour guidelines for children and youth which propose limits on screen time.

There is a rapidly growing body of literature which suggests that greater amounts of time spent being sedentary (watching TV, screen time, sitting time, total sedentary time) are associated with an increased risk for markers of cardiometabolic disease, cardiovascular disease, diabetes, some cancers and premature death (references here and here).  Sedentary behaviours refer to the time spent sitting or lying down and in a state where there is relatively minimal energy expended (not just the absence of MVPA).

While there has been a lot of research looking at the effectiveness of physical activity interventions, little has been done to examine whether these interventions also decrease the time we spend being sedentary.  Prior to this review I often wondered whether the opposite might occur whereby individuals who increased their physical activity levels may become more sedentary almost has a consequence of the satisfaction that they had already undertaken the necessary amount of physical activity needed to meet physical activity guidelines.  Although in its infancy compared to the physical activity field, the sedentary behaviour field is now proposing and testing a variety of interventions targeting sedentary behaviours exclusively  (with the majority to date having focused on office environments, where many of us spend the majority of ours days sitting at desks in front of computers).  While the efficacy of physical activity interventions is more known, it remains unknown whether these intervention also have the capacity to decrease sedentary time.  Further it is unknown whether interventions which target sedentary behaviours are any better at reducing these behaviours than physical activity interventions.

Therefore, the objective of our research was to systematically review the literature and compare the effectiveness of interventions with a focus on physical activity and/or sedentary behaviours (e.g.physical activity only interventions vs. physical activity + sedentary behaviour interventions vs. sedentary behaviour only interventions) for reducing time spent being sedentary in adults.

What did we do?

To examine all available literature we conducted a systematic review which searched six different bibliographic databases (you can see more details on this in the full article) looking for any study which described a physical activity and/or sedentary behaviour intervention and reported on changes in total sedentary time or time spent watching TV or sitting among adults. All of the studies included in the review can be found in the supplemental tables found here.  We were also very fortunate to obtain several unpublished results provided to us upon request from authors of original studies where sedentary time was captured, but not reported upon in previous articles.

We assessed the quality and risk of bias of every individual study and also used the GRADE (Grading of Recommendations Assessment, Development and Evaluation) framework, essentially the gold standard for assessing the overall quality of the evidence and for rendering a recommendation based on the current evidence.

[Travis’ note: This was a lot of work!!!]

What did we find?

Figure 1, Prince et al.

After we removed duplicate papers, we ended up retrieving 9,107 relevant papers.  That was a lot of papers to screen!  After many hours and days looking at the abstracts and then the full articles, 63 studies were kept in the review having met our inclusion criteria.  Of these 63, 33 were used in the meta-analyses which allowed us to group quantitative results to yield an overall effect of the interventions.  See Figure 1 for the PRISMA flow diagram to get a sense of how we screened out papers.

Figure 3, Prince et al. Click figure to view full size.

When we examined all of the evidence looking at both the more descriptive results of what the studies found and also at the quantitative results (see Figure 3 above) we found that on average the physical activity interventions resulted in significant, though very small reductions in sedentary time (average difference of 19 minutes/day).  When interventions had both a physical activity and sedentary behaviour component they resulted in significant, but slightly greater reductions in sedentary time (average difference of 35 minutes/day) (Figure 4). Most promising is that when interventions focused solely on the behaviour itself, they yielded an average reduction of 91 minutes/day.

Figure 4, Prince et al.

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Category: Peer Reviewed Research, Physical Activity, Sedentary Behaviour | Tagged | 2 Comments

Why you should stop eating sandwiches

sandwichNew research published in the Journal of the Academy of Nutrition and Dietetics suggests that much of our excessive salt intake can be blamed on the consumption of sandwiches.

Specifically, assessment of one day of dietary intake from 5,762 adults in the US participating in the What We Eat in America, National Health and Nutrition Examination Survey 2009-2010 revealed that approximately 1/5th of the sodium intake of American adults comes from eating a sandwich.

The study also found that on any given day, 49% of American adults consume a sandwich, with the rate of sandwich consumption being significantly higher among men than women (54% vs 44%).

Current guidelines suggest that adults should consume under 1500 mg of sodium per day, and should never exceed the upper limit of 2300 mg/day. By these thresholds, sandwiches alone contributed 30-46% of the recommended upper limit of daily sodium intake.

But we shouldn’t really be surprised.

First of all, as a population, approximately 80% of North Americans exceed the upper limit of sodium every single day.

Secondly, many of the things we squeeze between two pieces of bread – hamburgers, chicken burgers, cheese, hotdogs, deli meats, etc. – are chock full of salt.

And it’s not just sandwiches that deserve all the blame. As I’ve discussed before, fast food is a huge contributor to our collective salt intake:

• 56% of meals purchased at fast food outlets contain more sodium than should be consumed during the entire day (>1500mg), with 20% of meals exceeding the uppermost limit for daily sodium intake (>2300mg)

• Chicken fast food places have the worst sodium levels per meal with 83.8% of meals exceeding the daily recommended level (1500mg)

• Only 1 in 36 purchased meals at fast food joints met the Food and Drug Administration “healthy” sodium level for meals (600 mg)

• The high sodium intake wasn’t necessarily driven by a high calorie intake, but rather by a high sodium per calorie ratio, with an average of 2136 mg sodium per 1000 calories purchased. Thus, even those eating lower calorie meals are likely to exceed their daily sodium limit within a single meal.

As is well established, a diet high in sodium is a key contributor to the development of cardiovascular problems.

Since hypertension and a fondness for salt run in my family,  I certainly need to be careful.

As I’ve admitted before, I love salty foods. Put chocolate or something else sweet in front of me and I can happily ignore it, but put a bag of chips or pretzels within arm’s reach and I just can’t help myself. Also, being of European upbringing, the deli sandwich is a lunch favorite of mine. There’s a local deli I frequent at least once per week where a lovely Italian gentleman prepares me masterpieces of turkey, salami, gruyere, brie, and others between two slices of olive ciabatta. I can’t imagine I’m not bumping up against that 1500mg sodium ceiling after one of those sandwiches.

But, damn they’re good!

Thanks to this new research as a reminder, I’ll try and limit my intake of deli sandwiches, and when I have a serious craving I’ll try and select ingredients that are lower on the sodium scale (e.g. low-sodium turkey vs. prosciutto or salami).

What about you? How do you keep your sodium intake in check?



Sebastian RS, Wilkinson Enns C, Goldman JD, Hoy MK, Moshfegh AJ. Sandwiches Are Major Contributors of Sodium in the Diets of American Adults: Results from What We Eat in America, National Health and Nutrition Examination Survey 2009-2010. J Acad Nutr Diet. 2014 Oct 1. pii: S2212-2672(14)01217-9.

Category: News, nutrition, Obesity Research, Peer Reviewed Research | 8 Comments

“No sugar added” candy lists sugar as first ingredient

sugar free

No sugar added?

Add this to the #facepalm files.

I took the above photo at a convenience store in Charlottetown this summer.  As you can see on the package, the candy is proudly advertised as “no sugar added”.  The package also announces that the candy is sweetened “only with maltose”.  This seemed somewhat surprising to me, because (as you may have guessed), maltose is a form of sugar.  The Canadian Food Inspection Agency defines sugar as “all mono- and disaccharides, including sucrose, fructose, glucose, glucose-fructose, maltose, etc”.  For that reason, foods that contain added maltose cannot be advertised as “no sugar added”.

As you might expect, a quick look at the ingredients showed that these candies were basically just maltose with a bit of added flavoring.  This whole episode is another reminder of how “no added sugar” is a meaningless concept.

I did email the company, and it appears that this was a mistake made out of ignorance rather than a deliberate attempt to mislead. Here is the response from the company (emphasis mine):

It might be something that is outdated, as I have looked over and only found old bags that state “no sugar added.”

Although if it helps your questioning any, Maltose [is] a very complex carbohydrate that dissolves slower than cane sugar.  It means you have less of a spike effect from the sugars.

As noted above, maltose is a sugar (coincidentally, it’s very important for brewing beer), and has a higher glycemic index than table sugar.  All of which highlights the fact that you should not take nutrition advice from candy manufacturers, and most foods that sport front-of-package health labels are probably bad for you. 


Category: Miscellaneous, News, nutrition | Tagged | 1 Comment

Lancet editorial misses the boat

Just came across an interesting editorial in Lancet Diabetes & Endocrinology via @Dr_Burr and @Skeila on Twitter. The article focuses on physical activity and dietary guidelines, but takes a moment to critique the recent Canadian Society for Exercise Physiology position stand on the risks and benefits of promoting activity in kids (full disclosure: I’m a CSEP member, and have collaborated with/studied under several of the authors of the position stand, although I had nothing to do with the article itself).

Here’s the critique from Lancet Diabetes & Endocrinology (emphasis mine):

Disappointing, then, is the position statement on the benefits and risks of exercise in children that was released by the Canadian Society of Exercise Physiology in August, 2014. Although the society acknowledges the great benefits of physical activity for physical and mental health in children, they strongly suggest that the risks should not be ignored. They advise against promotion of physical activity in children unless information about potential activity limitations is available. Lead author Pat Longmuir (Children’s Hospital of Eastern Ontario Research Institute) said that “[vigorous activity] might precipitate a cardiac arrest due to an unrecognised cardiac condition”. With the substantial gains being made in recent years—reversing the trend of ever-increasing childhood obesity rates—this scaremongering report seems a step in the wrong direction. The only result can be defensive, with schools, sports coaches, or other professionals who should be promoting activity practising caution for fear that any child could have a rare heart condition. The onus should be on parents to tell coaches and schools if their child has a heart condition and whether they are therefore fit to exercise, not on these professionals.

I was surprised that these particular authors would argue that we shouldn’t promote activity unless info about limitations is available, because that seems pretty onerous.  And it would probably have a negative impact on physical activity, as the Lancet editorial authors suggest.

So I checked out the position stand,  and I think the Lancet may have grossly over-reacted. Here are the most relevant recommendations from the CSEP position stand (emphasis mine):

The experts convened in June 2012 to consider an appropriate approach to promoting increased physical activity in children. They recommended that given the limitations of current evidence, the following question be used for the purpose of determining whether children less than 15 years of age are apparently healthy: “Has your healthcare provider ever told you that your child should not do some types of physical activity?”

Taken together, the goal of these question(s) would be to identify children at increased risk during physical activity without falsely identifying children who are not at risk and to indicate whether a child should be referred to a physician before engaging in increased physical activity. The expert group also recognized that it is typically not feasible to collect background information for unstructured physical activity (e.g., children swimming in a local pool or playing in a local park). Therefore, the use of these questions is recommended only for structured settings and organized programs. Primary healthcare provider-prescribed activity restrictions, conveyed directly from the healthcare provider or by the parent/guardian, must always be respected by the physical activity leader. The need to inquire about healthcare provider-prescribed activity limitations or other relevant information (e.g., allergies, special needs, medical history) is the same for high-intensity and more sedentary pursuits, and regardless of the setting (e.g., competitive, recreational, research)

Parents and professionals should encourage all children to accumulate at least 60 min of physical activity daily.

It is widely recognized that apparently healthy children should perform at least 60 min of daily physical activity that is of at least moderate intensity, and that exceeding 60 min per day offers even greater benefit (Tremblay and Haskell 2012). Vigorous-intensity activity and muscle and bone strengthening activities are recommended at least 3 days per week (CSEP 2012). What may not be recognized is that the same physical activity recommendations apply to children with disabilities or who have conditions that require primary healthcare provider physical activity restrictions. Modifications or restrictions to the frequency, intensity, duration, or type of physical activity permitted can enable physical activity that is appropriate to each child’s condition (Bar-Or and Rowland 2004b).

So they are not proposing that we only allow kids to participate in activity if they have info on their health risk.  Instead, the question is meant to simply identify kids who have already been identified as being at high risk.  I know this, because I used this specific question as a means of screening participants in a previous study.  Here’s how it was worded on the consent form:

Pre-Participation Health Screening

Please answer the questions:

1.  Has a doctor ever told you that there are some types of exercise or physical activity that you should not do? (please circle)

Yes / No

2.  If you answered yes, please describe the types of exercise or physical activity that you cannot do at this time:

Not surprisingly, almost no one answers yes to these questions (especially among kids who are involved in organized sport). But if there was a reason that someone shouldn’t be exercising, or a specific limitation, it would be helpful to know.  In fact, not asking seems almost negligent.  The whole reason we used this question in our study was specifically because we wanted a way to identify the kids who were known to be at high risk (which is a reasonable requirement of most research ethics boards), without accidentally screening out a bunch of healthy kids, or subjecting them to unnecessary screening.  In other words, this question is meant to avoid the scenario that is described in the Lancet editorial.  In my experience, this question is a good way to quickly assess whether a child has any known risk factors for adverse events during exercise, without any real negative consequences.

Obviously I have some inherent biases at play here, so I’m curious to hear what others think.  And I realize that this may seem like a pretty minor issue, but since the Lancet literally called people out by name (and accused them of “scaremongering”), I thought it was worth pointing out that they seem to be mistaken.


Category: News | 1 Comment

Participants Needed: Standing desk edition

Exciting news – researchers at the University of PEI (myself included) are beginning a study on the impact of standing desks.  If you live in the Charlottetown area (or know someone who does) and work a desk job, we’d love to hear from you.

To get involved email upeiexerciselab (at) gmail (dot) com, and Brittany will be in touch.

Category: News | 3 Comments

Time is of the essence: How to best spend 30 minutes for your health

Today’s post comes from Jonathan Kurka and Matthew Buman, discussing a recent paper that they published in the American Journal of Epidemiology.  Below is a video of Dr Buman explaining the main findings of his study, which was recorded in the fall of 2012.  More on Mr Kurka and Dr Buman can be found at the bottom of this post.

It seems there is never enough time in the day, and this is often the reason people tend not to exercise even if they know they should. There are only 24 hours in a day and all of our daily behaviors can be broken down into three basic categories. Sedentary behaviors include any activity in which you aren’t active, such as sitting while watching TV, sitting while at a computer at work, driving your car, or lying down without sleeping. Active behaviors include walking, jogging, exercising, or even performing household chores such as cleaning, cooking, and vacuuming. Sleeping behaviors include naps and your nightly rest period.

Note: in research, we often break activity behaviors up, based on intensity, into light intensity (LIPA; activities that don’t require a lot of effort, but are still active, such as walking and cleaning) and moderate-to-vigorous (MVPA; activities that really make you sweat!) physical activity.

Because the total time in one day equals the sum of sleep, sedentary behavior, LIPA, and MVPA, if you increase time in one behavior, you’ll have to decrease time in another. So if we were able to add a 30 minute jog (that’s MVPA) to our day, what other behavior would we be doing 30 minutes less of? Would that jog replace watching a TV show (sedentary)? Or cleaning the kitchen (LIPA)? Or perhaps going to bed 30 minutes earlier (sleep)?

We know for many years of previous research that MVPA is associated with markers of cardiovascular disease (e.g. waist circumference, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, insulin levels, glucose, and C-reactive protein). It turns out that sleep duration is also related to many of these same biomarkers. Most recently, we have come to realize that sedentary behavior, independent of MVPA, is uniquely associated with these biomarkers as well. But how do all these behaviors fit together? What are the trade-offs, one behavior for another? This was the focus of our analyses. We sought to explore the effects of re-allocating 30 minutes/day from one behavior to another on markers for cardiovascular disease.

To do this we conducted isotemporal substitution models using data from the National Health and Nutrition Examination Survey (NHANES). NHANES is a program of studies designed to assess the health and nutritional status of adults and children in the United States. The program includes an in-person home interview and a laboratory examination in a mobile examination center. By incorporating a complex sampling strategy and weighting system (details can be found on the Centers for Disease Control and Prevention website), a sample that is statistically representative of the entire U.S. population can be created. After removing ineligible persons, 2,185 remained with data for waist circumference and HDL and 923 remained with data for triglycerides and insulin.

We used a statistical technique called isotemporal substitution modeling. These types of models have more commonly been used in studies involving food intake, but we applied this technique to the context of daily behaviors. These models estimate the “substitution association” of reallocating 30 minutes/day from one behavior to another (e.g., reallocating 30 minutes/day of sedentary behavior to 30 minutes/day of MVPA). We also controlled for several other variables to make sure any results were due to the re-allocation of behaviors and not due to the sex, ethnicity, marital status, education, work status, ratio of family income to poverty level, smoking, depressive symptoms, intake of total energy, saturated fat, caffeine, and alcohol; general health rating; previous diagnosis of cancer or malignancy, diagnosis of CVD or diabetes, or current use of diabetic, antihypertensive, lipidemic, or other CVD medication.

What did we find?

We’ve provided a graph that highlights our findings. Briefly, a relative risk < 1 (a marker to the left of the vertical line) indicates that by reallocating 30 minutes/day of one behavior to the other reduced the value  for that cardiovascular risk factor. A marker to the right of the vertical line indicates an increased  value in that risk factor from the reallocation of 30 minutes/day of one behavior to the other.

Impact of 30-minute reallocation of time (Source)

Impact of 30-minute reallocation of time (Source)

It is pretty clear from this graph that by reallocating 30 minutes/day of either sleep, sedentary, or LIPA behaviors to MVPA decreases waist circumference risk (that’s a good thing, as larger waist circumference indicates obesity), increases HDL cholesterol risk (that’s a good thing, because HDL is the “good” cholesterol), decreases triglycerides (that’s a good thing because triglycerides increase risk for obesity), and decreases insulin risk (that’s a good thing, as this is an indicator for diabetes). All good things!

Another interesting finding is that it doesn’t take MVPA to improve health. By reallocating sedentary behavior to LIPA, there was a 1.9% reduction in triglycerides and a 1.4% reduction in insulin levels and reallocating sedentary behavior to sleep resulted in a 2.4% reduction in insulin.

What’s the take home message?
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Category: News, Obesity Research, Peer Reviewed Research, Physical Activity, Sedentary Behaviour | 1 Comment