Arya M. Sharma, MD

For today’s kids, walking or biking to school has become the exception rather than the rule.

A study by Anna Price and colleagues, published in the Journal of School Health, now explores the perceptions of school administrators in South Carolina regarding the factors that influence childrens’ active travel to school.

According to their survey of 314 school and district leaders of elementary and middle schools, the two most commonly raised issues were concerns about the safety of crossing streets (54%) and the availability of sidewalks (54%).

Additional factors included distance to school (46%), traffic volume (42%), parental attitudes (27%), traffic speed (27%), neighborhood condition (24%), and student attitudes (10%).

Some respondents also expressed concerns about liability issues related to students’ active travel to school.

Overall, the survey left no doubt about the considerable concerns of schools administrators about the safety of students while walking to school.

Based on these findings, the researchers suggest that active travel to school may be increased by addressing the (perceived?) safety of street crossing and the number of sidewalks, and by educating school and district leaders about liability and safety issues related to students walking to school.

If my readers can think of other barriers or novel ideas how to address them, I’d certainly love to hear them.

AMS
Edmonton, Alberta

Price AE, Pluto DM, Ogoussan O, & Banda JA (2011). School Administrators’ Perceptions of Factors That Influence Children’s Active Travel to School. The Journal of school health, 81 (12), 741-748 PMID: 22070505

This question appears almost a ‘no-brainer’ and many readers will once again put the very fact that I touch on this topic down to ’sports-bashing’ - but, the ‘uncomfortable truth’ for youth sports enthusiasts is that the answer to this question is far less clear than one would perhaps expect.

Given the rather mixed literature on whether or not (organized) youth sports can provide a solution to the obesity problem, Toben Nelson and colleagues from the University of Minnesota, Minneapolis, have taken a careful look at the published literature on this issue - their findings are published in the latest issue of Current Sports Medicine Reports.

While their review of 19 studies on this topic showed that kids participating in sports were indeed more physically active than kids who did not participate, overall they found no clear relationship between participation and weight status. While 12 studies did note some (albeit small) differences in body weight in selected subgroups (but not the entire study population in these studies), the other 7 studies found no differences in body weight at all.

Further analyses of these studies revealed some ’surprising’ findings that may well explain these findings:

Firstly, there were substantial disparities between the overweight and obesity rates between sports: sports with a higher level of obesity included rugby, swimming, judo, and tennis, and sports with lower levels of obesity included gymnastics, handball, horse riding, and dance.

Thus, as the authors note:

“The lack of a clear difference in weight status between participants and nonparticipants observed in some of the studies reviewed may be attributed to the type of sport studied and the specific body type suited for that sport.”

Secondly, although kids participating in sports tend to have more activity than non-participating kids, the overall differences are not as large as one would assume. While in one study, on the days on which kids participated in sports added about 30 mins of moderate to vigorous physical activity to that day, another study that objectively assessed physical activity of youth sport participants in soccer, baseball, and softball, found that fewer than one in four met recommended levels of activity during their sport team practice.

“It is not clear from these studies how much of the sedentary time in sport was spent in these sport-related activities and it is also not clear what extent to which physical activity can be optimized in these settings without sacrificing instruction and skill development.”

Thirdly, it is very possible that participation in youth sports can negatively affect both the quality and quantity of food and drink consumed, potentially resulting in net positive energy balance.

Thus, although one study found that youth involved in sport had better overall nutrient intake than youth not involved in sport, several other studies showed that total caloric intake often exceeded actual expenditure. One study of middle and high school youth found a positive association between sports team participation and frequency of fast food consumption and that sport team participation during middle school predicted greater fast food consumption into the high school years. In other studies, sport participants were more likely than nonparticipants to consume sports drinks and fruit juice and were equally likely to consume soft drinks.

As the authors point out:

“Candy, confectionary, sugar-sweetened beverages (including sport drinks), and ice cream are commonly sold at youth sport events or brought to the event by contestants and parents. Youth sport marketing is a key part of food and beverage marketing strategies, and voluntary industry guidelines may actually encourage food and beverage companies to associate those products with health and fitness activities such as youth sport.”

“Among some sport teams and leagues, the practice of providing snacks and beverages is institutionalized, wherein volunteer parent coordinators develop and assign a snack schedule. The snacks and beverages provided are often packaged convenience food (e.g., sport drinks, soda pop, candy bars, cookies, chips, “fruit” snacks) and, in combination, could total 300 to 500 calories or more.”

This is certainly problematic as,

“Youth, parents and coaches may have little or no awareness of the large number of calories contained in snacks and beverages commonly offered in youth sport settings or the relatively small number of calories children expend during sport.”

The authors also discuss the observations that:

“In addition to direct access to excess calories available in sport settings, participants are subject to time pressures associated with attending sport practices and events. Time pressures may lead to more consumption of fast food and other processed food, which tend to be convenient but less healthy options. Regular family meals are associated with healthful dietary behaviors but may be sacrificed due to sport participation. Parents of youth sport participants report that sport-related time pressures influence meal planning and preparation, interfering with family meals.”

Another issue concerns the almost inevitable discontinuation of sporting activity, which may occur for numerous reasons including personal factors such as lack of enjoyment or motivation, time constraints, pressure to perform, and low achievement orientation and organizational factors such as coaching issues, lack of playing time, and lack of opportunities to participate.

“Regardless of the reason for dropping out of sport, decreasing energy expenditure without replacement with other forms of physical activity and/or decreasing caloric intake can promote energy surplus and weight gain. Childhood eating patterns help establish adult dietary habits, and these findings highlight the importance of promoting good nutrition in conjunction with youth sports.”

Overall, the authors conclude that:

“Given the limited available research, there is not sufficient evidence to conclude that sport participation protects against the development of obesity. Additional research is needed to understand weight status and weight gain among sport participants and to determine whether, and under what conditions, sport can effectively prevent unhealthy weight gain.”

At a minimum:

“Additional discussions among key stakeholders are needed, and interventions to reduce the exposure to the excessive calories and other unhealthy food and beverage options available in youth sport must occur before the promise of obesity prevention in youth sport can be realized.”

As I have discussed before, it appears that both the potential benefits and downsides of sports as a means to tackling obesity have more to do with the impact of sports (and sport settings) on caloric intake than expenditure.

AMS
Edmonton, Alberta
Nelson TF, Stovitz SD, Thomas M, Lavoi NM, Bauer KW, & Neumark-Sztainer D (2011). Do youth sports prevent pediatric obesity? A systematic review and commentary. Current sports medicine reports, 10 (6), 360-70 PMID: 22071397

Canadian kids (and adults) are steeped in an epidemic of sedentariness - not just those with excess weight are not moving enough - no one is!

So, while clinicians may be familiar with the recommendation for adults to aim for 10,000 steps a day (an ambitious goal by most standards), step recommendations for kids are less clear.

This issue was now addressed by CON Bootcamper Rachel Colley and colleagues from the Children’s Hospital of Eastern Ontario Research Institute, Ottawa, Ontario - their findings were just published in Medicine and Science in Sports and Exercise.

Using accelerometer and pedometer data collected on children and youth aged 6-19 years (n = 1,613) in the Canadian Health Measures Survey the researchers complete correlation analyses of daily step counts and minutes of moderate-to-vigorous physical activity (MVPA) by age and sex.

It turns out that the daily step count equivalent to 60 minutes of MVPA is about 12,000 steps per day (range 11,290 and 12,512). This is slightly lower than the 13,500 steps that have been previously recommended as a target for children and youth.

In a word to both researchers and clinicians, the authors propose that 12,000 steps per day (as assessed by a pedometer or accelerometer) be used as a target to determine whether children and youth aged 6-19 years are meeting the current physical activity guideline of 60 minutes of daily MVPA.

While this number is reassuring to know, it is unlikely to change much unless parents actually do start sending their kids outdoors to kick around the neighbourhood till the lights come on.

I am not sure the kids would mind - but this generation of ridiculously overprotective ‘helicopter parents’ will probably lose sleep over the very idea of letting their kids be kids.

AMS
Edmonton, Alberta

Colley RC, Janssen I, & Tremblay MS (2011). Daily Step Target to Measure Adherence to Physical Activity Guidelines in Children. Medicine and science in sports and exercise PMID: 22051570

Yesterday, I blogged about the rather weak relationship between BMI and health risks in the Manitoba Centre for Health Policy (MCHP) Report on Adult Obesity, and suggested that the results may have looked very different had the same data been analysed using the Edmonton Obesity Staging System.

Today, I want to address another interesting finding of this report, namely, the researcher’s attempts to identify the ’causes’ of obesity in Manitoba.

Variables examined included age, sex, marital status, education, employment, household income, activity restrictions, occupational physical activity, self-perceived life stress, satisfaction with life, self-rated mental health, sense of community, eating fruits and vegetables, physical activity leisure and travel, sedentary activities, current smoking, binge drinking, recent changes to improve health, food insecurity, and regular doctor.

Among these, location of residence, age, sex, education, employment, and marital status were particularly strong predictors of excess weight.

Interestingly, the psychological variables had little additional ‘effect’.

leisure– and travel–time activity level was the most strongly associated variable and showed a dose–response relationship—higher levels of activity were associated with lower likelihood of obesity. Other important variables were smoking (which was associated with a lower likelihood of obesity) and time spent in sedentary activities (more than 30 hours per week was associated with a higher likelihood of obesity).

Notably, only age and geography were significantly related to BMI values in youth.

Apart from the fact that such analyses cannot actually prove ‘causality’ as they are merely associated and therefore assumptions about modifying any of the modifiable variable will in fact reduce BMI, the researcher also made another notable observation:

“It is important to note that despite including many variables, this study was only able to explain a small amount of why people are obese. This means there are other reasons for the recent rises in weight, perhaps changes in our diets or our physical and social environment.”

Indeed, I would easily have predicted that factors not considered in this analysis, including parental BMI, birth weight, maternal weight at inception and birth of the participant, duration of sleep, etc. may well have accounted for some of the increase in obesity.

This should not detract from the importance of factors like sedentariness, stress, food insecurity and other variables that had some influence on obesity rates in this study.

It should, however, make us cautious in accepting the commonly held notion that the ‘root cause’ of obesity is simply increased sedentariness and eating too much.

Clearly, this is not the whole (and perhaps not even the biggest part) of this ’story’.

AMS
Edmonton, Alberta

Yesterday, I posted about the observations that the same genes that confer athletic ability by increasing ‘fuel efficiency’ may also promote obesity when such activity ceases. This is in line with the ‘thrifty gene’ hypothesis, that obesity is the ‘natural’ response to genes that conferred survival advantages in our ancestors in the face of famines and increased demands on physical activity.

Interestingly, a study by Abdoulaye Diane and colleagues from the University of Alberta, just published in OBESITY, demonstrates that genetically obesity-prone animals, do in fact have a considerable survival advantage over lean-prone animals, an advantage that is further enhanced, when such animals have previously experienced caloric restriction.

The researchers took advantage of the fact that limiting access to food in mice (by restricting feeding hours) leads to an incremental increase in ‘voluntary’ wheel running associated with reduced food consumption (activity-induced anorexia) and even more running till the animals ultimately exhaust themselves and die.

In their experiments, while food restriction resulted in increased wheel running and reduced food intake in both obesity-prone and lean-prone juvenile mice, the former survived almost twice as long and lost far less of their body weight (percent and absolute values) than the lean-prone mice, which rapidly succumbed to the challenge.

Furthermore, even obesity-prone rats, who were kept lean by restricting their food to the levels of the lean-prone rats (by ‘pair-feeding’), lived longer, suggesting that this was not an advantage conferred simply by greater ‘caloric reserves’.

Interestingly, obesity-prone juvenile mice, who had previously undergone food restriction and regained their weight prior to the challenge, did even better.

Thus, not only was there a clear survival advantage in the genetically obese-prone mice but previous food restriction appeared to confer even more ‘resistance’ to the challenge.

It appear that not only do ‘obesity-prone’ genes allow animals to better cope with the dual challenge of starvation and increased physical activity, but that this ‘metabolic’ prowess can be further enhanced by prior experience with food restriction (weight loss).

Translated to humans, this later finding would suggest that ‘dieting’ makes you even more fuel efficient (which may well explain why dieting increases the risk of subsequent weight gain).

Or as the authors discuss:

“Our results show that juvenile obese-prone rats gain a survival advantage over lean-prone under famine-like conditions, and this advantage is further enhanced by physiological and behavioral changes induced by prior food restriction. In the wild, this survival advantage in young animals, that are the future breeders, would confer increased reproductive success. At a basic level, these results support the “thrifty gene” hypothesis of obesity.”

The authors further conclude:

“Thus, caloric restriction at early ages may predispose obese-prone individuals to become more metabolically efficient. An inducible increase in metabolic efficiency may help to explain the increased obesity in low- and middle-income countries where childhood under-nutrition exists in the context of rapid economic development and rural/urban migration. Thus, the obese-prone phenotype, that is highly deleterious in a food-rich environment, confers a real survival benefit in an unstable and scarce food environment, that is enhanced by prior caloric restriction.”

In summary, if these findings are indeed transferable to humans, they would have several important implications:

1) Genetically obese-prone individuals are better equipped to survive times of scarcity and/or increase physical demand.

2) This ’survival’ advantage can be further enhanced by previous exposure to caloric restriction (weight loss).

While these findings may also explain the ’survival paradox’ of obesity, where obese humans with chronic illnesses tend to live longer than skinny people with those illnesses, they also suggest an explanation for why dieting can make you fat.

I certainly do not envy the folks, who have to translate these findings into coherent ‘public health’ recommendations:

a) having genes that promote obesity is actually a survival benefit (if you should happen to encounter a famine)

b) if you are lucky enough to have these obesity genes, you can further increase your survival benefit (to famines) by (periodically?) losing weight

c) however, if you do (periodically?) lose weight, you may also end up getting even more obese - which, although a survival benefit during the next famine, will increase your risk for obesity-related health problems (in case the famine does not come).

I guess you can’t have it all.

AMS
Calgary, Alberta

Diane A, Pierce WD, Heth CD, Russell JC, Richard D, & Proctor SD (2011). Feeding History and Obese-Prone Genotype Increase Survival of Rats Exposed to a Challenge of Food Restriction and Wheel Running. Obesity (Silver Spring, Md.) PMID: 22016097