Dr. Sharma's Obesity Notes

Readers will recall my recent post on the notion that the weight-loss that occurs in some people with exercise is probably related more to the impact that exercise has on caloric intake than on the actual amount of calories burnt.

It is therefore not all that surprising, that a systematic review and meta-analysis of the literature on the impact of isolated aerobic exercise on body weight, by Adrian Thorogood and colleagues from Montreal and Quebec, published in the latest issue of the American Journal of Medicine, shows rather limited impact of this intervention on body weight.

In their study, the researchers, searched for all published randomized controlled trial reports of aerobic exercise through January 20, 2010 and identified 14 trials involving 1847 overweight and/or obese patients.

While six-month programs were associated with about 1.6 Kg reduction in weight and about 2 cms reduction in waist circumference, twelve-month programs did not lead to any additional weight loss.

As the authors note:

“Previous systematic reviews suggest a linear dose-response relationship between aerobic exercise and weight loss, but only for interventions <16 weeks in duration with a controlled diet. This relationship has not been shown for longer interventions.“

These findings have some important clinical implications.

1) When indicated(!), taking up an aerobic exercise program alone (i.e. without also changing your diet), is not the most effective way to achieve even a modest 5% weight loss.

2) The study also shows that maximum weight loss with this intervention is probably achieved after about six months, whereafter, continued exercise helps maintain weight loss, but does not reduce weight further.

Of course, none of this should be taken as an excuse to abandon or not include a healthy bout of aerobic activity into your daily routine. However, if your only goal is to lose weight (which, by the way, it should not be), you are likely to be disappointed.

Indeed, there is ample data showing that including regular exercise into your routine increases your chances of maintaining weight stability and avoiding weight regain.

And of course, there are countless benefits of exercise, that cannot be measured on a scale.

In the end, weight loss requires reducing and restricting caloric intake - the idea that you can ‘burn’ enough calories through exercise to lose and significant amounts of weight is nonsense - alas, a myth that sells gym memberships and keeps hosts of weight-loss TV shows in business.

Finally, let’s always remember that neither diet nor exercise alone should ever be seen as a treatment for obesity, at least not without first conducting a careful evaluation of the potential causes and consequences of excess weight and carefully weighing the pros and cons of any weight-loss recommendations.

AMS
Cambridge, UK

Thorogood A, Mottillo S, Shimony A, Filion KB, Joseph L, Genest J, Pilote L, Poirier P, Schiffrin EL, & Eisenberg MJ (2011). Isolated aerobic exercise and weight loss: a systematic review and meta-analysis of randomized controlled trials. The American journal of medicine, 124 (8), 747-55 PMID: 21787904

Regular readers will recall my recent posts on the notion that the benefits of regular exercise on body weight are largely mediated by the positive impact on caloric intake rather than by the number of calories burnt.

This notion is based on the idea that exercise modulates eating behaviour by reducing stress, improving mood, and perhaps, even by reducing the ‘reward’ response of palatable foods.

The latter assumption, is supported by a recent stud by Maciej Buchowski and colleagues from Vanderbilt University, Nashville, Tennessee, published in PLoS.

The study was conducted in 12 sedentary or minimally active non-treatment seeking cannabis-dependent adults, who attended 10 supervised 30-min treadmill exercise sessions standardized using heart rate (HR) monitoring (60-70% HR reserve) over 2 weeks.

Self-reported drug use reduced from about 6 joints per day to less than 3 joints a day during the exercise intervention and remained at 4 joints per day 2 weeks after the end of the study.

Average Marijuana Craving Questionnaire factor scores for the pre- and post-exercise craving assessments were also markedly reduced for compulsivity, emotionality, expectancy, and purposefulness.

As the authors discuss:

“Consistent with the changes in cannabis use reported by participants, subjective cravings elicited by cannabis cues were also significantly reduced by exercise, suggesting the possibility that the potential therapeutic effect of exercise may be mediated via brain mechanisms responsible for cue-induced craving.

These same brain mechanisms have been invoked in behavioral addictions involving non-drug rewards, as is observed in overeating and obesity, problematic hypersexuality, and pathological gambling. Analogously, it has been reported that exercise activates some of the same reward pathways as are activated by addictive drugs. For instance, acute bouts of exercise increase central dopamine concentrations and chronic exercise leads to sustained increases in dopamine concentrations and compensatory alterations in dopamine binding proteins in brain regions relevant to reward.”

Thus, the findings from this rather small study provides the basis for conducting a much larger and longer-term study on the use of exercise as a treatment for marijuana addiction.

On the other hand, given important role of the brain’s reward circuitry for food in take, it may not be expected if such a study also demonstrates a positive effect on overconsumption of highly palatable foods.

AMS
Dushesnay, Quebec

Buchowski MS, Meade NN, Charboneau E, Park S, Dietrich MS, Cowan RL, & Martin PR (2011). Aerobic exercise training reduces cannabis craving and use in non-treatment seeking cannabis-dependent adults. PloS one, 6 (3) PMID: 21408154

Regular readers may recall that I posed this question in a post earlier this year.

In it, I proposed that the positive impact of regular exercise on body weight has more to do with the positive effect of exercise on dietary caloric intake than on the number of calories ‘burnt’ - in other words, exercise is more about ‘calories in’ than ‘calories out’.

Following the rather enthusiastic response to this post, Jean-Philippe Chaput (a former CON Boot Camper and now an Assistant Professor at the Childrens’ Hospital of Eastern Ontario in Ottawa) and I co-authored an editorial on this topic for the British Journal of Nutrition.

The original post can be read here.

AMS
Edmonton, Alberta

Regular readers of these pages may be well aware that there are considerable variations in how individuals respond to changes in their diets and activity levels. Some people lose weight on some diets, others don’t - some people eat less food when they exercise, others eat more.

The same applies to almost any variable that has been measured - people simply respond differently to different interventions - diet, lifestyle, medications, or even surgery.

One of the key determinants of how individuals respond, is certainly genetic. Thus, for example, a considerable body of evidence supports the notion that the response of cardiovascular risk factors like blood pressure, lipids, insulin resistance, etc. to exercise are highly heritable - in other words, some people experience significant improvements - others, performing the same amount of exercise, don’t.

So far, however, exactly which genes (let alone which variants of these genes) could determine this variability in response is largely unclear.

Nevertheless, researchers working in genetics (and the many companies involved in developing genetic tests), justify their considerable efforts with the promise of ‘personalised’ medicine, which would allow to predict disease risk and thereby allow people to adopt behaviours that could mitigate such risk (although so far there is virtually no evidence that telling people that they are at higher genetic risk for anything has any impact on their behaviours - in fact, some folks may rather take a fatalistic approach and simply decide to continue eating, drinking, and being merry).

The reason why we should probably not be holding our breath in anticipation of a genetic test that will predict who will benefit most (or least) from exercise is now outlined in an article by Jim Hagberg from the University of Maryland, published in the latest issue of the Journal of Applied Physiology.

Thus, although there is some evidence supporting “possible” candidate genes that may affect responses to exercise training - APO E and CETP for plasma lipoprotein-lipid profiles, eNOS, ACE, EDN1, and GNB3 for blood pressure, PPARG for type 2 diabetes phenotypes, and FTO and BAR genes for obesity-related phenotypes - there is one very significant barrier to advances in this field.

This limitation relates to the fact, that one would need to generate vast amounts of data from exercise interventions studies - an undertaking that may be both unfundable and unfeasible.

The need for such large sample sizes is becoming more and more evident, as attempts to find genes for diabetes, obesity or blood pressure, despite utilizing populations of 10,000 to 250,000 subjects, have found few genes that have largely minor effects - too small to have any clinical utility in predicting these conditions with any reasonable sensitivity or specificity.

As the impact of individual genes on exercise responses are likely to be of similar magnitudes, one would need to perform exercise studies in 10s of thousands of individuals to have any hope of ever finding the genetic determinants of exercise response.

This does not mean that genetics is not an important determinant of exercise response - it just means that finding the genes responsible for differences in responses is a virtually hopeless undertaking.

The same is likely true for other attempts at finding genes to predict individual responses to ‘lifestyle’ interventions.

It may well be that ‘personalised’ medicine in the future will largely be no different from ‘personalised’ medicine today, consisting namely of listening to your patients relating their personal concerns or problems and using your best judgement, your interpretation of clinical evidence (where available) and your (hopefully extensive) clinical experience to advise them the best you can.

When you think about it, it seems quite funny how the use of the term ‘personalised’ medicine in the context of genetic testing, if it ever becomes a reality, will actually result in a further ‘depersonalisation’ of medicine - sounds a lot like Orwelian Douplespeak to me.

AMS
Edmonton, Alberta

Hagberg JM (2011). Do Genetic Variations Alter the Effects of Exercise Training on Cardiovascular Disease and Can We Identify the Candidate Variants Now or In the Future? Journal of applied physiology (Bethesda, Md. : 1985) PMID: 21565989

Seems like this is injury week on these pages.

After blogging about injury patterns in obese US high-school athletes on Monday, today’s article is some Canadian data just published by Warsh and colleagues from Queen’s University, Kingston, Ontario, in the International Journal of Injury Control and Safety Promotion, looking at whether overweight and obese kids take longer to recover from injury.

The data source was the 2002 Canadian Health Behaviour in School-Aged Children (HBSC) survey, which included 7266 youth in grades 6 through 10 sampled from all Canadian provinces and territories. Of these, 2831 students reported an injury event and were included in the analysis.

Youth who were obese and suffered a combined injury (broken bone and strain/sprain) took significantly longer to recover compared to normal weight youth but the recovery time for uncomplicated injuries (fractures or strains alone) was not significantly higher.

Clinicians providing an injury recovery prognosis may need to take into account BMI status and allow for extra recovery time for heavier patients in this age range.

AMS
Heidelberg, Germany

Warsh J, Janssen I, & Pickett W (2011). Do overweight and obese youth take longer to recover from injury? International journal of injury control and safety promotion, 1-7 PMID: 21424972