Nevertheless, for what it is worth, a publication by Ruth Brown and colleagues from York University, Toronto, published in Obesity Research and Clinical Practice, suggests that people today may be more susceptible to obesity than just a few decades ago.
The study looks at self-reported dietary from 36,377 U.S. adults from the National Health and Nutrition Survey (NHANES) between 1971 and 2008 and physical activity frequency data from 14,419 adults between 1988 and 2006 (no activity data was available from earlier years).
Between 1971 and 2008, BMI, total caloric intake and carbohydrate intake increased 10-14%, and fat and protein intake decreased 5-9%.
Between 1988 and 2006, frequency of leisure time physical activity increased 47-120%.
However, for a given amount of caloric intake, macronutrient intake or leisure time physical activity, the predicted BMI was up to 2.3kg/m2 higher in 2006 that in 1988.
So unless there was some major systematic shift in what people were reporting (which seems somewhat unlikely) it is clear that factors other than diet and physical activity may be contributing to the increase in BMI over time – or in other words, it appears that people today, for the same caloric intake and physical activity, are more likely to have a higher BMI than people living a few decades ago.
There are of course several plausible biological explanations for these findings including epigenetics, obesogenic environmental toxins, alterations in gut microbiota to name a few.
If nothing else, these data support the notion that there is more to the obesity epidemic than just eating too much and not moving enough.
In my dealings with patients living with obesity, I am certainly aware of the many health problems attributed to excess weight – but that there may be a link between carpal tunnel syndrome (CTS) and obesity is new to me.
Thus, I was surprised to see a meta-analysis of Shiri and colleagues, published in Obesity Reviews, which shows a rather clear increased risk for CTS with increasing BMI.
Their analysis included 58 studies consisting of 1,379,372 individuals.
While having overweight increased the risk of CTS or carpal tunnel release 1.5-fold, having obesity increased this risk twofold. Each one-unit increase in body mass index increased the risk of CTS by 7.4%.
The associations did not differ between men and women, and they were independent of study design.
Exactly why excess weight would have an adverse effect on the median nerve is unclear but the authors speculate that this may have to do with increased workload or mechanical stretch.
Whether or not weight loss would help alleviated or prevent CTS is unclear.
I wonder is any of my clinical colleagues will have noted this in their patients.
In my conversations with skinny runners, they often cannot stop telling me how much satisfaction and enjoyment they get from their “runner’s high”. No wonder, they so often seem “addicted” to their runs (or other workouts).
In contrast, a “runner’s high” seldom comes up when any of my patients living with obesity talk about their exercise experiences (yes, many people with obesity exercise regularly).
Now, work by Maria Fernandes and colleagues from the University of Montreal, published in Cell Metabolism, reports findings in rats, which, if applicable to humans, may provide a biological explanation for this observation.
Building on previous studies showing that leptin modulates multiple components of brain reward circuitry, particularly in dopamine (DA) neurons of the ventral tegmental area (VTA), an area of the brain allegedly responsible for the “runner’s high”.
Using an elegant set of experiments, the researchers showed that leptin markedly reduces mice’s willingness to work for access to a running wheel or show other signs of seeking out exercise-induced reward.
In contrast, mice with a deletion of the signal transducer and activator of transcription-3 (STAT3), involved in leptin signalling in dopamine neurons of the VTA, showed greater interest in voluntary running.
In other words, STAT3 deletion increased the rewarding effects of running whereas intra-VTA leptin blocked it in a STAT3-dependent manner.
Together these findings strongly suggest that leptin influences the motivational effects of running via LepR-STAT3 modulation of dopamine tone.
Or, in other words, higher levels of leptin (as seen in people living with obesity) directly inhibit the rewarding nature of running, making it less likely to experience a runner’s high, than in someone with low leptin levels (as seen in people with low fat mass).
As to why this may be the case, the authors offer the following explanation:
“We speculate that in conditions of restricted food availability the mesolimbic DA system engages motivational processes concerned with obtaining food and more readily responds to leptin to decrease appetitive physical activity. On the other hand, during fed states, the actions of leptin may be biased toward hypothalamic processes that could increase physical activity as a means to maintain energy homeostasis.”
“While heightened physical activity during food restriction seems paradoxical to the maintenance of energy reserves, it is considered an expression of increased food acquisition behaviors. The capacity for endurance running in cursorial mammals is considered to enable food attainment when it is distant or requires pursuit. Correspondingly, the runner’s high may have evolved to encourage stamina and thereby increase the probability of return on this energetic investment.”
As the authors note, this line of reasoning is supported by the recent observation that exercise addiction in men is associated with low, fat-adjusted leptin levels.
In light of these findings, I also wonder if the “increase in energy levels”, which is rather consistently reported by my patients when they lose weight, may simply be reflective of their often dramatic reduction in leptin levels.
The amygdala is a part of the so-called limbic system that performs a primary role in the processing of memory, decision-making, and emotional reactions. The amygdala has also been implicated in a variety of mental health problems including anxiety, binge drinking and post-traumatic stress syndrome.
A study by Xu and colleagues, published in the Journal of Clinical Investigation now shows that in mice, activity of the estrogen receptor–α (ERα) in the medial amygdala may have a profound influence on the development of obesity – an effect, which appears to me largely mediated through effects on physical activity.
Building on previous work showing that ERα activity in the brain prevents obesity in both males and female rats, the researchers used a series of complex experiments to demonstrate that specific deletion of the ERα gene from SIM1 neurons, which are highly expressed in the medial amygdala, cause a marked decrease in physical activity and weight gain in both male and female mice fed with regular chow, without any increase in food intake. In addition, this deletion caused increased susceptibility to diet-induced obesity in males but not in females.
Deletion of the ERα receptor also blunted the body weight-lowering effects of a glucagon-like peptide-1-estrogen (GLP-1-estrogen) conjugate.
In contrast, over-expression or stimulation of SIM1 neurons increased physical activity in mice and protected them from diet-induced obesity.
These findings point to a novel mechanism of neuronal control of physical activity, which in turn appears to have important effects on the susceptibility to weight gain.
Today’s guest post comes from Kristy Wittmeier, PhD (and CON Bootcamper), a physiotherapist at the Winnipeg Health Sciences Centre and Director of Knowledge Translation at the Manitoba Centre for Healthcare Innovation. She has a special interest in physical activity as a tool to prevent and manage obesity-related conditions in youth. Her current positions and affiliation with the Children’s Hospital Research Institute of Manitoba allow her to combine research and practice to improve patient outcomes. Twitter: @KristyWittmeier
If you were trying to build a coordinated provincial strategy to promote healthy weight in children and youth, where would you start? This has been a question on the minds of a team of healthcare providers and researchers in Manitoba for some time now.
Manitoba has the highest rate of type 2 diabetes in children in Canada, a condition that is in part related to obesity. In Manitoba, youth are diagnosed with type 2 diabetes at a rate 20 times higher than in any other province.
There are well-established, multidisciplinary clinical programs in our province that work with youth living with type 2 diabetes. For example, the Diabetes Education Resource for Children and Adolescents, which has existed since 1985, runs two weekly clinics and an outreach program for youth affected by type 2 diabetes.
Recently, the diabetes care team joined forces with pediatric kidney specialists in the province to provide a combined clinic for youth affected by both type 2 diabetes and kidney complications.
Manitoba is also home to the Maestro Project, which helps teens living with type 2 diabetes navigate what could otherwise be a difficult transition from pediatric to adult health care services and teams.
Similarly, research teams that include community advisors and families are tackling important questions related to the origins of type 2 diabetes and exploring innovative interventions to improve the health and quality of life for kids with this diagnosis.
Members of the DREAM (Diabetes Research Envisioned and Accomplished in Manitoba) Theme at the Children’s Hospital Research Institute of Manitoba are studying important biological, social and psychological factors linked with early kidney disease in youth with type 2 diabetes in a study called iCARE (Improving renal Complications in Adolescents with type 2 diabetes through REsearch).
While we have made significant progress in the area of type 2 diabetes care and research, we have made less progress in the areas of prevention and treatment of obesity in children and youth. We are one of the few provinces in Canada without a specialized clinical team dedicated to pediatric obesity. We lack a comprehensive provincial strategy that can link health care providers to each other, or to existing community programs that might help families. Gaps in services can leave families without access to care that could help their children. This is the issue that we have decided to tackle in a study that was recently funded by the Children’s Hospital Research Institute of Manitoba.
Our study is called “Mapping the state of pediatric weight management programs in Manitoba.” We will start with a survey within Manitoba, to identify existing programs that are available to families affected by obesity in our province. We want to know what is currently available. Where can health care providers refer families? And importantly, what resources are missing in our province to be able to provide an evidence-based approach to pediatric weight management?
While the title suggests we are solely focused on Manitoba, we are in fact looking to shape our provinces’ approach by learning from others across Canada and the United States.
To do this, the second part of the study will involve updating a 2010 study that mapped Canadian pediatric weight management programs to understand what has changed on the national landscape. What new programs exist and where? What programs are no longer offered and why?
Then we will move on to more in-depth conversations with members of the eight clinics involved in the Canadian Pediatric Weight Management Registry (CANPWR), and an additional eight clinics in the United States to better understand how their approaches evolved, barriers and successes that they have experienced and other key learnings that they can share to help inform a Manitoba approach.
Once we have brought the information from these activities together, we will hold a meeting for families, community members, clinicians, researchers, healthy living organizations and policy makers in the province. We will look at the data together and prioritize the next important steps on this journey.
We all need to work together to build healthier families, healthier communities and healthier populations. This novel approach that integrates the experiences and priorities of others will ensure that when we launch a new direction for pediatric obesity management in Manitoba, it will be relevant and targeted to everyone’s needs.