The surprising science of fat: you can get fatter and become healthier

fat cellsA new study in obese mice suggests that increasing the growth of fat located under the skin (subcutaneous) actually led to an improvement in glucose tolerance and insulin sensitivity, both precursors to diabetes. The expansion of subcutaneous fat was also associated with a reduction in the fat stored in places that aren’t meant to store fat, such as the liver.

The study, published online at the journal Obesity, induced the growth of subcutaneous fat through hyperplasia (increasing the number of fat cells) rather than hypertrophy (growth of existing fat cells) by injecting “acellular adipogenic cocktails” around the subcutaneous fat depots in obese mice. Ten weeks post-injection, the mice showed evidence of subcutaneous fat expansion and the corresponding metabolic improvements described above.

So, just to recap: obese mice became healthier by getting fatter.

Should we be surprised? Not if you’ve been following our blog over the years.

Let’s do a quick review.

First, it is important to understand that fat, or adipose tissue, which is mostly composed of many individual fat cells (adipocytes) is not inherently unhealthy. To the contrary, adipose tissue is absolutely necessary to allow the body to store excess calories during times when we ingest more calories than we expend through activity and resting metabolism. By doing so, adipose tissue acts as a buffer of excess calories, and thus protects other tissues of the body from accumulating fat (i.e. heart, liver, muscle). This notion is best represented by the fact that individuals who completely lack fat tissue (a disorder known as congential lipodystrophy) are very unhealthy and are almost guaranteed to develop diabetes and heart disease, despite having an athletic and lean appearance.

In other words, fat tissue is essential for health.

Where many people get into trouble is when they have exhausted their body’s ability to store more calories in adipose tissue – we all have a certain threshold to which our fat depots can expand. When we get to that point, our fat cells become so big that they are no longer able to buffer excess calories and thus cannot protect other tissues from fat accumulation and damage. This is when many of the classical metabolic problems of obesity become apparent – increased blood fats, blood glucose levels, etc.

But wait, isn’t losing fat through diet and exercise good for health?

Yes, when we expend more energy (exercise) or reduce the amount of food we ingest (diet), or both, our body draws on our extra stores of energy in our adipose tissue – this process gradually reduces the size of the individual fat cells. That is, fat loss occurs due to a reduction in size of fat cells, not a reduction in the number of fat cells. Not surprisingly, your pants start fitting better. Also, this process makes fat cells more efficient at sucking up excess calories the next time we again eat more than we expend.

What about liposuction?

Fat loss through diet/exercise is completely different from the scenario of liposuction, where a whole bunch of fat cells are removed from the body – that is, you reduce the number of fat cells, but the remaining ones don’t get any smaller or healthier. In fact, the opposite may be true, with less place to store excess calories than before surgery, so enlargement of those fat cells left behind.

In a 2004 study, obese women who underwent abdominal liposuction, losing approximately 30- 45 % of the subcutaneous fat in the abdominal region (~10kg of fat), did not show improvements in any of the metabolic markers assessed, including insulin sensitivity, blood pressure, blood glucose, insulin, or lipid levels.

Just to recap: simply surgically removing subcutaneous fat tissue does not make one healthier.

How about increasing subcutaneous fat stores in obese people? Do they also become healthier like the fat-gaining obese mice?

In a prior study, 12 overweight or obese and metabolically unhealthy subjects were given a drug (Pioglitazone) for a duration of 12 weeks. Pioglitazone belongs to the thiazolidinediones (TZD) class of drugs that seem to upregulate the production of healthy new fat cells (a process known as adipogenesis) – that is they make you fatter. By doing so, these drugs increase the storage capacity of your fat tissue – something that is limited in unhealthy obese individuals.

And that is precisely what happened in these subjects following 3 months of pioglitizone administration. First, they gained about 2kg of body weight. Their amount of subcutaneous fat in the belly went up by about 10% and that in their butt/thigh by about 24%. Interestingly, their amount of dangerous visceral fat decreased by about 11%.

Also, a fat biopsy from the belly of the subjects showed that the increase in fat mass was due to an increase in the number of small and healthy adipocytes (hyperplasia – just like in the mice study) which are better able to take up more circulating fat.

And what happened to their insulin sensitivity?

It improved by over 28%!

That’s right – they got fatter and yet healthier. Just like the mice.

As we have attempted to highlight over the years, fat is not inherently unhealthy. Losing fat isn’t always beneficial nor is gaining it always detrimental to health. Matters related to excess fat and health risk are much more nuanced than previously thought.

Peter

References:
1. Qiqi Lu et al. Induction of adipocyte hyperplasia in subcutaneous fat depot alleviated type 2 diabetes symptoms in obese mice. Obesity. 2014
2. Klein S. et al. (2004). Absence of an Effect of Liposuction on Insulin Action and Risk Factors for Coronary Heart Disease New England Journal of Medicine, 350, 2549-2557
3. McLaughlin, T et al. (2009). Pioglitazone Increases the Proportion of Small Cells in Human Abdominal Subcutaneous Adipose Tissue. Obesity.

Category: Obesity Research, Peer Reviewed Research | 5 Comments

Make Life Harder

I’ve just returned from the final day of the Global Summit on the Physical Activity of Children.  The highlight today was a keynote by Mike Evans, a physician who has created a number of extremely successful viral videos on health-related topics.

His talk was of interest to me as both as a health researcher, and as someone who is actively involved in knowledge translation (KT).  I think the most important thing that he discussed was the idea that failure is ok, and even crucial to success in both research and in KT.  He talked about making a Minimum Viable Product, which is basically the best thing you can duct tape together, warts and all.  You then constantly evaluate and tweak the product, with each iteration sucking slightly less than the one before.  It’s the model that Peter and I have used here at Obesity Panacea (www.obesitypanacea.blogspot.com was very different from the blog you see today!), and continue to use as we play around with Youtube and Twitter and podcasts.

But Dr Evans talked about using the Minimum Viable Product idea to go from an idea to having a working healthcare intervention in a span of just 90 days. In other words, do a bit of homework, talk to your target audience, then try out a basic intervention. Then evaluate, build on what worked, and drop the rest. I can see some hurdles with that approach (just getting ethics approval in <90 days can be a real challenge sometimes) but I think it makes sense, especially when compared with the alternative of spending years developing an intervention that may be tossed aside or irrelevant by the time it is ready to roll out.

During his talk Dr Evans also showed one of his videos, this one focusing on making life harder as a means of embedding physical activity into your day. I personally use almost all of the strategies in the video, and I think it does a great job of getting the message across.

As a last thought on the conference, I just wanted to say congrats to Mark Tremblay and all the organizers, as well as the folks at Active Healthy Kids Canada (especially Lindsay Whiting) for putting on a great conference. Hope to see you all again soon.

Travis

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Physical activity vs sedentary behaviour; what is more important for kids?

My personal highlight from day 2 of the Global Summit on the Physical Activity of Children was a debate on the relative importance of sedentary behaviour and physical activity for child health.  Arguing for physical activity was Dr Ulf Ekelund, while sedentary behaviour was argued by David Dunstan.  Rather than go point by point, I thought I’d touch on some of the main themes that were discussed. And just to be clear, this was my perception of the debate, so if anyone had a different perception I’d love to hear it in the comments (similarly, if anyone feels I misunderstood the points of the speakers please let me know).

Objective and Subjective Sedentary Behaviour Are Not the Same

One of the first points raised by Ulf Ekelund is that objectively measured sedentary behaviour is not consistently associated with health outcomes in children.  In contrast, screen-based measures of sedentary behaviour are much more consistently linked with negative health outcomes.  Take, for example, this paper from my PhD that found that screen time was strongly associated with health risk in kids aged 8-11 years, whereas objectively measured sedentary time showed no association with health outcomes.  In other words it may be the screens that matter, rather than the sitting.

Physical Activity Gives the Biggest Bang For Your Buck

In contrast to the wishy washy evidence linking objectively measured sedentary behaviour and health in kids, there is pretty consistent linking physical activity with health in this same group.  Dr Ekelund has done some interesting work in this area.  For example, the below figure shows data from one of Dr Ekelund’s studies which found that moderate intensity physical activity was associated with health outcomes in kids irrespective of how much time they spent being sedentary.  In contrast, sedentary behaviour was not associated with any health outcome after adjusting for moderate physical activity.  In other words, physical activity was the more important to health than sedentary behaviour for these kids (JP Chaput found similar results using a cohort of Canadian children).

Kids and Adults Are Not the Same
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New Zealand & Mozambique Get Top Grades on Physical Activity Report Cards

Image via Active Health Kids Canada (Source)

Image via Active Health Kids Canada (Click to view full size)

Today is the first full day at the Global Summit on the Physical Activity of Children, and it began with the unveiling of Physical Activity Report Cards from 15 different countries.  Canada has been releasing an annual Report Card on childhood physical activity for 10 years, but this year they were joined by countries ranging from England and the USA to Ghana and Kenya. Canada and the USA received overall grades of D- (not a big surprise who for those of us that have followed these things over the years), while New Zealand and Mozambique had the top grades (B for both countries).  In addition to overall physical activity, the report cards also looked at different key indicators for each country.

Interestingly, Canada scored relatively well on indicators related to school physical activity, family and peer support, and government policy and the built environment (I say relatively well because the grades were still typically low, but they were nonetheless in the top third of countries).  In other words, in Canada we seem to be doing a good job of putting the supports in place for kids to be active (or at least paying it lip service), but it’s not making much of a difference in terms of actual physical activity levels.  Below is a video of Joel Barnes, lead author of the Canadian Report Card, explaining their key findings for this year.


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Category: Interview, Miscellaneous, News | Tagged | 2 Comments

Come find me at the Global Summit on the Physical Activity of Children

This week I head to the Global Summit on the Physical Activity of Children in Toronto, Canada. I’ll be an official blogger at the conference and I’m looking forward to a bunch of great sessions (Full disclosure: several colleagues, including my former supervisor, were heavily involved in organizing the conference, and as a blogger my registration fees have been waived. That being said, I had already committed to attend the Summit anyway because it looks like a great conference).

Since beginning my Post Doc in December my research has been focusing on adult populations (specifically people with heart disease and other chronic conditions), so it will be nice to be back to pediatric research for a few days! I’ll be blogging more throughout the week, but I wanted to list my general itinerary here in case anyone wants to pop over and say hello. Also, if you’re planning to attend/blog about other sessions let me know and I’m happy to link to it here. For anyone tweeting about the conference, the official hashtag is #AHKCSummit.


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Active Transportation and Health: Cycling > Walking > Driving

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Photo by Tejvan Pettinger (Source)

Today’s guest post comes from my friend, colleague, and former labmate Richard Larouche.  You can find out more about Richard at the bottom of this post.

Regular readers of Obesity Panacea will know that today’s children are not active enough. For example, according to the 2007-2009 Canadian Health Measures Survey, only 9% of boys and 4% of girls meet the Canadian physical activity guidelines (Colley et al., 2011, available here). These guidelines recommend that children and youth accumulate at least 60 minutes of daily moderate-to-vigorous physical activity – that is activities that are intense enough to increase one’s heart rate and accelerate breathing.

There are many sources of daily physical activity including organized sports, physical education, active transportation, household tasks, etc. Today, I will focus on active transportation, which is the use of non-motorized means such as walking and cycling to travel to and from places.

Travis and I have recently published a comprehensive review of 68 studies that looked at active transportation to and from school among children and youth (Larouche et al., 2014a, available here). To be eligible for the review, studies needed to examine the relationship between active transportation and one of the 3 following outcomes: 1) physical activity; 2) body composition (i.e., body weight and waist circumference); and 3) cardiovascular fitness.

We found consistent evidence that active transportation was associated with higher physical activity levels, not only during the journey to and from school, but during the whole day as well. Furthermore, the difference in physical activity between children using active vs. motorized travel modes was even greater among those who traveled longer distances.

35% of the studies showed that active travelers had a more favourable body composition. However, over half of the studies found no such differences. In our article, we proposed several potential explanations for these findings. I will briefly mention 3 of these hypotheses:

  1. Active travelers may compensate for the increased energy expenditure during active transportation by eating more during the rest of the day.
  2. The energy expenditure of active transportation may simply be insufficient to have a substantial impact on body composition for the typical child who walks or bikes to and from school over a short distance.
  3. Active transportation tends to be more common among children from low socio-economic status families (e.g., families with lower income and/or parental education level). Previous studies indicate that these children are more likely to be overweight or obese.

Finally, for cardiovascular fitness, our findings differed by travel mode. Indeed, the association between walking to and from school and fitness was inconsistent: some studies showed no differences and others found that walkers were slightly fitter. However, all 5 studies that specifically examined cycling found that cyclists were substantially fitter. This included a 6 year longitudinal study which showed that children who switched from motorized travel to cycling increased their fitness over time.

The Canadian Health Measures Survey

More recently, I performed a series of analyses using data from the 2007-2009 Canadian Health Measures Survey (Larouche et al., 2014b, available here). This survey conducted by Statistics Canada is representative of the overall Canadian population.

In the survey, 1,016 youth aged 12-19 years were questioned on the amount of time that they usually spend walking and cycling while traveling to and from school or work or while doing errands. This provided an opportunity to examine active transportation beyond the school trip and how it relates to physical activity, body composition and cardiovascular disease risk factors.

Both walking and cycling were associated with higher physical activity levels, even after controlling for gender, age, parental education and the complex survey design.
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