Over the last 3-5 years you have probably come across the importance of visceral fat to your health. Visceral fat is not the fat you can pinch at your belly – that fat is subcutaneous fat. Visceral fat is inside the abdominal wall. It is the fat that is thought to be responsible for chronic inflammation (as measured by CRP, IL-6, and TNF-alpha levels), and is thought to be a major contributor to metabolic syndrome/diabetes along with cardiovascular diseases (CVD).
We had known for a long time that being overweight is detrimental to our long term health – but scientist started weeding out the culprit – it is not any fat, but rather the visceral fat which is the problem. In many ways you could argue it doesn’t really matter, the take home message is the same – don’t get too fat. But despite that, I will try to give you some knowledge about visceral fat.
That pot belly that we have all seen protruding out over the pants is more than likely caused by visceral fat, than simple subcutaneous fat. But the only way to really know is to get ‘scanned’. Now it is likely for most of us as we gain weight we first enlarge our subcutaneous fat stores and once they get full we start putting more into the visceral fat stores (of course it is not exactly that simple). But of course there are individual differences (like everything else – we are all special snowflakes) of our storage tendencies.
Visceral fat removal study:
A small study, which was not published in a high end journal (not that you should discount it for that reason), examined the relationship between visceral fat and lifespan in rats (Muzumdar et. al., 2008). They wondered what would happen if you surgically removed visceral fat (one time) and examined how long they would live.
Now the normal liposuction, which is one of the most popular surgeries in America, does not remove visceral fat – but rather subcutaneous fat.
Rats that had their visceral fat (VF group) removed at age 5 month lived longer than the control animals, but not as long as the third group of animals which were on calorie restriction (CR). The visceral fat removal group lifespan appeared in between the control group and the CR group – but the authors state that the VF group had approximately 20% of the longevity effect of CR. So while visceral fat is important CR still works considerably better.
So one problem with this study was they don’t have a time series measurement of the level of visceral fat (which can be done in rats with modern scanning techniques). Though at 20 weeks into the experiment they did measure body fat in a subset of animals (n = 8). Interestingly, the visceral fat removal group weighed slightly more than the control group (VF 610 g +/- 18 vs control 570 g +/- 16). The overall fat percentage did not differ between these two groups (VF 27.9% +/- 1.9 vs control 29.2% +/- 0.8, CR 13.3% +/- 1.8). However, in regards of visceral fat the VF group had 8.8 g +/- 1.2 which was significantly less than the control group 26.9 g +/- 2.3 (CR group = 5.9 g +/- 0.7). I was a little surprised at the lack of return of visceral fat in the VF group at 20 months of age as they had it removed at 5 months since this group gained considerable weight during this period and ended up weight slightly more than the control group. The authors point out that the VF group must have larger levels of subcutaneous fat to end up as the same percentage as the control group for overall body fat percentage.
Now I would call this work preliminary but interesting, and deserves further experiments where a more thorough analysis of the effect of visceral fat removal can be obtained.
Neuronal control over visceral fat levels:
Now what controls visceral fat storage? Well that is a huge complicated series of checks and balances which I can’t begin to cover in this blog piece. But as you can imagine for something so important for survival evolution has provided an intricate system that works very well (unless you are in times of extreme abundance as seen in modern human society – developed countries).
But I will tell one part of fat control – motor and sensory innervations of fat. Interestingly, while way back in 1898 they ‘knew’ that fat was innervated it was either considered wrong or ignored until very recently (Bartness et al., 2005: very good review). I was stymied that it has only been in the last 5 or so years that this has really been studied (maybe because of the obesity epidemic and the final realization that fat is not an inert organ – but rather an active dynamic endocrine organ). Fat is innervated by sympathetic peripheral nervous system which sends signals to induce fat release (when needed for energy requirement). Additionally, sensory info from the fat is sent to the dorsal root ganglion and up the spinal cord. So as good thinking individuals what do you think would happen if the spinal cord is injured and the information is no longer sent?
What happens if you remove the innervations to visceral fat?
In humans that have a spinal cord injury (SCI) (either at the cervical or thoracic level) despite having similar BMI , waist circumference, and even higher activity level than age matched able bodied controls the SCI subjects have roughly 41-45% more visceral fat (Edwards et al., 2008, Maruyama et. al., 2008). Now the little you know about visceral fat and its effect on general health what do you think the lifespan is for SCI subjects – (looking at survival of those subjects that have lived beyond the initial 3 years after injury – so you get rid of the confounding variable of the acute trauma)? People with spinal cord injury die approximately 13 to 25 years earlier than able bodied counterparts (depends on the level – cervical vs thoracic, and how complete is the injury) (Strauss et. al., 2006). Since the confounding variable of the acute trauma complications is eliminated it appears that the spinal cord injury leads to quicker rate of death in people with SCI. People with a SCI appear to die from the same leading causes of death in able body subjects: heart disease, cancer, etc. Additionally, people with SCI have chronic inflammation similar to what is seen in people with high levels of visceral fat (CRP, IL-6, TNF-alpha).
Could the increase visceral fat play a role in the earlier death of SCI subjects? And why in general would SCI subjects despite being very active, healthy, and not a big waist still have such a high accumulation of visceral fat? It seems to make sense that it is due to the loss of information sent up and down the central nervous system – but surprisingly us scientist really don’t know. In reality spinal cord scientist have not bother to study animal models of reduced lifespan after SCI. In addition, this dramatic reduction of lifespan seen in people with SCI is rarely mentioned in the field.
It appears that the data from SCI subjects give further evidence (but not conclusive in anyways since there are so many other variable altered in SCI subjects) of the negative role visceral fat may play in lifespan.
Do your best to control your fat level, specifically your visceral fat – which really means eat well and exercise – don’t become overweight.
Is visceral fat removal for a longer lifespan coming to a plastic surgery clinic in a mall near you? I am not sure how feasible this surgery is in humans – but if it is possible I can see the surgeons rubbing their hands.
And maybe, just maybe, we should be looking into why people with spinal cord injuries die 13 – 25 years earlier than able bodied subjects (nothing to do with acute effects of the trauma). Smokers die 8-10 years earlier than non smokers to give you a comparison – and anti smoking campaigns have been a high priority in developed nations for over 40 years. It appears that the loss of 8-10 years is considered a just cause for serious intervention then what about people with a spinal cord injury? While the number of people with SCI are obviously far less than the number of smokers – the loss of lifespan in greater.
While millions and millions have been spent on research in hope of making them walk again, with really no success, research investigating intervention to give them a more normal lifespan has been ignored.
Update: check out this post on how increase fat intake and visceral fat might be playing a role in the spread of cancer cells to other organs -which is what ends up killing most people with cancer (metastasis).