Friday, 25 December 2015

Do these people need to go on a diet?

And if so, what diet should they go on? Should we fast them? starve them? low-carb them? haul them to the gym?

Also, what kind of increased fatness are they appearing to suffer from? adipocyte hypertrophy? hyperplasia? ( I suppose the one on the right is quite typical of what you would find in western women these days )

How did they get like that? Did they eat too much? Exercise too little?.......   Think about what kind of initial "intuitive"  judgement youd pass on these people.

The picture was pulled from this paper  where the subjects have a genetic condition referred to as "cohen syndrome".   But you didnt know that from just looking at the picture. I bet you just thought they ate too much , or maybe too many carbs?

What I find interesting is how they could just pass for normal random fatties by todays public standards, despite the fact the have an underlying genetic condition that makes their preadipocytes more sensitive to differentiation into mature adipocytes, they appear quite symbolic of the kind of increased fatness you can expect in "normal" people.

Even more interesting, I expect youd be less inclined to recommend "lifestyle" interventions to these people now you know they have a genetic condition, yet "lifestyle" interventions are recommended to normal obese people everyday despite the fact we are all suffering from the same condition, I.E. excess preadipcoyte recruitment. When it comes to obesity, it seems we are more inclined to prescribe treatment that is dependent on how we view the causality to have progressed.

Got fat by eating too much/exercising too little/ too much carbs? -> solution is to cut cals/carbs/exercise more! Trying fasting for a month maybe.

Got fat by having an underlying genetic condition ???? -> hmm probably need medical intervention.

Anyway I want to talk a bit more about what exactly is increased adiposity. Lately I have been reading more on adipocyte differentiation / adipogenesis, and I really feel this is primarily whats happening in all forms of obesity regardless if it is genetic or ,  :cough:,  "lifestyle" induced.

I wrote a another post on this idea here   I think theres probably a few people in the literature that also think hyperplasia is the primary thing in obesity.

Adipogenesis, the differentiation of precursor cells into mature, terminally-differentiated adipocytes, occurs throughout the human life cycle and is believed to be the primary cause of increases in body fat.*

If preadipocyte recruitment is the primary lesion in increased fatness , this ties together so many loose ends, It fits in with bauer's "lipophilia" hypothesis, and helps explain why obesity is persistent, ( dieting probably doesnt cause adipocyte de-differentiation )

Personally I think low-carbing only works to solve the adipocyte hypertrophy part of obesity, that part of your increased bodyweight that is due to insulin induced hypertrophy rapidly resolves upon low-carbing, but the part of your increased weight that comes from new pre-adipocyte differentiation is ""sticky" and doesnt resolve after lowering your insulin.**

I always make the analogy with MT2 and freakles/moles, with super levels of melanocortin receptor agonism I differentiated additional stem cells in my skin into melanocytes but they didnt go away when I stopped MT2. Similarly with super levels of insulin from carbs I differentiated additional preadipocytes into mature adipocytes that dont go away when I lowered insulin with low carb.

Is there any hope?

I remain highly pessimistic but anyway, another paper caught my eye recently.. Now I didnt know this but apparently most in vitro work on adipose study is done with newly differentiated preadipocytes, and the reason being because mature adipocytes harvested from living organisms rapidly undergo de-differentiation in cell culture.

That is, they turn back into preadipocytes and relinquish their lipid hoard ( I.E. you lose wt )  and regain their ability to differentiate into other cell types.

Since adipocytes are terminally differentiated, they can be used immediately for test purposes.6 
Several studies have been performed to establish the isolation and characterization of mature adipocytes in between the 1960s and 1990s.7–10 Since then, mature adipocytes were only rarely used, probably because of their mainly cited drawbacks such as vulnerability and dedifferentiation under in vitro conditions. 
It is well known that these cells start to dedifferentiate after 1 or 2 weeks,7,11,12 at which point, the cells reach a multivacuolar morphology while they are diminishing their cell volume.9,13 Elongated, nonlipid filled dedifferentiated fat cells (DFAT) are further able to proliferate and exhibit multilineage potential.14,15 These cells are known to express stem cell markers, such as CD73.

My earlier work on adipocyte apoptosis was probably a bit pointless now as I realize its probably not necessary to kill excess fat cells with apoptosis but rather just make them de-differentiate back into their preadipocyte non-lipid filled state.

Easier said than done though I suppose ! So the big question is if we can get fat cells to de-differentiate so easily in cell culture how can we do it in vivo and lose weight?

I dont know the answer and neither do the authors, although they mention that agents/hormones that promote lipolysis seem to be facilitating de- differentiation this is just speculation, and I'd be quite surprised if the reason adipocytes de-differentiate just because they lose lipid from increased lipolysis, and more likely the agents/hormones are causing epigenetic chromatin changes to the adipocyte gene's, re-coiling up those parts of the DNA and silencing those adipocyte markers.

adipocyte dedifferentiation in pubmed yields 141 search results. its not a well studied area, and perhaps thats why we still have an obesity epidemic.

* I need to check his references to make sure they actually support that statement

**I think its possible that some adipocytes may de-differentiate while dieting, I cant rule things out without experimental data, I think we have to assume though that most people dont experience this as when dieting they reach a plateau.

Saturday, 3 October 2015

Does adipose tissue determine appetite?

Ive long held this belief that it does.

That, somehow the adipocytes drive to keep itself "filled" will not only alter systemic hormones and calorie partitioning to accomplish this but also drive the host to eat more.

I think this goes much beyond leptin, which is not an "anti-obesity" hormone that many people still think it is ( leptin resistance is a hoax lol, get over it ) but rather it is an anti-starvation hormone. Leptin becomes important when your deficient, and that is all.

A quick shout-out to Bauer's 1940 paper OBESITY , ITS PATHOGENESIS, ETIOLOGY AND TREATMENT,

I know, you might be thinking, "lol this paper is from 1940! we are much smarter "now" and have advanced much in the research and knowledge "now" ". ..... HAHAHA

Well youd be damn wrong. Read the damn paper. If you think your "smarter" than people that were around in the 1940's or earlier just because its "ancient history" , seriously, think again.

Anyway, I want to do a more formal post on bauers paper but I think it would be alot of work also it is not easy chasing his old references. Suffice to say he brings up alot of interesting points regarding obesity and dismisses the CICO idea, he puts forward the lipophilia hypothesis ( which is what I actually believe is the cause of obesity* ) This lipophilia idea is basically that it is the adipose tissue itself, factors intrinsic to the adipocyte, that determine its "drive" to store fat and that is the reason people become (maintain ) obese. Due to intrinsic factors, the adipose tissue not only is more willing to suck up and store fat, but it is simultaneously less willing to release that stored fat.

Infact this idea is a good fit with the observed fact that the vast majority of obese people who attempt to lose weight end up rebounding back to their starting weight and this even occurs in bariatric surgery though to a lesser extent. If we accept the idea that the adipose tissue has its own drive and blueprint for the size and shape its suppose to be ( determined by intrinsic factors like cell number, genetics, histone/methylation status etc ) then it makes complete sense why virtually everyone rebounds.

Theres plenty of evidence for the "lipophilia" hypothesis, adipocyte hyperplasia, cathecholamine resistance, I.E. adipocytes resist release of stored triglyceride, this study was another example where the average half-life age of triglycerides is increased in obese suggesting their fat cells like to "retain" fat. A 2008 study also found increased cavolin-1 in adipose tissue of  obese, this is something that is much less known about in the diet and fitness industry. Cavolin-1 helps make caveolae in adipocytes which are basically little docking harbors for nutrients to enter the cell, although I prefer to think of them as calorie uptake suckers.

A dramatic increase in the cell surface expression of caveolae is what happens when a pre-adipocytes morphs into a mature adipocyte and almost certainly is what facilitates the massive increase in lipid storage that occurs in the transformation. This is probably what they were observing in this 1983 paper when they state      ... quote...
 a ninefold increase in small invaginations as the cell differentiates from the fibroblast to the adipocyte phenotype;

ok enough of that , just read bauers paper.

Back to the topic of this post, which relates to this paper  they didnt know about leptin in 1977 but they had strong reason to believe that body weight and fat mass was "regulated" around a certain point. The reason for this paper was the continuing investigations into compensatory adipose growth that sometimes occurred in rodents with surgical removal of their adipose depots. In some cases, surgical removal of some adipose depots caused enlargement of the remaining ones so that total body wt stayed close to that of intact controls. Hence giving rise to the notion that wt is "regulated" to a certain value.

In this study, they cut out a large portion of the epididymal fat depot aswell as some of the subcutaneous inguinal fat depot, ..... THEN ...... they split the rats into 2 groups, chow diet and high fat diet.

On the chow diet, as expected, there was compensatory growth in the un-touched fat depots of the lipectomized rats such that their fat mass got to a level similar to intact controls.

However on the high-fat diet something unexpected happened, the lipectomized rats ate less than the normal rats on high-fat and ofcourse ended up with less total fat mass.

The cause/effect direction of the results of this study are open to "debate" but the crux is this, why did the lipectomized rats on the high-fat diet eat less and gain less fat than the high-fat controls?

If you assume that they gained less fat BECAUSE they ate less, your still left with the corollary that removing adipose tissue reduces appetite. I dont see any way around this conclusion.

Alternatively, you could take the taubsian stance and postulate that they ate less BECAUSE their adipose storage capacity was reduced. ( or rather their potential for adipose growth was reduced. )

Either way, your stuck with the inescapable suggestion that adipose tissue controls appetite.

* - about the asterisk above, I wouldnt say that the lipophilia is *the cause* , but rather , it is what is responsible for the maintenance and persistence of the obese state. I still believe that the cause and triggering event is high glucose and insulin concentrations.

Monday, 27 July 2015

Cryolipolysis gone wrong

Cryolipolysis is relatively new method of getting rid of excess subcutaneous fat. It works by freezing the localized area to 0C for about 1 hour.

The way this works is that lipids in the adipocytes freeze a bit sooner than water, basically you can trigger an apoptosis pathway in the adipocyte before the freezing causes significant local damage to all the other tissues.

"Crystallization of cytoplasmic lipids within the adipocytes initiates a cascade of events, characterized by adipocyte apoptosis, panniculitis, and eventual loss of adipocytes. Clinically, this translates into an effective decrease in fat layer thickness"

The fat gradually "melts" away 2-3 months post treatment as the adipocytes undergo apoptosis, however, there are some rare case reports of the opposite happening, where the treatment site initiates an increase of fat mass via hyperplasia,. The main article is here..

Whats interesting is that the fat growth hyperplasia is restricted to the treatment area. If the patient had gained weight in a more evenly distributed pattern over his body, the doctors would accuse him of eating too much and exercising too little. Its things like this where hopefully intelligent people will start to wake up and realize that the CICO model of fat mass has to be wrong.

If we couldnt apply the CICO model here, why can we apply it in more generalized obesity?

The caveat is ofcourse that we cant apply the model of systemic hormonal control of fat in this situation either.

The only possible way to explain the localized growth of the fat is to look at localized factors, I.E. the tissue and cells there. The treatment had obviously caused some kind of change in the gene expression patterns of the cells in that area and/or initiated an adipogenesis program to the pre-adipocytes in that region.

Recall from my previous posts, that once a pre-adipocyte morphs into a mature adipocyte its guaranteed to store fat, regardless of food intake, exercise, insulin, leptin, etc  once the activity of lipogenic enzymes increases and the cell surface gains significant caveolae, the jig is up.

The how and why of why the cryolipolysis causes this is a mystery at this point in time. The only clue seems to be that its more common in male patients, but the sample size might still be too small.

As an aside, it seems the incidence with which this happens may also be under-reported, the first paper estimated the cases to be  0.0051%. while a revision put the number closer to 0.47% or 2 in 422.

Tuesday, 23 June 2015

Leptin and trying to starve yourself thin

Im rather bored writing posts on why calorie restriction or starving is a retarded way to try and get thin. No matter how much physiological  and endocrine evidence is presented ppl are stuck with this meme infecting their brains ,  ....constantly renewing the idea that eating less can make them thin.

Ive lost the link,  its buried deep in my tweets somewhere ........but I found a study where they attempted to starve an ob/ob mouse, to get it the same weight as normal lean chow fed mice. Not only did they have to restrict it to 50% of what the normal chow mouse ate ( that would be like you as a fatty eating 900 calories a day to be the same weight as a normal lean thin person eating 1800 per day ) , but the ob/ob lost a disproportionately large amount of lean mass, such that when it did get down to the same weight as the normal lean mouse, the ob/ob mouse was still "relatively obese" because its body composition was still 45% fat mass.

Given its body composition ( % of weight as fat mass ) that ppl really want to target, you can see that leptin is absolutely crucial to the mixture. Without sufficient leptin, calorie restriction produces exaggerated loss of lean mass, leaving you still "fatty", even if you lose *weight*.

But how exactly does leptin work?

I need to write a more detailed post with links to studies, which I will do when I have more time, but after looking at the FIRKO study, these mice had extremely high leptin levels despite zero insulin action on adipose tissue. A closer look at the study revealed increased food intake in the FIRKO models on high-fat diet or gold thioglucose injury.

In light of this, it would seem that leptin levels are more a reflection of total food intake rather than insulin action on adipose. We also have the well known fact that leptin levels fall disproportionally more and faster in response to calorie restriction than fat mass declines, and this fall in leptin brakes further fat loss.  This point again supports the idea that leptin levels are ultimately a reflection of total food intake, and less so about total fat mass.

It is my contention that even normal lean thin people "over-eat" , since they could easily survive on 1000 calories per day. But they are in "energy balance" while eating 2000 calories per day. Thats because of something referred to as dietary thermogenesis, an increase in body temperature  and energy expenditure in response to food, which is primarily mediated by leptin.

After food intake , calories are stored in adipose tissue, leptin is secreted in response and finds its way to the brain where it activates POMC and alpha-MSH.

In turn, alpha-MSH acts on brain MC4R's , which increases sympathetic outflow to adipose tissue. The sympathetic nerves innervating adipose tissue discharge norepinephrine and this acts on the beta-adrenoreceptors on the adipocytes. This initiates an energy expenditure program, lipolysis increases and fat oxidation is increased.

Beta-adrenoreceptors seem to be responsible for the "browning" of adipocytes, fat liberated by beta-receptors not only flows around the body but there is some evidence the fat is burned within the adipocyte, generating heat. In this way, the body can easily "burn off" extra calories consumed ( over-eaten ) with an energy wasting heat generating furnace in the adipocyte.

This is why a lean thin person eating 2000 calories per day can stay lean, because the intricate leptin-thermogenesis feedback loop is working properly.

Thermogenesis, thats one of the main things leptin "does".

There is a chink in the armor of leptin though. Its called AgRP.

When you calorie restrict or starve yourself, ghrelin produced from the stomach goes up, this finds its way to the brain and increases gene-expression of AgRP, which is a well known antagonist of MC4R, . With MC4R increasingly blocked, sympathetic discharge of  norepinephrine into adipose tissue is culled reducing thermogenesis and energy wasting. The end result is that more of the food you eat ends up staying stored in adipose as as opposed to being burnt off.

I fully expect this is the "starvation mode" people anecdotally speak off, ...I.E.  .when.... after a period of reduced food intake, food seems to more easily cause fat gain.

So, as you can see, aslong as you have functional ghrelin and AgRP, trying to starve yourself thin is futile, because thermogenesis and dietary thermogenesis will drastically drop and youll just store more of the food you eat instead of burning it.

The additional caveat in obesity

Obese people have an additional problem known as cathecholamine resistance. Basically the beta-receptor signal transduction in the adipocytes of obese people is attenuated, there is less Hormone-sensitive-lipase stimulated lipolysis in response to beta-receptor activation. The cause of this is unknown. Although I expect it might ultimately be due to epigenetic changes in gene expression patterns in the adipocytes. This is one of the things that contributes to my idea of  "dysfunctional" adipose tissue being the root thing that makes obesity persistent.

You can see this phenomenon at work because the average age and triglyceride age half-lives are increased  in overweight people, indicating that the adipose tissue of obese people "retains" triglyceride more efficiently.  See below for study.

Adipocyte triglyceride turnover and lipolysis in lean and overweight subjects.

Adipocyte triglyceride age was markedly increased in overweight  compared with lean subjects with triglyceride T1/2 of 14 and 9 months, respectively. Triglyceride age correlated positively with BMI.

Noradrenaline-, isoprenaline- or dibutyryl cyclic AMP-induced lipolysis was inversely correlated with triglyceride age and BMI.

Saturday, 20 June 2015

All roads lead to no-where

Well I think this blog is coming to an end with regards to obesity research.

Ive spent the last 5 years and countless hours of my personal time going through thousands of studies on pubmed to try and solve this riddle that is obesity and I think I can safely say at this point I know more about this disease than 99.99% of other people out there including most doctors.

I dont consider myself to be especially clever, probably just above average, but the truth is in the details, and the research is there on pubmed for all to see for themselves.  That is what I have done.

If your one of the people reading this blog, or ANY other blog or website looking for the "special secret" thats going to finally make you lose weight and get slim, and STAY slim,.... well im sorry to say but you should stop wasting your time because it does not exist.  Do not be fooled by advertisements like "beach body, get slim" and my favorite "burn fat!" because its all a load of bollox.

This idea that "burning fat" is going to get you and keep you slim is the most retarded thing going. Obese people do not have a problem "burning fat", they have a problem of excessively storing triglyceride.  And fundamentally this is caused by gene expression changes in the adipocyte  and by having too many extra fat cells.

Obesity almost certainly involves the proliferation of pre-adipocytes and is best likened to a mole on the skin, I.E. a permanent growth of the skin cells. Unfortunately while the function of skin cells is just to produce melanin, the function of adipocytes  is to horde large amounts of triglyceride which results you gaining alot of physical weight.

There are currently no drugs on the market or even black market that is going to help you get and stay slim. I know because Ive tried most of them. The "weight loss" industry is nothing but a huge scam.

Lowering your insulin does offer *some* marginal relief, but your still fighting an uphill battle. There is however no *secret* to low carbing just as there is no secret to anything else weight related. its 90% genetic in my opinion.

Low carb will certainly improve your metabolic health and can certainly alleviate diabetes, but whether or not you will get slim is dependent on genetics. Pretty much EVERYTHING about you is almost entirely dependent on genetics.

And stop trying to eat less, your about as likely to get slim eating less as you are to shrink that mole on your back by eating less.

Anyway, I will continue to post on new studies as and when they become available and/if they offer new information, but for the most part, and without bragging, Ive been through all of pubmed, and they dont have an answer yet.

The cause of the disease is quite clear at the moment, it is hyper-insulin and/or hyperglycemic driven growth of the adipose tissue depots, and I firmly believe and growth of the pancreas also happens. The cure, though, if there even is one, doesn't currently exist. Although it might seem that bariatric surgery *cures* obesity, I dont believe this is what is happening. Rather it is just a profound change in hormonal signalling throughout the body which probably also causes various gene expression changes including in adipose tissue. I'd bet that if the surgery could be reversed, the weight and diabetes would return.

Sunday, 31 May 2015

Can you be fat without insulin?

Is it possible to still be fat even if we get our insulin low?

I mean really low.

I mean miniscule low.

Fuck it, I mean NO insulin at all.

The thing I am most irritated about, is that , while insulin clearly plays a very large part in weight and fat mass and hyperplasia, im fed up with alot of so called low carb "guru's" with their almost shill like behavior chastising people who cannot get normal BMI on a low carb diet.

The cause of the problem is obvious, low carb works, UNQUESTIONABLY, but its the people who arent doing it right!. They're secretly sneaking in carbs, or their gorging on millions of calories etc etc.

Basically, if you cant get normal BMI on low carb, the problem is YOU, ( not the diet ).

They are guilty of the same thing they attacked low-fat and CICO advocates for in the original uprising of lowcarb popularity.

To answer the question in point.... can you be "fat without insulin", I want to take another look at the FIRKO mouse study. ( Please Read peter's blog post on it here, to get a nice primer )

Insulin-receptor Knockout in Adipose Tissue Causes a Polarization in Adipocyte Size with Differences in Protein Expression

Skipping to Figure 6. in the study we see something rather peculiar..... In the normal state. the size distribution of adipocytes follows a Gaussian curve, but when you make insulin invisible to adipocytes, the size distribution shifts markedly into a bimodal pattern.

The key point of this figure is that, even with utter absence of insulin, a percentage of adipocytes still store a large amount of fat. I.E. some adipocytes are still "fat" even without insulin. Indeed if we go just by these 2 figures it looks like what insulin does is make adipocytes store an additional amount of fat , on top of the amount of fat they store in the basal state.

so, if some adipocytes can still store large amounts of fat without insulin directing them, you have to ask yourself what implications that might have for getting normal BMI on a low insulin low carb diet.....

The fact that we get a bimodal distribution of fat cell size in the absence of insulin is remarkably similar to what we observed in the insulin sensitivity post, I.E that the insulin responsiveness of a fat cell was also described by a bimodal distribution. Together, all this points to as I have been trying to say, that the properties of a cell can be strongly determined by "intrinsic" factors present in that cell, and the most likely explanation for those factors is gene expression.

A fat cell will have thousands of different gene's expressed at different levels, and the resulting phenotype of that cell will be the sum of all those factors, of all the various histone modifications and methylation status of those gene's.

What else can we learn from FIRKO

The researchers also looked at the protein levels of various factors known to influence fat cell metabolism.

GLUT1 is clearly highly sensitive to insulin, as it levels drop to 10% of normal with zero insulin. But look at SREBP-1 and FAS, there appears to be 2 dominant types of adipocytes in the FIRKO. One type is a large adipcoyte where SREBP-1 and FAS are relatively independent of insulin, and the levels of these proteins remain very high , and then there are small adipocytes, where the levels of SREBP-1 and FAS seem to be highly dependent on insulin.

Given that SREBP-1 and FAS are key proteins involved in fat metabolism and lipogenesis, they are a good explanation for WHY some adipocytes can remain large even in the absence of insulin. because the levels remain very high, even without insulin.

Overall this result is exactly what you would expect given the bimodal distribution we have already observed, I.E. 2 distinct types of adpiocytes, characterized by their expression of adipocyte gene;s which likely also affects their insulin responsiveness.

Other proteins levels 

Interestingly, the protein levels of GLUT4, PPARg and Leptin are independent of insulin. It would thus appear that insulin controls the translocation of GLUT4 to the cell surface, not the amount of GLUT4 in an adipocyte. The results of the PPARg and leptin also fly in the face of what I have blogged on before, even small adipocytes contain the same amount of leptin as large adipocytes. And PPARg does not appear to predict adipocyte size in this data set. ( I would of expected larger adipocytes to have higher PPARg, and vice versa for the small adipocytes. *shrug* )

Depiste reduced overall fat mass and complete lack of insulin acting on adipocytes, Leptin levels are hugely elevated in FIRKO

There is a huge amount of research detailing the interplay of insulin and leptin, so I wouldnt discount that connection just yet, but rather there is likely some fine tuning and *small print* regarding regulation of leptin levels.

Tying it all together

There is a 2004 spin-off study of FIRKO that examined adipocyte size heterogeneity in relation to insulin and gene expression.

They concluded......

 These data suggest an intrinsic heterogeneity of adipocytes with differences in gene expression related to adipocyte size and insulin signaling.

They also mention in the study, that adipocytes within the same adipose tissue depot may not be of the same lineage. And this has implications tying in with my last post, which detailed how hyperplasia is very likely a major factor in obesity and that the extra adipocytes you gain in obesity are *different* from your normal adipocytes. 

Imagine, as a person developes obesity, the stem cells he causes to differentiate into mature adipocytes hail from the "large, insulin unresponsive" lineage like those identified in the FIRKO? These adipocytes would be largely immune to weight loss in response to low carb dieting. 

In a similar fashion, if you differentiate adipocytes from the "insulin sensitive" lineage, youd probably have good success in low carb dieting as these adipocytes will likely shrink alot when you lower insulin, but youll easily and quickly regain weight if you went back to carbs and increased insulin again.

Does this sound familiar?

In all likeliness, obese people would likely contain different combinations of both adipocyte cell types, but the spread again might be normal distribution. I.E. some people respond REALLY well to low carb, ........most people will lose *some* weight on low carb........, failing to achieve normal BMI. And a few unlucky people will struggle to lose anything on low carb.

Final Note

Im not attempting to attack low carb diets here, They work exceptionally well for metabolic syndrome , but as far as weight goes, theres alot of other factors at play. Gene's,  gene expression and hyperplasia status COUNTS. And the so called "lowcarb" guru's should acknowledge this.

Tuesday, 14 April 2015

Obesity isnt "normal"

The more I learn about obesity the more depressingly obvious it becomes that it is an irreversible disease.

Thanks to libgen I got my hands on this paper which seeks to more closely examine the contribution of hyperplasia to obesity. ( basically hyperplasia is "recruitment of adipose progenitor cells" ) Normally adipose tissue is riddled with stem cells......( also referred to as fibroblasts etc ) .... think of them as building block cells.

These cells have most of their DNA coiled up tightly around the nucleosomes such that hardly any gene's are expressed, which means they essentially have no phenotype. Then, for whatever reason, at the on-set of obesity, these cells receive the message to differentiate into fully mature adipocytes, the DNA for the PPARg2 gene is uncoiled from the nucleosome, the activity of the triglyceride synthesizing enzymes increases many-fold, and the cell starts accumulating fat.

Here are some quotes from the paper.......

recent studies have found that adipocyte hyperplasia plays an important role in human obesity5,6. Specifically, obese individuals have significantly more adipocytes than lean individuals, and this trend is maintained throughout adult life5.

Even after obese individuals undergo severe weight loss, elevated adipocyte number is maintained5, indicating that increased adipocyte formation in obesity has lifelong effects on adipose tissue homeostasis and WAT mass.

In the study, they put mice on chow and HFD's and looked at when recruitment of pre-adipocytes occurs with respect to obesity development. Surprisingly, pre-adipocytes start to get activated within 1 day of HFD exposure, peak at 3 days,  and returns to baseline at 5 days. ( although it takes 7-8 weeks for them to fully differentiate into adipocytes and store fat, it seems you can get the "ball rolling" extremely quickly, i guess I need to think carefully next time before I indulge in a cheat meal...........)

Perhaps the most interesting part of the study is what they found when they tried to determine the pathway's involved in the activation of pre-adipocytes. They focused on the phosphoinositide 3-kinase (PI3K)-AKT pathway ( which is downstream of insulin ) . Specifically, they looked at AKT...

The AKT kinases regulate several processes, including cellular growth, survival and metabolism29. The most prominent mammalian isoforms are AKT1 and AKT2. Whereas AKT1 is widely expressed and promotes the growth of many tissues30,31, AKT2 regulates metabolic flux within liver, muscle and adipose tissue

They found that after several days of HFD exposure, AKT1 was unchanged while AKT2 was elevated, which led them to speculate it was AKT2 that got the pre-adipocytes ready for differentiation. Next they knocked out the AKT2 gene specifically in adipose tissue. The Akt2􀀀(-/-)  mice actually developed normally with normal body fat levels, and as expected, were resistant to weight gain and adipocyte hyperplasia when fed a HFD.

This actually has profound implications, it suggests that the "new bodyfat" you develop in obesity is different and distinct from your "normal" adipose tissue that you get from birth and when growing up. Obesity is like an addition of a "new" type of adipose tissue, it is not merely the expansion of your normal fat mass, but a completely new beast altogether....

Although the formation of adipose tissue in development,.... and the expansion of adipose tissue in obesity..... are often viewed as temporal variations on the same regulatory process, we show here that the formation of adipocytes in obesity and development are controlled by distinct molecular mechanisms. The existence of an aberrant mechanism of adipogenesis in obesity supports the American Medical Association's classification of obesity as a disease

What happens to an ob/ob ( leptin deleted ) mouse that is also akt2(-/-) ? ....Yes, they are also resistant to fat gain, further indicating the importance of hyerplasia in obesity development.

Our data suggest that even relatively short binges of altered eating behaviour may stimulate obesogenic adipogenesis, resulting in an intractable increase in adipocyte number5 that may make future weight loss more difficult.

The only caveat to mention is that almost all the hyperplasia was detected in the visceral depot with only small amounts in the subcutaneous depot. I would extrapolate this with caution to humans however, and im pretty sure the subcutaneous depot undergoes massive hyperplasia in human obesity, I mean you dont think a panniculus is due to hypertrophy do you? Or that all that excess skin is "just skin", and not billions of shrunken hyper-plastic fat cells......