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......

Tuesday, 24 March 2015

Crossing thresholds may permanently change you

My ranting and raving about melanotan 2 has inevitably made a few people ask me if the darkening in skin tone was long lasting or permanent. The darkening in skin tone was certainly "long-lasting" appearing to take about 9 months for me to fade back to my pale self, however there has been atleast one permanent side affect.......... I developed new freckles.

I cant say ive noticed any new freckles on my face however, just mostly on my body.

If you read other peoples personal accounts of melanotan 2, weight control doesnt seem to be listed all that often. This makes me think I may of been somewhat a super-responder to MT2. Probably because im both weight reduced .....and my obvious mc1r mutation which makes me tan resistant could indicate I have slight mutations in mc4r and mc5r aswell.

Another thing I noticed when injecting MT2 was that I usually always did the left side of my stomach and after sometime the left side appeared more deflated than the right side, making me think that MT2 might have local effects on adipocytes at the injection site. It appears there are mc5r's directly on adipocytes and that may have accounted for this effect.

Whats curious though is the permanent new freckles.

MT2 is a stronger analog of alpha-MSH, which activates melanocortin receptors, but MT2 also has a substantially longer half life.  oh and I forgot to mention, while on MT2, existing freckles went extremely dark almost to the point of black.

This was all sounding eerily familiar, and I suddenly got the idea that maybe alpha-MSH is to melanocytes as insulin is to adipocytes.

This notion is further supported by the finding that alpha-MSH actually can cause skin cells to differentiate into melanocytes, exactly like how insulin can cause pre-adipocytes to differentiate into full adipocytes.

Skin cells do not normally produce melanin, but they will do once they differentiate into melanocytes. Exactly like how pre-adipocytes do not store triglyceride,  until they differentiate into full adipocytes. BTW this explains where the new freckles comes from with MT2 use. I expect either existing stem cells and/or skin cells each have their own thresholds that must be appeased before they will differentiate into melanocytes, and my normal levels of alpha-MSH was too low to activate them

But once the super stimulus of MT2 is used, the threshold is passed, and additional cells morph into melancoytes = new freckles.  Exactly how like super levels of insulin and glucose causes pre-adipocytes to morph into full adipocytes and make you gain weight.

Even further! as I have said, the new freckles appear to be permanent, again exactly like how new fat cells in obesity appear to be permanent.

And lastly, as mentioned, MT2 caused existing freckles to become extremely dark, indicating that MT2 turbo-charged the production of melanin within these melanocytes.  Well... Lo and behold, this is very similar to what insulin does in adipocytes, it turbo-charges the production and accumulation of triglyceride.......

So,,,,, alpha MSH can cause cells to differentiate into melanocytes and cause over-production of the primary thing melanocytes are suppose to make.......melanin

And....insulin can cause cells to differentiate into adipcytes and cause them to over-produce the primary thing they are suppose to make........triglyceride.

What a coincidence..............

Anway,    there are other areas in biology where crossing thresholds seems to produce irreversible changes. Females that take exogenous androgens ( steroids ) become "permanently" masculinized. .  And its possible that satellite cells permanently morphing into myocytes may account for the phenomenon of "muscle memory" that most bodybuilders swear by.

In both of those cases we are again relying on certain hormones to cross threshold levels.

Monday, 23 March 2015

Fat cell insulin sensitivity

TL:DR at bottom

Is insulin resistance due to a graded loss of insulin response at the individual cellular level or does it reflect changes in the fraction of cells responding to insulin?.......

.... is the crux of a new paper(1) concerned with the insulin sensitivity of fat cells. We are all very use to the idea that the insulin sensitivity of a fat cell varies with its size such that large overstuffed fat cells are insulin resistant (IR) and small fat cells are insulin sensitive (IS). So, with the above question in mind,  it seems obvious that we should chose the former .... I.E. "its a graded response, varying with the size of the adipocyte"....... HOWEVER, this infact may not be true.

Or atleast, only partially true..

The first caveat to note, is that they are using GLUT4 translocation as the surrogate for the IS of the fat cell.

Systemic insulin responses, such as glucose clearance, represent the integrated GLUT4 translocations of all responding muscle and adipose cells

So the more GLUT4 translocation we get in a fat cell, the more IS it is deemed to be. Previously, the authors had discovered that human adipose cells cultured in vitro WITHOUT the hosts serum retain the IS status of their host. This would imply that circulating factors in host serum (i.e. hormone levels etc) may not play as important role in the IS of the individual as previously thought, and instead suggests that the IS of a fat cell is an intrinsic property of that cell.

Another interesting point is that, when adipose cells are isolated and tested individually for their IS, there is marked heterogeneity between cells in their responses.(2) That is, each individual adipocyte will display a unique and highly reproducible response.  As the authors of (2) say...

These data highlight that the response of a cell population to insulin is underpinned by extensive heterogeneity at the single cell level. This heterogeneity is pre-programmed within each cell and is not the result of intracellular stochastic 

Back to (1), they sought to ask the question and test, is the IS status of a host reflected in the IS status of all his individual fat cells. For example, if someone is 50% overall IR, is that because all his individual cells are 50% IR?

changes in adipose function are usually studied at the whole organ or population level and it is naturally assumed that any defect will be due to a similar disruption in all cells(2)

Testing and Data from (1)

The tests performed by (1) were to isolate 8 individual fat cells from the abdominal subcutaneous depot of 19 different subjects,  all of whom showed a very wide variation in their whole body IS status.

The cells were incubated in the absence ( basal ) or presence of 0.1 IU/ml insulin (maximal stimulation) and GLUT4 translocation markers were assessed.

The graph is plotted with the most IR subject on the left and the most IS subject on the right. And the graph proceeds from left to right in terms of the IS of the subjects...

Each blue dot represents an individual fat cell from 1 person in the basal state, and the red dot next to it is one of the individual fat cells in the insulin stimulated state. As you can see, as you move from left to right, more and more red dots jump above the dotted line, indicating that as you move from left to right, more and more cells respond to the insulin.  Red dots that stayed below the dotted line means they didnt respond to the insulin at all.

Interestingly, the major difference between cells from insulin-resistant and insulin-sensitive is not the individual cell response amplitude, but rather the number of cells that exhibit a 3–4 fold response. Simultaneously, in almost every subject, we observed some cells that do not exhibit any insulin response at all.

What this seems to suggest, is that the difference between IS and IR individuals is not how much the cells respond to insulin, but rather the number of cells that respond.  I.E. Insulin resistant people have a much lower number of cells that respond to insulin.  I found this very counter-intuitive and novel.

Infact, if you plot all the data on a BeeSwarm style graph... get a graph that looks like a bimodal function. I.E. 2 distinct states of normal distributions. Based on this the authors propose that fat cells exists in 2 distinct states, "basal" and "insulin stimulated".

Thus, GLUT4 translocation in individual adipose cells isolated from human subjects is better characterized as an all-or-none (bimodal) response than a graded response. Our single cell analysis of human adipose cells reveals a bimodal distribution for each of two characteristic properties of GSV, mobility and fusion, affected by insulin. This invariance in the underlying distributions, refractory and insulin-stimulated, with a clearly determinable fraction of cells populating these two states in each subject, is consistent with a threshold or switch-like transformation from the basal to the stimulated state upon addition of insulin

Threshold type triggering systems exists everywhere in biology, and it wouldnt surprise me if something similar exists for how adipose cells respond to insulin.  I (speculatively) envisage that each individual adipose cell probably has a threshold insulin responding level,  if it sees insulin below that threshold concentration, no response is initiated. However as soon as it sees insulin above the threshold concentration, it immediately enters the "insulin stimulated" state and simultaneously fires its entire GLUT4 cache.  This threshold level is probably changeable depending on hormonal inputs into the adipose cell.

Infact there is some evidence that the insulin sensitivity is dependent on the number on insulin receptors on it........ This quote from ref(2) suggests insulin sensitivity of a fat cell is dependent on receptor count.

"previous studies have shown that changes in insulin receptor number can change the sensitivity but not the maximum responsiveness of insulin action(3) ."

Even more intriguing from (1), the authors ruled out that fat cell size was the deciding factor in whether or not a fat cell responded to 0.1 IU/ml insulin, as no correlation was observed between fat cell size and GLUT4 translocation.

Findings from study ref (2).

The authors in ref (2) worked on groups adipocytes but performed atleast 1 study involving single adipocytes,  (3T3-L1 Adipocytes), but they still found evidence of extensive heterogeneity.

From fig 5a. , the response of the group of fat cells to different insulin doses was a graded response.

They noted that at the lowest insulin dose, only 30% of cells from the group displayed any detectable response, which is consistent with the idea that each cell has a threshold insulin trigger level that must be passed before it will show any insulin response.

However, somewhat contradictory to ref(1), they found fat cells that responded in both a graded response manner and a bimodal response...

I emailed the authors of ref(1) about this seeming contradiction, ( because (1) declared fat cells as being bimodal while (2) found evidence for graded responses aswell as bimodal)   and specifically asked how could they determine the presence or absence of a graded responses if they only tested with 1 different insulin dose. They have yet to email me back.


Three important conclusions from ref(2) are....

  1. These data imply that the cellular response to a specific dose of insulin is an intrinsic property of each cell.
  2. One possibility is that this represents discrete subpopulations of adipocytes that possess intrinsic differences in insulin sensitivity and responsiveness.
  3. changes in adipose function may rather depict changes in the relative abundance of subpopulations of adipocytes that comprise the organ.

Currently, adipocytes are divided into 3 subpopulations, (white, beige, and brown.) What seems likely is that even amoung white adipocytes they can be divided into even further subpopulations that differ in insulin responsiveness and sensitivity.

Personally, what *I* think is happening is that each individual cell has its own level of epigenetic expression of its gene's ( epigenetic = histone acetylation and DNA methylation ) that together makeup the phenotype of that cell. A large fat cell has increased histone acetylation on PPARgamma, and its possible epigenetic expression of that aswell as other gene's will determine its insulin responsiveness. 

Are small fat cells really more insulin sensitive?

Ref(4) found an enhanced number of small fat cells in insulin resistant subjects compared to insulin sensitive ones. This is not what you would expect if you just bluntly thought small fat cells = insulin sensitive.

Here's the key quote from the abstract...

The real-time PCR results showed two- to threefold lower expression of genes encoding markers of adipose cell differentiation (peroxisome proliferator-activated receptor gamma1 [PPARgamma1], PPARgamma2, GLUT4, adiponectin, sterol receptor element binding protein 1c) in insulin-resistant compared with insulin-sensitive individuals.

Although the authors of ref(4) attribute this to"impaired" adipogenesis,  I dont agree. The lowered expression of these adipose gene's *is* what makes the fat cells smaller and probably also more insulin resistant. But this is not a "defect" , but rather it is a reflection of their genetic inheritance.

We know insulin resistance has a genetic component and runs in families. I reckon what is happening is that offspring of insulin resistant parents are simply inheriting pre-adipocyte pools that have lower levels of histone acetylation of those adipogenic gene's in them. (particularly PPARgamma)

Remember from ref(5),  the histone acetylation ( H3 anyway ) of an adipocyte is maintained even in the de-differentiated state. This implies the pre-adipocyte already contains a blueprint for exactly what type of fat cell it should become ( large vs small etc ), if and when it ever gets the signal to turn into a  fat cell.

So.... as this normal person starts to eat obesogenic food ( processed carbs ) , morphological changes to the intestine and pancreas takes place, causing hyperinsulinemia and hyperglycemia, which in turn start to activate all his pre-adipocytes and turn them into mature fat cells. These new fat cells start to store their own fat  ( thats what fat cells do, calories are irrelevant, exactly like how myocytes are going to build myofibrils even if you keep protein intake low.. ) , and the person overall gets "fatter". No doubt the insulin also causes existing adipocytes to hypertrophy.

Depending on the genetics and epigenetics of the pre-adipocyte pools you inherited from your parents, these pre-adipocytes could turn into small insulin resistant fat cells, in which case youll only gain *some* weight.and as your insulin levels continue to increase, putting increased insulin sensitivity demands on your body, these fat cells cant fulfill that demand for increased insulin sensitivity, and youll been seen as "insulin resistant" and labelled diabetic ..........Or they could turn into large insulin sensitive fat cells, in which case youll get super obese. I also expect numbers pre-adipocytes in pools differs between individuals, which would further contribute to your propensity to get extremely fat.

So when a diabetes researcher harvests fat tissue from an obese insulin resistant subject and observes them under a microscope and sees lots of small fat cells and concludes "defect in adipogenesis!" . I say NO.

I say, your just observing the genetically inherited destiny.of his cells.

TL:DR conclusions

  • (1) concluded that fat cells respond to insulin ( GLUT4 translocation ) in an all or nothing manner.
  • It appears fat cells have an insulin threshold trigger level, if they see insulin below the threshold, the response is zero, but if they see insulin above that level, they immediately respond. 
  • contrary to (1),    (2) found evidence that the response of individual fat cells to insulin above the threshold can be both graded, and bimodal. 
  • graded responding fat cells will respond stronger as insulin doses increase, up to maximum dose, while bimodal responding fat cells always give the same response regardless of insulin dose.
  • (1) found that some fat cells will not show any response to insulin even at maximal doses.
  • the difference between insulin sensitive and insulin resistant individuals appears to be accounted for entirely by the number of fat cells that just stop completely responding to insulin. That is, as you progress from insulin sensitive to insulin resistant, more and more of your fat cells will completely ignore insulin
  • this defect is preserved in culture even without host serum, indicating that the response to insulin is an intrinsic property of each individual fat cell.
  • (4) found that insulin resistant individuals have a greater proportion of smaller fat cells with reduced expression of adipogenic gene's, countering the idea that smaller fat cells are always more insulin sensitive.


1. Human Adipose Cells In Vitro Are Either Refractory or Responsive to Insulin, Reflecting Host Metabolic State - link

2. Novel systems for dynamically assessing insulin action in live cells reveals heterogeneity in the insulin response. - link

3. Mechanisms of insulin resistance in obesity and noninsulin-dependent (type II) diabetes. - link

4. Enhanced proportion of small adipose cells in insulin-resistant vs insulin-sensitive obese individuals implicates impaired adipogenesis. - link

5. Heritability of fat accumulation in white adipocytes. - link