Once fat cells reach a certain size -- that is, they become filled to capacity with fat content -- then new fat cells will begin to form.  The fat cell number and size increases and shrinks based on deposits from food intake.
“We have a seemingly infinite capacity to recruit new fat cells, but we cannot get rid of them once they have been recruited" said Michael Rosenbaum, associate professor of clinical pediatrics and medicine at Columbia University. "in most cases, weight gain initially reflects ... enlargement of existing fat cells followed by an increased growth of new fat cells.”

Research has shown that obese people who have weight loss surgery have just as many fat cells two years after the surgery as before it, even though they have become much thinner.

Scientist, Dr. Rudy Leibel, says that "the body controls the number of its fat cells as carefully as it controls the amount of its fat". Fat cells die and new ones are born throughout life. Scientists have found that fat cells live for only about seven years and that every time a fat cell dies, another is formed to take its place.

Below see a 2017 New York Times article about this matter.

Are Fat Cells Forever?
              By Alice Callahan  
       February 17, 2017 - New York Times

Once fat cells are formed, can you ever get rid of them?

The number of fat cells in a person’s body seems to be able to change in only one direction: up. Fat cell number increases through childhood and adolescence and generally stabilizes in adulthood.

But this doesn’t mean that fat cells, or adipocytes, are stagnant. The size of individual fat cells is remarkably variable, expanding and contracting with weight gain or weight loss. And as with most cell types in the body, adipocytes die eventually.

“when old ones die, they are replaced by new fat cells,” said Dr. Michael Jensen, an endocrinologist and obesity researcher at the Mayo Clinic. Cell death and production appear to be tightly coupled, so although about 10 percent of adipocytes die each year, they’re replaced at the same rate.

Even among bariatric surgery patients, who can lose massive amounts of weight, the number of fat cells tends to remain the same, although the cells shrink in size, studies show.

Liposuction reduces the number of fat cells in a person’s body, but studies show the weight lost is typically regained within a year. It isn’t known whether this regain occurs through the production of new fat cells or expansion of existing ones.

People who are obese tend to have more fat cells than those who are not, and several studies have found an increase in fat cell number with weight regain following weight loss.

"The fact that fat cell number can be increased but not decreased most likely contributes to the body’s drive to regain weight after weight loss", said Dr. Kirsty L. Spalding, a cell biologist at the Karolinska Institute in Sweden and the lead author of a 2008 study showing that fat cells die and are replaced. Beyond their role in storing fat, adipocytes secrete proteins and hormones that affect energy metabolism.

“Following weight loss, adipocytes become smaller, generally smaller than those from people with a similar B.M.I.,” Dr. Spalding said. One hypothesis is that those smaller cells might send signals to increase appetite and fat storage, which could help to explain why weight loss is so difficult to maintain, though much more research is needed.

I continually read a great many books, articles, blogs, and forum posts on the subject of obesity.

No one,…. not even the most qualified medical doctor or scientist, … knows everything or holds only beliefs that are absolutely correct.

However, I am often amazed by the vast amount of existing misconceptions, myths, and wishful-thinking that gets spread and promoted by people who present themselves as obesity “experts” or “gurus”.

One thing that Scientists know for sure about obesity management, is the sad fact, that no diet, exercise, medication, not even bariatric surgery, will permanently reset the body’s tendency to defend and regain its body weight to its set point .... this generally being the highest weight that has been achieved and maintained for a notable length of time.



Thus, any effective long-term treatment MUST OFFSET the complex neurobiology which is designed to eventually doom every weight-loss attempt to ultimately "fail".

A comprehensive review recently published in Endocrine Reviews describes the complexity of  the biological system that regulates our body weight.

The 30+ page research paper, backed by about 350 scientific citations, was written by the undisputed leaders in the medical field of Endocrinology (Michael Schwartz, Randy Seeley, Eric Ravussin, Rudolph Leibel and colleagues)  and is actually a “Scientific Statement” from the Endocrine Society. 

In other words, these Scientists know that they are talking about when they speak about the Science of Energy Balance, and in this paper they outline in excruciating scientific detail just how complex the biological system that regulates, defends, and restores body weight actually is.

From the Abstract of this research paper:

We included evidence from basic science, clinical, and epidemiological literature to assess current knowledge regarding mechanisms underlying excess body-fat accumulation, the biological defense of excess fat mass, and the tendency for lost weight to be regained.

A major area of emphasis is the science of energy homeostasis, the biological process that maintains weight stability by actively matching energy intake to energy expenditure over time.

Growing evidence suggests that obesity is a disorder of the energy homeostasis system, rather than simply arising from the passive accumulation of excess weight.

Their position is that, despite all we have learned about this system, we are still far from fully understanding it.

Science knows about one of the pathways, but there are many pathways in a complex network of multiple interacting pathways that involve virtually every part of the brain.

They say that the medical field currently needs a great deal more information about the specifics of this issue:

The identification of neuromolecular mechanisms that integrate short-term and long-term control of feeding behavior, such that calorie intake precisely matches energy expenditure over long time intervals, will almost certainly enable better preventive and therapeutic approaches to obesity.”

To be viable, theories of obesity pathogenesis must account not only for how excess body fat is acquired, but also for how excess body fat comes to be biologically defended.

Answering this question requires an improved understanding of the neuro-molecular elements that underlie a “defended” level of body fat. What are the molecular/neuroanatomic predicates that help establish and defend a “set point” for adiposity? How do these elements regulate feeding behavior and/or energy expenditure, so as to achieve long-term energy balance? By what mechanisms is an apparently higher set point established and defended in individuals who are obese?”

They conclude that:

Given that recovery of lost weight ... (the normal, physiological response to weight loss irrespective of one’s starting weight) ... is the largest single obstacle to effective long-term weight loss, we cannot overstate the importance of a coherent understanding of obesity-associated alterations of the energy homeostasis system.”

So, in essence, this scientific paper shows why no simple solution to obesity is in sight; details the existence of an enormous Problem; and raises Questions for which Science still needs to find answers.

To get a simple explanation of the basic concept, see: Set Point. 

Any “health & wellness” professional, medical doctor, or guru who claims that any particular Diet, Behavior, or LifeStyle can fundamentally change the part of the body’s biology which acts to protect and restore body fat in the long term is Simply Wrong. 

They are either spreading a Lie, sharing a Myth, or offering a hypothesis for which no proof or reasonable evidence exists… which means that they are simply sharing their own Wishful-Thinking.

At this point, all credible Scientific Research indicates the following:

No matter how much weight gets lost, or is maintained for the short-term, …
No matter whether that weight loss was slow or fast, ...
No matter when food intake occurs ...
No matter whether “unprocessed” or “healthy” food is eaten, ...

Ultimately NO diet or behavior
manages to “reset” the body-weight set point to a lower level,
in order to biologically “stabilize” weight loss for the long-term.

NOTE: Originally posted on 7/23/2017.  Bumped up for new viewers.

We do not understand how the body resists weight change and why, after weight loss, so many people regain it. The concept of a set point for weight is widely accepted.

The set point is like the thermostat in our central heating system. It is switched on when the temperature falls below a critical (set point) temperature and is switched off when that is exceeded.

Using the word “rachet” might help one conceptualize the set point concept.

To rachet is to cause to increase or decrease by increments. A rachet is a mechanical device consisting of a toothed wheel or rack engaged with a pawl that permits it to move in only one direction.

A person has an existing set point. That person gains weight, and then gains and sustains even more weight gain. This causes the set point to be racheted up, and once it passes each rachet, there is no going back. The rachet is the biological set point and it can be easily driven upwards, but is very difficult to drive back down.

Using the fat cell theory is helpful to further explain how this works.

For an example, let’s assume an average fat cell contains 0.4 micrograms of fat each. A person gaining weight might see that fat cell load expand to 0.6 micrograms. This is an acceptable load increase, and when the person loses weight, the fat cell level drops back to 0.4 micrograms.

 This seesaw can go on forever, but when the weight gain loads the fat cell up to 0.8 micrograms, a tipping point is reached, and the fat cell divides. Now we have two fat cells, each containing 0.4 micrograms. Click! That was the ratchet turning irreversibly.

When we want to return to the previous weight, we must lose half the fat we gained. The problem with this is that each fat cell now has the standard fat load of 0.4 micrograms each, and to halve this to just 0.2 micrograms per cell requires us to get the cells to live a life they do not like. If we let our mind tell us what to eat, we can overcome the disgruntled fat cells which are below their fat quota. But all the time the basic animal biology of our body will be waiting to return to 0.4 micrograms per cell.

Then, along comes an event like a vacation, a holiday, or other eating occasion, and we take our eye off the ball .. lose our mental concentration, but the fat cells in our body didn’t rest, and we’ve regained our weight. The body is now back to the new set point it made when we went past the older set point and hit a new rachet.

   In a 2007 research study, a team of Swedish researchers examined fat biopsies from about 680 lean and obese Swedish people. They found obese people can have as much as twice the number of fat cells as do lean people. The researchers also followed 20 gastric bypass patients who lost weight after their operations. Over the course of two years, their fat cells shrunk in size, but the total number stayed constant.

Fat cells can shrink, but once created, they never disappear. The body’s job is to work hard to get all of its cells (including fat cells) to survive and even to thrive. It is easy to continually rachet the biological set point up, but it is almost impossible to rachet it down.

A fat cell is not merely a passive container that stores fat. Leptin is one of the hormones produced by fat cells. Among other things, leptin tells the brain how much fat is in the body, and provides a direct communication link between the brain and fat cells.

Fat cells are the hub of a complex communication system that regulates many metabolic functions, continuously telling the brain how much energy the body has left, signaling muscles when they can burn fat, instructing the liver and other organs when to replenish fat stores, and controlling the flow of energy in and out of cells.

Because fat is so vital to survival, nature has created a complex system of overlapping feedback loops that make it very difficult to override the body's imperative to store energy. People with extra fat cells tend to regain lost weight rapidly.

 This biological truth is the basic problem that exists with all of those “Non-Diet”, “Intuitive Eating” theories. A reduced obese person cannot rely on one’s BODY to make or to keep him/her lean. In fact… it is just the OPPOSITE. A reduced obese person’s BODY has the specific biological imperative of refilling EACH fat cell to its basic quota, which will return that person back to his/her former obesity set point.

The DietHobby ARCHIVES contain many other articles which also discuss this issue.

NOTE: This article was bumped up for new viewers.  Originally posted on 12/9/2012.

 
                
This article "hits the nail on the head" in the way it accurately describes my own personal experience, as well as what I’ve witnessed for years while watching the experiences of others.

It contains one of most accurate analogies for Weight-loss and Maintenance that I’ve ever heard.

Some might find it depressing, but here in my 8th year (now starting my 12th year) of maintaining a very large weight-loss, I find it encouraging and positive to hear a medical professional, who is an expert in obesity, speak the unvarnished Truth.

Despite the fact that this Truth is rather unpleasant, and isn’t something we’re ever going to hear from Marketing Interests… (which includes most doctors and nutritionists) …. Facing it, Understanding it, and Accepting it, can be very helpful.

Running Down the Up Escalator 
                 By Dr. Ayra Sharma, M.D. (a Canadian Obesity Specialist)

One of the games I used to play as a kid was to run Down the UP escalator.

To get to the bottom, I had to run faster than the escalator was moving up. If I ran any slower, the escalator would gradually but steadily take me back to the top.

In fact, even to just stay half-way down, I’d have to keep running at about the speed the escalator was moving up. If I stopped running even for a second, I’d be moving up again.

As you may guess, I am using this analogy, to illustrate the challenge of losing weight and keeping it off.

The escalator represents all the complex neuroendocrine responses to weight loss that will always want to take you back to the top – the only way to reach the bottom or to even maintain your place half-way down is to keep running.

Alas, in real life, the weight-loss escalator is even trickier. For one, there is no real bottom – i.e. no matter how fast you run, you will never reach the bottom and be able to simply get off. No matter how far down the escalator you manage to get, you are still running on the escalator and it will keep moving you back up to the top the minute you stop running.

But things get even more depressing, because, the further down the escalator you get, the faster it runs. This means that the further down the escalator you manage to get – the harder you have to keep running to just stay where you are.

Or, in other words, when you start from the top, the escalator is running relatively slowly and you may easily manage to get down the first 5 steps. But as you go down, the escalator picks up speed and so, if you just keep up running with the speed you started at, you may not even manage to hold your place 5 steps down.

And, to get to 10 steps down, you’ll definitely have to speed up – unfortunately, with every additional step you manage to make your way down, the escalator moves up even faster.

By the time you manage to get down 20 steps, the escalator is moving upward so fast that it is all you can do to just try and not be carried back up.

Depressing?

If we could only find a way to slow down the escalator. Or even better, if you could only get to the bottom and get off!

Alas – that is not how our bodies work.

Yes, for some people the escalator moves more slowly than for others – this is why they find it easier to run down and it takes them less effort to maintain their position half-way down. Others have to fight harder to get there and for others, the escalator simply gets too fast, eventually carrying them all the way back up – no matter how hard they try.

Bariatric surgery and obesity medication can help slow down the escalator or rather, prevent it from speeding up quite as fast as you try to run down. This is why you can maintain a lower spot on the escalator with the same effort as before – but go off your meds or reverse the surgery and the escalator speeds up again only to carry you back all the way to the top.

Why is the escalator analogy important to understand?

At this point I want to add a couple of important points to this analogy.

Firstly, it is important to remember that whatever took you to the top of the escalator, if not addressed, will make the descent even harder (if not impossible).

In the simplest case – to use an analogy that a reader sent in – imagine trying to run down the escalator on one leg – it’s going to be so much harder than with two legs. So if arthritis in one knee took you to the top of the elevator in the first place, trying to get back down while your knee is still killing you is going to be so much more difficult than if your knees were OK.

Similarly, if depression or binge eating took you up the escalator, trying to get down that escalator while still depressed or still not in control of your eating is going to to be so much harder than if these problems were resolved.

It may help to think of whatever took you to the top of that escalator as additional baggage that you have to lug along as you try to run down – the heavier the bags, the harder it is going to be.

As readers will realize, those excess bags could be anything – from a genetic predisposition, to medications that you might be on, to lack of sleep, to high stress levels, to intimate saboteurs, to relationship issues, to loneliness, to body image issues, to childhood trauma – the list goes on and on….

This is why it makes a lot of sense to first deal with what took you to the top before beginning your journey down that up-escalator.

Clearly, simply jumping on that escalator without first dealing with the underlying problem will make losing weight and keeping it off so much more difficult - remember, running down the escalator with no baggage is already hard enough

But, even if the underlying problem is dealt with – you will still be trying to run down the up-escalator – that unfortunately will never change – it will only get somewhat easier the less baggage you have to carry.

But why does the escalator move up in the first place and why does the escalator analogy have important implications for how we address obesity treatments?

Why use the escalator analogy at all? Why is the escalator moving up? Why does it get faster as you get further down? And why is there no bottom, where you can simply get off?

Let’s start with the upward moving escalator – most of us are on it to start with as most of us tend to gain weight with age – unfortunately, some people faster than others. Very few of us manage to keep our teenage weights into late adulthood. There are many reasons for this – for one, our metabolism “slows down” as we get older, so do our levels of physical activity. Then there are other drivers of weight gain that tend to accumulate as we get older – stress, lack of sleep, arthritis, medications, to name a few. This means that for most of us, to not be carried higher on that escalator, we already have to take the occasional step down – the faster our personal escalator is moving up, the more effort we will have to put into simply “marking time”.

But that’s the easy part (preventing initial weight gain is always easier than treating obesity). To lose weight, you have to actually start moving down the escalator faster than it is moving up. Depending on how fast your personal escalator is moving up, the more effort this will take. The tricky part comes when the escalator starts speeding up as you make your way down – this is what is often referred to as the “starvation response” – a complex series of metabolic and behavioral responses aimed at preventing further weight loss and promoting weight regain.

In previous posts I have discussed some of these factors – leptin, ghrelin, sympathetic nerve activity, body temperature – the net result is that as you get lower down on the escalator, the fewer calories you need and the greater your hunger and appetite gets. This is why, keeping weight off gets harder and harder rather than easier and easier the more weight you lose. (Many people think that if I can only lose the first 20 lbs, losing the next 20 will be easier – that is almost never true).

Finally, why is there no bottom where I can simply get off? This is because based on the “setpoint theory” (which is actually far more than just a “theory”), your body always wants to get back to its highest weight (or back to the top of the escalator). Unfortunately, from everything we know about weight management, there is no “cure” for obesity – meaning you will always have to continue doing whatever it is you did to lose the weight to keep it off.

As I noted in my previous post, anti-obesity medications or surgery may make keeping weight off somewhat easier, but they do not “cure” obesity – stop your medications or reverse your surgery and your weight comes right back. This appears to be a rule in weight management – when you stop the treatment, the weight comes back (the same goes for “diet and exercise” as a treatment).

Although depressing, I do hope the escalator analogy is helpful in understanding how weight management works, why keeping weight off is so difficult, why very few people can ever hope to reach and maintain their “dream weight”.

Anyone, who promises you anything else is simply not being honest.

No doubt we need more effective treatments for obesity and perhaps one day we may even find a “cure” – till then, we’ve got to work with what we have.

                                  Dr. Sharma’s Obesity Notes – www. drsharma.ca

 I’ve experienced a lifetime of dieting in order to avoid, and to end, my obesity. I always thought that: if, and when, I got to normal weight, and managed to stay there for 5 years, by then my body would adjust to being normal size, so that eating only what my body needed to maintain my weight-loss, would become more “natural”, and therefore be less difficult.

This has not been the case.

Here in my 8th year, (now working on my12th) I am still running Down the Up escalator, and the past several years, that escalator HAS been speeding up. Maintaining my body at a normal weight is harder now in my 8th year (now 12th year) than it was the first two years after arriving at my goal weight. … and it was NOT easy then.

Nevertheless, I am committed to continue.

NOTE:  DietHobby originally posted this article on 7/7/2013, and I'm bumping it up for new members.

Whatever method one chooses
as a “Diet”…

including Diets that are called:

• “Way-of-Eating”,
  
• “Lifestyle-change”, or 
  
• “Non-Diet”

… this Truth always remains.



 When a body with excess fat consistently takes in LESS food
(meaning: calories within one or more of the three macronutrients)
THAN IT USES as energy, that body will access stored fat for energy.

The process of losing excess fat takes a long time.

Weight-loss diets ultimately fail approximately 95% of the time.  This means that most people fail to lose very much weight on any type of diet, and very few manage to maintain any long-term weight loss.

Losing weight and losing fat isn’t exactly the same thing. However most doctors, nutritionists, dietitians ... and the people who follow their advice ... don’t clearly distinguish the process of reducing body fat from the process of reducing body weight.

Most people sort of KNOW that body weight and body fat are different, and vaguely understand that the scale can register body weight higher due to “water gain”.

 To understand the difference between these two things, it is important to understand that there are two principal components of body weight. We can label these two: constant weight and variable weight.

• The variable weight is a sum of all the digestive fluids inside the GI tract, the undigested foods already in the stomach and the small intestine, the stools inside the large intestine, and water, which can be safely lost with sweat, urine, and perspiration. These variable components of body weight normally represent between 7 and 30 pounds, depending on one’s original diet, one’s current weight, and one’s digestive health.
  
  
• The constant weight is everything else — the remaining fluids, such as the blood plasma and lymph, the weight of one’s skin, bones, internal organs, muscles, and adipose tissue, or body fat. Of course, body fat is actually the only substance in the body one actually wants to get rid of.
  
  
• Variable weight swings from day to day depending on the amount of foods and fluids one consumes and expels, workload, and environment. A day on the beach, an hour in the hot tub, or an intense workout in a sweat suit, for example, can reduce one’s body weight by several pounds simply from sweating.
  
  
• Constant weight remains stable for longer stretches of time because loss of body fat is quite slow on any diet, and requires a considerable time to produce measurable and permanent results.
  
  
• In practical terms, when anyone starts a weight loss program, the first 7 to 20 pounds of weight reduction are almost exclusively made up from the following components:
  
  (a) A reduction in the total weight of foods that have been consumed over the past few days.
  
  (b) A reduction in digestive fluids. As soon as one starts eating less, the body reduces the amount of saliva, gastric, and pancreatic juices involved in digestion. This amount can range from 5 to 7 quarts per day, and may be halved by the reduced calorie diet.
  
  (c) A loss of water throughout the body, particularly with urine. This happens because reduced calorie diets have a pronounced diuretic and dehydration effect.
  
  (d) Loss of stools from the bowels. As one reduces food intake, particularly fiber, the total volume of stools inside the large intestine may drop three to five times.

  The total of all of the above can be termed a phantom weight loss.

While the covers of diet books, magazines, and diet plans tend to ignore this fact of human physiology, it is actually the BASIS of their promises of quick weight-loss from to seven to twenty pounds.

The loss of phantom weight during the first two weeks or so of any dietary change, also explains why so many people yo-yo back to their original weight as soon as they stop dieting … the cumulative weight of foods, digestive juices, water, and stools start coming back the moment one returns to one’s regular diet.

Even a quick reduction of the waistline is a popular diet hoax: because as one’s stomach, intestines, and bowels clear out their respective contents, the waistline around them can then shrink down a few sizes, even though practically all the body fat remains exactly where it was before commencing the diet.

That claim of a weight loss plateau is another gimmick intended to absolve weight loss counselors from any responsibility for their advice, and to blame us and our metabolisms for an inability to lose weight. The simple truth is … if or when … after months of dieting effort … a person simply cannot overcome a weight loss plateau that seems to have started after the first few weeks of losing weight, … it means that person has lost the initial phantom weight, but not body fat. This is happening because their food intake (whatever it may be) is providing them with the exact amount of energy that their body requires to be that body size.

 In Summary:

• Anyone commencing a reduced calorie diet will demonstrate an appreciable loss of weight, but this is not a loss of actual body fat, but a loss of phantom weight related to the much smaller intake of foods and fluids.
  
  
• Weight loss diets that have a pronounced diuretic and dehydrating effect may demonstrate an even larger phantom weight loss at the expense of body fluids. One can accomplish pretty much the exact same effect by restricting fluid intake or sweating out in a sauna.
  
  
• Reaching a weight loss plateau normally means simply that one has lost only phantom weight, but has not lost and won’t lose any body fat…without additional restrictions on their food intake.
  
  
• A rapid weight rebound shortly after resuming a regular diet simply means that one has simply restored the weight of fluids, undigested foods, and stools in one’s body back to their original volume.

 So, why don’t all those diet books talk about this?

Probably two reasons. First, their authors simply may not know or may not want to know about this unwanted phenomenon. Second, telling readers the truth — that it actually takes a LOT of time and a LOT of effort to lose body fat — gets in the way of selling no-sacrifice diet books, cookbooks, classes, tests, diet-branded foods and snacks.

However, here’s the hard truth: If one is thinking of losing weight, the lost weight needs to be the fat under the skin, not undigested foods, fluids, and stools inside the gut. Losing actual body fat takes time, because even on a very low calorie diet the best almost anyone can count on is losing just a very few fat ounces (under 60 to 90 grams) daily.

 The next natural questions are:

1. How long does it take to lose real body fat?
2. How much Effort is required to do that?
   

 The Simple answers to these questions are:

1. A long time.
2. A whole lot.
   

 AND, In order to KEEP that fat from returning,
it will take a similar amount of Effort, … FOREVER.
 

Note: Originally posted on April 3, 2013.  Bumped up for new viewers.