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 created a Weight Range Maintenance Chart
in order to make my maintenance weight goals clearly visible. 
This is my Current Chart. 

Here is a scale photo of my current weight. 

I have been successfully maintaining a very large weight-loss for many years.  You can find my history in the ABOUT ME section which contains a great many links to detailed weight and calorie charts.

I reached my goal weight of 115 pounds in January 2006, and since that time I’ve been making ongoing, consistent, diligent efforts to maintain my weight near that number.

I work to keep my weight within a certain number range, rather than at an individual “goal weight” number. 

I find this necessary because my body has frequent large weight bounces due to salt/water/waste issues. 

Despite my best efforts, during any one-month period, my daily weight tends to bounce back and forth inside a 5 to 8 pound range.

For the past 12 years, I’ve been able to keep these bounces between 115 and 135 pounds. 

On occasion however, my weight has BRIEFLY been as much as 10 pounds below and 5 pounds above that basic bounce range.

The yearly weight chart posted here shows my very lowest yearly weight during each of the past 12 years.

In order to demonstrate that the increases in these yearly lowest weights were NOT due to periods of inattention or a lack of effort, I’m also posting a corresponding yearly calorie chart showing my average daily calories during each of these passing years. 

I’ll be writing more about this issue in an further article on the subject of Biological Adaptation to Weight Loss and Maintenance.

My current Weight Range Maintenance Chart shown at the top of this article is a modification and simplification of this previous chart. 

During my 12 year maintenance period, although I’ve kept the Basic weight-range maintenance chart format, I’ve made several modifications to it.

If interested, you can read about it in the following articles.

Setting a Goal Weight Range
Change in my Weight Range Maintenance Plan
Weight Range Maintenance Plan Changes Again

You can also find further charts and detailed information about my weights and my food intake in the BLOG CATEGORY Status Updates.

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.