Let’s meet Mr. Fat. I’ll bet the word “fat” isn’t pleasant to your ears because most of us see Mr. Fat as an enemy. At least, I did. Fat was something I wanted to get rid of.

How do we go about meeting the real Mr. Fat? The worst way to meet him is to go to a dictionary such as the Oxford Dictionary.

Fat: A natural oily or greasy substance occurring in animal bodies, especially when deposited as a layer of the skin or around certain organs.”

Oxford Dictionary

Or a Lay Perspective

Picture of colored dots with a quotation that says: Being fat is like having your most humiliating secret visible for the world to see and judge. Purpose is to show the emotional problems caused by being overweight.

Being fat is like having your most humiliating “secret” visible for the world to see and judge.

Mr. Fat’s Aliases

I’ll keep jargon to a minimum, but you do need to know a few terms. Fat tissue in general is known as adipose tissue. Fat tissue inside the body is called visceral adipose tissue or VAT, but fat cells under the skin are called subcutaneous fat. The scientific name for a fat cell is an adipocyte.

Why Meet Mr. Fat?

“Boo,” you say. I already know what fat is! Maybe you believe meeting the real Mr. Fat will be boring, but I’m here to argue that you’re wrong. I had many mistaken beliefs about fat, and I’ll bet you a cup of coffee that you do too.

Let me put it this way. Learning about the real Mr. Fat made my head swim. I learned he is quite a fascinating fellow, but. I also discovered how he got into my life and began to dominate my thoughts.

Silly picture of Mr. Fat as I imagine him. I see him as Mr. Peanut

Sorry guys, no slur is intended by my choice of masculine gender. Somehow, I can’t get Mr. Peanut out of my mind.

My Misguided Beliefs About Fat

These were my misguided beliefs about fat. Read each one, and ask yourself, “Do I believe this?”

  • Fat is a passive, yellow bag of goo that gets bigger and bigger when I eat too much. Kind of like overstuffing a suitcase.
  • All fat in the body is the same– looks the same, acts the same.
  • Thin people are healthier than fat people.
  • Fat doesn’t do much except hold our extra calories until the body needs them.
  • We’re born with a fixed number of fat cells.

Back to the Dictionary

Don’t be surprised if you also hold these mistaken beliefs about fat because the dictionary gets it wrong too. Fat is not grease. Fat is not passively deposited here and there like a squirrel hiding acorns for the winter. Fat doesn’t lie helplessly about the body. Fat is not nasty or awful. In fact, Mr. Fat has an important “secret life.” To get a head start, read the Secret Life of Fat by Sylvia Tara. https://www.amazon.com/dp/B01BZ1V6CI

The Secret Life of Fat

Cover of the book by Sylvia Tara entitled The Secret Life of Fat. I highly recommend this book.

Poor fat! So reviled, so shameful, so unloved.

Sylvia Tara, Ph.D.

Dr. Tara’s book introduced me to Mr. Fat, and I was so intrigued that I started reading the scientific literature. My attitude toward fat changed, so I don’t look at my stomach roll with the same disgust. Maybe I should have titled this post Befriending Mr. Fat because I like my fat more now. Thanks Dr. Tara.

Dictionary Definitions of Organ

  1. A differentiated structure (such as a heart, kidney, leaf or stem) consisting of cells and tissues and performing some specific function in an organism
  2. bodily parts performing a function or cooperating in an activity.

Name a Few Organs in Your Body

What comes to mind when you think of a body organ? The heart, the lungs, or the brain are common answers. We do not think of fat as an organ because fat seems to be everywhere. The heart and the lungs aren’t scattered about the body, but fat can be found in our arms, legs, belly, etc. Nonetheless, Mr. Fat is an organ. It is a differentiated structure as per Merriam Webster. It is made up of cells and tissues, and fat performs specific functions and cooperates with other fat cells and other organs.

Mr. Fat Is an Endocrine Organ

Fat is an endocrine organ because it secretes hormones which enter the bloodstream and act on other cells in the body. The best known endocrine organs are the pituitary gland, the thyroid gland, the ovarian glands (or testes), the pancreas, and the adrenal glands. Our endocrine glands control many essential body functions including growth, development, metabolism, and fertility. Anyone who has a lazy thyroid gland can tell you how powerful the endocrine organs are.

MedicineNet Illustration of the Endocrine System (2007)
Illustration of the Endocrine System drawn in 2007. Fat is not included in the illustration.

Try to Find Mr. Fat in the Illustration

Fat is not included in this illustration. Why? Even recent illustrations such as this one have fallen behind. Our understanding of fat is evolving at a smoking rate because scientists are discovering its astonishing complexities. Fat cells have a major role in the control of our metabolism and many other essential body functions, so toss the notion that fat is simply a series of tiny suitcases which can be filled with excess calories.

It’s astonishing that to this day, we’re still discovering [fat] hormones that we didn’t know existed,” says endocrinologist Brian J. Feldman of Stanford University. “And they’re not doing esoteric, small jobs– they have quite potent, major physiological implications.”

Madhusoodanan, 2018

A Short List of Adipose or Fat Cell Hormones

Don’t be intimidated by the following table of hormones produced by fat cells (Madhusoodonan, 2018) https://pubmed.ncbi.nlm.nih.gov/30276236/. You won’t need to learn the names of these hormones to understand this post. The table shows the fat cell hormones discovered between 1994 and 2018 as well as their functions. Pretty impressive, huh? Our fat is involved in the regulation of appetite, inflammation, blood vessel formation, ovulation, blood pressure, insulin resistance, developmental patterning, glucose metabolism, and skeletal muscle respiration.

Table of Fat Hormones
Table with chronological listing of fat hormones discovered since 1997.

Does Fat Have a Mind of Its Own?

Fat cells don’t have a brain in the way we usually understand the term. Fat can’t compose an opera, write a poem, or tell a joke. What fat does have are the following:

  • The ability to adapt to change
  • The ability to communicate with other fat cells and with organs in the body

We are resistant to the idea that fat has a life of its own. I think human beings dislike the notion that we are not fully in control. The idea that there some strange genetic variance in our brain driving us to put our hands in the cookie jar — many doctors have a difficult time accepting this.

Sylvia Tara

Why We Need Fat

What does Mr. Fat do with his day? He is a very busy fellow, and he has the following major jobs:

  • Store excess energy
  • Manage Energy
  • Produce Heat
  • Insulate body organs
  • Serve as a messenger for the immune system

Fat Cell Types

The three types of fat cells are brown, beige, and white. The color of the fat cell comes from the number of mitochondria in the cell. The brown fat cell has more mitochondria than does the white fat cell. In the illustration, the mitochondria are pink oval structures. The beige fat cell has an intermediate number of mitochondria. Note that the white fat cell contains a large lipid droplet. Fat droplets are yellow circles. Fat from unused energy is stored in the droplets. The cell nucleus is the brown circle. The mitochondria in the brown fat cells produce heat (thermogenesis).

Illustration of white beige and brown cells which shows the cell's major components-- the nucleus, mitochondria, lipid droplets
Set of brown, beige and white fat cells. iStock photo

Are Subcutaneous and Visceral Fat Cells the Same?

No, they are not. One type of fat accumulation is more likely to make you sick. When you compare fat below the skin with fat around the visceral organs, there is one very significant difference. Fat accumulation around the visceral organs is strongly associated with complications like cardiovascular disease or diabetes. The difference between the two types of fat deserves its own post.

How Old Are Your Fat Cells?

When your body weight is stable and your weight is in the normal range, approximately 10% of your fat cells are replaced each year. The mean age of a fat cell is a little more than 9 years, and the energy in a fat cell is turned over approximately 6 times during a fat cell’s lifetime. If you are overweight, you may not turnover the energy stored in the cell as often. As the fat cells grow, insulin resistance and dyslipidemia develop (Arner et al., 2011; Arner, 2018 ) https://pubmed.ncbi.nlm.nih.gov/21947005/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797910/pdf/zdb105.pdf

Brown and White Fat Cell Distribution

Adults have much less brown fat, and it is all located around internal organs. Brown fat cells generate more heat than white fat. See the illustration below which shows brown fat in the neck, near the clavicle, around the aorta, around the vertebrae of the spine, and around the kidneys. Brown and beige adipocytes use fatty acids and glucose at a high rate. The beige fat cell is also called a brite adipocyte.

Illustration showing the location of brown and white fat cells in an adult
Ascoli et al., 2015

Quick Change Artist

A white fat cell doesn’t have to live out its life filled with large lipid droplets because fat cells can change from white to brown, a process known as “browning” (Laidman, 2012). https://pubmed.ncbi.nlm.nih.gov/22499899/ Because brown cells may be more important in weight loss, we’ll talk more about white cell browning in another post.

Obesity and Energy Use by the Fat Cell

In normal energy storage, the energy which goes into fat cells equals the energy released by the white fat cells. White fat cells don’t have many mitochondria (often described as the energy factories for a cell), so they use less energy than a brown cell.

Hyperplasia and Hypertrophy

What we call obesity is an accumulation of energy-containing triglycerols in the white fat cells as these cells take in more energy than they use. As white cells load up with triglycerols, the number of fat cells increases (hyperplasia), the fat cells(hypertrophy) enlarge, and the hormonal output changes (White and Rasvussin, 2019). https://link.springer.com/content/pdf/10.1007/s00125-018-4732-x.pdf

Overeating Makes Fat Cells Sick

The illustration below shows fat cells which are balanced, and their energy in equals their energy out. With time and excessive eating, more fat cells accumulate and they are larger. One of the hazards of overstuffed fat cells is the development of cancer (shown in the bottom half of the figure. The figure is from a paper published by Divella et al. (2016). jcav07p2346.pdf (nih.gov)

Illustrations of health lean fat cells and overweight sick cells
Divella et al., 2016

Sick Fat Hormones

The transformation of healthy fat cells due to overcrowding and/or poor quality food changes the hormones that the fat cell makes. Understanding how fat gets sick is the subject of another post. Sick Fat: The How and the Why

Peter Arner Talks About Fat

Dr. Arner knows a lot about fat. Watch this brief video.

Take Aways

There are 5 take aways in this YouTube clip.

  1. Children add fat cells as they become obese. You may want to read this post. Undernutrition in the Womb
  2. The fat cells added during childhood will stay with the child for the rest of his or her life even if he or she loses weight.
  3. Adults also add fat cells when they gain weight.
  4. Fat cells do not disappear when we lose weight, but they are smaller.
  5. Yo-Yo dieting is the worst relationship you can have with Mr. Fat. Each time you gain, you add fat cells. It is best to stay at your weight and eat better food if you cannot make a commitment to weight loss.

Amount of Body Fat and Health

You go to the doctor’s office, and the doctor measures your height and weight to calculate your Body Mass Index or BMI. For a definition of terms, see this post. Terms You’ll Want to Know. Then your BMI is classified as normal, overweight, obese, or morbidly obese. As you graduate from level to level, you’re told that your risk for heart disease and other metabolic disorders is higher. At some point, your doctor will pull out a prescription pad and suggest that you take a medication to lose some weight. The implication is clear — the fatter you are, the sicker you are. Let’s call this the volume model.

BMI Is Not a Good Predictor of Health Risk

The three problems with the volume model. A volume measure like BMI is not a good predictor of your long-term health risks. You may not be necessarily growing sicker as you grow fatter. For example, there is a heavy genetic loading for weight gain.

Mistaken Belief that Being Thin Equals Health

The second problem is more serious. Take the example of a thin woman who lives on junk and processed food. Her BMI says she’s doing well. Maybe she is, but maybe she isn’t doing so well because skinny people without much fat can become diabetic. They can also develop cardiovascular diseases including atherosclerosis.

How You Gain Weight and Your Race or Gender Are Important

Men and women have different risks of developing these diseases at the same BMI, and races differ significantly in susceptibility to cardiovascular disease. Why? Let’s look at one reason.

Body Fat Distribution

Part of the answer may be in the distribution of our fat. Some of us carry our weight around our middles, some below the middle, and some in our legs and thighs. For The last few years, we’ve thought that having an apple shaped fat distribution put us at greater risk for diabetes and cardiovascular disease, but we haven’t had the faintest clue why. How our fat is distributed is part of the answer. Carrying your weight in your thighs is healthier than carrying your weight in your abdomen.

Picture from a newspaper in Ireland which shows an apple and pear shaped woman

A pear shaped fat distribution is healthier than an apple shape. Photo from The Irish News 9/13/2018. https://www.irishnews.com/magazine/science/2018/09/13/news/which-body-shape-is-healthier-pear-or-apple-scientists-have-the-answer–1432513/

What Is Your Body Shape?

Are you an apple, pear, hourglass, inverted triangle, or ruler? Use the illustration from the University of Pennsylvania to decide. https://www.pennmedicine.org/updates/blogs/health-and-wellness/2019/september/body-shape

Figure showing different body shapes. Classify yourself.

Metabolic Obesity

Whatever you think about obesity, throw out your old ideas. Develop some new concepts.

We need a new definition of obesity. Hamdy et al. (2006) argue that it is where the fat is located in the body that makes it unhealthy. Fat around our viscera Is both physiologically and biochemically different from the fat which is under our skin. Thus, a little extra fat around your thighs is not nearly as dangerous as a little extra fat around your liver.

These accumulating observations also urge our need for a new definition of obesity based on anatomical location of fat rather than on its volume, especially when cardio metabolic risk is considered (Hamdy et al. 2006)


I’ll cover some fascinating research discussing the complexities of metabolic obesity in another post. Metabolic Obesity You might also be interested in a post on calories. I had to revise many of my beliefs about calories. I Come to Bury Calories – 1

Now that you have a brief introduction to fat, remember that my fat doesn’t work the same as yours. Although understanding how fat works isn’t simple, I think digging into the secret life of fat is worthwhile. I believe that understanding the real Mr. Fat will help you maintain your weight at a healthy level for you.


Arner, P. (2018). Fat Tissue Growth and Development in Humans. Nestle Nutr Inst Workshop Ser, 89, 37-45. doi:10.1159/000486491

Ascoli, C. (2015). Brown and Beige Fats: Basic physiology and novel therapeutics. Paper presented at the Rockland Antibodies and Assays, Snowbird, Utah.

Arner, P., Bernard, S., Salehpour, M., Possnert, G., Liebl, J., Steier, P., . . . Spalding, K. L. (2011). Dynamics of human adipose lipid turnover in health and metabolic disease. Nature, 478(7367), 110-113. doi:10.1038/nature10426

Bordicchia, M., Liu, D., Amri, E. Z., Ailhaud, G., Dessi-Fulgheri, P., Zhang, C., . . . Collins, S. (2012). Cardiac natriuretic peptides act via p38 MAPK to induce the brown fat thermogenic program in mouse and human adipocytes. J Clin Invest, 122(3), 1022-1036. doi:10.1172/JCI59701

Divella, R., De Luca, R., Abbate, I., Naglieri, E., & Daniele, A. (2016). Obesity and cancer: The role of adipose tissue and adipo-cytokines-induced chronic inflammation. Journal of Cancer, 7, 2346-2359. doi:10.7150/jca.16884

Hamdy, O., Porramatikul, S., & Al-Ozairi, E. (2006). Metabolic obesity: the paradox between visceral and subcutaneous fat. Curr Diabetes Rev, 2(4), 367-373. doi:10.2174/1573399810602040367

Jung, S. M., Sanchez- Guertin, D. A. (2019). Brown Adipose Tissue Development and Metabolism. Handbook of experimental pharmacology, 251, 3-36. doi:10.1007/164_2018_168Gurmaches, J., &

Laidman, J. (2012). The secret life of fat suggests new therapeutic targets. Circ Res, 110(8), 1049-1051. doi:10.1161/RES.0b013e31825540af

Madhusoodanan, J. (2018). The Secret Life of Fat Cells. ACS Cent Sci, 4(9), 1078-1080. doi:10.1021/acscentsci.8b00633

Tabuchi, C., & Sul, H. S. (2021). Signaling Pathways Regulating Thermogenesis. Front Endocrinol (Lausanne), 12, 595020. doi:10.3389/fendo.2021.595020

Tara, S. (2017). The Secret Life of Fat. New York: Norton & Co.

White, U., & Ravussin, E. (2019). Dynamics of adipose tissue turnover in human metabolic health and disease. Diabetologia, 62(1), 17-23. doi:10.1007/s00125-018-4732-x

Zoico, E., Rubele, S., De Caro, A., Nori, N., Mazzali, G., Fantin, F., . . . Zamboni, M. (2019). Brown and Beige Adipose Tissue and Aging. Frontiers in Endocrinology, 10(368). doi:10.3389/fendo.2019.00368NoI

Linda J. Gummow

Linda J. Gummow

L. J. Gummow, Ph.D. and Robert E. Conger, Ph.D. are Clinical Psychologists. L. J. lost 25% of her body weight by following by reducing carbohydrates. In the process, she learned that much of what we're taught about weight loss is wrong. She and her co-author researched weight loss diets and the results show that sugar consumption is our public health enemy number one. R. E.

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