What is Skinny Fat?

Skinny fat is a very popular phrase that is widespread across the internet, especially on social media. As a very young science, at present it is grossly misunderstood.

So, what is skinny fat science, exactly? 

Technically, skinny fat is normal weight obesity (NWO) and scientifically/medically defined (1) as having too much/excess body fat even when within healthy/safe/normal Standard BMI (2), which is 18.5 to 24.99. In 2006, A De Lorenzo (3, 21) is credited with the first (4) known use of the term normal weight obesity. Subsequently, later that same year Dr. Jimmy Bell (5, 39) coined the acronym TOFI — “thin on the outside, fat on the inside” — which has come to commonly be known as skinny fat.

By roughly 2010, skinny fat started to emerge as a term in health and fitness communities. The first NIH normal weight obesity definition was published in 2016 (1). As of 2024, skinny fat is not yet formally recognized as a medical diagnosis.

What Is Skinny Fat – The Six Types

According to the Standard BMI* definition (6, 7, 8, 9, 10, 11), once you are within safe/normal Standard BMI you no longer have any excess white fat/yellow fat (regular fat) on your body and are not overweight (BMI 25 to 29.99) or obese (BMI 30+). Being skinny fat (NWO) directly contradicts the Standard BMI definition and is technically impossible.

How is it possible to be within safe Standard BMI and still have too much/excess body fat?

Normal weight obesity (type #6) is possible because the excess body fat the person is experiencing is not excess regular white/yellow fat, it is one or more of the other 5 types of skinny fat which include:

1) Cellulite (main type),
2) Thin Fat (main type),

3) Loose Skin (typically a result of excess regular white/yellow fat weight loss and making thin fat or cellulite worse),

4) Saggy Skin (typically a result of excess regular white/yellow fat weight loss and making thin fat or cellulite worse), and

5) Crepey Skin (can be made worse by excess regular white/yellow fat weight loss).

Skinny fat is different than regular obesity which is defined as having too much regular white/yellow body fat (7, 8, 9, 10, 11) on your body, taking you outside safe BMI.  Metabolically healthy obesity/MHO (12, 13) is defined as having normal vitals and, all things considered, being healthy yet experiencing BMI obesity. Whereas thin fat, cellulite, loose skin, saggy skin, and crepey skin can exist at any BMI, while normal weight obesity can only exist within safe/normal BMI. 

Is Skinny Fat Unique Tissue?

Muscle is unique tissue. Regular white/yellow fat is unique tissue. 

Cellulite is unique fibrous tissue (14, 15). More than 80%+ of women (15, 16) and less than 10% of men (16) globally have cellulite, yet 0% have ever gotten rid of it. At this time, there is no FDA-approved way to permanently (15, 16) get rid of cellulite or any other type of skinny fat. You can only reduce it. 

Although the science of skinny fat is young and we are not sure what kind of tissue thin fat (20, 21) is, we are certain that thin fat tissue is not muscle tissue or regular fat tissue. Can thin fat tissue turn into cellulite tissue or vice versa? We don’t know without more scientific research.

But we do know that you can technically lose 100% of your white/yellow/regular fat but your skinny fat will remain. Skinny fat tissue and regular fat tissue are not the same tissue, they are different. Visceral fat (22, 23) is only regular fat (or brown or beige fat). Skinny fat tissue — thin fat and cellulite — is unique tissue and is ONLY subcutaneous (24). Whether skinny fat is actually a kind of fat tissue or not is debatable and requires more scientific research. 

Skinny Fat Science Is Very Young and Evolving

According to Google, skinny fat is too much visceral fat as well as too much regular white/yellow fat (body fat) even when within safe BMI (which absolutely contradicts the Standard BMI definition). Please do explain how this BMI 22.7 person who is experiencing skinny fat is experiencing visceral fat as well as too much regular fat (body fat):

Research Participant 1170

This 23-year-old research participant (25) has a safe Standard BMI of 24.6 (three left images) with obvious skinny fat including thin fat, cellulite, and normal weight obesity. The right three pictures are after further safe weight loss and reaching a safe Standard BMI of 21.3, yet the skinny fat remains.

According to mainstream science/medicine, once you are within safe Standard BMI you are the Standard Body Type One (BT1) found in any scientifically approved human body anatomy book/resource (18, 19, 17) with all 600+ muscles developed. However, research participant 1170 is well within safe BMI while having indisputable skinny fat tissue where they should have default genetic muscle/mass. They are not a Standard BT1, just like BMI 22.7. 

What Causes Skinny Fat?

The typical spiel on social media and online, in general — including most medical professionals — is that poor diet (too many carbs, too little protein), exercise (too much cardio, too little resistance), and lifestyle cause loss of muscle tissue and that lost muscle tissue turns into skinny fat tissue. But, it is an undisputed scientific/medical fact that this is not how human tissue works (26, 27).

Muscle tissue cannot become any kind of fat tissue, be it regular fat, brown fat, beige fat, or skinny fat. No amount of diet/protein, exercise, or lifestyle magically turns skinny fat tissue into muscle tissue or gets rid of, prevents, or avoids skinny fat, or the like. This is not how human tissue works!

For example, here is Christian Bale, genetically blessed with a Standard Body Type One, after extreme weight loss for a movie role including obvious lost muscle mass tissue:

According to basically everyone everywhere, including medical professionals, Christian Bale should be experiencing skinny fat. But there is no sign of any type of skinny fat tissue on his body, even when he is emaciated. The muscle definition is crystal clear, even with significant loss of muscle mass.

Skinny fat is real genetic tissue (thin fat, cellulite) and is influenced by diet, exercise, and lifestyle. 

Genetics and Body Composition

Genetics is the foundation (28, 29, 30, 31, 32) of the human body and determines unique genetic body composition. Diet, exercise, and lifestyle directly influence body composition including skinny fat, but they do not determine body composition. At this time, you cannot naturally, permanently (33) change your unique genetics including skin color, hair color, eye color, height, breast size, genital size, facial features, body composition, etc. You can, indeed, temporarily (epigenetically)(38, 33) change/recomp your body composition with diet, exercise, and lifestyle. And, with enough hard work for your entire life, you may even be able to maintain the changes.

The younger you are, the more motivated you are to recomp/change your body. Then life happens, and motivation wanes for most people and you eventually return to your original default genetic body composition, like Research Participant 378 (34). Which is the current nature of human genetics. The younger you are, the harder it can be to discern skinny fat (which is only subcutaneous). Especially thin fat. 

How To Fix Skinny Fat

*It is important to note that the Standard BMI (Body Mass Index) is the current standard — its’ first known mention in the medical literature was in July 1972 (35), it became the international standard (World Health Organization/WHO) in the early 1980s (35), and in June 1998 the U.S.A National Institute of Health approved the current BMI as the standard (36, 35) — but it is not particularly accurate. The Standard BMI fails to effectively account for genetics, excess muscle/mass (genetic or added via exercise), any type of skinny fat, race, gender, or age, no less, and is best used as a guideline. The Body Type Science Theory research (37) is working on making the Standard BMI, Standard BMR (basal metabolic rate), and Standard Body Type One (BT1) more accurate. 

References

1. NIH, National Library of Medicine: Normal-weight obesity syndrome: diagnosis, prevalence, and clinical implications, September 2016 (Epub Jul 29, 2016), Lana P Franco, Carla C Morais, Cristiane Cominetti. https://pubmed.ncbi.nlm.nih.gov/27473199/
2. NIH, National Heart, Lung, and Blood Institute: Calculate Your Body Mass Index, https://www.nhlbi.nih.gov/health/educational/lose_wt/BMI/bmicalc.htm
3. NIH, National Library of Medicine: Normal weight obese (NWO) women: an evaluation of a candidate new syndrome, December 2006 (Epub March 3, 2006), A De Lorenzo, R Martinoli, F Vaia, L Di Renzo. https://pubmed.ncbi.nlm.nih.gov/17126766/ 
4. ScienceDirect: Normal Weight Obesity: An Underrecognized Problem in Individuals of South Asian Descent, August 2019, Nitin Kapoor MD (Medicine), DM (Endocrine), John Furler MBBS, PhD, Thomas V. Paul MD(Medicine), DNB (Endocrine), PhD, Nihal Thomas MD (Medicine), FRCP, PhD, Brian Oldenburg MPsychol, PhD. https://www.sciencedirect.com/science/article/abs/pii/S0149291819302917
5. Huffington Post: Why ‘Skinny Fat’ Can Be Worse Than Obesity, July 2015 (Updated July 30, 2016), Mark Hyman, MD. https://www.huffpost.com/entry/why-skinny-fat-can-be-wor_b_7904706
6. ScienceDirect: Body Mass Index, Encyclopedia of Applied Psychology, 2004. https://www.sciencedirect.com/topics/psychology/body-mass-index
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14. University of New Mexico: Cellulite: A Review of its Anatomy, Physiology and Treatment, 2009, Len Kravitz, Ph.D. and Nicole J. Achenbach, B.S. https://www.unm.edu/~lkravitz/Article%20folder/cellulite2.html
15. NIH, National Library of Medicine: Cellulite: Current Understanding and Treatment, June 21, 2023, Allen Gabriel, Vivian Chan, Marissa Caldarella, Tanya Wayne, and Erin O’Rorke. https://pmc.ncbi.nlm.nih.gov/articles/PMC10324940/
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17. Britannica: human muscle system, Shane W. Cummings and Robin Huw Crompton (Fact-checked by the Editors of Encyclopaedia Britannica. https://www.britannica.com/science/human-muscle-system
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20. US News: Could Having ‘Skinny’ Fat Cells Encourage Weight Gain?, Dennis Thompson (HealthDay), May 13, 2024. https://www.usnews.com/news/health-news/articles/2024-05-13/could-having-skinny-fat-cells-encourage-weight-gain
21. NIH, National Library of Medicine: Thin Fat Obesity: The Tropical Phenotype of Obesity, March 2021, Nitin Kapoor, MBBS, MD. https://www.ncbi.nlm.nih.gov/books/NBK568563/
22. Cleveland Clinic: Adipose Tissue (Body Fat), August 18, 2022, https://my.clevelandclinic.org/health/body/24052-adipose-tissue-body-fat
23. NIH, National Library of Medicine: Switching harmful visceral fat to beneficial energy combustion improves metabolic dysfunctions, February 23, 2017, Xiaoyan Yang, Wenhai Sui, Meng Zhang, Mei Dong, Sharon Lim, Takahiro Seki, Ziheng Guo, Carina Fischer, Huixia Lu, Cheng Zhang, Jianmin Yang, Meng Zhang, Yangang Wang, Caixia Cao, Yanyan Gao, Xingguo Zhao, Meili Sun, Yuping Sun, Rujie Zhuang, Nilesh J Samani, Yun Zhang, and Yihai Cao. https://pmc.ncbi.nlm.nih.gov/articles/PMC5313060/
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25. Fellow One Research: Body Type Test (Quiz) Results 1170 – Body Type Three (BT3) Female (Woman), Generation Z, February 2022. https://www.fellowone.com/fellow-one-research/the-four-body-types/body-type-quiz/body-type-test-quiz-results-1170-body-type-three-bt3-female-woman-generation-z/
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30. NIH, National Library of Medicine: Brain Basics: Genes and the Brain, https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-genes-and-brain
31. Fitnescity: Body Composition: Nature or Nurture?, February 16, 2023. https://www.fitnescity.com/blog/body-composition-nature-or-nurture
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33. Skinny Fat Science: How To Fix Skinny Fat, July 27, 2024. https://skinnyfat.fellowone.com/how-to-fix-skinny-fat/
34. Fellow One Research: Research Participant 378 – Body Type Two (BT2) Male (Man), Millennial (Generation Y). https://www.fellowone.com/fellow-one-research/the-four-body-types/body-type-quiz/research-participant-378-body-type-two-bt2-male-man-millennial-generation-y/
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36. The New York Times: U.S. to Widen Its Definition Of Who Is Fat, June 04, 1998, The Associated Press. https://www.nytimes.com/1998/06/04/us/us-to-widen-its-definition-of-who-is-fat.html
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39. The Guardian: Are you a Tofi? (That’s thin on the outside, fat inside), December 10, 2006. https://www.theguardian.com/science/2006/dec/10/medicineandhealth.health