SOFI: Skinny on the Outside, Fat on the Inside

Just because you are skinny or slim doesn’t mean you don’t have the same metabolic derangement going on inside as a fat person. You can. One aspect is fat distribution. It can vary greatly among individuals, even when they appear similar in size and with similar abdomen measurements. Magnetic resonance imaging (MRI) can reveal these marked differences. MRI is a medical imaging technique that uses strong magnetic fields to generate pictures of the anatomy and physiology of the body. Look at the image below of two men of similar size.

Coronal Image of a TOFI and a Normal Control by ImagingFat

The individual on the left side has a disproportionate amount of visceral fat (fat that is located around the organs) compared to the control on the right side. Despite being of a similar age, gender and body mass index (BMI), the man on the left has 5.86 liters of visceral fat and the man on the right has only 1.65 liters. What we see on the left is an example of skinny on the outside, fat on the inside (SOFI). It is also referred to as thin on the outside, fat on the inside (TOFI).

Individuals defined as SOFI are associated with a higher risk of developing insulin resistance and type 2 diabetes due to insulin insensitivity, higher abdominal fat and a more atherogenic lipid profile. It is also observed that this group has elevated levels of fat in the liver.

Variation in visceral fat in men with the same waist circumference by ImagingFat

People in a state of SOFI could have a rare condition called lipodystrophy. This is a genetic or acquired state where the body cannot maintain healthy fat tissue. With a lack of fat tissue comes a lack of leptin. Leptin is a signaling molecule, a hormone, that tells your body how much energy you have. It is important in energy regulation and inhibits the feeling of hunger. Lipodystrophy is associated with insulin resistance, non-alcoholic fatty liver disease and hypertriglyceridemia (high levels of triglycerides, the main part of human fat, in the blood).

It is this kind of data that pokes holes in conventional theories of obesity. In an article in The New York Times called “Skinny and 119 Pounds, but With the Health Hallmarks of Obesity” a doctor is quoted: “The usual instructions to patients to lose weight made no sense in this case.” The article talks about a woman with lipodystrophy. Indeed, with a weight of 119 pounds, there isn’t much to lose. The usual advice for obesity, eat less and exercise more, doesn’t hold up. At least the ‘eat less’ part doesn’t. It is at the edges that we notice how common knowledge isn’t holding up mustard.

Further reading

https://en.wikipedia.org/wiki/TOFI

https://en.wikipedia.org/wiki/Lipodystrophy

Skinny and 119 Pounds, but With the Health Hallmarks of Obesity. In: The New York Times. https://www.nytimes.com/2016/07/26/health/skinny-fat.html [28 June 2018]

Lipodystrophy: metabolic insights from a rare disorder. DOI: 10.1677/JOE-10-0272

LEPTIN-REPLACEMENT THERAPY FOR LIPODYSTROPHY. N Engl J Med, Vol. 346, No. 8, 570-8; February 21, 2002. www.nejm.org

Excess body fat in obese and normal-weight subjects. doi:10.1017/S0954422412000054