You might consider yourself lucky if you’ve always been a “normal” weight without having to try too hard.
On the surface everything looks fine. You’re not carrying around any obvious excess body fat.
You’re happy enough with what you see in the mirror and best of all, your weight has been stable for the past 10, 20, or even 30 years.
So what’s the big deal?
What if I told you that the mirror, your stable weight or the ever confusing Body Mass Index (BMI) only tells part of the story? And worse, not even a clear-cut story at that.
You see, being naturally thin isn’t necessarily all that it’s cracked up to be from a health point of view. You could be slim but have the metabolic health of someone who’s insulin resistance or has full-on diabetes.
You could be skinny fat.
What is skinny fat?
You might be thinking to yourself, “What the hell is skinny fat?”
It’s like the ultimate oxymoron. How could anyone be both skinny and fat? Turns out it IS possible. Skinny fat is the colloquial phrase used for the medical term “metabolically obese, normal weight”, a.k.a. “normal weight obesity”.
PRO TIP: “normal weight” is misleading and potentially judgmental. Better terms are low, medium or high-risk weight
Skinny fat is used to describe people who look “healthy” and “fit” (e.g. not overweight) on the outside but who aren’t necessarily so. They look typically thin with a low to average BMI, but despite this, may have health problems brewing beneath the surface, often for a decade or more.
Thin outside, fat inside
A study in the Journal of the American Medical Association found that one in four “skinny” people have pre-diabetes (insulin resistance) and are effectively metabolically obese (1).
To put another way, about 25% of the assumed low-risk weight study subjects fit the skinny fat syndrome/definition, also known as “TOFI” or thin on the outside, fat on the inside. Call it what you want, it’s all the same.
Upon further evaluation, skinny fat people will show the same diagnostic markers of insulin resistance, typically seen in overweight and obese individuals:
- High fasting insulin
- High blood pressure
- High fasting blood sugar
- or a fasting blood sugar that’s trending upward over the years
- Low HDL
- High triglycerides (TGs)
- Elevated A1C
- or an A1C that’s trending upward over the years
- Elevated inflammation (high CRP)
BMI
But what about BMI, or body mass index?
BMI is is a measure of body fat based on height and weight that applies to adult men and women using data from a large sample size of the population. BMI still has some value as a screening metric but it’s not the be all and end all.
At a population level, BMI is associated with health outcomes. An adult with a BMI of 15 will be very underweight; they’ll have both significant fat and muscle loss. We call that adipose and lean mass wasting. This is predictive of increased morbidity (disease) and mortality (death). Conversely, someone with a BMI of 35 will likely have a lot fat which may also put them at increased risk for poorer health.
The main criticism of BMI is that it’s been simplistically used to assess and determine a person’s risk for poor health at the individual level but it doesn’t apply universally.
It doesn’t apply to pregnant women or those who are highly muscular; both will have BMIs outside (e.g. greater) the range seen as ‘healthy’; 18.5 to 25. Just because a person has a BMI of 30 (Class I Obese) doesn’t automatically mean they’ll have poor health. They could have a healthy blood pressure, acceptable fasting blood sugar, be insulin sensitive etc.
Conversely, just because someone’s BMI is within the ‘normal’ range, doesn’t automatically confer health either as you now understand. BMI needs to be considered within the whole clinical picture.
PRO TIP: don’t assume that overweight = unhealthy or that being thin = health
What’s the problem with being skinny fat?
As mentioned above, those who are skinny fat have the same metabolic derangement as those who are metabolically obese.
Thing is, most people (even health professionals) assume that being overweight automatically means a person’s weight is high-risk and that the opposite must also be true: if you’re thin, you’re good to go.
But as we now know, it’s not that simple.
Because of the reductive “health based on body weight” approach, those who are thin who might be at risk for metabolic syndrome (better described as insulin resistance syndrome) will be overlooked when it comes to health assessments.
Yes, it’s true that the majority (about 70 percent) of North Americans, and many in other Western societies, are at risk for diabesity because of the extra body fat they’re carrying, but so are lots of other folks who fall into the TOFI camp.
If BMI and physical appearance are essentially piss poor at determining metabolic heath risk, then what, if anything, can be done?
DEXA scan
Cue the DEXA scan.
Dual-energy X-ray absorptiometry (DXA or DEXA) is a means of measuring bone density.
BUT it does more. In addition to evaluating bone mineral density, the whole-body scan can also be used to measure body composition: lean mass (muscle) and fat mass. In other words, DEXA gives a detailed snapshot of your body composition, including how your body weight breaks down into fat, bone and lean tissue.
Research shows that the scan is highly accurate compared with most other methods for determining body composition such as using skin fold calipers and BIA (Bio-electrical Impedance Analysis). DEXA is highly useful for tracking change in muscle and fat over time. Body weight tells us nothing about composition.
You could have a low-risk BMI but have heaps of body fat in relation to a relatively low amount of muscle. That is a recipe for disaster my friends.
Little old me getting my DEXA scan 🙂
Only DEXA will tell you how much total muscle and fat you have, and when it comes to metabolic health, where you’re carrying your body fat. When it comes to being skinny fat, your thin frame and skinny appearance may be deceiving you. If you’re fat is carried within your abdomen, surrounding your organs, you may be at risk for poor metabolic health. Also known as insulin resistance syndrome.
Knowing this, I naturally had to check it out for myself. I went to a DEXA scan nearest me at The Bone Wellness Centre in Toronto to see what my body fat percentage is.
Looking at the scan below (left), anything that is yellowish orange is fat, a.k.a. adipose. You can see that most of it is on my shoulders, inner thighs and in and around my abdomen. I have about 15% body fat by weight (10.6 kg or 23.4 pounds) and 59.7 kg or 131.5 of lean tissue (muscle and bone).
Looking at the coloured scale above, my BMI is 22.3. On the surface this seems great but as a stand alone number, tells me nothing about my composition as already stated. I could have a lot more fat and less muscle and have the same BMI. Oops!
Metabolic big picture
The limitation of the DEXA is that it’s not sophisticated enough to tell me how much of the fat that’s in and around my abdomen is subcutaneous (the stuff that you can pinch. It’s fat later that lies between your skin and the abdominal wall or “abs”) versus visceral, the fat that surrounds your organs.
To answer the question,,”Should I be worried?”, we only need to consider the usual suspects when it comes to assessing metabolic health and risk for future diseases like diabetes, high blood pressure, and cardiovascular disease like heart attacks or stroke:
- Lipids (total cholesterol, LDL, HDL and triglycerides)
- Blood pressure
- Fasting blood sugar
- A1C
- Inflammation markers
Because my metabolic profile is great as reflective by optimal values in the indices above, the location of the abdominal fat that my DEXA results revealed are of no meaningful concern for me.
If they were, I might go for an ultrasound to assess the location of the fat cuz I’m a data nerd that way. Alternatively, if my blood work needed improvement, I could just get my act together to fix them and skip the extra tests.
Body composition
Despite having a ‘healthy’ BMI, most TOFIs have low muscle mass. This is often due to a sedentary lifestyle and a lack of exercise, specifically weight training often coupled with a poor protein intake or by not spreading their protein intake throughout.
In our modern world, we wake up, get in the car or commute to work, sit at a desk all day with minimal activity, get back into the car to head home and then sit on the couch till bedtime. Repeat x many decades = disaster. The results are the predictable health crisis that we face today in the modern world.
What’s great about a DEXA, is that it gives you a snap shot of how much muscle and fat you have in your limbs, legs and trunk. This information can be used to track progress (gains) if you decide to take on a muscle-preserving, quality-of-life enhancing exercise program. People often have repeat DEXAs every 6 to 12 months to get an objective and visual metric of their efforts.
Sarcopenia
Sarcopenia is the degenerative loss of skeletal muscle mass (0.5–1% loss per year after the age of 50), muscle quality, and muscle strength associated with aging. It’s a component of the frailty syndrome; an insidious lose of strength, quality of life and independence.
Incredibly sarcopenia starts at age 40 and accelerates with age. By the time you’re 65, you’ve lost between 8 and 27% of the muscle mass you had when you were 20 to 30 years of age. Unless you’re making an effort to build and hang onto the muscle you have with weight resistance exercise and adequate amounts of HIGH quality protein, you’re on the fast track to losing it.
Again, the DEXA scan is a great way to assess your muscle status. It estimates your Relative Skeletal Muscle Index (RSMI) expressed as muscle mass per area of muscle. Using the example above, I’m happy to report that my trips to the gym and spinning classes, coupled with my ideal protein intake has proved to be helpful.
With a RSMI of 9.32 kg/metre squared, I’m well above the cut off for the clinical diagnosis of sarcopenia for men of 7.26. It’s good to know that as I head into my older years, I’ll be in a great position to reduce the risk for age-related muscle loss such as falls, loss of independence, and metabolic disease.
PRO TIP: you have to “use it or lose it” as the saying goes. Without stimulation, you will lose muscle AND simply getting enough protein isn’t enough, it helps but you need to do more.
Bottom line
Alone, BMI or appearing physically “thin” or “slim” is no measure of health.
Historically, BMI has been used to assess individuals’ risk for metabolic health: the larger the BMI, the greater the risk. The unintended consequence is that those with a BMI that falls within the ideal/low-risk range (18.5 to 25) aren’t considered at risk for metabolic syndrome.
However, studies show that those with a ‘normal’ BMI can have low muscle mass and be carrying around excess abdominal fat AND be at increased risk for poor metabolic health such as insulin resistance syndrome or diabetes.
Also known as skinny fat
Assessing metabolic health with traditional metrics such as blood work (lipids, blood sugar and A1C) and blood pressure can provide a snapshot in time. The problem is, they fall short when to comes to knowing what’s going on below the surface and a normal weight won’t help the assessment.
A great way to go deeper is using a DEXA scan. This will tell you exactly how much lean tissue (bone AND muscle) and fat you have AND where that fat is located. It will also give you a sense of your risk for sarcopenia. What’s not like?
By getting a better sense of your overall clinical picture, you can take steps to taking control of your health including preserving both muscle and independence as you get older.
BTW, it’s a complete and utter myth that it’s unsafe or dangerous for older adults to pump iron. Of course you want to do it right and use appropriate weights and exercise programs appropriate for a person’s fitness levels, age etc. This is why it’s best to work with a professional like a certified kinesiologist or exercise physiologist.
Do your homework, the title ‘Personal Trainer’ means nothing because it’s not a regulated title. Get their credentials, education and training details AND work with a regulated nutrition professional such as a Registered Dietitian for your nutrition needs.
Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, mental health. Follow me on Facebook, Instagram and Twitter.