The Unhealthy Skinny-Fat Phenotype


Metabolically Obese, Normal Weight

Obesity is a well-known health risk, contributing to cardiovascular disease, cancer, and diabetes, among others, but some people who are not overweight have the same risks. Those are people with the unhealthy skinny-fat phenotype.

Obesity is associated with insulin resistance, and whether as cause or effect, insulin resistance is probably behind many of the adverse effects of health of obesity.

The causes of both insulin resistance and obesity are hotly debated, but it’s also apparent that insulin resistance can appear in non-obese people, in whom it will increase the risks for disease just like obesity will.

People who have the metabolic abnormalities such as insulin resistance but who are not themselves obese have been termed “metabolically obese, normal weight” (MONW).

In more common language, these people are skinny-fat.

The Skinny-Fat Phenotype

“Phenotype” means simply the observable characteristics of an organism, resulting from the interaction of the organism’s genes with its environment.

“Skinny-fat” refers to a person with a normal body mass index (BMI), who has a low muscle mass and a high amount of body fat.

In the case of a skinny-fat person, BMI does not capture the true health risks associated with that person’s body composition, i.e. the fractions of lean mass and fat mass that make up his or her body.

BMI is a rough-and-ready measure of where someone fits into weight categories, with their attendant health risks, but is actually a surrogate measure for the two most important body components.

The real factors in the relation between body weight and health are

  • amount of muscle
  • amount of fat

I showed extensively in my book Muscle Up just how and why having a relatively large fraction of body weight as muscle, and a low fraction as fat, is extremely important for health. That doesn’t mean you need to look like or be a bodybuilder, only that virtually everyone should do resistance training to enhance their muscle mass and keep muscles in good metabolic shape.

A skinny-fat person is simply someone whose relative proportions of fat and muscle are skewed in the wrong direction, i.e. too much fat, not enough muscle, while being of a “normal” weight.

People in  the highest tertile (third) of body fat had 4 times the risk of metabolic syndrome, the prelude to diabetes, than did people in the lowest tertile.1

For men, that was at a body fat of >23%, and for women, >33%.

When these people were grouped by waist size, the results were even worse. See chart below.

normal weight obesity risks


Those in the highest third of waist size had around 60 times the risk of cardiovascular disease than those in the lowest third.

Keep in mind that all of these people had a normal body weight, with body mass index of <24.9.  Also keep in mind that by definition, one third of all people (in that study, which should be representative) were in the top third of body fat percentage.

For good health, you must avoid the skinny-fat phenotype.

Causes of the Skinny-Fat Phenotype

As is to be expected in any case of body composition, the causes of the skinny-fat phenotype can be boiled down to two: diet and exercise.

Diet: Lack of sufficient protein and excess carbohydrates will tend toward the loss of muscle and the gain of fat. Excess carbohydrates also adds a double whammy in that they will predispose to insulin resistance, the cardinal feature of the metabolic syndrome. In turn that leads to hypertension, abnormal blood lipids, and eventually atherosclerosis.

Exercise: Insufficient exercise also leads to loss of muscle and fat gain. Not only insufficient exercise, but doing the wrong kind of exercise, namely, so-called aerobic exercise or “cardio”.

Measuring the Skinny-Fat Phenotype

How do you know whether you’re skinny-fat?

First, you must have a normal BMI, less than 25. If you are over this, you’re just plain fat — although there are exceptions, such as in very muscular people, mainly amateur or professional bodybuilders or other athletes.

The gold standard for determining normal weight obesity, or the skinny-fat phenotype, is body fat percentage, and to be done accurately requires a DEXA scan, which can be done at clinics or hospitals.

A faster, cheaper method is to measure your waist circumference.

Your waist circumference should be one half (0.5) or less of your height.2 While this method was developed to test for obesity in children, it’s applicable to adults too.3

In the study cited above, tertiles of waist circumference, from lowest to highest, and in men and women respectively, were:

  1. < 31.4 and < 29.4 inches
  2. 31.4 to 34.4, and 29.4 to 32.2 inches
  3. >34.4 and > 32.2 inches

(See chart above for dimensions in centimeters.)

In terms of body fat percentage, the lowest (safest) tertile for men was <18%, and for women, <27%.

If you fall into any category other than the lowest in terms of waist size or body fat percent, you have work to do.

How to Stop Being Skinny-Fat


If you are not already, increase your protein intake to 1.2 to 1.8 grams per kilogram of body weight. For a 70 kg man, that comes to 84 to 126 grams a day. Do this by eating meat, eggs, and dairy. Eating adequate protein increases muscle growth and decreases fat mass.

Cut out the refined carbohydrates and sugar, which lead to increased fat mass.


Forget the aerobics/cardio. Lift weights.

Aerobic exercise can lead to muscle loss, which you’re trying to avoid, and will not put on muscle.

Lifting weights will add muscle and decrease fat. There’s nothing like it.

By lifting weights, you’ll improve your insulin sensitivity in two ways:

  1. Better body composition through more muscle and less fat leading to better whole-body insulin sensitivity
  2. Direct action of lifting weights on skeletal muscle insulin sensitivity


As we’ve seen, the top one-third of people in waist size or body fat percent, with a normal body mass index, are at risk for a slew of diseases, through the mechanism of insulin resistance.

So don’t count on the fact of a normal BMI to keep you in good health.

Even if you’re not overweight, you need to keep your body fat percent down.

And you can do this through eating right and lifting weights.

PS: Read my book Muscle Up to see why everyone should lift weights, and how to do it.

PPS: Check out my Supplements Buying Guide for Men.


  1.  Romero-Corral, Abel, et al. “Normal weight obesity: a risk factor for cardiometabolic dysregulation and cardiovascular mortality.” European Heart Journal (2009): ehp487.
  2.  McCarthy, H. David, and Margaret Ashwell. “A study of central fatness using waist-to-height ratios in UK children and adolescents over two decades supports the simple message–‘keep your waist circumference to less than half your height’.” International journal of obesity 30.6 (2006): 988-992.
  3.  Ashwell, Margaret, and Shiun Dong Hsieh. “Six reasons why the waist-to-height ratio is a rapid and effective global indicator for health risks of obesity and how its use could simplify the international public health message on obesity.” International journal of food sciences and nutrition 56.5 (2005): 303-307.

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  1. ted says:

    Thanks pd. Are you familiar with hyperthermic conditioning and its positive effects? If so what are your thoughts on it?
    I was reading dr Rhonda Patrick’s material on it, sounds very exciting

    • P. D. Mangan says:

      I’m tolerably familiar with it and it seems legit, though I don’t have anything to add beyond what Rhonda Patrick has said. I don’t have access to a sauna myself so I haven’t tried it. Cold showers may have some of the same benefits, through activation of heat shock proteins – which lead to increased autophagy.

  2. Nicholas says:

    I need to finally ask about body types. I know the 3 (mesomorph, ectomorph, endomorph) are points on a plane, but I’ve never figured out where I (naturally) belong on it. When I was skinny I wasn’t skinny-fat, and now I’m coming back down from simply overweight to what I should be – but knowing the natural type seems like it could help.

    In my natural state (that of high school/college, before years of desk jockeying took its toll) I was very tall and slim: 6’4″ and, as a high school senior, 185#. I was actually much thinner than that sounds, because I have absurdly heavy and thick bones. Junior year I weighed 175# but working out added that 10# of muscle, even knowing as little as I did. I was a swim sprinter: no long distance for me, since I sank like a rock.

    Since then I have added a fair bit of muscle and way too much fat, but I sense that my correct weight will show my actual body type, my actual starting physique. So how does that classify: tall, slim, heavy bones, fairly broad shoulders? I’m like a reinforced ectomorph, and I’ve never heard of such a thing.

    • P. D. Mangan says:

      That sounds about right. if you look at older photos of American men, you see, or it seems like, the majority of men were ectomorphs. That being the natural state that featured a decent diet, or at least not too much food, and plenty of physical activity.

      • Nicholas says:

        Ectomorphs are always described as light-boned and narrow-shouldered, which ain’t me at all, but the rest of it fit (pre-desk-jockey). Thank you! I’ve been looking for a solution to this for a while, now.

  3. Lee says:

    Over the last couple days while researching about longevity I bumped into quite a bit of research showing that increased protein, and in particular BCAA’s, contribute to metabolic syndrome/obesity/diabetes/shortened lifespan.

    It seems counterintuitive that the long-lived people of the so-called “Blue Zones” largely have in common low protein and fat and super high carb intake but that is what they do (mostly).

    This citation may not be the best example but if a person is curious they know where to look. I was shocked as I have been a low carber/high fat guy and have a physique and bodyfat similar to Bruce Lee but more muscular. Perhaps my diet choice earned me the stent I got last year.

    • Ole says:

      BCAA is an excellent choice for muscle gain, but apart from driving up mTor, it apparently also carries some extra risks for developing ALS (in bodybuilders/athletes at least) and for development of diabetes2, caused by an imbalance in gut microbiome.

      • Lee says:

        To me, the take-away point is that excess protein (>1 gram per kg BW) is unhealthy since most protein consumed as food or supplements have BCAA’s as a component.

        Protein cycling likely reduces total protein necessary by providing it intermittently when needed instead of chronically.

        • bigmyc says:

          It’s important to remember that protein is quite insulinogenic. I know from experience, that when I resistance train to get bulked up, even when I’ve eaten a low carb diet, the calories needed to fortify my anabolic endeavor are derived from more fat but of course, more protein…in some cases, a lot more protein. Invariably, I end up acquiring adipose tissue along with muscle. “Cutting” is easy enough though. It just stands to reason that perhaps your pulmonary issues are the result of the insulin spikes that high amounts of protein will cause…..I mean, you did say that you are more muscular than Bruce Lee….

      • Lee says:

        Thanks PD. Mouse studies are useful for clues but are you aware of any high protein consuming human population groups that are long-lived?

        The only long-lived groups I am aware of all consumed very low and mostly plant-based protein.

        • P. D. Mangan says:

          So, you posted a link to a study in which rats were fed a high-fat diet plus BCAAs and they developed insulin resistance. Yet you say the mouse study I posted isn’t relevant. Help me out here – I’m not seeing your logic.

          The metabolomic profiles of obese and lean humans (same study) doesn’t mean what you think it does. The authors of the study say it plainly in the first sentence: “Metabolomic profiling of obese versus lean humans reveals a branched-chain amino acid (BCAA)-related metabolite signature that is suggestive of increased catabolism of BCAA and correlated with insulin resistance.” It has nothing to do, so far as we know, with what they were eating, which was not measured.

          “Thus, obese subjects appear to have a [physiological] preference for oxidation of non-lipid fuels (glucose and amino acids) compared to lean controls (as indicated by the higher RQ), even though they have substantially larger total, subcutaneous, and visceral fat depots.” This means that they are breaking down muscle tissue for energy. It has zilch to do with dietary BCAAs.

          As for those long-lived Blue Zone people, are there any studies that show that they eat less protein than others? If they don’t, then the reason they live longer is not due to protein. They also have lots of other characteristics like a high level of physical activity, close social ties, religious beliefs, less iron in their bodies, high relative consumption of fish (which is high in protein BTW), sometimes fasting (among Eastern Orthodox). None of those people so far as I know exclude eggs, meat, fish, cheese, yogurt, and the like from their diets.

          • bigmyc says:

            Very nice, P.D. Eloquently put as well.

            You never know when someone has an agenda and even more to the point, if that agenda leads one to intellectual dishonesty either wittingly or unwittingly.

            Of course, the case could always be that someone has misinterpreted information at face value but concerning the study link that the precious poster provided and thus their immediate dismissal of a study with essentially the same subjects, it seems suspicious.

            With all due respect to that poster, I thought that I smelled a rat. Pun intended.

          • Lee says:

            No agenda, just sharing a discovery. Won’t post any more links as the information is out there to be discovered.

            Best wishes.


  4. bigmyc says:

    In other words, these tulips are not jacked.

  5. AJ says:

    Excellent article.

    Although I think it was on this blog that I found you had a reference showing correlation of HIIT with decreased biomarkers of insulin resistance. Not sure which article but it was a study on swimmers doing 6-10 cycles of HIIT for 6 months. Diet was not controlled. Surely this is evidence that HIIT on its own also has significant benefits.

    BTW I like the new banner photo. Nice car. I read this at work and I did used to get some questionable looks before.

  6. Belovar says:

    I think I fall into the skinny-fat category. But due to some medical reasons I can’t do weight training or HIIT at the moment and for the forseeable future.

    I think I eat enough protein, and overall I eat very little carbs, and quite alot of fat (mostly from dairy).

    Is there anything else that can be done to to improve ones muscle-fat ratio, except from weight lifting or HIIT?

    • P. D. Mangan says:

      I think I’d concentrate on fat loss with adequate protein, assuming you have difficulty with exercise.

      • Belovar says:


        Should that be done with caloric deficiency? Or just diet + intermittent fasting?

        Do you think that is possible without loosing muscle? Or is it inevitable that muscle loss will occur without exercise, but that the ratio will improve?

        Also, what’s your take on Mark Sisson?

        • P. D. Mangan says:

          I’m not a big believer in calorie counting. A decent low-carb diet and fasting would be my preferred way – keeps you from getting hungry and blowing all the calorie-counting. Retaining your muscle without exercise could be difficult; your best shot is to keep your protein intake high.

          As for Mark Sisson, I think he’s great and I can’t offhand think of anything I disagree with him on.

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