Is Muscle/Mass Genetic and How Does It Affect Skinny Fat?

Is muscle/mass genetic? Genetics are the foundation of the human body and muscle/mass tissue is highly heritable (1, 2). Some people are genetically blessed with fully developed muscle/mass, as per the Standard Body Type One (BT1)(3, 4). Others, not so much.

Technically, there are two types of muscle fibers (5, 6, 7, 8, 9): slow twitch (Type I) and fast twitch (Type II, A & B). Type I slow twitch muscle fibers, AKA red fibers because they contain more blood-carrying myoglobin, can provide their own source of energy and sustain basic force for an extended time while being resistant to fatigue. For instance, the muscles responsible for maintaining posture have a higher density of slow-twitch fibers. More aerobically efficient, these fibers are particularly receptive to muscular endurance (toning).

Whereas, Type II fast twitch muscle fibers, AKA white fibers because they do not contain much blood, are defined by two variations. Type IIA fibers are fast oxidative glycolytic, use oxygen to help convert glycogen to ATP, and are relatively resistant to fatigue. Type IIB fibers are fast glycolytic, rely on ATP stored in the muscle cell to generate energy, and fatigue rapidly. Fast-twitch muscle fibers are more suited for strength, power, and explosive performance.

Is Muscle/Mass Genetic and How Does It Affect Skinny Fat?

The total number of default genetic muscle fibers a person has is set at or around birth (10, 11, 12, 13). The rate of muscle growth is by far the greatest in the late stages of pregnancy and in the early postnatal period. At this time, the only reliable way to accurately know how much genetic default muscle/mass tissue you have is via a Magnetic Resonance Imaging (MRI)(14, 15) scan, which is very expensive and uncommon. The only way to know your Type I and Type II muscle fiber ratio is through an invasive muscle biopsy (16, 9), which is also expensive and uncommon.

Thus, the vast majority of human beings — nearly all — have no idea what their genetic muscle/mass measurements are and never have. Their doctors do not know. No one knows. But we do know that many people are born with less muscle mass. Just as we know genetics play a significant role in how much muscle a person can build (17, 18, 19, 20, 2, 12), including the BCL6 gene. 

What Happens When a Person is Born with Deficient Genetic Default Muscle/Mass Tissue?

Is any missing/lacking genetic muscle/mass tissue replaced by something, like fat? What kind of fat? Did research participant 1170 (21) lose muscle mass during their weight loss? Or did they never have the genetic default muscle/mass tissue from birth?

They started their regular fat weight loss within safe/healthy Standard BMI at 24.6 — meaning by scientific/medical BMI definition (22, 23, 24, 25, 26), they have no excess regular white/yellow fat (adipose tissue, the main kind of body fat). This is literally how doctors discern the difference between healthy weight and being overweight or obese. A person cannot have too much regular white/yellow fat and be within safe BMI – it is 100% contrary to and destroys the BMI definition (yes, we know the Standard BMI is inaccurate, but it is the current standard (27, 28) and better than no standard at all).

Does Genetic Skinny Fat Tissue Replace Genetic Default Muscle/Mass?

Research participant 1170 is clearly experiencing normal weight obesity. The excess body fat tissue all over their body — which cannot be and is not regular white/yellow fat (adipose tissue) — is skinny fat tissue in the form of thin fat and cellulite. They lost even more regular fat weight and got down to BMI 21.3, yet the genetic default muscle/mass (as per the Standard Body Type One) did not magically appear. The skinny fat tissue is still clearly evident in all the same places it was at BMI 24.6.

In fact, they could lose regular white/yellow fat tissue all the way down to safe BMI 18.5, and the genetic default muscle/mass that every Standard Body Type One (BT1) has, will not magically appear. This person is not a Standard BT1. They are likely a genetic scientific Body Type Three (BT3)(27), which is defined by how much skinny fat tissue they have relative to vertebrae.

Lost Muscle/Mass Tissue Is Not Replaced By Any Kind Of Fat

Many people claim that they just lost muscle mass during weight loss. And now they have regular fat tissue where the muscle tissue was. But what they are claiming is that muscle tissue turned into fat/skinny fat tissue, which is not possible (29, 30, 31). Here is Christian Bale when he lost a severe amount of weight for a movie role:

He lost obvious muscle mass, yet no skinny fat tissue. Genetics. Even when emaciated the muscle definition is crystal clear. Those people making such claims have no explanation. Or like this 22.7 BMI person with obvious skinny fat tissue on his lower back and love handles:

Why did only the muscle on his love handles and lower back turn (impossible)(29, 30, 31) into skinny fat? With no explanation for any of that, the same people will shout “stop using genetics as an excuse!” while continuing their outrageous claims by further claiming that with enough hard work with diet and exercise, especially protein and weightlifting, you can turn your skinny fat tissue into muscle tissue (impossible)(29, 30, 31). The best news of all is, thanks to epigenetics, the work you do is permanent (it is not).

Alas, none of that is true (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44). Added muscle mass (above and beyond genetic default) due to epigenetic body recomposition (which does temporarily increase muscle fibers) changes from exercise and diet, no less, is gradually lost if the exercise that built it ceases consistency and regularity. Epigenetics are not permanent. Muscle cannot turn into fat or vice versa. Genetics are not an excuse when it comes to default genetic body composition – how much muscle/mass tissue and skinny fat tissue a person has from birth.

Although, genetics are, indeed, not an excuse to be unhealthy. The more skinny fat tissue you are experiencing the more diligent you will have to be with healthy, science-based diet, exercise, and lifestyle choices throughout your life to be a healthy weight and remain healthy.

Is Muscle/Mass Genetic and How Does It Affect Skinny Fat?

All that said, with enough hard work you can reduce any skinny fat tissue you have by safely losing regular white/yellow fat weight and adding muscle mass; you may even look like the Standard BT1 (or close) And with enough hard work consistently and regularly throughout your life, you can possibly maintain those changes. Moreover, maybe, if you are one of the very rare few people who tempt evolution and cause a positive genetic mutation (45, 46, 47, 48) that is permanent, you might pass it on to your next generation progeny.

Yes, muscle/mass is genetic while being directly influenced by diet, exercise, and lifestyle. The more genetic default muscle/mass you are lacking/missing, the more skinny fat tissue you have. The more skinny fat tissue you have, the more it affects your regular white/yellow fat weight loss and gain efforts as well as metabolism (49), diet (50), exercise (51), and lifestyle (52). The Scientific Health Quizzes help make sense of all of that, free options are available.

References

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