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A number of readers asked if the association between body type and temperament could be altered by losing or gaining weight. For example, can a skinny ectomorph assume some of the personality traits of a mesomorph by lifting weights and putting on muscle? Or can a fat endomorph do the same by losing fat and toning up? Likewise, can a mesomorph become less insensitive by getting fatter or skinnier? Being able to do so would seem to discredit the idea that body type and personality are biologically linked.
My answer to them is a qualified yes, based on nothing more than drawing conclusions from real world test cases mixed with a bit of educated speculation and adjustment of premises.
First, body type is not based on your weight. Or, it’s not supposed to be. It’s based on your skeletal frame, which is unalterable (except in small degrees by intensive weightlifting or PED use). A mesomorph may gain fat or lose muscle, but his generally larger, broader frame will stay the same. Similarly, an ectomorph can beef up in the gym, but his wrists and ankles will never be naturally thick around like a classic endomorph’s or mesomorph’s wrists and ankles.
Therefore, the premise itself is shaky. Weight may change, but bone structure remains the same. And if the bone structure is the same, then the link with one’s personality is the same as well.
Second, a large gain of muscle (or a loss of fat) can psychologically influence a man’s self-perception and boost his confidence, leading to a concomitant temperament change. This can occur despite there being no alteration of the biological link between his frame size and his temperament. We are adaptation maximizing animals, after all.
Those objections aside, I answer the readers with a qualified yes, because I do think the underlying biological connection between body type and personality can be fundamentally altered. The simple explanation is testosterone. Fat is a known T suppressor/estrogen increaser, so an endomorph who sheds fat cells will experience the effects of a hormonal boost of T. An ectomorph who puts on muscle will feel better and more confident from the increase in his T. These are deep, biological changes, not ephemeral psychological alterations, that will lead to personality changes.
Caveat: the changes aren’t going to be large. You can’t change the intrinsic contours of your personality wholesale by raising your T, because we are gradually learning that a lot (50% or more) of our personality is genetically conditioned, stamped in our cortical rivulets as permanent etchings from conception. But you can make changes around the edges, pushing yourself in one direction or another. Testosterone isn’t the only way to do this. Changes in status have also been shown to alter personality. If you are looking to improve your success with women, even a small, say 10%, change in your personality to one that is more outgoing or confident will bring huge pussy benefits relative to what you were accustomed to enjoying.