Insulin: An anabolic hormone

Someone on my insulin resistance list took extreme exception to my post there yesterday on insulin response (upon which my blog post yesterday, “Insulin response: It ain’t just the carbs” is based).

I’d quoted from “The Anabolic Power of Insulin: An Interview with John Berardi”:

The current rage in health and fitness is to manage the hormone insulin. But few people really understand this temperamental hormone. You see, insulin is an anabolic giant.

My correspondent didn’t see it at all that way. Insulin, she claimed, is the hormone that “stuffs carbohydrates into fat cells,” an action that she deems as catabolic, not anabolic.

Never mind that catabolic means “breaking down,” & that building fat cells or stuffing things into fat cells isn’t breaking down, but building up — i.e., is anabolic, albeit of fat cells, not the muscle we care about. So she got her terminology mixed up: I did understand what she meant.

She is essentially claiming that insulin’s action is entirely geared toward managing our blood glucose — in ways that aren’t very beneficial to the insulin resistant person or any other person who already has too much body fat. Insulin takes those excess carbs we eat — the stuff that goes beyond what we need to give our brains energy, & replenish the glycogen stores in our muscles — & deposits it into our fat cells.

It does do that. And up until two days ago, I would’ve agreed with her that that’s all insulin really did.

But I would’ve been wrong. And today, I went to PubMed (something she often advises people to do) to back it up.

Several quotations from abstracts of studies located at PubMed based on a search on the terms “protein insulin amino muscle”:

Insulin induces protein accretion by stimulating protein synthesis and inhibiting proteolysis. However, the mechanisms of regulation of protein metabolism by insulin are complex and still not completely understood…. Finally, although the role of insulin has been doubtful and has long been considered to be minor in ruminants and in avian species, this hormone clearly regulates protein metabolism in both species.

[Tesseraud S, Metayer S, Duchene S, Bigot K, Grizard J, Dupont J. “Regulation of protein metabolism by insulin: Value of different approaches and animal models.” Domest Anim Endocrinol. 2006 Jun 30]


Despite being an anabolic hormone in skeletal muscle, insulin’s anti-catabolic mechanism in humans remains controversial with contradictory reports showing either stimulation protein synthesis (PS) or inhibition protein breakdown (PB) by insulin…. In conclusion, using amino-acyl tRNA as the precursor pool, it is demonstrated that in healthy humans in the postabsorptive state, insulin does not stimulate muscle protein synthesis and confirmed that insulin achieves muscle protein anabolism by inhibition of muscle protein breakdown.

[Chow LS, Albright RC, Bigelow ML, Toffolo G, Cobelli C, Nair KS. “Mechanism of Insulin’s Anabolic Effect on Muscle – Measurements of Muscle Protein Synthesis and Breakdown Using Aminoacyl tRNA and Other Surrogate Measures.” Am J Physiol Endocrinol Metab. 2006 May 16]


Insulin promotes muscle anabolism, but it is still unclear whether it stimulates muscle protein synthesis in humans. We hypothesized that insulin can increase muscle protein synthesis only if it increases muscle amino acid availability…. In conclusion, physiological hyperinsulinemia [high insulin levels] promotes muscle protein synthesis as long as it concomitantly increases muscle blood flow and amino acid availability.

[Fujita S, Rasmussen BB, Cadenas JG, Grady JJ, Volpi E. “The effect of insulin on human skeletal muscle protein synthesis is modulated by insulin-induced changes in muscle blood flow and amino acid availability.” Am J Physiol Endocrinol Metab. 2006 May 16]


A reduced response of older skeletal muscle to anabolic stimuli may contribute to the development of sarcopenia [the degenerative loss of skeletal muscle mass and strength in the aged]. We hypothesized that muscle proteins are resistant to the anabolic action of insulin in the elderly…. In conclusion, skeletal muscle protein synthesis is resistant to the anabolic action of insulin in older subjects, which may be an important contributor to the development of sarcopenia.

[Rasmussen BB, Fujita S, Wolfe RR, Mittendorfer B, Roy M, Rowe VL, Volpi E. “Insulin resistance of muscle protein metabolism in aging.” FASEB J. 2006 Apr;20(6):768-9.]

There are others, but this is enough to confirm that the scientific community assumes, as a matter of course, that insulin plays an anabolic (building up) and anti-catabolic (breaking down) role with regard to muscle. A lot of the research has to do with exactly how it does that, & at least one study (the first one above) concludes that it does by preventing by inhibiting the breakdown of muscle proteins, rather than by stimulating the synthesis of new proteins, at least in some states. (I’m sure other studies will be conducted to try to duplicate or refute those results.)

So it turns out that John Berardi is right: insulin is anabolic with regards to muscle. Whether he’s right in some of his specific recommendations, I don’t know, but I sure feel confirmed in my belief that his stuff is worth checking out further. And in feeling that the whole picture of insulin is a lot more complex than insulin being just “the hormone that stuffs carbohydrates into fat cells.”

I don’t know yet what this means in terms of what insulin resistant people like me should do about it. I aim to find out.

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