Insulin is Extremely Anabolic

Summary: In 14 healthy volunteers, forearm insulin
concentrations were raised 1,000-fold above basal levels while maintaining
euglycemia for 4 h. Amino acids (AA) were given to either maintain basal arterial
(n = 4) or venous plasma (n = 6) AA or increment arterial plasma AA by 100% (n
= 4) in the forearm. Measurements were taken of forearm muscle glucose,
lactate, oxygen, phenylalanine balance, and [3H]phenylalanine kinetics at
baseline and at 4 h of insulin infusion.

Results: Extreme hyperinsulinemia strongly reversed
postabsorptive (fasting) muscle’s phenylalanine balance from a net release to
an uptake. This marked anabolic effect resulted from a dramatic stimulation of
protein synthesis and a modest decline in protein degradation. Furthermore,
this effect was seen even when basal arterial or venous aminoacidemia was
maintained. With marked hyperinsulinemia, protein synthesis increased further
when plasma AA concentrations were also increased. Forearm blood flow rose at
least two fold with the combined insulin and AA infusion, and this was
consistent in all groups. These results demonstrate an effect of high
concentrations of insulin to markedly stimulate muscle protein synthesis in
vivo in adults, even when AA concentrations are not increased. This is similar
to prior in vitro reports but distinct from physiological hyperinsulinemia in
vivo where stimulation of protein synthesis does not occur. Therefore, the
current findings suggest that the differences in insulin concentrations used in
prior studies may largely explain the previously reported discrepancy between
insulin action on protein synthesis in adult muscle in vivo vs. in vitro.

Discussion: Insulin is an obvious topic of interest among
the largest physiques in the culture of bodybuilding. In my search for
definitive answers as to the anabolic potential of exogenous insulin
administration, I have been sorely disappointed in the lack of human studies
showing the anabolic properties of insulin in adults. Many studies show insulin
to slow protein break down but data showing insulin to be truly anabolic in
muscle tissue was virtually non-existent. Despite this lack of clinical
evidence, insulin use still pervades in bodybuilding.

There are a few things that need to be addressed when
considering this study. First, the amount of insulin used in this study is
extemely high. The quantities of insulin used are far above what should ever be
attempted by bodybuilders. Second, the anabolic properties of extreme
hyperinsulinemia are likely do to insulin’s interaction with IGF-1 receptors,
not traditional insulin receptors. Finally, the anabolic effects of extreme
hyperinsulinemia were only seen with concomitant amino acid infusion. This
means that if there are no amino acids floating around, you will not build
muscle no matter how much insulin you are using.

The high levels of insulin used in this study are not
practical for bodybuilders to consider using. The subjects blood glucose was
kept constant through artificial means to prevent hypoglycemic coma. In other
words kiddies, DON’T TRY THIS AT HOME! Besides the danger involved with raising
insulin levels 1,000 times above normal without a controlled infusion of
glucose, it isn’t really necessary if you want to get an anabolic response.
Think of what was done in this study like flooding the basement in order to
water the lawn. The anabolic effects produced in this study were most likely
due to excess insulin binding to hybrid IGF-1 receptors. The same effect through
can be achieved without all the insulin by simply adding a little IGF-1. After
all, you should always use the right tool for the job. I will admit that
further research is necessary to further support my (and the authors of this
study) assertions that the anabolic effect of insulin seen in this study was
caused by interaction of insulin with IGF-1 receptors. Nevertheless, it would
be nice to see bodybuilders use less insulin and perhaps begin to incorporate a
mixture of compounds that more closely resembles the complex interaction of
hormones which exist naturally in the body.

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