Testosterone and Appetite
A few men
Peak Testosterone Forum
who have started HRT have reported increased appeitite and have
wondered if the
two are related. The answer, it turns out, is surprisingly involved. First of all, testosterone definitely affects the two most
well-known appetite and hunger hormones, gherlin and leptin.
Let's start with leptin. Leptin is proportional to body fat and, therefore
the more overweight you are, the higher your leptin levels. And rising leptin levels slowly turn
off your appetite, which, of course, is a good thing if you have put on some extra
weight. However, the reverse situation can really cause men difficulty when dieting:
as you lose weight, your leptin falls and hunger increases. This, of
course, makes it significantly more difficult to stick with a diet (along with a
dozen other nasty hormonal changes including plummeting testosterone levels that I
discuss in my link on Why Crash Dieting
Usually Does Not Work).
So how does testosterone tie into this? Simple: researchers have
noted that leptin goes down if you put a man on testosterone. One study
found that the "serum leptin concentration correlated inversely with that
of testosterone in elderly men. This inverse correlation was still present when
body mass index and plasma insulin were included in the analysis. The
administration of testosterone to young men suppressed serum leptin from the
pretreatment level of 3.4 ± 1.4 to 1.9 ± 0.6 μg/L during the therapy. After
cessation of testosterone injections, serum leptin concentration returned back
to the pretreatment level." 
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The authors went on to say that testosteone is a a kind of leptin suppressor
actually and, of course, this will be good for your weight management.
Therefore, all things being equal, it does appear that testosterone could
increase appetite, right?
Well, it turns out that is probably not the case and here is why: hypogonadal
men tend to have overly high leptin levels and giving them testosterone merely
brings them back to where they should be. One study stated that "we conclude that
hypogonadal men exhibit elevated OB [prolactin] levels that are normalized by substitution
with T." 
And this is verified by the fact that many stuidies have shown that men
who go on HRT (testosterone therapy) actually lose weight. In fact, they
lose weight without making any other change except increasing testosterone.
In addition, they
gain muscle as well. So even if testosterone does increase
appetite a little through leptin reduction, this is apparently more than
compensated for by something else, including things like
a) increasing a man's desire to workout due to mood elevation and improved
recovery, b) lower insulin levels and
c) lower cortisol "reactivity." (The latter two should help a guy
better manage visceral fat.) Again, though, testosterone in hypogonadal
men more than just returns them to their baseline levels.
But there is yet another reason that testosterone may actually control appetite
in men: gherlin. As I discuss in my link on Weight Loss
and Your Hormones, gherlin is another big player that has been the focus of
significant research in the last 10-15 years.
Gherlin is the opposite of leptin in the sense that, as body fat increases,
gherlin levels tend to decrease as shown by the fact that weight loss through
dieting increases gherlin levels (in obese individuals).  Furthermore,
ghrelin levels increase significantly right before a meal and drop shortly
after. In other words, increasing gherlin means increasing appetite.
One study found that control-matched men has significantly lower gherlin levels
and that giving them testosterone restored their gherlin levels to normal. 
Now this may seem like a bad thing, because one would want gherlin as low as
possible to suppress appetite, right? Well, not so fast. It turns
out gherlin is VERY important for the brain and having adequate levels may be
critical for protecting the all-important hippocampus. Researchers noted that
"Here we report that circulating ghrelin enters the hippocampus and binds to
neurons of the hippocampal formation, where it promotes dendritic spine synapse
formation and generation of long-term potentiation. These ghrelin-induced
synaptic changes are paralleled by enhanced spatial learning and memory.
Targeted disruption of the gene that encodes ghrelin resulted in decreased
numbers of spine synapses in the CA1 region and impaired performance of mice in
behavioral memory testing, both of which were rapidly reversed by ghrelin
In other words, artificially lowering gherlin is NOT a good idea and, once
again, testosterone is protecting your brain. (See other examples in my
page on Testosterone and the Brain.)
Thus, generally speaking, testosterone should not increase
your appetite to unhealthy
levels but rather just return them to your normal, youthful baseline levels.
And I suspect that the reported increase in appetite from testosterone therapy
is usually resulting from the longer, harder workouts from
finally feeling good.
The Journal of Clinical Endocrinology & Metabolism, Sep 1 1998, 83(9):3243-3246,
"Inverse Correlation between Serum Testosterone and Leptin in Men"
2) N Engl J Med, 2002 May 23, 346(21):1623-30, "Plasma ghrelin levels after
diet-induced weight loss or gastric bypass surgery"
3) The Journal of Clinical Endocrinology & Metabolism, Aug 1 1997,
82(8):2510-2513, "Testosterone Substitution Normalizes Elevated Serum Leptin
Levels in Hypogonadal Men"
Testosterone therapy J Clin Endocrinol Metab. 2003 Sep;88(9):4139-43,
"Testosterone replacement therapy restores normal ghrelin in hypogonadal men"
5) Nature Neuroscience, 2006, 9:381 - 388, "Ghrelin controls hippocampal spine
synapse density and memory performance"