On Mon, 4 Mar 2002, Adrienne Smith wrote:

> Thanks so much for responding -- your thoughts are very helpful.  I am a bit
> confused though regarding how consuming saturated fat can increase
> cholesteral levels -- I thought that low carb advocates say the exact
> opposite.

Low-carb advocates say that the cause of elevated cholesterol is
insulin, which stimulates the liver to produce more cholesterol.
So if you reduce insulin you reduce cholesterol.  This is true,
but not the whole truth.  Another factor is that certain
saturated fats (palmitic and myristic acids, maybe others) have
the effect of downregulating hepatic LDL receptors, slowing
cholesterol reuptake.  A Nobel Prize was awarded for this
research some years back, in fact, as it had been a mystery how
saturated fats had any effect on cholesterol at all.  A third
factor, possibly, is one that we have been discussing recently,
i.e., that saturated fats alter cell membrane fluidity, making
them less permeable to insulin and thus increasing insulin
resistance, which would then cause elevated cholesterol by the
first route.  It is still unclear, to me anyway, whether this is
actually caused by SFA abundance or EFA shortage.

In short, there are two variables here: the rate at which
cholesterol enters the blood and the rate at which it exits.
Saturated fats may have an effect on both.  A further factor
affecting the exit rate is soluble fiber, which binds to the
cholesterol-laden bile salts and pulls them from the body.
Insoluble fiber may have an effect too, by reducing gut transit
time, so there is less opportunity for the reabsorption of
cholesterol in the gut.

> Could it be that some individuals are more "sensitive" to dietary
> saturated fat??

It certain looks that way.

> Also, why are high HDL levels are supposed to be "desirable"
> when they can also be a symptom of hypothyroid?

Because HDL particles are the ones that bring cholesterol back to
the liver to be recycled.  I had not heard that high HDL is a
sign of hypothyroid.

> I am going to give the
> Cordain Paleo Diet version a few weeks, but if I continue to gain, I'll go
> back to ultra-low carb so I can lose weight .  It is very discouraging to
> think that the only diet that has allowed me to lose weight (ultra low-carb)
> also makes me constipated and tired at the gym.

Try limiting fruit to no more than a cup per meal.

Todd Moody
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