Insulin has a relatively short life in circulation, similar to
C-peptide, which is why C-peptide is a good surrogate, and why
intermediate and long acting insulins have to be stored in a
biologically inactive intermediat form until needed (proinsulin, or as
a hexamer attached to a Zinc Protamine molecule).

Minimed at least to claim the 1500 rule.  Take your daily insulin
requrement, 1500 by the number of units, and you have the grams of
carbohydrate 1 unit of insulin will cover.

Igor wrote in message ...

 AFAIK,  insulin is destroyed very rapidly after release to the blood.    I
have seen at least one medical citation to that effect but Lord knows where.

By "carbs per unit of insulin" rules, I assume you are talking about the
1500 rule,  the 1800 rule, and the 500 rule.

These are wholly arbitrary,  totally empirical,  and only approximate rules.
They are good starting points.   They were devised by a genius** of a doctor
whose name I have lost.   I think he practices in Atlanta.    He figured out
these rules which the CDE I know use all the time.

(**  In his spare time, I think he writes reference books on economics)

A way to look at them analytically:

1800 rule:

 a.  A 200 lb male T1 might be expected to eat 300 gram of carb per day.
 b. Each gram of carb contributes 3 mg/dL to his daily blood sugar.
 c.  That means he needs a daily bolus containing enough insulin to handle
300 x 3 = 900 mg/dL
 d.  If he is anywhere close to control,  then one can calculate his
bG/insulin response by dividing 900 mg/dL by his daily bolus
 e.  However,  it is easier, and more accurate if he is using a peaky basal
like NPH,  to just sum all of his daily insulin and use that in the
calculation.
 f.   In theory,  his basal is about 50% of his total daily insulin.
Therefore, to simplify the calculation,    double the 900 mg/dL and divide
by the total daily insulin.  q.e.f.  a simplistic derivation of the 1800
rule.

   Therefore,  divide 1800 by his total daily insulin to determine his
"tweak" ratio,  or how much insulin he must shoot to knock down a peak.

500 rule

a.  Assume the diabetic eats about 250 gram carb per day   (last ADA diet I
saw said aim for  200 - 300 gram/day)
b.  To calculate his carb to insulin ratio,  divide 250 by his total daily
bolus  (assuming he is close to control)
c.  See "e" and "f" above.   It is easier and more accurate to sum his
total daily insulin,   double the 250 gram of carb per day, then divide the
resultant 500 by his total daily insulin to derive his carb per unit insulin
ratio for calculating a bolus.

Derivations full of "If's , assume's, guesses and sort of's"  but they work
well as **** Predictive Starting Points ****.

Regards
 Old Al

.

Analogy time. You have 10 super soldiers. You're facing an army of
5000. Each guy takes out 10 of the evil Carbohydration army before
they die.

Both questions answered. The transference of sugar to fuel burns up
the insulin completely as it hits your bloodstream over time.

And the 10/1 rule? Been using it for about 8 or 9 years, but my level
is more like 1/12, whist my wife's is more like 1/8. You'll figure it
out by trial and error, but do take the time to do so. It's handy for
those unexpected snack sessions...