There have been scads of scientific
papers published on this subject. I promise not to cite any of them in this piece. Instead, I will offer the example
of two people’s A1c’s and fasting glucoses to illustrate the wisdom of using
the A1c rather than the fasting blood glucose in diagnosing incipient or “incident
T2DM” (see The Nutrition Debate #182).
Until a few years ago the ADA
criterion for diagnosing T2DM (Type 2 diabetes) was 2 consecutive fasting blood
glucose tests (on separate office visits) of ≥126mg/dl. The ADA also guided that a
fasting value of 100-125mg/dl was to be considered “Pre-diabetic.” A “normal” fasting
glucose was then 70-100mg/dl.
The A1c increasingly became the diagnostic
tool of choice in 2009, although the fasting glucose test, while seriously
flawed, is still widely used. So, what is the A1c test? Technically, the A1c (glycated
hemoglobin A1c), is a percentage measurement of the glucose on the surface of red
blood cells. Since red blood cells live about 2 to 3 months (before they die and
bone marrow replaces them), the test is then a surrogate measurement of the
level of glucose circulating in your blood 24/7 for that 2 to 3-month period. It’s
like wearing a blood glucose monitor!
The advantage of the A1c over a
fasting blood glucose is that the A1c test captures all the postprandial spikes
(called “excursions”) that your blood sugar takes after eating.
Everyone’s blood sugar surges after eating. As food digests, to the extent that
there are carbohydrates in the food, they will break down to glucose, be
absorbed in the blood, and be transported, by insulin secreted in the pancreas for
the purpose, to the cells. That is how your body gets the “energy” from
carbs delivered to, and hopefully into,
your cells. In people with a “normal” metabolic function, the glucose moves
from the blood into the cells. Then, after a couple of hours when all the
circulating glucose has been “taken up,” the level of glucose (and insulin) in
the blood lowers to where it began.
However, in people whose metabolism
has developed a specific “dysregulation” called Insulin Resistance, the receptor
cells on the surface of the destination cells refuse to open, and the level of
both insulin and glucose in the blood remains “elevated.” The energy is not
taken up. As a consequence, you get hungry and tired and lack energy, literally.
So, these people will have a higher A1c, corresponding to the higher blood
glucose that is circulating for hours/days, even continuously, if you regularly eat
carbs at every meal and with in-between-meal snacks.
Now, the two examples I promised: Person #1 is the email
correspondent referred to in Retrospective #195R. He was diagnosed a Type 2
diabetic (A1c 6.5%) about 9 months ago. In response, he changed his diet (“just
stopped eating bread, potatoes, pasta and ice cream”). That’s not
an “extreme” or “very low carb” diet. The result: nine months later he had
“lost 20 pounds” and his “A1c (was) “totally normal” (5.7) and fasting glucose
(was) at “100-105 over 3 blood works.” To be clear, he is still a type 2 diabetic.
He still has Insulin Resistance, but he has learned how to control his blood
glucose, and thus his diabetes, through a moderately low carbohydrate diet.
His A1c, at 5.7%, is “borderline.” You could say that his diabetes is almost “in remission,” but it will be so only
so
long as he stays “moderately low carb.”
Person #2 (lab tests read to me over the phone): fasting glucose 100mg/dl;
A1c test = 5.0%. Note: this person has the same blood glucose value (+/-100mg/dl),
but a “normal” A1c (for a 70 year old male) of 5.0% This person eats a typical
American “balanced diet,” between 40% and 60% carbohydrate, and is not diabetic
or even close to being Pre-diabetic, whereas Person #1 definitely is diabetic, even though both have identical fasting blood glucoses.
The A1c test is what differentiates
#1 (controlled diabetic) from #2 (non-diabetic). And, the A1c is what made a
diagnosis of incipient Type 2 diabetes possible in Person #1, and permitted him
to take early action to address it.
Person #1 learned he could control
his diabetes through diet alone. That’s what keeps his A1c
in the clinically “non-diabetic” range, so long as he stays moderately
low carb. I hope this is instructive, for all the Pre-diabetics and
newly diagnosed Type 2s out there. If you have Insulin Resistance (as measured
by your A1c), watch what you eat!