Ketosis, Carbohydrates and the Brain - Q&A | BodyRecomposition - The Home of Lyle McDonald
Question: I’ve been doing the CKD effectively.
However, I have a major exam on Friday. Is there any effect on limited
carbs on cognitive processes? Does limiting carbs ( 20g / day) have a
negative effect or could it retard my performance on a major exam, i.e.
MCATs, Series7, etc? Is there any study or suggestion you could give
based on your research?
Answer: First a quick definition for anyone who isn’t familiar with the abbreviation: as discussed in the Comparing the Diets Series
, a CKD refers to a cyclical ketogenic diet. This is simply a diet
that alternates between periods of very low-carbohydrate eating
(typically 4-6 days) and very high-carbohydrate eating (1-3 days). Dan
Duchaine’s Bodyopus, Mauro DiPasquale’s Anabolic Diet and my own Ultimate Diet 2.0 are all examples of CKD’s. My first book The Ketogenic Diet discusses CKD’s generally in mind-numbing detail.
Now back to the question: does ketosis negatively impact on cognitive
function? And the answer is one huge it depends. Certainly early
studies found that, in the short-term (first 1-3 weeks),
low-carbohydrate diets tend to cause some problems. For this reason
short-term studies (usually a week long) tend to report decrements in a
lot of things including cognitive performance.
Empirically, as well, many report fatigue, lethargy and a sort of
mental ‘fog’ until they adapt to the diet (the brain adjusts to using
ketones for fuel over those first 3 weeks). I’d note that supplementing
with sodium, potassium and magnesium seems to go a long way towards
limiting or eliminating that feeling of fatigue.
So, for most I certainly wouldn’t recommend starting a very
low-carbohydrate/ketogenic diet right before some major test or
cognitive challenge. Odds are it’s going to cause problems.
But what about someone who has adapted to being in ketosis. There
there tends to be huge variance. Some people are sort of neutral to it
but I know of many who report far better brain functioning when they are
in ketosis. I couldn’t tell you the mechanism, this is just one of
those self-reported things. But it tends to be highly variable (and I
can’t think of any studies that have examined cognitive performance
after long-term adaptation to low-carbohydrate diets).
CKD’s add another complication, outside of some exercise research on Cyclical Ketogenic Diets and Endurance Performance
that looked only at performance, I’m unaware of any work on CKD’s and
cognitive performance. I bring this up as some people do report changes
switching back and forth between very low and very high carbohydrate
intakes.
Quite in fact, many who find that they feel ‘great’ in ketosis feel a
bit dopey or sleepy when they switch back to high carb intakes. This
is probably related to either blood glucose swings or a big increase in
brain serotonin (which tends to cause lethargy and fatigue) but it does
occur.
Similarly, some seem to go through at least a brief re-adaptation (in
terms of fatigue, etc.) going back from high carbs to low-carbs.
Again, this is pretty variable, many people can switch back and forth
from one extreme to the other and don’t seem to notice anything. I have
no idea why, just reports I’ve seen.
So back to the question, should you switch out of ketosis for your
test? It’s a hard question to answer and you’d have to think back to
your previous switches from low- to high-carbs during the CKD. If you
find that you’re fully adapted to ketosis and function fine mentally,
and that you get dopey going back to high-carbs, I’d probably suggest
you stay on low-carbs through the test.
If you’re one of those people who don’t seem to have ever fully
adapted to being in ketosis (they do exist), you might want to move back
to at least moderate carbs a day or two before your test. Unfortunately, there’s just too much variability for me to give you any advice beyond that.
Chino on
March 16th, 2011 5:41 pm
I am one of those people who have better concentration, focus, and
mental/physical performance in a CKD (in my case SKD) diet. I’ve adapted
well and also feel weak/tired as soon as I start hooking into the
sugar.
I would also expect, for obvious reasons, not to undertake things like exams when entering a refeed/carb-load phase.
Bartjan on
March 17th, 2011 6:39 pm
read in a study (can’t find the source now) that people are able to
concentrate better and are cognitively sharper when they are hungry.
Which (biologically) seems logical as we need our intellect to hunt and
we don’t need it when we just fed.
That would suggest having few carbs would be beneficial to your cognitive abilities.
I’d suggest the questioner doing an online IQ test while on CKD (in both
phases) and while on a ‘normal’ diet to estimate if it has any impact
on you.
starskeptic on
March 17th, 2011 10:53 pm
you have a lot of homework to do; try reading some of Lyle’s articles on this site first…
Fredrik Gyllensten on
March 21st, 2011 12:34 pm
question, and answer. I myself would probably make sure to have fasted
for at 10-15 hours before my exam, as I seem to do best mentally then.
Andrea on
March 21st, 2011 5:37 pm
with Fredrik. Regardless the diet, being fasted for 12-20 hours prior
to an exam seems to clear the head and assist with test-taking, and this
seems especially helpful when one has to “cram” before the test.
Just my experience, anyway…