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Mixed Brain Fuel – Q&A

Question: On a ketogenic diet, how rapidly does the brain flip between glucose and ketones for fuel? Can it use both fuel sources simultaneously?

Answer: The above question sort of encompasses a few different potential things and I’m not 100% sure which you’re asking so I’ll just cover them all.  First realize that one fuel that the brain cannot use is fatty acids, at least not directly.  This has led to the oft-stated belief that the brain can only use glucose. But this is incorrect as the brain has an alternative fat derived fuel which are ketones (or ketone bodies, the two major of which are beta-hydroxybutyrate and acetyl-acetate).

Ketones are produced primarily in the liver (from the breakdown of fatty acids) and exist predominantly as an alternative fuel source for the brain (they can also be used by skeletal muscle) during periods of low-carbohydrate availability.  This probably was originally important during periods of complete starvation; now very low-carbohydrate diets (defined here as any diet containing less than 100 grams per day of carbohydrates) effectively ‘exploit’ this mechanism.

Now, on a carbohydrate based diet, the brain runs essentially on 100% glucose since ketones are generally not produced in significant amounts … Read More

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Ketosis Carbohydrates and the Brain – Q&A

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 … Read More

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What’s Causing My Muscle Cramps – Q&A

Question: I have been following a very low-carbohydrate diet and taking the ephedrine/caffeine stack for the past 4 months.  Recently I have been having problems with cramping in the gym, I find that if I get too close to failure on a set, I get very bad cramps.  I’m drinking plenty of water and taking a multivitamin and I can’t figure out what’s wrong. Please help.

Answer: Cramping is unfortunately a very complicated topic and while many simple solutions are often thrown out, they don’t always seem to work.   Usually the culprit is issues with hydration per se or electrolyte levels; electrolytes are things like potassium, calcium, sodium and magnesium they are involved in transmission of the electrical signals in the body.  Hence their name.

I’d note that hydration and electrolyte levels are intertwined as the amount of water in the body affects the relative concentrations of the electrolytes in the body. So if there is more water present, the relative concentration of each of the electrolytes will be lower because the water will dilute them.  By the same token, if you are dehydrated, the relative concentrations of the electrolytes goes up.

Most ideas about cramping tend to focus on … Read More

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Ketosis and The Ketogenic Ratio – Q&A

Question: Do you still believe in the ketogenic ratio for getting into ketosis?  I am having trouble showing ketones. Any tips? Sorry to bother you again but can drinking 2 gal of water per day dilute your urine so you don’t show ketones?

Answer: Ok, let me take these on one at a time.

In my first book The Ketogenic Diet, I talked about something called the ketogenic ratio (KR) which is an equation/concept used in the planning of ketogenic diets for epilepsy patients. The equation basically gives you the potential ketone producing potential of a given meal depending on the relative ketogenic or anti-ketogenic effect of the different macronutrients.

So the KR of a given combination of nutrients can be estimated with the following equation:



Protein turns out to be partially ketogenic (46%) and partially anti-ketogenic (58%), reflecting the fact that some amino acids can be made into ketones, while other are made into glucose).  Carbohydrate is 100% anti-ketogenic and fat is mostly (90%) ketogenic (the 10% anti-ketogenic is due to the fact that the glycerol portion of triglycerides, explained in A Primer on Dietary Fats, can be converted to glucose in the liver).… Read More

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Carbohydrate Intake and Depression – Q&A

Question: I’m a 45 year old female. I currently weigh 221lbs. I’ve lost 30lbs in the last three months. My protein intake is roughly 120 to 130 grams per day.  I’m limiting my carb intake to 180 to 200 grams a day. I suffer from life long depression and I find that when I limit by carb intake I slowly slide into a depressed state after two or three months (it’s happening to me now). My sleep is disturbed, I develop anxiety I’m bitchy as hell and I’m dragging ass.  Is there a correlation between carb intake and production of neurotransmitters? If so, how can I eliminate the effect lower levels of carbs is having on me? Any information is greatly appreciated.

Answer: Dieting in general tends to lower serotonin in the brain and this can cause depression in susceptible people.  Interestingly, this effect seems to be more likely to occur in women than men (women being more susceptible to depression in general).  In my experience, low carbohydrate/higher proteins diets tend to be even worse in this regards for reasons I’ll explain now.

First and foremost, nutrient intake per se affects the production of neurotransmitters with the effects being both … Read More