Brain Chemistry

[Heather]

Please forgive me in advance if this has been asked before.

I was talking to my friend who is a registered nurse and also a diabetic regarding low cabohyrdate diets and she said that she's only heard one bad thing about this WOE. She said that if a person does not get enough carbs that the brain will pull what it needs from lean muscle tissue. The brain doesn't use protein or fat, but degenerates muscle tissue if there isn't enough carbs in the diet.

She didn't say how much is not enough, and I know that not eating any carbs is not recommended. I just wanted to hear from the resident experts if they've heard of this and what do they know about how the brain works and what kind of energy is required to fuel it.

Thanks in advance!!

[razzle]

I'm not sure what substance she thinks is being pulled from muscles, but whatever it is (glucose?), it can be derived from today's eaten protein more easily. (In the absence of other mitigating factors, the body won't eat itself up for stuff that's coming in new and is running around in the bloodstream, as a matter of metabolic efficiency. The exception to this rule that we all care about is with fat--which cannot be stored in the absence of high insulin levels and must be metabolized from storage in the presence of glucagon, even tho we have just eaten lots of fat.)

Some of what carbs used to give us ketone bodies now do. (and just cuz they don't show in your urine doesn't mean your body is not producing them and using them as fuel). This replaces glycogen, perhaps that substance she's thinking of (?)

You might find the first question answered on this (http://www.blackdirt.net/lowcarb/eades/eades_2.html) website useful. HTH!

[Kent]

Hi Heather,

Your nurse friend has based her knowledge on one of the many myths about nutrition. A quick review of any college text book on human anatomy and physiology will show that the body can make glucose from either dietary protein or fats. Research also shows your friend to be wrong as follows:

Effects of Low-Carb Diet on the Brain

Effects of unbalanced diets on cerebral glucose metabolism in the adult rat.
al-Mudallal AS, Levin BE, Lust WD, Harik SI. Department of Neurology, Case Western Reserve University School of Medicine, Cleveland, OH, USA.
Neurology 1995 Dec;45(12):2261-2265

We measured regional cerebral metabolic rates for glucose and selected cerebral metabolites in rats fed one of the following diets for 6 to 7 weeks: (1) regular laboratory chow; (2) high-fat, carbohydrate-free ketogenic diet deriving 10% of its caloric value from proteins and 90% from fat; and (3) high-carbohydrate diet deriving 10% of its caloric value from proteins, 78% from carbohydrates, and 12% from fat. In preliminary experiments, we found that moderate ketosis could not be achieved by diets deriving less than about 90% of their caloric value from fat. Rats maintained on the ketogenic diet had moderately elevated blood beta-hydroxybutyrate (O.4 mM) and acetoacetate (0.2 mM), and a five- to 10-fold increase in their cerebral beta-hydroxybutyrate level. Cerebral levels of glucose, glycogen, lactate, and citrate were similar in all groups. 2-Deoxyglucose studies showed that the ketogenic diet did not significantly alter regional brain glucose utilization. However, rats maintained on the high-carbohydrate diet had a marked decrease in their brain glucose utilization and increased cerebral concentrations of glucose 6-phosphate. These findings indicate that long-term moderate ketonemia does not significantly alter brain glucose phosphorylation. However, even marginal protein dietary deficiency, when coupled with a carbohydrate-rich diet, depresses cerebral glucose utilization to a degree often seen in metabolic encephalopathies. Our results support the clinical contention that protein dietary deficiency coupled with increased carbohydrate intake can lead to CNS dysfunction.

Comments: The brain's primary fuel is glucose. Some people worry that on a low-carb diet, there would be a shortage of glucose to fuel the brain. So they tested it on rats. They gave the rats a low-carb diet. Of course, the usual low-carb things happened: their blood glucose dropped, and their livers started manufacturing ketones (ketosis). After a while, they checked the rats' brains. First, they found that while the blood glucose was low, the brains contained the normal amounts. This means the body was making sure that the brain had enough glucose, and was not having a problem doing it. Second, they found that the ketones were going straight to the brain. Now, ketones are a fuel source. So, very likely, this means that the brain was using ketone as a substitute fuel, to keep from running down the glucose supply. Meanwhile, the group that ate the low-fat diet ended up with a protein deficiency. This deficiency made it difficult for their brains to use glucose. In short, the brains of the low-carb rats received adequate energy supplies, the brains of the low-fat dieters were damaged by energy shortages.

http://www.lowcarbretreat.com/josh_yelon/topic5.html

[Heather]

Thank you both for the insightful, reassuring replies. It appears both your brains are in perfect condition!!! :)