The brain issue The brain is a particularly greedy organ when it comes to energy requirement. To put this comment in perspective consider the following: though our brain represents only about 2% of our body mass, it accounts for about 20% of our energy expenditure. (In children, by the way, this may be closer to 40-50% of basal metabolic demand.) So, beyond the ATP issue, above, there is a substrate issue with the brain as neurons derive most of their energy from glucose. While there is emerging evidence that neurons can also oxidize fatty acids directly in small amounts and may even prefer lactate (over glucose), these two substrates do not approach the levels of consumption by neurons that glucose does. So, for the purpose of this discussion, let’s just focus on the need of the body to provide glucose to the brain. You’ll recall, from the point I made above, that my brain requires about 400 to 500 kcal of glucose per day (100 to 120 gm). You’ll also recall (from the video, above) that I can store about 100 to 120 gm of glucose in my liver. While I can store much more in my muscles, (on the order of about 300 to 350 gm), because muscles lack the enzyme glucose-6-phosphatase, glucose stored in muscle as glycogen is unable to re-enter the bloodstream and is meant for the muscle and the muscle alone to use. In other words, muscle glycogen is a stranded asset of glucose in the body to be used only by the muscle. So, if I’m deprived of a dietary source of glucose, I depend solely on my liver to release glycogen (a process known as hepatic glucose output, or HGO). How long can HGO supply my brain with sufficient glucose? It depends on a few things that impact both the “source” and the “sink” of glucose. Other competing sinks for glucose (e.g., activity level, thermogenic needs) and sources (e.g., glycerol and gluconeogenic amino acid availability) can make a difference for a while. But, in a state of starvation we’ve only got about one to three days before we’re in trouble. If our brain doesn’t get a hold of something else, besides glucose, we will die quite unceremoniously. Take home message #2: No glucose for 24-72 hours equals the need for something else the brain can use instead (that is not fat or protein, since neurons can’t oxidize fat and the last thing we want to do is start muscle wasting at a geometric rate). eatingacademy/nutrition/ketosis-advantaged-or-misunderstood-state-part-i Comment: Interesting studies. The last para says Muscle Wasting, if glucose is insufficient for the brain. Which means it can result on a long run, to Muscular Dystrophy too. That means, fruit glucose is important even for diabetics, and all brain disease events. I am strongly of the feeling that, even diabetics should take more fruits even less sugary fruits,so that their brain will get sufificient amt of fruit sugar. And what about the DM, could it be repaired by more fruit glucose. that is fructose. intake? Doc Red Doc Paul Blake
Posted on: Thu, 11 Jul 2013 11:45:19 +0000
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