https://www.youtube.com/watch?v=0di...eature=youtu.be

Not sure if this has gone around before, but I'm curious if anyone knows the science here, and whether this is accurate.

At about 1 minute in, it states that you're OK not eating for about 72 hours, but that the ketone bodies are short-chain derivatives that can't pass the blood/brain barrier, and only 75% of the brain's energy can come from ketones, and the rest needs to come from glucose. So, apparently, your cognitive function declines after approximately 72 hours of fasting.

I'm really not that great with science, but I have read Gary Taubes and tried to work through some of the scientific articles, and I thought that the body could convert some other energy sources to glucose to make up that deficit. Am I wrong here? And why only 75%?

Or is this video accurate? I'm not really planning to fast more than 72 hours, but would like to know if fasting does affect cognitive function, as I kinda need my brain to be working properly for my job.

RE the title of this thread: I'll never stop eating video! Totally addicted.

Seriously...I haven't watched the video you noted. However, for an excellent discussion of fasting of all kinds, check with Dr. Fung at Diet Doctor. I'm pretty sure LCHF provides plenty of nutrition to carry a person through with energy to spare. Without even looking, I can say that your body makes glucose all the time to keep the brain going. The glucose we eat gets used up pretty fast. If we didn't make enough for our brains to function, we'd all die in our sleep at once.

Allow me to introduce you to Jason Fung, MD.

https://intensivedietarymanagement.com/blog/

You can scan through the blog entries and find many, many articles on intermittent fasting. Dr. Fung also has a new book, "The Obesity Code," it's a terrific book and I highly recommend it. I am reading it now.

I think your brain will be just fine with fasting, in fact, once you enter ketosis, your brain kind of "wakes up" and you are clicking on all cylinders. It's pretty neat.

P. S. Watched the video. The science is okay--but he's talking about totally NOT EATING for weeks. That's starvation. He's leading up to a commercial about helping feed people around the world who really are starving.

LCHF, or any other LC plan, is not that.

Don't worry.

This doesn't seem to be based on anybody pointing at mechanisms in the brain that demand that a minimum 25 percent of energy be produced from glucose. Instead, they look at the longest fasting studies that have been done, and call the low levels of glucose oxidized in those studies the "minimum" requirement. I think maybe it just comes down to there being a minimum protein attrition that's going to occur one way or the other, so the amino acids released in the process might as well be used to produce glucose, and the glycerol from fat breakdown doesn't really have any more important fate than to be used to produce glucose, so because of this, there's no point in brain glucose metabolism going all the way down to nil. Also keeping some brain glucose metabolism going might make things go more smoothly at the end of the fast when glucose is reintroduced.


I think there's some truth in the article, in that people new to fasting (or low carb) can experience brain fog on their first attempt, but that's just a matter of adapting to a new stressor.

I really need a "biochemistry for dummies" book if I'm going to continue with my own research -- some of these processes are hard for me to understand without that basic knowledge. I read Dr. Fung's book The Obesity Code quickly, but I've got to go back and really try and understand the science. This is what I tell my students to do with reading, so I need to follow my own advice.

It was mostly the blood/brain barrier and percentages that I really didn't understand.

I find Dr. Fung's blog posts most informative. For one reason, I'm a visual learner, and his graphs really stick in my mind. I just searched his blog for blood/brain barrier, but I guess he hasn't addressed that yet. However, I found a great website which might help. It's also on my own level:
Neuroscience For Kids

Also........

Many of the "new techniques" like LC and fasting, make perfect sense when you think of them in ancestral terms. Our bodies are little changed from 10,000 years ago. If we missed a kill for 3 days, or there was a drought and a herd we depended on for food moved on/the tubers we gathered died...then we would have died in a matter of days if our energy source did not switch to stored fat/ketones.
If we used up our stored protein instead of fat so it weakended our muscles and we couldn't walk to leave the drought area. https://intensivedietarymanagement....asting-part-14/
Or our brain stopped working and we couldn't figure a clever option to find food. elsewhere.https://intensivedietarymanagement....ion-fasting-24/

Man would never have evolved and survived if he had to eat 3 squares a day.

Not to mention snacks . . . . . . .

Thanks for the links, guys -- I'm going to do some reading now.

One of the doctors familiar with IF, I can't remember which one stated we have enough reserves to go 3 days with water only. The body cannibalizes glycogen, old proteins, enzymes etc. This does a body good on occasion.

After that I assume it then starts to eat itself, thinking muscle tissue? Not good.

To answer the glucose question, it says in the video to body can manufacture glucose from protein. It just works better when its food rather than your body like zero carbs can do.

I thought it was a given that ketogenic eating had an 'adaptation' period.

PJ

The body can also manufacture carbs from fat. But, more importantly, it can use fat for energy quite nicely. The survival reason for using carbs preferentially seems to be to protect that fat for when we really need it.

But we DON'T really need it, at least, not most of us, do we?

Yep, that's true. The herd is always right there at the supermarket