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FITCHALLENGER SparkPoints: (0)
Fitness Minutes: (10,690)
Posts: 349
11/1/11 2:06 P

At 30 grs of carbs per day I'b be brain dead by now... and I'm the valedictorian of my MBA class. So I agree... BS.

RUSSELL_40 Posts: 16,826
11/1/11 12:09 P

Thank you DEY. Someone needed to correct this BS.

We forget that prehistoric man survived under circumstances we would probably fail at today, if you loaded a teenager up on carbs , and let him loose in the wilds. If they had been sluggish of mind from low carb, they probably would have been eaten. I have been hearing this for 2-3 weeks now. Now I know they are just repeating it from the quiz.

DEY101 SparkPoints: (15,463)
Fitness Minutes: (5,646)
Posts: 94
11/1/11 10:20 A

It is a myth that the brain can only use glucose for fuel. Glucose is the preferred fuel, however it can adapt quite easily to using ketones as fuel.

“The brain’s first choice for energy is glucose. However, when glucose is not available, the brain uses ketone bodies. Using ketones meets the energy requirements of the brain and maintains its proper function.” (Amiel, S.A., "Organ Fuel Selection: Brain," The Proceedings of the Nutrition Society, 54(1), 1995, pages 151-155.)

"Ketones are particularly important for the brain. When glucose is not available, the brain turns to the alternative energy source of ketones. Ketosis (elevated ketone levels in the blood) is normal during fasting, after prolonged exercise and when a high-fat diet is consumed." (Mitchell, G.A., Kassovska-Bratinova, S., Boukaftane, Y., et al., "Medical Aspects of Ketone Body Metabolism," Clinical and Investigative Medicine, 18(3), 1995, pages 193-216.)

"Most tissues in the body can readily use fatty acids for fuel just as easily as glucose. There are a few tissues such as the renal medulla, red blood cells and one or two other that can only use glucose. However, those cells essentially make their own glucose by recycling lactate (produced from glucose metabolism) back into glucose.

The brain is in its own weird category. Under most conditions, it relies exclusively on glucose. And while it can’t use fatty acids directly, it can use a fatty acid derived fuel in the form of ketone bodies. After roughly three weeks of adaptation to using ketones, the brain may only need 25 grams/day of glucose or so, which can be made by the body (in the liver and kidney) from sources such as lactate, pyruvate, amino acids and glycerol." (

UNIDENT Posts: 33,498
10/31/11 2:24 P

The link you provided explains it clearly enough.

Different nutrients have different uses. The only fuel the brain uses is glucose. However, fuel isn't the only thing your brain needs.

Like a car. Would you get far if the only thing you ever did to your car was put petrol in it? You'd be fine for a while. Maybe weeks or even a month or two. But soon you're going to need oil. Then tyres, valve changes, pipe replacements, a new gasket head, etc.

Just because the 'fuel' is petrol doesn't mean you don't need that oil for other purposes.

BEARCLAW6 SparkPoints: (0)
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Posts: 1,939
10/31/11 2:23 P

To build a little on the previous post, your liver can convert amino acids (proteins) and the glycerol (backbone of fats) into glucose. It does this pretty much any time you go several hours without eating (like while you sleep). Generally, people can go a lifetime without eating a single molecule of carbohydrate and be just fine. But.....most people find that it is easier to exercise and easier to live in our American sugar-eating society if you eat at least some forms of carbohydrate. It also means that you need to consume enough protein when not eating much carbohydrates or your body will start using muscle for fuel. Carbohydrates are also more quickly accessible than fats for hard-core endurance athletes, as well. If you try to do an Ironman triathlon without carbohydrates, you will probably be sad....but how many of us do that?

10/31/11 10:15 A

The brain uses only glucose as fuel, yes. Glucose is a carbohydrate. We can feed our brain either by eating carbohydrate foods OR the body can convert fats and/or proteins to glucose

10/31/11 10:01 A

One of the answers to the trivia questions is that carbohydrates are the only fuel the brain. Yet from what I've read, the brain utilizes nutrients that are gained from fats and proteins as well. For example :
If someone who is an expert can clarify, I would appreciate if.

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