[mattieuga]

> My brain and focus is just way better running on fat than on glucose.

Your body runs on sugar not fat. Fat will be transformed into sugar to be used as energy in your body. With that said, it won't create a huge spike in your blood sugar like drinking a soda, and won't cause a giant release of insulin.

[bcheung]

Your body can run on either glucose or ketones. When you follow a low carb, high fat diet your body uses a higher percentage of ketones as energy (derived from fat). It's a much more stable form of energy since it is a constant and even supply instead of the spikes and lows from traditional carb heavy diets.

If you are referring to gluconeogenesis, yes, fat and protein can be converted to glucose but the amounts are fairly negligible. If you eat fat or have fat the body will convert the fat to ketones and use that in the absence of glucose. It's a much more efficient metabolic pathway than going through gluconeogenesis. The vast majority of the body functions quite well on ketones for energy. Most people are not able to metabolize fat at the rates required to avoid fatigue without undergoing ketoadaptation though. It takes anywhere from 3 days to 3 weeks depending on the individual and seems to be correlated with insulin resistance.

[billyum]

Fat isn't transformed into sugar, it breaks down into fatty acids which are metabolized using a different pathway. http://en.wikipedia.org/wiki/Fatty_acid_metabolism http://en.wikipedia.org/wiki/Fatty_acid_degradation

[nmjohn]

Sometimes - but they ARE metabolized through the same pathway.

Essentially:

    Glucose ->[0] pyruvate ->[1] acetyl-coa -> TCA cycle

vs

    Fatty acids ->[2] acetyl-coa -> TCA cycle

The TCA is cycle is the actual main energy generating step.

Other times fat absolutely is converted to sugar. It all depends on the metabolic needs of the body and one building blocks are available, and what protein "workers" are able to use the ones that are available.

For example, fatty acid synthase converts acetyl coa back to a fatty acid [3].

[0] Glycolysis: http://en.wikipedia.org/wiki/Glycolysis

[1] pyruvate dehydrogenase: http://en.wikipedia.org/wiki/Pyruvate_dehydrogenase

[2] beta oxidation: http://en.wikipedia.org/wiki/Beta_oxidation

[3]: http://en.wikipedia.org/wiki/Fatty_acid_synthase

[wavegeek]

None of your refs justify your claim that "fat absolutely is converted to sugar".

[nmjohn]

That wasn't my claim, please don't misquote me. What I actually said was "Other times fat absolutely is converted to sugar." There is a very significant difference.

[wavegeek]

So what are those "other times" and where is the evidence?

[frou_dh]

http://en.wikipedia.org/wiki/Ketone_bodies