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Old 03-31-2009, 06:21 AM   #13
Darryl Shaw
Senior Member
Join Date: Apr 2008
Posts: 708

Originally Posted by Ben Fury View Post
Glycogen is overrated. Get keto-adapted and burn ketones like an Inuit. The Inuit regularly crossed astonishing distances in the Arctic on an almost zero carb diet. The first two weeks of keto-adaptation aren't fun. But after that, you're cruising.

Your body will rip apart proteins for the few absolutely essential tasks it needs glucose for.

See Westman, et al:
Low-carbohydrate nutrition and metabolism

That review article relates mostly to diabetics and the few paragraphs that deal with athletic performance merely state that submaximal endurance can be maintained on a ketogenic diet. The review failed to provide any evidence that ketogenic diets actually improve performance and clearly acknowledged that anaerobic performance is limited by low muscle glycogen concentrations. It's also worth noting that supplements were required in order to maintain circulatory competence even during submaximal exercise as well as to achieve nitrogen balance.

Low-carbohydrate diets and exercise

Over the past several years, 2 reviews focused on LCKD and
exercise have been published. One of these reviews concluded
that submaximal endurance performance can be sustained despite
the virtual exclusion of carbohydrate from the human diet
(46). The other review addressed the intramuscular enzyme adaptation
that occurs with these diets (47).

Several important issues arise in the consideration of LCKD
studies in general and of exercise studies in particular: 1) the time
allowed for keto-adaptation, 2) the use of electrolyte supplementation,
and 3) the amount of protein intake. To try to examine the
first issue, we can consider the multiple studies comparing lowcarbohydrate
with high-carbohydrate diets to test the hypothesis
that “carbohydrate loading” can enhance physical performance.
None of the studies that support this hypothesis maintained the
LCD for 2 wk (48), and most maintained the LCDs for 7 d
(49). No studies have carefully examined the process or duration
of keto-adaptation, but clinical observation suggests that it probably
takes from 2 to 4 wk for keto-adaptation to occur.

The second issue has to do with the maintenance of adequate
mineral supplementation as long as the ketogenic state is maintained.
One group of investigators provided supplements containing
3–5 g sodium/d and 2–3 g potassium/d and found that
circulatory competence during submaximal exercise was sustained.
These supplements also allowed the subjects to achieve
nitrogen balance, which had not been achieved in studies that did
not use supplements (20).

The third issue affecting physical performance is adequate
protein intake. It is generally accepted that the preservation of
LBM and of physical performance during any degree of energy
restriction occurs when protein is in the range of 1.2 to 1.7 g kg
reference body wt1 d1. The use of the mid-range value of 1.5
g kg1 d1 for adults with reference weights ranging from 60
to 80 kg, this translates into total daily protein intakes of 90 to 120
g/d. When adequate protein intake is expressed in the context of
total daily energy expenditures of 2000 to 3000 kcal/d,15% of
daily energy expenditure should be provided as protein.

Further research on exercising under conditions of LCDs is
needed. These studies may be optimized by careful attention to
the time needed for keto-adaptation, to mineral supplementation,
and to the daily protein dose. Therapeutic use of ketogenic diets
should not limit most forms of physical activity, with the caveat
that anaerobic performance (ie, weight lifting or sprinting) may
be limited by lower-muscle glycogen concentrations.
"Fat adaptation" for athletic performance: the nail in the coffin?

Darryl Shaw is offline   Reply With Quote

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