Low-carbohydrate diets and exercise
Over the past several years, 2 reviews focused on LCKD (Low Carb Ketogenic Diet) and
exercise have been published.
One of these reviews concluded that sub-maximal 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 low carbohydrate 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.(Means body will use energy from Fat adipositas and fat acids instead from Carbs and musle)
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 sub-maximal 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 1.5g 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) maybe limited by lower-muscle glycogen concentrations.