The human metabolic response to chronic ketosis without caloric restriction: Preservation of submaximal exercise capability with reduced carbohydrate oxidation
There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
To study the effect of chronic ketosis on exercise performance in endurance-trained
humans, five well-trained cyclists were fed a eucaloric balanced diet (EBD) for one
week providing 35-50 kcal/kg/d, 1.75 g protein/kg/d and the remainder of kilocalories
as two-thirds carbohydrate (CHO) and one-third fat. This was followed by four weeks
of a eucaloric ketogenic diet (EKD), isocaloric and isonitrogenous with the EBD but
providing less than 20 g CHO daily. Both diets were appropriately supplemented to
meet the recommended daily allowances for vitamins and minerals. Pedal ergometer testing
of maximal oxygen uptake (VO2max) was unchanged between the control week (EBD-1) and
week 3 of the ketogenic diet (EKD-3). The mean ergometer endurance time for continuous
exercise to exhaustion (ENDUR) at 62%-64% of VO2max was 147 minutes at EBD-1 and 151
minutes at EKD-4. The ENDUR steady-state RQ dropped from 0.83 to 0.72 (P less than
0.01) from EBD-1 to EKD-4. In agreement with this were a three-fold drop in glucose
oxidation (from 15.1 to 5.1 mg/kg/min, P less than 0.05) and a four-fold reduction
in muscle glycogen use (0.61 to 0.13 mmol/kg/min, P less than 0.01). Neither clinical
nor biochemical evidence of hypoglycemia was observed during ENDUR at EKD-4. These
results indicate that aerobic endurance exercise by well-trained cyclists was not
compromised by four weeks of ketosis. This was accomplished by a dramatic physiologic
adaptation that conserved limited carbohydrate stores (both glucose and muscle glycogen)
and made fat the predominant muscle substrate at this submaximal power level.