Previously, we’ve discussed ketogenic diets. Phinney 2004 wrote a review of the evidence demonstrating why ketogenesis is not the demon it is generally made out to be.

He spends the first part of his article retelling the stories of medical doctors and explorers of the far northern regions of Canada and how within 2-3 weeks they completely adapted to a diet of reindeer and seal meat and blubber and reported no major malnutrition or physical deficits in that time.

Interestingly, according to Phinney, one of the main reasons for the acceptance of carbohydrates as a major dietary source was a study by Kark in during World War II. He would take Canadian soldiers, spend 3 weeks acclimatizing them to a grain based diet. He would then record their performance on physical tests. He would switch them to a diet of dried meat and 3 days later record their performance. Clearly it was poorer as no time for the necessary metabolic changes occurred. This lead to governments taking a position on nutrition for the war effort and a policy began.

He goes on the look at more modern studies. He cites the Sims and Horton 1980 study during which subjects spent 6 weeks eating 1.2g/kg bw of protein and supplemented with 1g potassium daily. The diet was also hypocaloric.

A baseline VO2max was established by treadmill test with endurance time to exhaustion determined before the protocol. Over the 6 weeks, the subjects lost on average 10kg. On the endurance test on the last day of the study, the subjects wore a backpack equivalent to the weight they had lost. VO2max remained constant at 2.49L/min, time to exhaustion increased from 168 minutes to 249 minutes. Now, this was also hypocaloric and the subjects lost weight so some confounders are occurring but it raises some interesting questions.

He then cites the study he and Bistian 1983, completed. The study used university aged competitive cyclists. They spent 4 weeks on a high carb diet (67%) during which time baseline measurements were determined. They then switched to 4 weeks of 83% fat, 15% protein and 2% carbohydrate with 1.5g/day potassium supplement as well as 600mg calcium and 300mh magnesium.

VO2max on baseline diet was 5.1L/min, on the keto diet it was 5.0L/min. VO2 at Exercise respiratory quotient came in at 0.83 carb and 0.72 keto- demonstrating slower breathing while exercising. Muscle glycogen was also measured lower in the post-test. Endurance time is most interesting, 147 min before and 151min after- essentially no change.

This demonstrates that a highly trained athlete can switch fuels and with a period adaptation suffer no performance losses on a ketogenic diet. While not necessarily advocating this diet for everyone; given its benefits to those with epilepsy, type 2 diabetes, in fat loss and indicating no loss in performance while increasing neuro-protection and hyperglycemia, it is definitely worthy of consideration.