The Science of Ketogenic Exercise

There is remarkably little scientific research available around exercise while on a Ketogenic Diet. The only useful research I found was a single study by Phinney in 1983. While this is a fascinating study, it has few subjects, it has not been confirmed with other studies and the results of the study are somewhat ambiguous. I've included some other studies that are on Non-Ketogenic Low Carbohydrate Diets.

1 Phinney's Study of Elite Cyclists

A classic study was performed in 1983 by Stephen Phinney on the effect of four weeks on a Ketogenic Diet on 5 elite cyclists, and found that on average their endurance was maintained. However, this average represents two subjects that dramatically improved their endurance, one that didn't change and two subjects that had dramatically reduced endurance. One of the subjects that had reduced performance was Overtrained, and if their results are excluded the average is a 13% improvement.

• The diet was 15% of calories from protein, 85% from fat, with less than 20g of carbohydrate.
• Subjects performed V̇O₂max and endurance tests before and after the Ketogenic Diet.
• The five subjects had an endurance time of 147 minutes on the normal diet and 151 minutes on the Ketogenic Diet. However, the individual responses are rather different.
  • Two subjects dramatically increased their endurance time on the Ketogenic Diet, one by 57% and another by 30%.
  • One subject had an almost identical endurance time.
  • Two subjects had a dramatic decrease in their endurance, one by 36% and another by 28%. The subject that decreased their performance by 36% had complained of overtraining and had reduced his training level the month before the trial.
• Of the five subjects (see table below for details):
  • JP: Endurance improved by 57% and had much lower final muscle Glycogen levels on the Ketogenic Diet than the normal diet (41.5 compared with 59.2).
  • IK: Endurance improved by 30% and had similar final Glycogen levels on normal and Ketogenic Diets.
  • MK: Endurance was the similar (2% improvement) and had higher final Glycogen levels on the Ketogenic Diets.
  • BK: Endurance reduced by 28% and had higher final glycogen levels after the ketogenic endurance test than the normal diet (38.1 compared with 58.4).
  • WB: Endurance reduced by 36%.
    • WB was Overtrained and reduced training volume from 300 miles/week to 100 miles/week.
    • WB had higher final glycogen levels after the ketogenic endurance test than the normal diet.
    • WB had higher VO₂ on the Ketogenic Diet.
• Unlike typical fat metabolism, the oxygen cost of calories was not different on the Ketogenic Diet. This is a huge deal, as the big problem with burning fat is that it requires more Oxygen to produce the same amount of energy. However Phinney provides no details of the power outputs.
• The RQ on the VO2max test dropped from 1.04 to 0.9, and on the endurance test from 0.83 to 0.72, indicating a shift in substrate metabolism. However, because Ketone metabolism can produce RQ values that vary significantly, it's not possible to estimate what fuel is being metabolized. (The conversion of fat to Ketones consumes Oxygen without producing Carbon dioxide, the metabolism of Ketones has an RQ of 1.0, with the overall RQ matching that of Fat.)
• The endurance test did not include any fuel, just water. It is likely that the endurance test would have had a better result in the control condition with carbohydrate supplementation.
• Blood glucose during the endurance test was similar after the Ketogenic Diet to before, but the rise and fall were somewhat reduced. At no point did blood glucose drop to the point of hypoglycemia. Blood glucose provided an estimated 28% of calories on the normal diet and 9% of calories on the Ketogenic Diet.
• Blood levels of the Ketone 3-hydroxybutyrate (BOHB), which indicates ketogenisis, were insignificant on the normal diet and elevated (1.28 mmol/L) on the Ketogenic Diet.
• Muscle Glycogen levels where higher before the endurance test on the normal diet than on the Ketogenic Diet (143 and 53 respectively). Both tests had similar muscle glycogen levels after the endurance tests. It is interesting to see that muscle glycogen levels were replenished somewhat on the Ketogenic Diet, even though the subjects continued normal training for the four weeks.

	Endurace-1	Endurance-2	Change	Glycogen Pre-1	Glycogen Post-1	Drop in Glycogen	Glycogen Pre-2	Glycogen Post-2	Drop in Glycogen	Change in final levels	Difference in drop	VO2-1	VO2-2	Change
JP	148	223	51%	144.8	59.2	-59%	81.7	41.5	-49%	-30%	-10%	3.30	3.20	-3%
IK	100	130	30%	179.7	62.9	-65%	67.5	63.5	-6%	1%	-59%	3.10	2.97	-4%
MK	178	181	2%	142.8	46.6	-67%	65.1	57.6	-12%	24%	-56%	3.09	3.01	-3%
BK	169	121	-28%	120.8	38.1	-68%	80.7	58.4	-28%	53%	-41%	3.79	3.97	5%
WB	140	89	-36%	124.9	57.8	-54%	82.6	60.1	-27%	4%	-26%	2.61	2.95	13%
Average			4%			-63%	75.5		-24%	10%	-38%			2%
Exclude WB			13%			-65%	73.8		-24%	12%	-41%			-1%

2 Other studies

There are a few other studies that are of interest, though they do not directly deal with exercise capacity and the Ketogenic Diet.

2.1 Non-Ketogenic Low Carbohydrate Diet (NKLCD) and Exercise

A 1994 study looked at the effect of a low carbohydrate diet on cycling performance. This study explicitly avoiding being ketogenic, providing calories from 67% fat, 7% carbohydrate and 25% protein, with a control condition of 70% carbohydrate. The exercise test protocol was rather unusual; a maximum strength test was followed by a Wingate test, then a high intensity (85% V̇O₂max) endurance test to exhaustion, a 20 minute rest, then a moderate intensity (50% V̇O₂max) endurance test to exhaustion. The high fat and high carbohydrate conditions were not statistically different except for the moderate intensity test where the low carbohydrate condition produced significantly better endurance (80 minutes rather than 43.) However, while the high intensity exhaustion test was not significantly different, the low carbohydrate condition was only 8.3 minutes rather than 12.5. This is not statistically significant, but it does suggest the high carbohydrate condition could have been far more tiring than the low carbohydrate condition. There have also been other studies showing that a rest period between exercise bouts can produce low blood glucose, so this study might be the result of the rather unusual structure.

2.2 Exercise capacity in obese subjects undergoing Protein Sparing Modified Fast

An earlier study by Phinney looked at untrained, obese subjects that were treated using a Protein Sparing Modified Fast (PSMF) that provided 500-750 Calories/Day. Because a PSMF requires medical supervision, the subjects were in admitted to a medical facility for the 8 week study. Using a treadmill walking test to exhaustion showed that endurance dropped to 80% of baseline after one week, but after Ketoadaptation their capacity increased to 155%. This is a fascinating study, but the nature of the subjects, their weight loss, and the difference between the PSMF and a Ketogenic Diet, all make it hard to draw general conclusions.

2.3 Post-exercise ketosis in post-prandial exercise- effect of glucose and alanine

A study of 33 trained endurance runners on a low carbohydrate diet looked at the effect of glucose and alanine (an amino acid). The diet was not ketogenic as their blood BOHB was only 0.23 and they were on the diet for only 48 hours before the tests (no Ketoadaptation). This study showed that 50g (200 Calories) of Glucose before or immediately after a 90 minute half-marathon distance run did not impact blood ketone levels. (Taking 50g 2 hours after exercise will cause a dramatic drop in ketone levels). However, the alanine reduced ketone levels when taken before or after the run.

2.4 The effects of a ketogenic diet on exercise metabolism and physical performance in off-road cyclists

This study looks promising, but sadly it does not appear to actually use the Ketogenic Diet. The diet the study used consisted of 70% fat, 15% protein and 15% carbohydrates, and provided an average of 2,865 Calories, which works out to ~145g of carbohydrate per day, a level generally considered far too high to be Ketogenic. In addition, while the Ketone Levels increased, the level of BOHB only rose to 0.15 mmol/L. The recommended minimum level to be considered Ketogenic is 0.2 mmol/L (BOHB+AcAc), though other researchers recommend a BOHB level of 0.5. While the study was not Ketogenic, it had the subjects on the low carbohydrate diet for four weeks to allow adaptation. The low carbohydrate diet reduced body fat, which explained some improved performance metrics. The low carbohydrate diet also resulted in a higher oxygen requirement.

3 See Also

• The classifications and types of Low Carbohydrate Diet.
• An introduction to the Ketogenic Diet.
• My experiences with ultrarunning on the Ketogenic Diet
  • How the Ketogenic Diet can be used for the treatment and management of disease.
    • Using the Ketogenic Diets to mitigate and treat Epilepsy
    • How Ketogenic Diets might help with Cancer
    • A look at the possible mechanisms of action of the Ketogenic Diet
  • Health Risks of the Ketogenic Diet
    • Health Checks for the Ketogenic Diet
    • Supplements for the Ketogenic Diet
  • The time frame and changes that occur with Ketoadaptation
  • What are Ketones
    • How to measure Ketones
    • What ketone levels to aim for
  • The pros and cons of the Ketogenic Diet for athletes
    • The Science of Ketogenic Exercise
  • The Types of Ketogenic Diet
    • The "traditional" Ketogenic Diet based on the Ketogenic Ratio
      • The ways the Ketogenic Ratio can be calculated
        • The different definitions of Net Carbohydrates
    • Low Glycemic Index Treatment
    • MCT Diet
      • MCT
    • Modified Atkins Diet (M.A.D.)
• My Ketogenic Recipes
• Non-Ketogenic Low Carbohydrate Diets