This study appeared in the Journal Frontiers in Physiology
Words to know
Ketones: In this study, include:βHB (D-Beta-hydroxybutyrate) and AcAc (acetoacetate)
Ketones are being labeled in the popular media as “the fourth nutrient”. This nomenclature is due to the ability of peripheral tissues such as the brain and heart to preferentially utilize ketones over other fuels such as carbohydrate (glucose or stored glycogen) Ketones are produced under conditions of starvation or low carbohydrate availability as well as “ketogenic” diets that purposefully lower carbohydrate intake and rely on high intakes of dietary fat.
The interest in ketone bodies as a potential source of fuel for skeletal muscle during long term endurance exercise has increased recently. Ketone bodies are usually associated with conditions of starvation/voluntary fasting when they are produced by the body to be used as fuels for the brain and heart. The ability of ketone esters to enhance performance may lie in their ability to spare muscle glycogen stores during long term exercise. Exogenous (not produced by the body) forms of ketones have recently been synthesized and are now being investigated for use by athletes. To date, only a few studies have demonstrated higher blood ketone concentrations and improved time trial (TT) improvement following ingestion of a ketone ester and carbohydrate vs. carbohydrate alone. However, these conditions were not “real world” in terms of the preparation involved and cycling protocol used.
What’s new in this study?
This is the first study to investigate the performance enhancing effects of ketone-diester ingestion under conditions of “real world” cycling conditions in highly trained elite male cyclists. Real world cycling conditions include a simulated World Road Cycling championship course, optimal pre-race nutrition (Carbohydrate rich meal) and proper warmup.
This study included 11 internationally competitive male cyclists (avg. age 25 years) who were all members of the ORICA-BikeExchange UCI world tour cycling team. 8 athletes were world class elite (stage-medalists at major international races) and others were highly trained riders on the same team.
Outline of study procedure
Race-preparation procedure was well controlled
- Strict dietary control the night/morning before the time trail
- Carbohydrate and caffeine intake standardized
- Meals prepared by team chef; consisted mainly of carbohydrate rich foods similar to what would be consumed by athletes for a normal competition
- No alcohol 24 hours prior to time trial
- Pre-race breakfast provided
- Recovery drink given post-time trial 20 minutes after completion
What was measured?
- Blood ketones, glucose, and lactate before, during, and after each time trial
- Participants perceived exertion (RPE) for each trial
- Power output (PO) continuously throughout the trial
- Expired gases (02,C02) for metabolic calculations
- Concentration of free fatty acids
- Post-time trial interview included questions about beverage ingestion, discomfort, and perceived effort during the time trial
- Questions about the ketone drink (if they would consider using for performance)
Before each trial, an indwelling cannula was inserted into the cephalic vein of each participans to allow for blood samples to be taken before, continuously during, and after the time trial. A standard carbohydrate breakfast + 200mg caffeine was provided to mimic race-day conditions for each athlete (this was a consensus among the cyclists as to what a normal pre-race meal would include.) The first dose of ketone (KET) or placebo (PLAC) were ingested 20 minutes prior to commencing the time trial warmup and subsequent time trial. Each time trial completion was followed up with a structured interview in which participants provided answers to questions regarding perceived effort, motivation, and comfort during the time trial.
- 2% increase time to complete the time trial in ketone condition versus placebo
- 7% reduction in average power output in ketone versus placebo condition
- Lower average heart rate in ketone time trial
- Lower blood glucose/lactate concentration in ketone versus placebo
- RPE was similar between trials (same subjective effort recorded)
- All participants reported some degree of gastrointestinal (GI) distress following ingestion of the ketone ester
- One participant was unable to complete the time trial following ketone ingestion due to severe comiting and dizziness
- Other symptoms: dry retching, nausea, reflux
- Placebo trial induced none of the above symptoms and was well-tolerated
- Participants reported that removal of potential side effects would be required if they were to attempt to use this in a real race situation
Implications of the findings
- Ketone ester ingestion DID effectively raise circulating blood ketone concentrations, indicating effectiveness of the product
- “Nutritional ketosis” seems to be less beneficial than standard pre-race nutrition (carbohydrate)
- However, in this study, no apparent performance benefit of increased blood ketones was observed
- Decreased performance likely due to consistent finding of GI discomfort among participants
- May be due o the fact that none had ever used a ketone ester product
- A “real world” simulation of professional cycling was used to investigate the efficacy of ketone supplements, including a standard pre-race dietary routine agreed upon by all cyclists
- Evidence that ketone ester is not compatible with current pre-race routines, may require an “adaptation” phase or weaning into the diet before benefits can be seen?
While this study provided zero evidence for ketone esters to enhance endurance performance through nutritional ketosis – it is just one study in one very homogenous population (world class elite cyclists). Therefore, the generalizability is low. However, there are still wide implications for endurance athletes given the fact that highly trainined and motivated cyclists were unable to see a benefit of a ketone ester product. It is hard to say whether a trained population of cyclists would experience more or less of a side effect when using a new product.
Again, this is just one of a few studies that have investigated ketone esters for sport performance. Much more literature is available regarding ketones in health and disease – and this research looks promising. For now, it seems like experimenting with ketone esters yourself would be the best route if you want to see how performance may be effected. Ketones may be something tolerated on an individual basis. More evidence is required, I think, before firm conclusions can be made on the basis of supplemental ketones for endurance performance.