Ketone Ester Supplement Boosts Trainees' Post-Exercise Glycogen Repletion by 18% in Insulin-Clamp Study, But...

For the average gymrat, the 18% increase in glycogen repletion PWO is 100% irrelevant and the amounts of glucose you'd need to facilitate it (even w/ ketones) would do more harm than good to your health and physique goals.

Who would have thought that? A ketone ester drink ramps up the already elevated insulin levels you'll see after the post-workout ingestion of a bolus of glucose. Probably everyone who doesn't vilify insulin and believes blindly in the label claims of supplement producers. After all,  D-β-hydroxybutyrate has long been known to promote insulin secretion in animals - two decades ago Laughlin et al. were among the first to realize their insulinogenic prowess (Lauglin 1994).

Even before Laughlin et al. researchers suspected that the ketone-body-induced increases in insulin will go hand in hand with a significant increase in glycogen synthesis as it has been observed in vitro 40 years ago by Maizels et al (1977). What would be news, though, is the fact that this increase would facilitate a statistically significant increase in glycogen synthesis in a real-world post workout situation.
That, however, is not what the latest study by Holdsworth et al. shows. While the scientists observed a significant increase in glycogen storage, when they gave their subjects 0.573 ml/kg of the ketone ester, (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, this observation was made in a physiological state that has absolutely nothing to do with the real world: the infusion of glucose during a hyperglycemic insulinemic clamp test during the post-workout period. Before we discard the results as irrelevant, however, let's take a look at what Holdsworth et al, whose study involved twelve male, well-trained, athletes (mean ± SD: age, 33.0 ± 6.5 years; body weight, 75.8 ± 5.0 kg; height, 1.70 ± 0.10 m VO2max, 57.0 ± 4.8 ml/kg/min; peak power output, 316 ± 34 W) with a weekly training volume of 6-8 hours, actually did: They had their subjects perform a standardized glycogen depletion protocol after a 12-hour overnight fast:

3g taurine also improve PWO glycogen resynthesis significantly | more

"Following a 10-minute warm-up at 50% VO2max, participants commenced exercise at intermittent intensity for two-minute intervals, alternating 90% PPO efforts with 50% PPO recovery. When fatigued at this intensity, the upper interval workload was decreased progressively in 10% PPO increments. Exhaustion, and protocol completion, was defined by the inability to complete two minute at 60% PPO. Each participant‟s heart rate was monitored throughout (Polar H7 heart rate monitor, Polar, Kempele, Finland) and water was consumed ad libitum" (Holdsworth 2017).

Then, right after said torturing glycogen depletion exercise, the participants consumed either a ketone drink or an isocaloric taste- and appearance matched control drink of equal volume.

• The ketone drink, which had no side-effects, contained 0.573 ml/kg of the ketone ester, (R)-3-hydroxybutyl (R)-3- hydroxybutyrate (12, 13). The natural bitter taste was partially masked with citrus flavoring (Symrise, Holzminden, Germany) and proprietary sweetener (aspartame, NutraSweet™, Chicago, USA). 
• The control drink contained the same citrus and sweetener components as the ketone drink. The bitter taste was matched with the addition of a weight-dosed commercial bitter agent (Symrise, Holzminden, Germany). 

The drinks were given immediately following the post glycogen-depletion muscle biopsy and the clamps started 30 minutes following ingestion.
To reliably assess the subjects' ability to stash away glucose, the researchers decided to use the hyperglycemic clamp according to the method described by de Fronzo and colleagues (DeFronzo 1979). Compared to the provision of a glucose containing drink, the clamp method of providing carbohydrate following exhaustive exercise has, as the scientists rightly point out, three advantages:

• The technique provided a way to standardize glucose available to skeletal muscle across different visits for the same participant, and between different individuals. 
• By delivering glucose intravenously, it is possible to avoid the variations in time and magnitude of glucose delivery caused by oral ingestion and enteral absorption. 
• It is possible to ensure that glucose delivery to the muscle is at least as high as would be provided by the recommended optimum post-exercise carbohydrate feeding of 1.0–1.2 g/kg/h over 4-6 hours. 

The scientists also explain that the chose to use supraphysiological target whole blood glucose of 10 mM so that "in the event that an increase in glucose uptake was evident following a ketone supplement, it would be likely to represent a biologically significant intervention" (Holdsworth 2017). In other words: They choose a method that would allow them to observe results... that's akin to using untrained individuals in resistance training studies and not a methodological no-go. It does, however, make it even more important that the supplement is re-tested in a realistic scenario.
As previously hinted at, the scientists' analysis of pre- vs. post-samples they got by the means of muscle biopsies from the subjects'vastus lateralis revealed that the addition of ketones increased the glycogen storage in the subjects' skeletal muscle significantly. It is yet at least somewhat misleading when the scientists write in their abstract that "muscle glycogen was 50% higher (246 vs.164 mmoles
glycosyl units/kg dry weight, p < 0.05) than after the control drink" (Holdsworth 2017), because the layman will conclude that the ketone drink triggered a 50%" increase in glycogen synthesis, when the actual comparison of the relative increases in Figure 1 (no such figure in the FT of the original study, be the way), clearly indicates that the difference is as low as 18%.

Figure 2: One has to look at the relative increase in glycogen to arrive at a practically relevant (albeit less advertisable) statement about the effects of ketone-esters on glycogen synthesis (calculated base don data from Holdsworth 2017).

This is less than what I recently reported for caffeine and unquestionably less marketable than the 50% increase from the abstract you can easily misunderstand as an inter-group difference, but it is certainly more realistic in view of the fact that the 100% increase in insulin levels (31 vs. 16 mU/l, p < 0.01) sped the whole body glucose uptake (including liver, fat, splanchnic organs etc.) up by "only" 32% (1.66 vs. 1.26 g/kg, p<0.001) - to expect this increase to translate to a 50% increase in glycogen synthesis in the muscle is IMHO quite naive. After all, there's no reason to believe that the exuberant level of insulin would act, as the scientists imply. when they write that any extra glucose that was not stored in the leg musculature (the weight of which they estimate based on data from average Joes and Janes (Janssen 2000), even though their subjects were, I quote, "well-trained") "was probably incorporation into skeletal muscle glycogen", exclusively on the subjects' skeletal muscles - and that's irrespective of the fact that exercise selectively increases skeletal muscle glycogen synthesis.
References:

• D'Agostino, Dominic P., et al. "Therapeutic ketosis with ketone ester delays central nervous system oxygen toxicity seizures in rats." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 304.10 (2013): R829-R836.
• DeFronzo, Ralph A., Jordan D. Tobin, and Reubin Andres. "Glucose clamp technique: a method for quantifying insulin secretion and resistance." American Journal of Physiology-Gastrointestinal and Liver Physiology 237.3 (1979): G214-G223.
• Holdsworth David A., et al. "A Ketone Ester Drink Increases Postexercise Muscle Glycogen Synthesis in Humans." Medicine & Science in Sports & Exercise (2017): Ahead or print.
• Janssen, Ian, et al. "Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr." Journal of applied physiology 89.1 (2000): 81-88.
• Kashiwaya, Yoshihiro, et al. "A ketone ester diet increases brain malonyl-CoA and uncoupling proteins 4 and 5 while decreasing food intake in the normal Wistar rat." Journal of Biological Chemistry 285.34 (2010): 25950-25956.
• Laughlin, Maren R., et al. "Nonglucose substrates increase glycogen synthesis in vivo in dog heart." American Journal of Physiology-Heart and Circulatory Physiology 267.1 (1994): H217-H223.
• Maizels, Evelyn Z., et al. "Effect of acetoacetate on glucose metabolism in the soleus and extensor digitorum longus muscles of the rat." Biochemical Journal 162.3 (1977): 557-568.
• Murray, Andrew J., et al. "Novel ketone diet enhances physical and cognitive performance." The FASEB Journal 30.12 (2016): 4021-4032.
• Pinckaers, Philippe JM, et al. "Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype?." Sports Medicine (2016): 1-9.
• Poff, A. M., et al. "Ketone supplementation decreases tumor cell viability and prolongs survival of mice with metastatic cancer." International journal of cancer 135.7 (2014): 1711-1720.
• Vandoorne, T., et al. "Intake of a Ketone Ester drink during Recovery from Exercise promotes mTORC1 signalling but not Glycogen Resynthesis in Human Muscle." Front. Physiol. (2017): Ahead or print | doi: 10.3389/fphys.2017.00310