The difference in peak blood d-βHB concentrations between matched amounts of βHB as ester or salts arose because the salt contained l-βHB, as the blood concentrations of d- plus l-βHB isoforms were similar for both compounds. It is unclear if kinetic parameters of KE and KS drinks would be similar if matched d-βHB were taken in the drinks. Unlike d-βHB, blood l-βHB remained elevated for at least 8 h following the drink, suggesting an overall lower rate of metabolism of l-βHB as urinary elimination of l-βHB was in proportion to plasma concentration. Despite similar concentrations of total βHB, breath acetone was ~50% lower following KS drinks compared to KE, suggesting fundamental differences in the metabolic fates of D- and L-βHB. These findings support both previous hypotheses (Veech and King, 2016) and experimental work in rats (Webber and Edmond, 1977), which suggested that the l-isoform was less readily oxidized than the d-isoform, and is processed via different pathways, perhaps in different cellular compartments. It seems that l-βHB is not a major oxidative fuel at rest, and may accumulate with repeated KS drinks. However, the putative signaling role of l-βHB in humans remains unclear. In rodent cardiomyocytes, l-βHB acts as a signal that modulates the metabolism of d-βHB and glucose, Tsai et al. (2006) although no differences in blood glucose were seen here. Furthermore, L-βHB can act as a cellular antioxidant, although to a lesser extent than D-βHB (Haces et al., 2008).
However, with the ketone esters, the effects are nearly immediate, and my entire body was humming throughout the entire day, but not in a jittery way. I was full of mental and physical energy that lasted without any sort of crash (it was a gradual taper). During my cognitive tests, things felt almost effortless as I played the various games. After my experiment was complete I continued writing code for several hours, then went to the gym to work out. I did forget to each lunch though, so there must be some suppressive effect on appetite.
Relationship between blood ketone and glucose levels: a BMS + MCT (5 g/kg) supplemented rats demonstrated a significant inverse relationship between elevated blood ketone levels and decreased blood ketone levels (r2 = 0.4314, p = 0.0203). b At week 4, BMS + MCT (10 g/kg) and MCT (10 g/kg) showed a significant correlation between blood ketone levels and blood glucose levels (r2 = 0.8619, p < 0.0001; r2 = 0.6365, p = 0.0057). Linear regression analysis, results considered significant if p < 0.05
However, we will not be commenting on ketone esters since there are big differences between them and ketone salts, and the ketone salts are the ones that have been heavily commercialized and marketed to the public over recent years. Ketone esters may be more difficult to market due to their having an unpleasant taste. We may look more deeply into the esters in the future.
[1] Shannon L. Kesl, corresponding author Angela M. Poff, Nathan P. Ward, Tina N. Fiorelli, Csilla Ari, Ashley J. Van Putten, Jacob W. Sherwood, Patrick Arnold, and Dominic P. D’Agostino (2016). Effects of exogenous ketone supplementation on blood ketone, glucose, triglyceride, and lipoprotein levels in Sprague–Dawley rats. Nutrition & Metabolism, 13(9)
I’m getting an increasing number of questions about exogenous ketones. Are they good? Do they work for performance? Is there a dose-response curve? If I’m fasting, can I consume them without “breaking” the fast? Am I in ketosis if my liver isn’t producing ketones, but my BOHB is 1.5 mmol/L after ingesting ketones? Can they “ramp-up” ketogenesis? Are they a “smart drug?” What happens if someone has high levels of both glucose and ketones? Are some products better than others? Salts vs esters? BHB vs AcAc? Can taking exogenous ketones reduce endogenous production on a ketogenic diet? What’s the difference between racemic mixtures, D-form, and L-form? What’s your experience with MCTs and C8?

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