Ketones probably don’t improve endurance performance. See https://www.ncbi.nlm.nih.gov/...articles/PMC7442417/ for a decent review.
Phil
A limitation with reviews is that they are by definition limited to research which has already been conducted.
Out of the studies cited, the results are decidedly mixed. Some positive, Many equivocal, Some negative. I always ask why this is.
It’s the early days of Ketone research and researchers are throwing pickles at the wall to see what sticks and what slides (you know you just pictured that…). I think it’s becoming clear that Esters have more potential than salts. Remove the research on Ketone Salts, and the remaining studies on Esters appear to have either positive or negative effects(Figure 3). Great, we’re getting somewhere.
So why either positive or negative?
Well, generally speaking, it appears that the research falls into two scenarios:
Those that are work-rate limited (e.g. Shorter Tests up to 45minutes) Leckey (31km cycling TT) / Evans (20 min shuttle run & 10km cycling TT) / O’Malley (10km cycling TT)
Those that a substrate availability limited (fasted or longer tests over 2 hrs). Poffe (120min) / Cox (Fasted 30min TT)
Frankly the 45 minute to 90 minute range is difficult to study due to individual variations in economy and substrate utilization. For someone like me, CHO and Ketones are absolutely beneficial at 45 minutes, but others may not see an effect from either.
In the work-rate scenario - Ketone esters do not appear to have a positive effect, and they likely have a negative effect through a potential inhibition of glycolysisIn the substrate limited scenarios - Ketone esters appear to have a positive effect barring any negative effect of GI Distress, etc.
That distinction is very relevant as many ergogenic aids need clear distinctions to determine efficacy (soda loading, exogenous carbs, cooling strategies,etc.)
I believe that moving forward, more research needs to be done on the ergogenic effect of ketone esters in endurance performance limited by substrate-availability before we have definitive answers, but I do believe that area shows promise.