Doping

John Hawley at the Mary MacKillop Institute for Health Research,
Australia, says he is perplexed by the suggestion that muscles can use
both ketones and glucose for energy at the same time.

The vast body of research shows that muscles only tap into ketones
after very prolonged exercise, when glycogen stores are spent, he
says. “The logic of this ketone supplement is that it spares your
muscle glycogen. But you have more than enough glycogen for 30 minutes
of cycling, so I can’t see why sparing it would do you any good.”

Hawley says that independent studies are needed, but says he has heard
anecdotal reports from endurance athletes who believe the ketone drink
improves their performance under certain conditions. “At the end of
the day, some athletes have said they feel a little bit better on
this, and that carries some weight,” he says.

That's been "coming soon" for 4-5 years

They are commercially available in the USA I first started seeing them about a year ago , I was intrigued but the cost is uninviting .

http://www.metaketosis.com/