The ketogenic diet was the most-searched health-related query on Google in 2018.
"It was the number one health-related search term on Google for 2018, and with good reason." (said at 0:22:17)
No published record matching the claim that the ketogenic diet was the number one health-related search term on Google in 2018 was located; this does not prove the claim false.
corroborated by web sources
According to Google's 2018 Year in Search data and reports from major health and news organizations, "What is the keto diet?" was the top trending health-related search question and the ketogenic diet was the most-searched diet of that year.