Iceland only has 300,000 people total.The question is which country has the least amount of lactose intolerant people.
According to https://ghr.nlm.nih.gov/condition/lactose-intolerance#statistics only 5% of northern Europeans are lactose intolerant. That is 15,000 for the entire country.
Along the same line of thinking Monaco (a principality) only has 38,000 people. Can't be too many LI people there.