According to annual Finnish health survey called "Health Behaviour and Health among the Finnish Adult Population", 13,4 % of all adult males and 16,4 % of all adult women followed low-carbohydrate diet in 2011. This was the third most popular choice of the studied diets after low-fat diet and lactose-free diet. However at the same time 60 % of the adult male and 44 % adult women population were overweighted (BMI >25 kg/mē). This is the first time the study included diet preferences.

You can see the distribution of diets on Table 123a on page 160 of the study.
Health Behaviour and Health among the Finnish Adult Population, Spring 2011