Objective: To compare dietary intake and physical activity (PA) between days of the week in a large sample of the Danish population; furthermore, to investigate the influence of gender and age as determinants for weekly variation.

Design: Analysis was based on cross-sectional data from the Danish National Survey of Diet and Physical Activity 2011-2013. Dietary intake and PA were assessed by 7 d of pre-coded food diaries and pedometer-determined step counts. Dietary intake and PA on weekdays (Monday-Thursday), Friday, and weekend days (Saturday and Sunday) were compared using linear mixed models.

Setting: Survey with national representation, conducted in Denmark between 2011 and 2013.

Participants: A random sample of 4-75-year-old Danes, n 3934 and n 3530 in analysis of dietary intake and PA, respectively.

Results: Energy intake during Friday and weekend days was 7-20 % higher compared with weekdays, while step counts were 10 and 17 % lower on Saturday and Sunday, respectively (all P < 0·001). Energy density of liquids and solids, consumption of added sugar, alcohol, discretionary foods, beer, wine and sugar-sweetened beverages were substantially higher, and consumption of dietary fibre, vegetables, fruit and wholegrain products were lower, during Friday and weekend days compared with weekdays (all P < 0·001). The observed patterns were present across gender and age, although weekly variation was most pronounced among children and relatively modest among the elderly.

Conclusions: Weekend health behaviours of Danes display less favourable eating and PA behaviour compared with weekdays, making the weekend an important target for public health interventions aiming to improve dietary intake and PA behaviour.