To investigate associations between dietary intake and patterns of food preparation by age group.

This cross-sectional study analysed dietary intake data from the most recent Portuguese National Food, Nutrition and Physical Activity Survey. Cluster analysis categorised dietary intake based on the source of food preparation. Regression models were used to study the association between dietary daily intake, Healthy Eating Score (HES) and patterns of food preparation.

Portugal, using data representative of the Portuguese population.

A total of 5005 Portuguese residents aged 3–84 years were included in the analysis. Dietary intake and food preparation patterns were examined by age group.

The predominant pattern of food preparation was food prepared by restaurants, canteens and other away-from-home establishments (45·9 %, 95 % CI = 43·8, 48·1). Children and adolescents in this pattern had significantly higher intakes of energy and carbohydrates but lower protein intake compared with those consuming predominantly home-prepared foods. Among adults and the elderly, this pattern was associated with higher intakes of energy, saturated fats, trans fats and free sugars and lower fibre intake. Additionally, children and adolescents whose diets predominantly included food prepared away-from-home showed a decrease in HES (β = –0·7, 95 % CI = –1·3, –0·2), and adults experienced a greater reduction (β = –1·2, 95 % CI = –1·5, –0·9).

In Portugal, consuming food prepared away from home is associated with poorer dietary quality, with higher energy and unhealthy nutrient intake and lower HES, suggesting a need for interventions focused on promoting healthier food preparation practices.