Table 1 Description of the Diet Quality Index (DQI) and its components

Dietary diversity

Expresses the degree of variaton in the diet (whether the subject used foods from the different food groups (FG) recommended in the Flemish food-based dietary guidelines) = (# different FG from main FG from which at least one serving was consumed)/total # main FG x 100 %

Dietary quality

Expresses whether the subject made the optimal quality choices

All food amounts were multiplied with a factor:

1 for items of the ‘preference’ food category

0 for items to be consumed with moderation from the ‘intermediate’ food category

−1 for items from ‘low-nutritious, energy-dense group’ (high caloric, but low nutrient density)

This was summed and divided by the total food amount consumed:

∑ (factor food item x food quantity food item)/∑ food quantity food item

Dietary equilibrium

Expresses the equilibrium/balance of food intakes = ∑₁ ^#FG(dietary adequacy FG—dietary excess FG)/# different FG x 100 % (see rules in adequacy and excess score below)

Dietary adequacy

Expresses the percentage of minimum recommended food intake actually consumed for all main FG = ∑₁ ^#FG(actual intake FG/min recommendation FG)/# different FG x 100 %

With the actual intake being truncated to the minimum recommended intake if exceeding the minimum recommended intake

Dietary excess

Expresses the percentage of intake exceeding the upperlevel of the recommendation = ∑₁ ^#FG((actual intake FG—upper level FG/upper level FG)/# different FG x 100 %

With the excess of a FG being truncated at 100 % when exceeding 100 % and at 0 when below 0 %

Meal index

Expresses the frequency of consumption of a breakfast, lunch and dinner per day (frequency breakfast/day + frequency lunch/day + frequency dinner/day)/3 x 100 %

Physical activity index (PA index)

Expresses the compliance with the physical activity recommendation (e,g, 30 min in moderate to vigorous phyical activity per day)

(total time spent in moderate to vigorous physical activity per day)/30 x 100 %

With the PA index being truncated at 100 % when exceeding 100 %

Total DQI = (dietary diversity score + dietary quality score + dietary equilibrium score + meal index + PA index)/5

Expresses the compliance of the subject with the Flemish food-based dietary guidelines (higher compliance gives higher DQI score)