Methods It was a quasi experimental intervention study with two groups: control and intervention group with pre-post evaluation of nutrition and physical activity intention and behaviour in each group. The target population was composed with students aged 12–16 years schooled in colleges of Sousse in Tunisia. To evaluate the intervention, a sampling was used to include 2200 students who participated to the questionnaire. All the students of intervention group received a standardised program with information about healthy nutrition and physical activity. An Arabic pre-tested and auto-administered questionnaire was used to assess nutrition and physical activity intention and behaviour before and after the intervention.

Results The intervention group's posttest intention and behaviour were significantly higher than the control group's posttest. Concerning “healthy behaviours”, in the intervention group, children improved significantly their vegetable intake. It passed from 45.4% to 56.8% (p<0.001). The proportion of children who practice 5 days per week physical activity for at least 30 min a day increased significantly from 23% to 44% (p<0.001).

Conclusion School based intervention to promote healthy diet and physical activity is benefit and important at the middle age to prevent obesity and cardiovascular disease risk factors.