Abstract We aimed to investigate the effects of a long-term, individualised, family-based lifestyle intervention on food consumption and nutrient intake from childhood to adolescence. We conducted an 8-year diet and physical activity intervention study in a population sample of children aged 7–9 years at baseline in 2007–2009. We allocated the participants to the intervention group (n 306) and the control group (n 198). We assessed diet by 4-d food records at baseline, 2-year follow-up and 8-year follow-up. We analysed the data using linear mixed-effects models adjusted for age at baseline and sex. The consumption of vegetables and vegetable oil-based spreads (fat ≥60 %) increased in the intervention group but did not change in the control group (P < 0⋅001 for time×group interaction). The consumption of fruits and berries increased in the intervention group but decreased in the control group (P = 0⋅036). The consumption of high-fat cheese (P = 0⋅029), butter-based spreads (P = 0⋅001) and salty snacks (P = 0⋅028) increased less, and the consumption of low-fat cheese (P = 0⋅004) increased more in the intervention group than in the control group. Saturated fat intake (P = 0⋅001) increased less, and the intakes of dietary fibre (P = 0⋅003), vitamin D (P = 0⋅042) and vitamin E (P = 0⋅027) increased more in the intervention group than in the control group. The intakes of vitamin C (P < 0⋅001) and folate (P = 0⋅001) increased in the intervention group but decreased in the control group. To conclude, individualised, family-based lifestyle intervention altered food choices towards more recommended diet and resulted in enhanced diet quality from childhood to adolescence.