Seminal health behaviour theories and behaviour modification techniques are applied to health behaviours individually. Limited empirical work investigates how change in one health behaviour may change another. This study proposes a food–alcohol competition hypothesis, where individuals tend to consume one rewarding substance to the other’s exclusion. In a large sample of adolescent girls assessed yearly from age 15 to 19, Latent Growth Modelling indicated that a tendency to consume processed or sweet high-fat foods ‘competed’ with a tendency to drink alcohol. In order to best improve overall health, it is important to consider interrelationships between food and alcohol consumption.