Substantial shifts in contemporary diets are needed to address the growing burden of chronic diseases and the accelerating climate crisis. To facilitate these changes, policy-makers must develop effective strategies to advertise and encourage healthy dietary choices among the population. In this work, to capture changes in dietary behavior we propose an opinion dynamics model where prejudiced agents can interact with their neighbors in a social network. Additionally, an external entity, such as a policy-maker or a government, can influence the agents through sequential campaigns towards a desired collective opinion. We investigate the impact of this exogenous influence under budget constraints, limiting, for example, the number of agents that can be influenced per campaign, and show how to optimize influence allocation. We conclude with an application of the proposed approach within the context of sustainability goals on food consumption set by the UK Climate Change Committee. Using baseline food intake patterns derived from survey data on the UK population, we evaluate the impact of campaigns promoting dietary shifts and mitigating environmental impacts.