Mass media campaigns can change attitudes and behaviours to improve population health. However, a key challenge is achieving share of voice in a complex and cluttered media environment. The aim of this study was to compare advertising expenditure on public health campaigns for obesity prevention (and related healthy eating and physical activity campaigns) with competing commercial categories of (a) sugary drinks, (b) artificially sweetened drinks and (c) diet/weight loss products and programmes. These commercial products may either undermine or dilute public health messages by directly contributing to poor health or confusing the public about the best ways to sustain a healthy lifestyle. Monthly estimates of advertising expenditure in Australian media (television, outdoor, cinema, radio, newspapers, magazines and digital) were obtained from Nielsen Media for 2016-18. Eligible public health advertising expenditure for the entire period (total AUD$27M) was vastly outweighed by the commercial categories of sugary drinks (AUD$129M) and diet/weight loss products and services (AUD$122M). Artificially sweetened drinks accounted for an additional AUD$23M of expenditure. These results highlight the need to rebalance the ratio of advertising to support public health in Australia through increased funding for obesity prevention and related campaigns, and critically, through government regulation to limit competing commercial advertising.