PurposeThe purpose of this study is to investigate the proportionality of market brand (MB) foods versus supermarket own brand (OB) foods sold on promotion and to compare their healthiness.Design/methodology/approachAn existing dataset containing nutritional information about a variety of foods on promotion (n = 6,776) from 48 stores across 8 retail chains in Northern Ireland (NI) was reanalysed. Product healthiness was measured using a score aligned to the Food Standards Agency's Front of Pack nutrient labelling system. MBs and OBs were considered as a whole and in their respective subsets–international/national and regional MBs, and premium, mid-market and value tiered OBs.FindingsResults found a balance in favour of health (52.4% amber/green versus 47.6% red) across retailers' promotions in NI. Further, OB products were often found to be superior to MBs with regards to overall healthfulness, and regional brands were found to be less healthy than international/national brands.Research limitations/implicationsFindings rationale further retail research to compare nutritionally OB and MB product types, and further consumer research regarding important attributes of OBs.Practical implicationsRetailers should communicate the comparative healthiness of their OBs in comparison to MB alternatives, in addition to communicating comparative price savings. There is opportunity for retailers to increase visibility of mid-market and value OB tiers, and for regional MBs to improve the nutritional profile of products in line with the consumer trend for health.Originality/valueThis study provides a contribution by using data on OBs and MBs on promotion, and by investigating the nutritional differences between different tiers of OB and MB products.