While there remains some debate [1
] excess dietary sodium has been identified by the World Health Organization (WHO) as a modifiable risk factor for raised blood pressure and a major contributor to cardiovascular disease (CVD) [2
]. In Australia, 11% of deaths from ischemic heart disease and 15% of deaths caused by stroke are attributable to excess dietary sodium [3
]. The estimated average salt intake of Australian adults is 9 g/day (3500 mg sodium/day) [4
] more than twice the Australian government’s Suggested Dietary Target of 4 g/day (1600 mg sodium) [6
]. As 75% of dietary sodium is contributed by packaged processed foods [7
] reducing added sodium in these foods would be a cost effective strategy to reduce the burden of preventable CVD [8
In Australia the supermarket sector is the largest retail industry [12
] and the majority of packaged processed food items are bought at supermarkets [13
]. For millions of consumers, supermarkets offer significant convenience as they provide a one-stop-shop made possible by the wide range of food categories stocked [14
]. The packaged food items within each food category may be branded and owned by the supermarket, and sold exclusively in the supermarkets’ own stores. Such items are often referred to as “supermarket brands”, “own label” or “home-brand”, and are hereafter referred to as “private-label” products. Supermarkets may also retail “branded products”, which are items owned by national and international food manufacturers and distributed to the general trade [16
]. While very few studies have conducted in-depth analyses comparing the nutritional quality of private-label versus
branded products, consumers have traditionally perceived private-label products to be of lower quality than their branded counterparts [16
]. Some retailers differentiate their private-label offering between value-, mid- and premium products [16
]. Likewise, the dollar share of private-label sales differs tremendously between countries (0%–45%) and between product categories, with total share predicted to rise in Australia from 24% to nearer 30% [16
Due to their large market share and popularity with consumers, supermarkets have substantial power to influence the healthfulness of the food environment by determining what products get onto the supermarket shelf. Supermarket demands to lower added sodium in their private-label products could be a significant contributor towards Australian efforts to meet the voluntary global target of a 30% reduction in the mean population intake of sodium by 2025 [23
]. Three of the four largest Australian supermarkets (ALDI, Coles and Woolworths have made voluntary commitments to reduce sodium content across nine food categories as part of the Australian Food and Health Dialogue (FHD) initiative which was launched in 2009 [24
]. Prior analyses suggest modest progress in sodium reduction for three food categories [25
] but whether the pace of change differed between private-label and branded products’ was not assessed. The objective of this study was to compare the sodium content of private-label versus
branded products across a broad range of food categories available in Australian supermarkets. Products were examined in both 2011 and 2013 to allow evaluation of changes over time.
2.1. Data Collection
Between 2011 and 2013, data were collected in the fourth quarter of each year from the same four supermarkets (ALDI, Coles, IGA/Metcash, and Woolworths) in Sydney, Australia. Data were obtained directly from the mandatory Nutrition Information Panel (NIP) on product packaging but where exactly the same branded product was for sale in more than one supermarket, it was recorded only once. Likewise, where the same private-label or branded product was presented in different pack sizes only one entry was recorded. For each product, the manufacturer, brand and product name, as well as the nutritional information per 100 g were recorded. Where the brand of the product was a proprietary brand name of the supermarket it was considered as a private-label product of that supermarket. Data were entered into The George Institute’s branded food composition database [26
] according to standardised procedures [27
]. Data were verified according to a defined quality assurance protocol and workflow which included screening for outliers and missing values, checking of data entry accuracy by two study personnel and resolving queries and discrepancies by a review of the original NIP data, consultation between the research personnel, review of the manufacturer website or follow-up with the manufacturer directly. Ethics approval was not required.
2.2. Identification of Food Categories
Major food categories included were those typically containing added sodium. In addition the category was required to contain at least 20 private-label and 20 branded products in each year to allow meaningful comparison and statistical inference. Categories included were biscuits; bread; breakfast cereals; cakes, pastries and muffins; cereal bars; cheese; crisps and snacks; desserts; nuts and seeds; processed fish; processed meat; ready meals; sauces; soup; and, vegetables. Table S1
lists the major food categories reported, foods included, and the number and percentage of private-label products in 2013.
2.3. Products Excluded
Products were excluded where the brand and manufacturer name could not be identified from information on the pack and we were unable to confidently confirm whether it was a private-label or branded product.
The primary outcome for the study was the mean sodium content (mg/100 g) determined from data reported on the NIP. The mean value was calculated by summing the sodium values in mg/100 g (assuming the density of liquid products was 100 g/100 mL) across included products and dividing through by the number of products.
2.5. Statistical Analysis
The mean, median and range of sodium content were first calculated overall and for each food category. Since the sample sizes were sufficiently large to not require assumptions of normality, analyses and reporting are based upon mean values and parametric tests [28
]. There were four main analyses done:
Comparison of the mean sodium values of private-label versus branded products for all products available for sale in 2013 (n = 5995). Differences in mean sodium content between private-label and branded foods were determined and compared using unpaired t tests.
Comparison of the mean sodium values of private-label versus branded products for the subset of products available for sale in both 2011 and 2013 (n = 2792). Changes in mean sodium between 2011 and 2013 were assessed by paired t tests.
Comparison of the mean sodium values of private-label versus branded products for the subset of products first introduced to the market in 2013 (n = 1870), differences in means were assessed using unpaired t tests.
Comparison of the mean sodium content of private-label products for each of the four supermarkets with data plotted graphically for 2011, 2012 and 2013 and unpaired t tests used to compare the 2013 mean values for all products combined.
In each case the analyses were done for all product categories combined and separately for the 15 major food categories studied. The primary analysis excluded data for 186 products in five minor sub-categories of products which had extreme sodium values and are consumed in small quantities (canned herring; capers; peppers/capsicum and other picked vegetables; satay and curry pastes; and black-bean/Asian ambient sauces) out of a total of 214 minor sub-categories. Sensitivity analyses were also done with these products included. Statistical significance was defined as two-sided α = 0.05. Formal adjustments for the multiplicity of testing were not made. However, all findings were interpreted in light of the number of comparisons made, the practical significance of any differences observed, and with a focus on the primary outcomes. Analyses were conducted using Stata 13.1 (Stata Corp., College Station, TX, USA).
Private-label products are traditionally perceived as low-cost, low-quality choices when compared to their branded counterparts. Recent data report although perceptions of private-label quality have improved Australian consumers still have quality concerns [18
]. These data suggest the quality concerns are unfounded in at least one important regard—the overall mean sodium content of Australian private-label products was consistently and substantially lower than that of branded products for the three years from 2011 to 2013. Furthermore, the difference was substantial at 17% less sodium. A lower sodium intake across the Australian population would translate into thousands less heart attacks and strokes each year and hundreds of millions of dollars savings through health care costs avoided [9
]. Excess sodium intake is a primary cause of high blood pressure which is a leading cause of premature death and disability in Australia and most other countries around the world.
The lower mean sodium content in private-label compared to branded products was a consequence of numerically lower mean sodium content for 11 of the 15 food categories studied. These differences were statistically significantly for four of these categories. Of which two (bread and processed meats) were prioritised for salt reduction by the FHD based on their relative high contribution to dietary intake of sodium [24
]. The corresponding numbers for branded products were four categories with numerically lower mean sodium content and just one, breakfast cereals also prioritised by the FHD for salt reduction, with a statistically significantly lower value. These differences were mostly already apparent in 2011 and persisted through to 2013 with little evidence of a change in the pattern over these three years—there were very small and comparable reductions in mean sodium content attributable to reformulation for both private-label and branded products, but private-label continued to introduce to the market products that were on average lower in sodium than new branded products. The reason why private-label products already had sodium content so much lower than branded products in 2011 is unclear but the production of foods lower in sodium by the major retailers seems likely to be a long-standing phenomenon.
There was also marked difference in the mean sodium content of the private-label products provided by different retailers. IGA (Metcash) stood out as having consistently higher mean sodium content than its counterparts, and ALDI for the very encouraging reduction in mean sodium content across its private-label range. ALDI aside, the absence of any overall change in mean sodium content for either private-label or branded products grouped, or by any of the other retailers, suggests limited activity on sodium reduction by most food suppliers across most food categories.
Our study data included well-known brand names, supplied by large manufacturers, many of whom have publicly committed to producing healthier foods [24
]. Assessing individual manufacturers was beyond the scope of our study, but it is probable that some companies have reduced the average sodium content of their product portfolio while others have not. Prior studies have also shown substantial heterogeneity in sodium reduction between branded food manufacturers, [25
] and our finding highlight such variability is also present amongst private-label. Government leadership of the FHD can establish a level playing field for sodium reduction in a broad range of food categories for supermarket retailers and branded manufacturers to work towards. A broadening of the FHD targets and strengthening private sector accountability will be vital if Australia is to have any chance of delivering upon the sodium reduction target committed to as part of the World Health Organization 25 by 25 chronic disease prevention goal [34
A key strength of our study is the consistent and systematic sampling method used to collect data over the years. Longitudinal data has allowed us to assess the overall sodium content of foods across time while separately evaluating the contribution that reformulation of established products and the development of new lower salt products has made. The large number of products sampled provided good coverage of foods in each category and enhanced statistical power to assess differences in mean sodium content. The inclusion of a broad range of categories makes an important contribution to understanding the status of sodium reduction across most of the packaged, processed food supply. The detailed categorisation of products enabled us to explore the product mix of private-label versus branded products. Including product sub-categories with extreme values of products eaten infrequently did not substantially alter the findings but in the case of sauces highlighted the importance of knowing product mix to interpreting the study findings.
The data also have some limitations and are likely to be incomplete because they were collected from only one store location for each of the four supermarkets. Incompleteness may be greater for private-label than branded products since branded products could be marketed by multiple different retailers but private-label products by only the parent retailer. We were also unable to include foods for sale exempt from labelling requirements such as products made and packaged on the premises from which it is sold or packaged and displayed in an assisted service display cabinet [35
]. We relied on the validity of the nutritional information on the NIP, although prior studies suggest this is generally accurate and reliable [36
]. In the absence of an agreed definition of “premium” and way to categorise private-label brands we were unable to differentiate between the tiered private-label brands that some retailers now market as value-based, mid-range, and premium [16
]. We also did not examine price and as our study examined foods only from Australia, which is unique in both the level of supermarket concentration and private-label share [16
], our results may not be generalizable to other countries.