Modelling impacts of a salt and sugar tax on intra-category food substitutions, BMI and environmental footprints

doi:10.21203/rs.3.rs-3958741/v1

Download PDF

Research Article

Modelling impacts of a salt and sugar tax on intra-category food substitutions, BMI and environmental footprints

https://doi.org/10.21203/rs.3.rs-3958741/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

Purpose

Taxes on unhealthy foods can help improve population health in the United Kingdom (UK), but the health effects of food substitutions resulting from these taxes are often unclear. We investigated the potential impacts of a salt and sugar tax on hypothetical intra-category food substitutions, cost, body-mass index (BMI), and environmental footprints.

Methods

Purchase panel data from Kantar (2017) were used to determine the most popular foods high in salt or sugar within eight ‘salt-intensive’/‘sugar-intensive’ food categories. Within food categories, the most popular lower salt (≤1.5g salt/100g product) and lower sugar (≤22.5g sugar/100g product) substitutes were also identified. Hypothetical swaps between high salt/sugar foods and lower salt/sugar substitutes were explored, focusing on changes to cost, caloric intake and BMI, and environmental impacts.

Results

The suggested intra-category substitutions were largely like-for-like and did not accrue an added overall cost to consumers. The substitutions reduced calorie intake by about 200kcal/day and lowered the prevalence of overweight and obesity in the UK from approximately 60-65% to about 40-45%. The proposed food substitutions led to a total reduction of -2.7Mt of greenhouse gases, ~ -500.000ha of land, -0.5km³ of blue water, -12km³ of scarcity weighted water, ~ -12.000t of phosphorus, and nearly -14.000t of sulphur dioxide over one year for the UK population due to reductions in calorie intake.

Conclusion

Food substitutions following a tax on salt and sugar could lead to significant benefits for health and the environment, without necessarily resulting in major changes to people’s expenditure on familiar salty and sugary snacks.

Nutrition & Dietetics

fiscal measures

obesity reduction

food expenditures

health promotion

environmental sustainability

Limiting intakes of salt and added sugar is one important action to halt the rising trend of chronic disease burdens and metabolic syndrome [1]. In the United Kingdom (UK), an estimated 90,000 avoidable deaths are yearly caused by diets that are low in foods such as fruits and vegetables and high in those containing high levels of salt and added sugars [1]. Overweight and obesity are currently estimated to cost the UK National Health Service £19.2bn each year [2], and this is projected to continue to increase [3]. At the same time, food and drink in the UK contribute to slightly over a third of the country’s total greenhouse gas emissions (GHGE) [4], as well as other environmental stressors [5].

Experiences from the enactment of the UK Soft Drinks Industry Levy (SDIL) in 2018 [6] indicate that targeted fiscal policies could be effective for directing the consumption of specific foods among consumers. Evidence shows that the total volume of sugar sold from soft drinks decreased by 29% as a result of the introduction of the levy [7]. Meanwhile, the voluntary sugar reduction programme (national guidelines for all sectors of the food industry on how to achieve a 20% sugar reduction across the top sugar contributing food categories [8]) has shown only marginal decreases in the levels of sugar in the food categories confectionery, cakes, biscuits, ice creams and other desserts [9]. In July 2021 the National Food Strategy (NFS) recommended a new “Salt and Sugar Reformulation tax” on manufacturers purchasing sugar and salt for use in processed foods and drinks [10]. Importantly, one of the major goals of this tax was to encourage reformulation of products rather than it being a tax on consumers, since the latter could have negative effects on the lowest-income households that already dedicate > 15% of total budgets to food purchases [11]. It is therefore important that any fiscal levers avoid constraining the most deprived households. Furthermore, there is some concern about insufficient alternatives with a lower sugar or salt content for food groups that would be subject such a tax.

The evidence is scarce and mixed when it comes to understanding what substitutions people would be inclined to make when faced with different options or increased cost of their preferred foods high in salt/sugar. For example, a fairly recent study exploring the effect of food price changes on consumer purchases [12] found that consumers increased the proportion of fruit and vegetables purchased when a saturated fat and salt tax were introduced. On the other hand, there is evidence suggesting that substitutions with similar foods within the same food category would be preferred in the context of price changes [13, 14]. In this study, we were interested to look into substitutions that may occur within food categories since such swaps, despite mixed evidence, are assumed to be more acceptable to consumers than substitutions across food groups. We also wanted to address the possibility of negative cost, health or environmental impacts from consumers making such swaps since, if they were likely to occur, these would be an important drawback to any future salt and sugar tax. More specifically, the aim of this work was to investigate the affordability of intra-category food substitutions (swapping from foods high, to substitutes lower, in salt/sugar) as well as to quantify changes to anthropometric and environmental indicators following the possibility of such substitutions occurring in practice.

Purchase panel data

Purchase data from the Kantar Fast Moving Consumer Goods (FMCG) Purchase Panel (Take Home) 2017 was used as a basis for all analyses. This data includes information on type of foods purchased by households in England and Wales, their weight, energy and nutrient content, and price per unit. It also includes sociodemographic information of households.

To enable the exploration of potential food category level substitutions, the most commonly purchased ~10 foods high in salt or total sugar were identified within eight food categories: Biscuits (e.g. plain, filled and chocolate covered biscuits, wafers), Crackers (e.g. flavoured, unflavoured and seeded varieties) Bread (e.g. garlic and/or cheese baguette, toast loaf, rolls) Breakfast cereals (e.g. muesli and cereals including those flavoured with chocolate, nougat, fruits/berries and nuts), Confectionery (chocolate products and other sweets), Desserts (e.g. ice creams, puddings, canned fruit), Savoury snacks (e.g. salted/flavoured varieties of crisps, corn-based products, nuts), and Spreads (jams, marmalades, nut-based spreads). These eight food categories are both ‘salt-intensive’/‘sugar-intensive’ and are food categories which people spend a comparably large share of their total food expenditures on [15], i.e. those categories which would impact household budgets the most if they went up in price due to the tax. Foods (substitutes) within the same category but lower in salt/sugar were identified by extracting the most commonly purchased ~10 foods in each category lower in salt/sugar. Unless otherwise specified (Supplementary Table 1), substitutes classified as lower in salt/sugar were those containing a maximum of 1.5g/100g of product for salt and a maximum of 22.5g/100g of product for sugar. This mirrors the NHS’s classification of products not high in salt/sugar [16, 17]. We chose to extract foods that were purchased by the households in the lowest income quintile to make sure that their favourite products would be covered in the cost-comparison. A sample of specific food items that were included in the extracted lists of high salt/sugar or lower salt/sugar substitutes within each food category are shown in Figure 1 and Supplementary Table 2. For example, plain digestives were one of the lower sugar substitutes for chocolate covered digestives (Figure 1). Further information regarding the data extraction and data management may be found in the Supplementary Methods.

Energy content of foods

The Kantar Purchase Panel database provides information on the kilocalorie (kcal) content per 100g of a purchased product. However, the kcal content per 100g might not be optimal for the comparison of the energy content of consumed foods as serving sizes can differ between foods. Because we wanted to create consumption scenarios based on the purchased foods (further details under Quantifying changes in consumption of kcal, bodyweight and body-mass index), the top ~10 purchased products high or lower in salt/sugar in each food category were assigned typical serving sizes based on those indicated on product labels/online databases [18–21]. Based on these values, an average serving size for foods high or lower in salt/sugar within each food category was estimated (Supplementary Table 3). Using these average serving sizes, and the kcal content per 100g of product, the average kcal content per serving could be calculated for foods high in salt/sugar and substitutes lower in salt/sugar, respectively within each category (Supplementary Table 3).

Environmental impacts of foods

The environmental impacts assessed in this study were the diet-related greenhouse gas emissions (GHGE), an estimate of the climate change impacts associated with each food product measured in kg carbon dioxide equivalents (CO₂e); Water Use, measured in litres of blue water; Weighted water scarcity (weighted blue water use to produce food products by regional water availability) measured in litres; Acidification (an estimate of sulphur pollution from food production) measured in grams of sulphur dioxide equivalents (SO₂eq); Eutrophication potential (an estimate of phosphate pollution from food production in aquatic environments) measured as g of phosphate equivalents (PO₄eq); and Land use (an estimate of how much arable land and pastureland is occupied to produce food product without biodiversity impacts), measured in square meters per year. These data were based on a meta-analysis of food product Life Cycle Assessments (LCA) compiled from published literature [22]. The environmental impact data covers impacts for 57,185 unique food products sold in eight UK and Ireland-based retailers. The impacts for individual foods are averaged for over >3000 Retail categories (By Department, Aisle, and Shelf), and they are calculated per 100 grams of food product. The LCA system boundaries include primary production to factory gate across different production systems (packaging, further distribution to shops and homes, meal preparation after delivery, and waste management are not included) (See Clark et al., 2022 for detailed methods on the environmental impacts).

Quantifying changes in the price of foods

The Kantar Purchase Panel data provides information on the price per unit of food and the weight per unit. With this information, the average price per 100g of food product was calculated. In this analysis we assumed a “worst case scenario” where reformulation is not undertaken in response to the introduction of a salt and levy, and that the full cost of the levy is instead passed on to consumers. Based on prices in the Kantar data (i.e. pre-tax prices per 100g of food product), the post-tax price per 100g of the most popular foods products high or lower in salt/sugar was calculated. The calculations of post-tax prices applied the proposed tax of £3/kg tax on sugar and a £6/kg tax on salt [10].

Quantifying changes in consumption of kcal, bodyweight and body-mass index

The UK National Diet and Nutrition Survey (NDNS) waves 9-11 (2016 to 2017 and 2018 to 2019) [23] was used to establish the current consumption of Biscuits, Crackers, Bread, Breakfast cereals, Confectionary, Desserts, Savoury snacks, and Spreads. The NDNS is a rolling program of cross-sectional surveys based on a 4-d food diary. These data were chosen as they presently constitute the only nationally representative dietary intake data for the UK population. For this analysis, dietary data from 1,844 adults aged 19-85 were used. The NDNS data provide sociodemographic and anthropometric information as well as quantities (in grams) of items eaten or drunk over 3-4 consecutive days, per main food group (e.g., “Biscuits”), sub-food group (e.g., “Biscuits (manufactured/retail”), and per individual (discrete) food item (e.g., “Cream cracker”). The eight relevant food categories were matched to their main food group in the NDNS (Supplementary Table 1). We calculated the mean consumption (in g per day) of Biscuits, Crackers, Bread, Breakfast cereals, Confectionary, Desserts, Savoury snacks, and Spreads for the adult UK population. This average included those consumers who did not consume each product at all. Based on the previously estimated average serving sizes (Supplementary Table 3), the average daily consumption in grams was translated to an average consumption in number of servings (Supplementary Table 4).

Using the current consumption (in servings) of the eight food categories and the estimated average kcal per serving of foods high or lower in salt/sugar (Supplementary Tables 3 and 4), we calculated the resulting kcal intake from these foods among the adult UK population under two different scenarios (see Results):

People consume foods high in salt or sugar from each category
People consume foods (substitutes) lower in salt or sugar from each category

The difference in kcal consumed per person per day between these two contrasting consumption scenarios was then used to quantify changes in body weight and body-mass index (BMI) in the adult UK population. Here, sociodemographic and anthropometric data from the NDNS (described above [23]) were used to provide a nationally representative cohort to which changes in body weight and BMI were applied. Firstly, each adult in the survey cohort was assigned their (baseline) BMI; i.e. their reported weight in kilograms divided by height in metres squared. We then assumed that a 1 kcal change in energy intake corresponded to a 0.042kg reduction in body weight based on the steady-state model originally developed by Kevin Hall et al [24]. New body weights (and thus new BMIs) resulting from a change in kcal intake were consequently calculated only for adults considered overweight (defined as BMI ≥ 25 kg/m²). The average BMI of the entire baseline adult population could then be compared to the average BMI of the adult population.

Quantifying changes in environmental impacts of foods

Environmental impact information for all foods relevant to each of the food categories were extracted and averaged based on the described environmental impacts data [22]. For example, the environmental impacts of 29 shelf-categories, covering 4,691 different types of chocolates and sweets were averaged to provide one single value per impact (i.e. average impact per 100g of food) for the category Confectionary (Supplementary Table 5). The same was done for all other food categories (Supplementary Table 5). The average environmental impacts per 100g for each of the food categories was divided by the average kcal content per 100g in order to obtain one single measure of kcal content per g (Supplementary Table 6). This was done to be able to compare changes in environmental impacts resulting from changes in kcal intake resulting from the dietary substitutions.

Description of nutrient content and consumption of food categories

As expected, average caloric and salt/sugar content was higher in foods high in salt/sugar than in substitutes lower in salt/sugar across all food categories (Table 1). The substitutes lower in salt/sugar in each food category contained 54% (Bread) to 71% (Snacks) less salt, and 30% (Desserts) to 85% (Spreads) less sugar per serving (Table 1). When comparing the different food categories relevant for salt, Bread contained the highest average amount of kcal and salt per serving in both the high salt foods (250 kcal and 1.3g salt per serving) and the substitutes lower in salt (142 kcal and 0.6g salt per serving) (Table 1). Crackers contained the lowest amount of kcal and salt per serving in both the high salt foods (114 kcal and 0.5g salt per serving) and the substitutes lower in salt (72 kcal and 0.2g salt per serving). Regarding food categories relevant for sugar content, Desserts contained the highest average amount of kcal and sugar per serving in both the high sugar foods (246 kcal and 27g sugar per serving) and the substitutes lower in sugar (173 kcal and 19g sugar per serving) (Table 1). Confectionery contained the next highest average amount of kcal and sugar per serving in the high sugar foods, but a considerably lower amount of kcal and sugar in the substitutes lower in sugar (119 kcal and 4.0g sugar per serving). Biscuits contained the lowest amount of kcal and sugar per serving in the high sugar foods (113 kcal and 9.8g sugar per serving) and one of the lowest contents of kcal and sugar per serving among the substitutes lower in sugar (101 kcal and 3.1g sugar per serving) (Table 1).

Table 1

Average energy, sugar and salt content per serving for the different food categories.
Food category	Higher salt/sugar foods vs. substitutes^a	Average kcal/serving	Average sugar content (g)/serving	Average salt content (g)/serving
Biscuits	Higher sugar	113	9.8	na
Biscuits	Lower sugar	101	3.1	na
Breakfast cereals	Higher sugar	139	13	na
Breakfast cereals	Lower sugar	134	6	na
Confectionery	Higher sugar	196	23	na
Confectionery	Lower sugar	119	4.0	na
Desserts	Higher sugar	246	27	na
Desserts	Lower sugar	173	19	na
Spreads	Higher sugar	83	13	na
Spreads	Lower sugar	81	2	na
Biscuits (crackers)	Higher salt	114	na	0.5
Biscuits (crackers)	Lower salt	72	na	0.2
Bread	Higher salt	250	na	1.3
Bread	Lower salt	142	na	0.6
Snacks	Higher salt	159	na	0.7
Snacks	Lower salt	135	na	0.2

^aHigh salt products contain > 1.5g/100g of product; Lower salt substitutes contain ≤ 1.5g/100g pf product (and ≤ 22.5g/100g pf product, no data shown); High sugar products contain > 22.5g/100g pf product; Lower sugar substitutes contain ≤ 22.5g/100g of product (and ≤ 1.5g/100g pf product, no data shown).

Of all food categories, Bread was consumed in the largest amounts on a daily basis both among males (1.2 servings) and females (0.8 servings) (Table 2). Crackers were consumed in the smallest amounts on a daily basis both among males and females (both 0.2 servings). As for energy, Bread and Desserts provided the largest, while Crackers provided the least, amount of calories for both males and females (Table 2). The daily consumed kcal per person of foods high in salt or sugar was higher than the consumed kcal per person of substitutes lower in salt or sugar across all food categories (Table 2). The largest difference was found for Bread (-128 and − 88 kcal for males and females, respectively), whereas the smallest difference was for Spreads (-1 kcal for both males and females).

Changes in prices

Applying the proposed NFS tax on the foods extracted for this analysis resulted in an increased price for all foods (Supplementary Table 7). The estimated price increase in high salt foods included in the analysis was between 4.4% (Crackers) and 12% (Bread), compared to 3.8% (Crackers) and 7.5% (Bread) in the substitutes lower in salt (Supplementary Table 7, Supplementary Fig. 1), owing to the relatively lower amount of salt contained in each product (Supplementary Table 7). The estimated price increase in the high sugar foods was much higher than for salt. Here prices increased by between 27–92% across high-sugar food categories, compared to 3–26% in the substitutes lower in sugar (Supplementary Table 7, Supplementary Fig. 1), owing to the relatively lower amount of sugar contained (Supplementary Table 7). Substitutes lower in salt/sugar were on average cheaper (comparing pre-tax price of high salt/sugar foods vs. post-tax price of lower salt/sugar substitutes) for almost all food categories except for Confectionery and Spreads (Supplementary Table 7). With the exception of the Bread and Desserts categories, lower salt/sugar substitutes were predominantly like-for-like (Fig. 1), Supplementary Table 2). Further information regarding food prices can be found in the Supplementary Results.

Table 2

Reported daily consumption of different food groups (in nr of servings) and the corresponding energy (in kcal) consumed for foods high in salt/sugar vs. substitutes lower in salt/sugar.
Food category	Daily consumed servings/person	Daily consumed kcal/person of foods high in salt/sugar	Daily consumed kcal/person of substitutes lower in salt/sugar	Change in daily kcal/person^a
Biscuits
Males	0.40	44	39	-5
Females	0.40	45	40	-5
Biscuits (crackers)
Males	0.2	27	17	-10
Females	0.2	28	18	-10
Bread
Males	1.2	296	168	-128
Females	0.8	203	115	-88
Breakfast cereals
Males	0.6	86	83	-3
Females	0.4	60	58	-2
Confectionery
Males	0.3	59	36	-23
Females	0.3	60	36	-24
Desserts
Males	0.3	72	50	-21
Females	0.2	60	42	-18
Snacks
Males	0.6	89	75	-13
Females	0.5	81	68	-12
Spreads
Males	0.6	53	51	-1
Females	0.5	42	41	-1

^aChange observed when comparing consumption of foods high in salt/sugar with substitutes lower in salt/sugar.

Changes in consumption of kcal, bodyweight and body-mass index

The total daily per capita kcal reduction from consuming substitutes lower in salt/sugar (as opposed to those high in salt/sugar), for all food categories, was − 204 kcal for males and − 159 kcal for females (Table 3). These reductions in energy intake were translated to a change in body weight of -8.6kg in males, and − 6.7kg in females (Table 3), with half of the weight change being achieved in about 1 year and 95% of the weight change in about 3 years [24]. This would reduce the average BMI in the adult UK population by 2.0 and 1.5 kg/m² for males and females, respectively (Table 3), and lower the proportion of individuals classified as overweight, i.e. having a BMI ≥ 25 (Fig. 2).

Table 3

Changes in total daily caloric intake, body weight, body-mass index and six environmental impact categories resulting from consumption of substitutes lower in salt/sugar vs. foods high in salt/sugar.
	Males + 18y	Females + 18y
Total daily kcal reduction	-204	-159
Weight reduction (kg)^a	-8.6	-6.7
Average BMI baseline	27.8	27.5
Average modelled BMI	25.8	25.9
BMI change	-2.0	-1.5

^aAssuming that 0.042 kg body weight is lost per calorie reduction, weight change achieved after ~ 3y [24].

Changes in environmental impacts

Table 4 presents daily per capita changes in environmental impacts per food category based on changes in consumed kcal when comparing the two contrasting scenarios of people in the UK consuming 1) foods high in salt/sugar vs. 2) substitutes lower in salt/sugar. Environmental impacts were reduced for all food categories with the greatest reductions observed for Bread, Confectionery, and Desserts across all environmental impact categories (Table 4).

Aggregating the daily changes in environmental impacts over 1 y and for a UK adult population of 53.2 million would amount to a total reduction of -2.7 Mt of CO₂eq (climate change impact), ~ -500.000 ha of land, -0.5 km³ of blue water, -12 km³ of scarcity weighted water, ~ -12.000 tonnes of PO₄eq (eutrophication potential), and nearly − 14.000 tonnes of SO₂eq (acidification) (Table 4).

Table 4

Daily absolute change observed in environmental impacts across eight food groups when comparing consumption of foods high in salt/sugar with substitutes lower in salt/sugar.
Food category	Daily change in g of CO₂eq^a	Daily change in m² land use^a	Daily change in m³ water use^a	Daily change in m³ water scarcity^a	Daily change in g PO₄e^a	Daily change in g SO₂e^a
Biscuits
Males	-3	-0.01	-0.6	-13.5	-0.01	-0.01
Females	-4	-0.01	-0.6	-14.0	-0.01	-0.02
Biscuits (crackers)
Males	-4	-0.01	-1.2	-32.6	-0.03	-0.03
Females	-4	-0.01	-1.2	-33.8	-0.03	-0.03
Bread
Males	-51	-0.12	-13.2	-391.2	-0.31	-0.37
Females	-35	-0.08	-9.0	-268.0	-0.21	-0.25
Breakfast cereals
Males	-2	0.00	-0.7	-18.9	-0.01	-0.02
Females	-2	0.00	-0.5	-13.2	-0.01	-0.01
Confectionary
Males	-44	-0.07	-3.1	-50.4	-0.12	-0.13
Females	-45	-0.07	-3.2	-51.7	-0.12	-0.13
Desserts
Males	-37	-0.05	-5.3	-102.9	-0.13	-0.18
Females	-31	-0.04	-4.4	-85.5	-0.11	-0.15
Snacks
Males	-5	-0.01	-2.0	-81.5	-0.05	-0.05
Females	-5	-0.01	-1.8	-73.9	-0.05	-0.04
Spreads
Males	-1	0.00	-0.4	-9.6	-0.01	-0.01
Females	-1	0.00	-0.3	-7.7	-0.005	-0.005
Total^b	-2.7 (Mt)	-486 793 (ha)	0.5 (km³)	12 (km³)	-11 697 (tonnes)	-13 769 (tonnes)

^aChange observed when comparing consumption of foods high in salt/sugar with substitutes lower in salt/sugar. ^bTotal change in environmental impacts when aggregating daily impacts over 1 y and for a UK adult (males + females) population of 53.2 million. CO₂eq = carbon dioxide equivalents (climate change impact); PO₄eq = phosphate equivalents (eutrophication potential); SO₂eq = sulphur dioxide equivalents (acidification); Mt = mega tonnes; ha = hectares.

The results of our analyses show that there’s opportunity for UK consumers to substitute foods high in salt and sugar with lower salt and sugar alternatives within the same food category. The suggested intra-category food substitutions would largely be like-for-like and—in the context of the introduction of a new sugar and salt tax— would not necessarily accrue an added cost to consumers, thus protecting households and low-income families in particular from potential price rises. Consuming foods lower (as opposed to those high) in salt and sugar could lead to important reductions in people’s daily calorie intake and body weight, lowering the prevalence of overweight and obesity in the UK from approximately 60–65% to about 40–45%. This in turn is highly likely to bring down the current estimated £19.2bn cost of overweight and obesity currently faced by the NHS. The proposed food substitutions, resulting in a lowered daily energy intake, also generated notable reductions in environmental impacts. For example, the total daily reductions in GHGE from the food swaps would lower the average daily per capita food-related GHGE (5.7 kg) of an adult in the UK by to 2–3% [25]. Importantly, these reductions would be achieved without the need for substantial dietary changes but brought about only with intra-category substitutions between foods that were not substantially different from one another in composition or ingredients (Fig. 1).

The affordability of the suggested food group substitutions is an important aspect to consider, especially since increased food prices (likely following a salt and sugar tax), could further increase food expenditures among the most deprived households in the UK that currently allocate > 15% of total budgets to food purchases [11]. Our findings show that the explored within food-group substitutions seem to be a viable option from a financial perspective since post-tax prices of substitutes lower in salt or sugar would overall not exceed pre-tax prices of high salt/sugar foods. These results mirror previous research demonstrating a lower cost of more nutritious diets [26–28]. Our results also show that the consumption of intra-category substitutes (on average 45–66% lower in salt and 48–83 lower in sugar depending on the category), could reduce overweight and obesity by about 20 percentage points in British adults. This is similar to other research that has reported reductions in the prevalence of obesity as a result of drops in intakes of added sugars [29, 30]. Modelling studies have shown both health and economic gains resulting from a reduced intake of added sugars [31–34], and as a result of the taxation of salt or foods high in salt [34–38]. Hence, the observed changes in overweight and obesity are likely to also generate improved health outcomes.

When comparing the two contrasting scenarios of people in the UK consuming 1) foods high in salt/sugar vs. 2) substitutes lower in salt/sugar, we found important reductions in daily kcal intakes and, besides resulting drops in overweight and obesity, also reductions in six environmental impact categories. These findings tally with previous research highlighting overconsumption of energy as a key driver of avoidable dietary related environmental impacts [39–43]. For example, the estimated GHGE from excessive energy consumption amounted to 10% of total food-related climate impacts in Sweden [40]. Furthermore, a comprehensive modelling study of diets in 37 countries showed that following national Food Based Dietary Guidelines (FBDGs) would reduce diet induced environmental impacts in high-income countries and that this would be mainly driven by reductions in caloric intake [43].

To the best of our knowledge, this is the first study to explore a wide range of impacts arising from plausible post-tax substitutions of foods high vs. substitutes lower in salt/sugar, within food groups rather than between them. Our analysis brings together various methods and different data sources to explore the co-benefits of dietary substitutions leading to reduced salt and sugar consumption. A notable strength is the ability to combine national data sources on both food purchases and food consumption to anticipate how these substitutions could lead to changes across dimensions of social and environmental sustainability. As opposed to only exploring people’s intake levels across different food groups, we also incorporate information on the most popular foods actually purchased within those same food groups. Our analysis is, therefore, likely to capture a more complete picture of the various possibilities and impacts of fiscal measures aimed at reducing intakes of salt and added sugars.

The UK government is committed to tackling overweight and obesity in the population [44] and the UK Committee on Climate Change (CCC) have set a goal to reduce domestic land-based emissions by 37 Mt by 2050 [45]. Based on our analyses, the prevalence of overweight and obesity in the UK would drop by approximately 20 percentage points, and yearly food-related GHGE would reduce by ~ 2%, from the 155 Mt estimated in 2020 (considering impacts from both domestic and imported food [4]) to 152 Mt (i.e. a ~ 3 Mt reduction). This would be achieved through intra food category substitutions of foods not substantially different from one another in composition or ingredients, thus, not likely to demand substantial dietary changes. Taken together, the proposed in-category substitutions, while yet untested, seem to be both metabolically and environmentally motivated and in line with governmental strategies and targets.

A limitation to our research is the uncertainty that lies in some of the assumptions made regarding food substitutions. In this study, we operate under the condition that people would continue to buy their daily salty and sugary snacks, just with a lower salt/sugar content. Although some research indicates that substitutions would be plausible within food categories, there is still the possibility that they would, if at all, occur across food groups, thus impacting nutrient, caloric and environmental aspects. For example, the taxation of salt and saturated fat in an experimental study led to increases in purchases of sugary foods [12]. This is likely not to happen in the context of the UK, as the proposed tax is targeting both salt and sugar. Furthermore, people might in reality, eat larger amounts of the lower-sugar food substitutes, to cover for the reduced caloric intake. Because calories consumed from foods high in salt/sugar tend to be “unconscious calories” (i.e. people eat them because they have a habit of eating a biscuit in a certain context and/or at a certain time [46]), it is unlikely that people would consciously experience that calorie deficit (as e.g. hunger) if they were to replace their usual snack with a snack that contains less calories. Given that we modelled changes in calories and bodyweight only in obese and overweight people (likely to have an energy surplus), it is more plausible that the suggested substitutions would lead to a stable reduction in energy intake and bodyweight. Yet, without any experimental evidence, we are not able to substantiate what kind of substitutions would occur, if at all, (with resulting impacts on food expenditures, BMI, and the environment) if a tax on salt and sugar was to be introduced in the UK. Our findings do, however, provide evidence that —even discounting the possibility that people would switch consumption to healthier categories of foods following a tax on sugar/salt—small within-category substitutions offer the potential for health benefits.

There are also some uncertainties related to the data underlying our analyses. Self-reported dietary intake data always comes with a certain level of bias in the form of e.g. under-/over-reporting linked to BMI, gender, social desirability, restrained eating, education, literacy, perceived health status and ethnicity [47]. However, the NDNS presently constitutes the only continuous nationally representative dietary data for the UK population, and thus the best alternative available for our analyses. We estimated changes in environmental impacts only from calorie reduction and not from actual within-category substitution based on differing ingredients of foods. Furthermore, impacts were averaged within each category and were not weighted for consumption level of specific food items. We computed averages for each food category because the level of detail in the available environmental impact data was not granular enough to match individual foods with their specific impact. In addition, there was very little variation in the environmental impacts of different food types (e.g. the 4,691 different types of chocolates and sweets) used for the averaging of impacts within food categories. The used environmental impact data itself is likely to be subject to a certain level of uncertainty since the footprints only cover impacts generated during the production phase. However, most LCAs for foods typically focus on activities up to the factory gate seeing that the main proportion of impacts is generated within this production-frame [48].

Lastly, we assumed a “worst case scenario” where reformulation is not undertaken in response to the introduction of a salt and sugar levy, and that the full cost of the levy is instead passed on to consumers. In reality, manufacturers may carry out some level of reformulation (as done following the SDIL [6]) which would enable consumers to afford their most preferred products and automatically also reduce their salt/sugar consumption.

By investigating the affordability of intra-food group substitutions and their effects on anthropometric and environmental indicators in the context of the introduction of a new combined sugar and salt tax, our work adds new evidence to support the introduction of targeted fiscal measures to reduce both salt and sugar consumption in the UK. We show that the suggested tax would not force people into major changes in their weekly shop and could allow them to still buy relatively similar salty and sugary snacks as they were used to. At the same time this could contribute to national goals of lowering the prevalence of overweight and obesity and reducing environmental damage. Despite raised uncertainties, our findings add to this previous body of research, and thus reinforce arguments for why currently high intakes of salt and sugar could be targeted using fiscal policies that are progressive and considerate of social and environmental sustainability.

Competing Interests: The authors declare that they have no conflict of interest.

Acknowledgements: We would like to thank Hannah Brinsden and Rebecca Tobi at the Food Foundation for their important contributions to designing this research. This study forms part of the Sustainable and Healthy Food Systems (SHEFS) project supported by the Wellcome Trust's Our Planet Our Health program (grant 205200/Z/6/Z). It was also supported by the af Jochnick Foundation. The funders had no role in the study design, data analysis or writing, or the decision to submit for publication.

Author contributions: PEC: Conceptualization, Methodology, Investigation, Data curation, Formal analysis, Project administration, Writing – Original Draft; RG: Conceptualization, Methodology, Funding acquisition. Writing – Review & Editing; SNE: Conceptualization, Methodology, Resources, Writing – Review & Editing; GS and RS: Conceptualization, Methodology, Writing – Review & Editing; PS: Conceptualization, Methodology, Resources, Supervision, Funding acquisition, Writing – Review & Editing.

Data availability: Code used to for analyses is study is available from the corresponding author upon reasonable request. The data used is available for purchase from Kantar.

Afshin A, Sur PJ, Fay KA, et al (2019) Health effects of dietary risks in 195 countries, 1990–2017: a systematic analysis for the Global Burden of Disease Study 2017. The Lancet. https://doi.org/10.1016/S0140-6736(19)30041-8
The Rising Cost of Obesity in the UK. In: Front. Econ. https://www.frontier-economics.com/uk/en/news-and-articles/news/news-article-i20358-the-rising-cost-of-obesity-in-the-uk/. Accessed 12 Oct 2023
Janssen F, Bardoutsos A, Vidra N (2020) Obesity Prevalence in the Long-Term Future in 18 European Countries and in the USA. Obes Facts 13:514–527
Forbes H (2021) Tracking UK Food System Greenhouse Gas Emissions: 2022 Update, Prepared by WRAP. United Kingdom
Murphy-Bokern D Environmental impacts of the UK food economy with particular reference to WWF Priority Places and the North-east Atlantic. World Wildlife Fund
Scarborough P, Adhikari V, Harrington RA, Elhussein A, Briggs A, Rayner M, Adams J, Cummins S, Penney T, White M (2020) Impact of the announcement and implementation of the UK Soft Drinks Industry Levy on sugar content, price, product size and number of available soft drinks in the UK, 2015-19: A controlled interrupted time series analysis. PLOS Med 17:e1003025
Bandy LK, Scarborough P, Harrington RA, Rayner M, Jebb SA (2020) Reductions in sugar sales from soft drinks in the UK from 2015 to 2018. BMC Med 18:20
Public Health England (2017) Sugar Reduction: Achieving the 20% A technical report outlining progress to date, guidelines for industry, 2015 baseline levels in key foods and next steps.
Public Health England (2018) Sugar reduction and wider reformulation programme: Report on progress towards the first 5% reduction and next steps.
Dimbelby H (2021) The National Food Strategy: The Plan.
Family Food 2017/18. In: GOV.UK. https://www.gov.uk/government/publications/family-food-201718/family-food-201718. Accessed 23 Jul 2020
Waterlander WE, Jiang Y, Nghiem N, Eyles H, Wilson N, Cleghorn C, Genç M, Swinburn B, Mhurchu CN, Blakely T (2019) The effect of food price changes on consumer purchases: a randomised experiment. Lancet Public Health 4:e394–e405
Epstein LH, Finkelstein E, Raynor H, Nederkoorn C, Fletcher KD, Jankowiak N, Paluch RA (2015) Experimental analysis of the effect of taxes and subsides on calories purchased in an on-line supermarket. Appetite 95:245–251
Goldfield GS, Epstein LH (2002) Can fruits and vegetables and activities substitute for snack foods? Health Psychol 21:299–303
Griffith R, Jenneson V, James J, Taylor A (2021) The impact of a tax on added sugar and salt. Institute for Fiscal Studies, UKRI - Economic and Social Research Council
Reducing your Salt Intake. In: Milton Keynes Univ. Hosp. https://www.mkuh.nhs.uk/patient-information-leaflet/reducing-your-salt-intake. Accessed 21 Jul 2023
How to cut down on sugar in your diet. In: nhs.uk. https://www.nhs.uk/live-well/eat-well/how-to-eat-a-balanced-diet/how-to-cut-down-on-sugar-in-your-diet/. Accessed 13 Oct 2023
Nutritional Values For Common Foods And Products. https://www.nutritionvalue.org/. Accessed 13 Nov 2023
Nutracheck - Keeping track of your diet. https://www.nutracheck.co.uk/Home. Accessed 13 Dec 2023
Calorie Counter and Nutrition Information for foods. https://www.fatsecret.com/calories-nutrition. Accessed 13 Nov 2023
Tesco - Supermarkets | Online Groceries, Clubcard & Recipes. In: Homepage. https://www.tesco.com/. Accessed 13 Nov 2023
Clark M, Springmann M, Rayner M, Scarborough P, Hill J, Tilman D, Macdiarmid JI, Fanzo J, Bandy L, Harrington RA (2022) Estimating the environmental impacts of 57,000 food products. Proc Natl Acad Sci 119:e2120584119
NDNS: time trend and income analyses for Years 1 to 9 (2019). Public Health England
Hall KD, Sacks G, Chandramohan D, Chow CC, Wang YC, Gortmaker SL, Swinburn BA (2011) Quantification of the effect of energy imbalance on bodyweight. The Lancet 378:826–837
Murakami K, Livingstone MBE (2018) Greenhouse gas emissions of self-selected diets in the UK and their association with diet quality: is energy under-reporting a problem? Nutr J 17:27
Springmann M, Clark MA, Rayner M, Scarborough P, Webb P (2021) The global and regional costs of healthy and sustainable dietary patterns: a modelling study. Lancet Planet Health 5:e797–e807
van Dooren C, Tyszler M, Kramer GFH, Aiking H (2015) Combining Low Price, Low Climate Impact and High Nutritional Value in One Shopping Basket through Diet Optimization by Linear Programming. Sustainability 7:12837–12855
Eustachio Colombo P, Elinder LS, Lindroos AK, Parlesak A (2021) Designing Nutritionally Adequate and Climate-Friendly Diets for Omnivorous, Pescatarian, Vegetarian and Vegan Adolescents in Sweden Using Linear Optimization. Nutrients 13:2507
Mytton OT, Eyles H, Ogilvie D (2014) Evaluating the Health Impacts of Food and Beverage Taxes. Curr Obes Rep 3:432–439
Wang YC, Coxson P, Shen Y-M, Goldman L, Bibbins-Domingo K (2012) A Penny-Per-Ounce Tax On Sugar-Sweetened Beverages Would Cut Health And Cost Burdens Of Diabetes. Health Aff (Millwood) 31:199–207
Basu S, Lewis K (2014) Reducing Added Sugars in the Food Supply Through a Cap-and-Trade Approach. Am J Public Health 104:2432–2438
Mekonnen TA, Odden MC, Coxson PG, Guzman D, Lightwood J, Wang YC, Bibbins-Domingo K (2013) Health Benefits of Reducing Sugar-Sweetened Beverage Intake in High Risk Populations of California: Results from the Cardiovascular Disease (CVD) Policy Model. PLoS ONE 8:e81723
Vreman RA, Goodell AJ, Rodriguez LA, Porco TC, Lustig RH, Kahn JG (2017) Health and economic benefits of reducing sugar intake in the USA, including effects via non-alcoholic fatty liver disease: a microsimulation model. BMJ Open 7:e013543
Eustachio Colombo P, Milner J, Pastorino S, Green R (2023) Population health impacts and associated monetary gains from the taxation of salt and sugar in the United Kingdom. https://doi.org/10.1101/2023.08.16.23294155
Cobiac LJ, Scarborough P (2019) Modelling the health co-benefits of sustainable diets in the UK, France, Finland, Italy and Sweden. Eur J Clin Nutr 73:624–633
Smith-Spangler CM (2010) Population Strategies to Decrease Sodium Intake and the Burden of Cardiovascular Disease: A Cost-Effectiveness Analysis. Ann Intern Med 152:481
Ni Mhurchu C, Eyles H, Genc M, Scarborough P, Rayner M, Mizdrak A, Nnoaham K, Blakely T (2015) Effects of Health-Related Food Taxes and Subsidies on Mortality from Diet-Related Disease in New Zealand: An Econometric-Epidemiologic Modelling Study. PLOS ONE 10:e0128477
Nghiem N, Blakely T, Cobiac LJ, Pearson AL, Wilson N (2015) Health and Economic Impacts of Eight Different Dietary Salt Reduction Interventions. PLOS ONE 10:e0123915
Franco S, Barbanera M, Moscetti R, Cicatiello C, Secondi L, Massantini R (2022) Overnutrition is a significant component of food waste and has a large environmental impact. Sci Rep 12:8166
Sundin N, Rosell M, Eriksson M, Jensen C, Bianchi M (2021) The climate impact of excess food intake - An avoidable environmental burden. Resour Conserv Recycl 174:105777
Ridoutt BG, Hendrie GA, Noakes M (2017) Dietary Strategies to Reduce Environmental Impact: A Critical Review of the Evidence Base. Adv Nutr 8:933–946
Hendrie G, Baird D, Ridoutt B, Hadjikakou M, Noakes M (2016) Overconsumption of Energy and Excessive Discretionary Food Intake Inflates Dietary Greenhouse Gas Emissions in Australia. Nutrients 8:690
Behrens P, Kiefte-de Jong JC, Bosker T, Rodrigues JFD, De Koning A, Tukker A (2017) Evaluating the environmental impacts of dietary recommendations. Proc Natl Acad Sci 114:13412–13417
Department of Health and Social Care Tackling obesity: empowering adults and children to live healthier lives. https://www.gov.uk/government/publications/tackling-obesity-government-strategy/tackling-obesity-empowering-adults-and-children-to-live-healthier-lives. Accessed 12 Dec 2023
Committee on Climate Change (2020) Land use: Policies for a Net Zero UK.
Aarts H, Dijksterhuis A (2000) Habits as knowledge structures: Automaticity in goal-directed behavior. J Pers Soc Psychol 78:53–63
Coulston AM, Boushey C, Ferruzzi MG, Delahanty LM (eds) (2017) Nutrition in the prevention and treatment of disease, Fourth edition. Academic Press, London ; San Diego, CA
Poore J, Nemecek T (2018) Reducing food’s environmental impacts through producers and consumers. Science 360:987–992

The authors declare no competing interests.

Supplementarymaterials20240131.docx
Supplementary materials

Download PDF

Version 1

posted

You are reading this latest preprint version

Modelling impacts of a salt and sugar tax on intra-category food substitutions, BMI and environmental footprints

Status:

Version 1

Abstract

Figures

Introduction

Materials and methods

Purchase panel data

Energy content of foods

Environmental impacts of foods

Quantifying changes in the price of foods

Quantifying changes in consumption of kcal, bodyweight and body-mass index

Quantifying changes in environmental impacts of foods

Results

Description of nutrient content and consumption of food categories

Changes in prices

Changes in consumption of kcal, bodyweight and body-mass index

Changes in environmental impacts

Discussion

Conclusions

Statements and Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1