Taxation Online Experimental Supermarket (SUPERNET 2)

Impact of Taxation and Subsidies on the Nutrition Quality of Purchases in an Online Experimental Supermarket, Overall and by Income Level: a Randomized Control Trial

Scientific context The increase in the consumption of unhealthy food coupled with a suboptimal consumption of healthier options have increased the risk of non-communicable diseases (NCD) worldwide. Among other public policies to address the rise in NCD -such as front of pack labelling, regulation of food and beverages in schools, marketing regulations targeted to children- taxation has been recognized as a cost-effective strategy to reduce consumption of taxed products. Although subsidies have been used to reduce food insecurity, with the rise in NCD associated with unhealthy diets, studies have explored the feasibility of combining subsidies to incentivize the consumption healthy food with taxes on unhealthy options. The impact of prices on dietary behaviour of consumers has been demonstrated in experimental designs as well as in economic analysis of observational data on purchases. Although some experimental studies have been used to study the impact of taxation and subsidies among specific populations in France, none has evaluated the impact in the general population.

Objective The aim of the study is to evaluate the impact of implementing taxes on unhealthy food and beverages and subsidies to healthy food, separately and combined, on the nutritional quality of purchases, overall and by income level, in an experimental online supermarket.

Intervention description: The intervention includes taxation of lower nutritional quality products (identified using the front-of-pack nutrition label Nutri-Score - classes D and E) and/or subsidies for products of higher nutritional quality (identified as raw products or Nutri-Score A and B).

Design The intervention will be a parallel arm randomized trial stratified by income against a control situation with no changes in prices and the presence of the Nutri-Score on-pack for all pre-packed products in all interventions (control, taxes and subsidies).

Expected public health impact: This study will allow to investigate the potential synergistic effect on the nutritional quality of food choices of combining taxation and income-based subsidies in a context of social inequalities in rising non-communicable disease associated with poor diets. Following a proportional universalism perspective, income-based subsidies can mitigate the regressivity of taxation according to income. As no countries have implemented this combination of fiscal policies to improve diets, the results of this study will contribute to the scientific knowledge on the topic and will provide preliminary results to decision makers.

Study Overview

• Status: Not yet recruiting
• Conditions: Nutrition; Food Purchasing Intention
• Intervention / Treatment: Behavioral: Taxation; Behavioral: Subsidies

• Study Type: Interventional
• Enrollment (Estimated): 2239
• Phase: Not Applicable

Contacts and Locations

• Study Contact: Name: Chantal Julia, MD, PhD; Phone Number: +33 01 48 38 89 53; Email: c.julia@eren.smbh.univ-paris13.fr

Study Locations

• France
  • Bobigny, France, 93000
    • Université Sorbonne Paris Nord
    • Contact: Chantal Julia, MD, PhD; Phone Number: +33 0148388953; Email: c.julia@eren.smbh.univ-paris13.fr

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion criteria:

• Adult subjects (>18 years old) included in the NutriNet-Santé cohort study from all income levels.
• For the subsidies + taxation arm: inclusion only of low income-participants (below the poverty threshold 1,288€ - 60% of the median standard of living of the population)

Exclusion Criteria:

⁃ Subjects never engaging in grocery shopping. Participants will be excluded for this based on self-reported grocery shopping frequency using a short questionnaire at the inception of the study.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Double

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
No Intervention: Control; All eligible pre-packed products labeled with Nutri-Score
Experimental: Taxation; Taxation of food products: 8% for products labeled as D using the front-of-package label Nutri-Score; 16% for products labeled as D using the front-of-package label Nutri-Score. All eligible pre-packed products labeled with the front-of-pack Nutri-Score	Behavioral: Taxation; Taxation of 8% of Nutri-Score D-labeled products Taxation of 16% of Nutri-Score E-labeled products
Experimental: Taxation + subsidies; Subsidies in the form of a discount voucher of 15€/week/household member Taxation of food products: 8% for Nutri-Score D-labeled products; 16% for Nutri-Score E-labeled products. All eligible pre-packed products labeled with Nutri-Score	Behavioral: Taxation; Taxation of 8% of Nutri-Score D-labeled products Taxation of 16% of Nutri-Score E-labeled products; Behavioral: Subsidies; Subsidies in the form of a discount voucher of 15€/household member

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
NS-2023 NPM score	Nutri-Score-2023 Nutrient Profile Model (NS-2023 NPM score) The NS-2023 NPM Score provides a global assessment of the nutritional quality of foods and beverages. The NS-2023 NPM score for foods and beverages is computed considering nutrient content for 100g/100ml . It allocates positive points for content in energy (KJ;0-10 points), total sugar (g ;0-15 points), saturated fatty acids (g;0-10 points) and salt (g;0-20 points). Negative points are allocated to content in fruits, vegetables, and legumes (%;0-5 points), fibers (g;0-5 points) and proteins (g;0-7 points). Final NS-2023 NPM scores are based on a discrete continuous scale ranging theoretically from -17 (most healthy) to +55 (less healthy). Overall NS-2023 NPM score of the shopping cart will be assessed using a weighted average (by Kcal) NS-2023 NPM score of the items in the shopping cart, for 100g.	Peri-procedure (end of shopping session)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Energy	weighted average of Energy content of the shopping cart (Kcal/100g)	Peri-procedure (end of shopping session)
Saturated fatty acids	weighted average of saturated fatty acids content of the shopping cart (g/100g)	Peri-procedure (end of shopping session)
Sugars	weighted average of sugars content of the shopping cart (g/100g)	Peri-procedure (end of shopping session)
Salt	weighted average of salt content of the shopping cart (g/100g)	Peri-procedure (end of shopping session)
Fibers	weighted average of Fibers content of the shopping cart (g/100g)	Peri-procedure (end of shopping session)
Proteins	weighted average of protein content of the shopping cart (g/100g)	Peri-procedure (end of shopping session)
Fruit and vegetables	weighted average of content of the shopping cart in fruit and vegetables (%)	Peri-procedure (end of shopping session)
Food categories	Variation of different categories of untaxed products when prices of taxed products increase Decomposition of the total effect on the primary outcome based on the variation of volumes from the different categories of products in the basket.	Peri-procedure (end of shopping session)
Purchase cost	Total price of products in the shopping cart (€) for each participant	Peri-procedure (end of shopping session)
Lespeyres price index	Price index evaluating the fiscal impact of the intervention. ((∑〖p_1 q_0 〗)/(∑p_0 q_0 ))x100, where p_1 is the price of food i in the interventions arm, p0 is the price of food i in the control arm. q_0 is the quantity purchased of food i.	Peri-procedural (end of shopping session)
Passche price index	Passche price index: changes in prices paid relative to new patterns of consumption. Paasche price index formula: ((∑〖p_(i,1) q_(i,1) 〗)/(∑p_(i,0) q_(i,1) ))x100, where p_(i,1)is the price of food item i in the intervention arm, q_(i,1) is the quantity purchased of food item i in the intervention arm and p_(i,0) is the price of food i in the control arm.	Peri-procedure (end of shopping session)

Collaborators and Investigators

• Sponsor: University of Paris 13
• Collaborators: Paris School of Economics

Study record dates

Study Major Dates

• Study Start (Estimated): May 1, 2026
• Primary Completion (Estimated): September 1, 2026
• Study Completion (Estimated): September 1, 2026

Study Registration Dates

• First Submitted: April 10, 2026
• First Submitted That Met QC Criteria: May 11, 2026
• First Posted (Actual): May 18, 2026

Study Record Updates

• Last Update Posted (Actual): May 18, 2026
• Last Update Submitted That Met QC Criteria: May 11, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: Food taxation; Food subsidies
• Additional Relevant MeSH Terms: Health Care Economics and Organizations; Economics; Taxes
• Other Study ID Numbers: INSERM 25-1264

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Researchers from public institutions can submit a collaboration request including information on the institution and a brief description of the project to collaboration@etude-nutrinet-sante.fr. All requests will be reviewed by the steering committee of the NutriNet-Santé study. If the collaboration is accepted, a data access agreement will be necessary and appropriate authorizations from the competent administrative authorities may be needed. In accordance with existing regulations, no personal data will be accessible.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No