Research

Solo-authored.

Abstract: In February 2023, Costa Rica reformed its basic value-added tax basket on which a reduced rate applies to “guarantee a balanced diet”. This paper assesses ex-ante the impact of the reform on nutrient availability and household spending across income groups. Price elasticities are estimated using pooled National Household Income and Expenditure Survey data and a two-step censored quadratic almost ideal demand system model accounting for price and total expenditure endogeneity. Nutritional information is derived from food composition tables. Food items are grouped by processing level as a proxy to explore differences in own- and cross-price effects between ‘healthier’ and ‘less healthy’ items. The demand for ultra-processed sweet and savoury foods is price-inelastic (-0.74 and -0.81, respectively). Lower-income households’ demand is more price-sensitive. The reform applies a reduced rate to a significant number of ultra-processed savoury food items and is associated with an increase in household purchases of calories (0.7%), sugar (0.4%), and saturated fat (1.2%). A counterfactual scenario with a basic tax basket defined based on the Pan American Health Organization nutrient profile model criteria is associated with the largest reductions in calories (-0.2%), sodium (-1.0%), and saturated fat (-0.6%), with higher benefits for lower-income households. It results in minor decreases in household spending (-0.2%). While an increasing number of countries contemplate the taxation of foods high in fat, salt, or sugar, Costa Rica is unique in mandating the consideration of nutritional aspects in determining value-added tax rates. However, the recently adopted basic tax basket may not fulfil this potential. 

Seminar presentations: University of Birmingham (Centre for the Economics of Obesity); University of Costa Rica (School of Nutrition); Imperial College London (Centre for Health Economics & Policy Innovation; Public Health Policy Evaluation Unit)
Conference presentations: Quantitative Methods in Social Sciences conference (University of Warwick, 2023)

Dissemination materials: Slides; Twitter/X thread; Spanish abstract

Co-authored with Laure de Preux (Imperial College London).
Link to paper (version May 2024): https://dx.doi.org/10.2139/ssrn.4862789  

Abstract: Amid the current syndemic of obesity and climate change, little is known about the effect of extreme temperatures on dietary behaviour. Using exogenous daily variations in weather and a nationally representative consumer panel in the U.S., we find that extreme heat increases the volume purchased of sugary drinks, with persistent impacts after accounting for inter-temporal purchase shifts. We explore heterogeneous effects and a range of potential drivers, including changes in shopping habits, inter-channel substitutions, retailers' price adjustments, and psychological biases. Results reveal higher impacts among the most vulnerable households and no evidence of long-run adaptation by historical heat exposure. We combine our estimates with output from climate models for 2080-2099. Our projections indicate that climate change may increase sugary drink purchases.

Seminar presentations: Imperial College London (Economics & Public Policy)
Conference presentations: Agricultural and Applied Economics Association (AAEA 2024); Association of Environmental and Resource Economists (AERE 2024); European Association of Environmental and Resource Economists (EAERE 2024); European Health Economics Association (EuHEA 2024); Sustainable Food Systems Symposium (University of Gottingen, 2024); French Economics Association (AFSE 2024); Canadian Economics Association (CEA 2024); Maastricht Workshop on Applied Economics of the Environment (MAEE 2024)

Submitted in March 2025.

Co-authored with Jingmin Zhu* (Imperial College London), Jack Olney (Imperial College London), Daniel J Laydon (Imperial College London), William Joe (IEG, New Delhi), Manika Sharma (RTSL, New Delhi), Lindsay Steele (RTSL, New York), and Franco Sassi (Imperial College London).
* We both share first authorship.

Link to paper (version March 2025): https://doi.org/10.1101/2025.03.06.25323478   

Abstract: Background: Consumption of foods high in fat, sugar, and sodium (HFSS), and obesity, are rapidly increasing in India. Taxing HFSS foods has been proposed to promote healthier diets. This study estimates the effect of this approach on nutrient intake, diet-related disease, and associated health burden and economic benefits. Methods: We use nationally representative household expenditure survey data, dietary requirements, and food composition tables to model individual nutrient intake. Consumer responsiveness to food price changes for three income terciles is estimated using an Almost Ideal Demand System model. Longer-term policy impacts are estimated through microsimulation (Health-GPS model). Modelled policy outcomes include changes in risk exposures, disease incidence and burden, and total health expenditure. Findings: Applying the current highest Goods and Services Tax (GST) rate of 28% on HFSS foods is associated with a persistent average per capita decrease of 0·1kg/m2 in body mass index and 20mg in daily sodium intake. Over 30 years, this translates into a cumulative reduction of 9·4 million cases and 18·7 million DALYs from ischemic heart disease, chronic kidney disease, stroke, diabetes, and asthma and USD $15·3 billion averted in health expenditure. Effects are larger for higher-income households. The tax change generates a 20·8% increase in tax revenue and minor decreases in household spending. A 40% GST rate (i.e., current taxation of sugar-sweetened beverages) increases effects. Interpretation: Taxation of HFSS foods could mitigate rising diet-related diseases and morbidity in India, reduce healthcare costs and represent an important revenue source for the government.

Seminar presentations: Institute for Economic Growth (New Delhi, 2023)
Conference presentations: Delivering for Nutrition in South Asia (IFPRI, Kathmandu, Nepal, 2023)

Work-in-progress. Solo-authored.

Abstract: Nutrition in early life is paramount for child growth and development. There are concerns that climate change may slow or reverse progress against child malnutrition, particularly in Sub-Saharan Africa. The literature on climate and nutrition mostly relies on cross-sectional health survey data, usually precluding the identification of causal relationships. Several mechanisms have been hypothesised but rarely established as clear pathways. This study exploits a multi-country panel micro dataset to (1) examine the impact of extreme weather on child malnutrition (height and weight); (2) explore physiological effects and impacts on food consumption as drivers; and (3) investigate household income, own food production, and food prices as pathways to the latter. 

Work-in-progress.

Co-authored with Andrew Comstock (IFPRI) and Olivier Ecker (IFPRI).