**Background:** Poor diet is a leading preventable risk factor for the global burden of non-communicable disease, and the second leading risk factor in Canada. The COVID-19 pandemic has dramatically altered consumer food environments through lockdowns, economic precarity, and shifts in food purchasing patterns (e.g., stockpiling, increased online shopping). Prior to the pandemic, Atlantic Canadian provinces (New Brunswick, Prince Edward Island, Nova Scotia, Newfoundland and Labrador) already faced an excess burden of dietary risk compared to the rest of Canada, including the highest prevalences of food insecurity after Nunavut and the Northwest Territories, the lowest absolute expenditure on food, the lowest proportion of households eating fruits/vegetables 5+ times per day, and elevated rates of diabetes, cardiovascular disease mortality, and certain cancers. No published research had yet captured how altered consumption behaviour during COVID-19 affects dietary quality in Canada. Canada does not routinely collect quantitative individual/household food consumption data; government dietary surveillance is periodic (the CCHS-Nutrition has been collected only twice in two decades: 2004 and 2015), and existing economic monitoring (e.g., Consumer Price Index) does not record food items at sufficient resolution to infer nutritional quality.
**Methods:** This is an observational field nutritional epidemiology study. The target population is adults 19 years and older residing in the four Atlantic provinces. The goal is n=1000 for the Atlantic region, accounting for non-response and dropouts. Recruitment uses dual-frame calls (landline and cellphone) via random-digit dialled numbers, with up to four scheduled callbacks (six for cellphones). The purchased sample includes 12,000 RDD numbers and 8,000 active cellphone numbers allocated proportionally to provinces based on 2015 CCHS-Nutrition sampling fractions; approximately three-quarters of phone numbers are preverified. Stratification is first by province (by 2016 Census population), then by area frame following CCHS-Nutrition, with dual allocation (landline and cellphone subsamples), and finally age-sex group quotas corresponding to Dietary Reference Intakes. Data collection entails 12 weeks of participation: (1) enrolment with sociodemographics (age, sex, gender, pre-COVID-19 income, employment, household composition, receipt of economic relief, rural residence); (2) two 24-hour diet recalls using the online ASA-24 Canada 2018 tool on non-consecutive days at least 3 days apart; and (3) online uploads of household food purchase receipts over 12 weeks. Receipts are de-identified, food outlets matched to spatial coordinates, and food items matched to the Canadian Nutrient File. Incentives of CAD$40 per milestone (total maximum CAD$120) are offered for completion of enrolment, diet recalls, and the full study.
**Key Results:** As a study protocol, no results are reported. The paper describes planned analyses for three objectives. Objective 1 will estimate daily intakes of energy, vegetables, fruits, fibre, processed meats, sugar-sweetened beverages, protein, total and saturated fat, carbohydrate, total sugar, and sodium during COVID-19, dividing the population into quantiles by age-sex, gender, and income. The second diet recall will be used to account for episodically consumed foods using the National Cancer Institute method. Objective 2 will use a case-control design with matched historical controls from the 2015 CCHS-Nutrition (n=3514 adults 19y+ for the Atlantic provinces; provincial breakdown: NL 878, PE 728, NS 1020, NB 888). Quantile regression will examine change during COVID-19 using a COVID-19/CCHS dummy variable, adjusting for covariates including time spent on paid work, time spent on food shopping, receipt of economic relief, household size, and home ownership. Objective 3 will fit multivariate regression models to examine associations between six household purchasing measures (proportion from home-delivery, proportion from fruits and vegetables, average number of unique food outlets per month, average daily cost of diet, average cost of diet from delivery, average distance travelled) and dietary intakes.
**Clinical Implications:** This study addresses critical gaps in routine nutrition surveillance in Canada, where population nutrition data are collected only periodically (per decade) and no routine infrastructure exists to assess diet-related health during 2020–2021. The findings will inform four specific areas of policy consequence: (1) the dietary impact of economic precarity of unexpected scale and duration—prior to the pandemic, requiring social assistance was the single strongest predictor of household food insecurity in Canada, and Statistics Canada suggested 26% of Canadians were financially vulnerable to COVID-19 work interruptions; (2) food price inflation and inequitable impact for vulnerable households—analysis of the 2008 financial crisis showed food prices rose faster after the crisis than any other component of consumer spending in Canada; (3) the gap between typical consumer price monitoring and actual healthy diet measurement—the Canadian CPI match to diet varies by province, with Atlantic provinces faring among the worst; and (4) the long-term consequences of restricted physical access to food environments and the rapid expansion of online food purchasing, described as a 'double-edged sword' for diet quality. Results will be shared with provincial and national decision makers through a steering committee representing the four provincial governments, and disseminated via peer-reviewed journals and conferences. The study received CIHR funding (FRN VR5 172691) and ethics approval from Dalhousie University Research Ethics Board (initial approval 25 November 2020; final amendments 2 February 2021).