Where to buy and what to eat: The relationship between purchasing channels and nutrient intake in Japan

• Analysis of purchasing channels and nutrient intake. • Studied consumers over 40 using purchase history data and food frequency questionnaire. • Part of nutrient intake, mostly carbohydrates, remains stable across food access and demographics. • No evident relationship was found between food environment and nutrient intake. • Nutrient intake might be primarily driven by individual preferences, not food environment. Interventions in the food environment to improve nutrient intake are often proposed with the goals of reducing obesity and non-communicable diseases. Prior studies exploring relationships between the food environment and nutrient intake have assumed that most purchased food is consumed without examining direct correlations between purchasing channels and nutrient intake. This study addresses this research gap by analyzing correlations between purchasing channels, nutrient intake, and body mass index (BMI) using a unique dataset from Japan combining individual purchase records and nutrient intake data for men and women over 40 years of age. We also introduced a method to assess non-discretionary macronutrient intake ratios—proportions that remain stable across such factors as food access and demographics. Our results reveal a generally weak correlation between purchasing channels and both caloric intake and BMI; however, among individuals who are not overweight, frequent convenience store purchases were linked to lower caloric intake. We identified a non-discretionary macronutrient intake ratio, primarily carbohydrates, of approximately 3.5 % (standard error 9.7 × 10 −5 ) in non-overweight individuals. After accounting for non-discretionary intake ratios, the correlation between purchasing channels and macronutrient intake ratios remained weak. Policies targeting discretionary nutrient intake may have potential to improve overall nutrient consumption, because factors beyond purchasing channels are more likely to influence discretionary intake.