When does dietary knowledge matter to obesity and overweight prevention?

► Expected food availability (EFA) underlies the effects of dietary knowledge (DK). ► DK affects mainly the quantity of diet among the overweight when EFA increases. ► DK affects mainly the quality of diet among the non-overweight when EFA decreases. ► Using conventional models, the estimated effects of DK tend to be smaller. ► When EFA increases dietary education may be more effective than indicated before. Improving dietary knowledge has the potential to prevent obesity and overweight and, if effective, is a highly feasible policy measure. This paper proposes a new framework to examine the effects of dietary knowledge on nutrient intake and diet quality. The framework allows the effects to differ by one’s expectation about food availability (EFA). Using data from China, we find that dietary knowledge affects mainly the quantity of diet (e.g., lowering total calorie intake) when EFA is increasing, while it affects mainly the quality of diet (e.g., lowering the share of calories from oils) when EFA is decreasing. The effect on the quantity is larger among overweight adults, while the effect on the quality is more significant among non-overweight adults. Without distinguishing the direction of changes in EFA as in previous studies, the estimated effects of dietary knowledge tend to be smaller. Thus, as an anti-obesity measure, dietary education may be more effective than indicated by previous studies under the situations where EFA increases (e.g., introducing food coupons), while only marginally effective under the situations where EFA decreases (e.g., increasing real food prices).