Engel's law — named after the 19th century German statistician Ernst Engel — states that as people's income rises, they spend a declining proportion of their income on food even if the actual amount they spend on food increases. Thus Engel's coefficient — the proportion of money spent on food in household expenses — is seen as an indicator of a nation's standard of living. The figure falls as a country's economic growth makes its people wealthier, and tends to rise when they get poorer. It is also said that today the correlation is no longer that simple as people's consumption patterns and lifestyles grow more diverse.

The Engel's coefficient for Japan, which topped 60 percent during the food shortage in the chaos right after World War II, steadily declined during the postwar reconstruction and subsequent rapid economic growth — until the figure began picking up again over the past decade. The figure reached 25 percent last year — compared with a low of 22.9 percent in 2005 — and continues to rise. In June, when an average household of two or more people spent a total of ¥261,452, a 2.2 percent decline in real terms from a year ago, the ¥69,945 that went for food (including dining out) accounted for 26.8 percent of the total. The figure is reportedly rising faster among lower-income people.

This may be another indication of how households have yet to reap the benefits of the Abe administration's economic policies, which pushed up corporate profits and share prices while people's net income fell as prices rose faster than wage hikes. It may also be attributable to other longer-term factors, including changing family lifestyles.