[3] Agnsäter was born in Älmhult, Sweden, the daughter of merchant Carl Johansson and Elesine Nilsson.

In 1946, the test kitchen became an independent division, and Agnsäter served as its head until 1980,[5] with the exception of 1948–1949, when she traveled to the United States to study and work for several months.

[6] Agnsäter's trip resulted in new ideas which she brought back to Sweden: upon her return, Agnsäter was the initiator of Kooperativa Förbundet's production of meat thermometers as well as a four-piece measuring cup set adapted for Swedish cooking, now common in Swedish homes.

With butter use rising after rationing ended in Sweden, Agnsäter's aim was to teach the Swedish population to eat more healthily and cut back on fat.

[10] First published in the magazine Vi, the concept was later exported to a number of countries and adapted to local conditions, including by the US Department of Agriculture in 1984.