It is difficult for those who constantly chant the mantra of dieting, to understand how marvelous the taste of 'sweet' is to people in this world, many of whom do not know what sweetness is at all in their lifetime.
In the Prime Material Plane, there are natural sources of sweetness like honey, fruits and such, but they are almost nonexistent in this world.
Thanks to being the children of the City Lord, Luther and Anna have had the chance to taste beetroot, a rare source of sweetness, but they could not indulge in them freely. If they could eat three to five per year, it would be considered quite good.
They are rather worse off in this regard. If you have never tasted sweetness, you will not perceive bitterness. But once you had tasted sweetness, all the days without it would seem bitter.
Aisike offered to trade beetroot for grain, but in reality, even several times more grain could hardly get beetroot due to its low yield.