I think in such a stressful situation one would reach for comfort foods all the more. They are also highly digestible: which is part of the problem, but sometimes such foods are all we can get past a tricky appetite.

There is something known as the "pediatric Davis experiment" where children seemed to exhibit cravings for specific foods that supplied what they had been diagnosed with malnutrition over. Once free of their illness, they would lose their taste for that food, and eat other kinds.

But this only works in situations where healthy foods are the only choices. We must exercise a lot of new habit-making to get past those old habits, and a stressful event like medical treatment makes it even more difficult. Also, the tradition is to urge "treats" because they know appetite is affected.