Letters 84.6

the food we have eaten, as long as it retains its original quality and floats in our stomachs as an undiluted mass, is a burden; but it passes into tissue and blood only when it has been changed from its original form. So it is with the food which nourishes our higher nature,—we should see to it that whatever we have absorbed should not be allowed to remain unchanged, or it will be no part of us.

Seneca, Letters to Lucilius 84.6, translated by Richard Mott Gummere