Crux of the chapter

अथात्रेयस्य भगवतो वचनमनुनिशम्य पुनरेव वामकः काशिपतिरुवाच भगवन्तमात्रेयम् -

भगवन् !  संपन्निमित्तजस्य पुरुषस्य विपन्निमित्तजानाम् च रोगाणां किममभिवृद्धिकारणमिति॥३०॥

तमुवाच भगवान् आत्रेयः हिताहारोपयोग एक एव पुरुषवृद्धिकरो भवति , 

अहिताहारोपयोगः पुनः व्याधिनिमित्तमिति॥३१॥

Translation : After deliberating upon Lord Aatreya's statement, once again King of Kashi, Vamaka said to Lord Atreya " O Lord ! What is the cause of growth of Purusha generated from wealth (Excellent condition) of factors and of diseases generated by defects in the same factors ?"

Lord Aatreya said to him " Only the use of wholesome food is the cause of growth of organisms and use of unwholesome food is cause of growth of diseases.

Commentary (Chakrapani) : The word Eka Eva is used here to show the predominance or supremacy of wholesome food and not to rule out other causes like behavior, sleep and sound etc. quoted elsewhere. In the word व्याधिनिमित्त the middle term  अभिवृद्धि is hidden as the question refers to cause of growth. Unwholesome food is already mentioned as cause of origin of diseases. Or unwholesome food is cause of origin and growth of diseases and therefore middle term is omitted.


Commentary (Vishnu) : The crux of the whole chapter is stated in this pair of verses. Whatever may be the origin of an organism or it's diseases; the progress of disease can be controlled through use of wholesome food. This is the take home message of this whole chapter. Healthy growth of organism is also dependent on use of wholesome food. Here the emphasis is not on just food items but the whole galaxy of factors like quantity, timing, surroundings, combinations state of previous diet etc. In short emphasis is on usage. Just as grammatically correct word usage leads to lucidity in meaning; correct usage of food from health point of view  leads to easy attainment of health, growth and longevity. 
Chakrapani has correctly pointed out the caveats and meaning between the lines. 
Just as proper use of food leads to health improper use is cause of both origin and growth of diseases. 
Sushrut says ' संक्षेपतः क्रियायोगो निदानपरिवर्जनम्॥ '  Avoidance of causative factors is treatment in brief. As long as causative factors are continuing the disease process will not stop or reverse. When causative factors are no longer operative the natural tendency of Doshas is towards restoration of equilibrium ( स्वभावोपरम सिद्धान्त ) is one of the basic principles of Ayurveda. This tendency is inbuilt in all organisms. This tendency is both necessary and sufficient in any organic system. In my opinion it is an Evolutionarily Stable Strategy (ESS) without which organisms cannot survive and reproduce. 
Therefore 
1. Stoppage of improper use of food and 
2.Proper usage of wholesome food 
are the two extremely important arms of correct treatment.  Both are necessary and in most of the diseases sufficient. Medicines play a minor role if these two arms are properly used.