SB 7.13.16-17

bibharṣi kāyaṁ pīvānaṁ
 sodyamo bhogavān yathā
vittaṁ caivodyamavatāṁ
 bhogo vittavatām iha
bhogināṁ khalu deho ’yaṁ
 pīvā bhavati nānyathā
Synonyms: 
bibharṣi — you are maintaining; kāyam — a body; pīvānam — fat; sa-udyamaḥ — one who endeavors; bhogavān — one who enjoys; yathā — as; vittam — money; ca — also; eva — certainly; udyama-vatām — of persons always engaged in economic development; bhogaḥ — sense gratification; vitta-vatām — for persons who possess considerable wealth; iha — in this world; bhoginām — of the enjoyers, karmīs; khalu — indeed; dehaḥ — body; ayam — this; pīvā — very fat; bhavati — becomes; na — not; anyathā — otherwise.
Translation: 
Seeing the saintly person to be quite fat, Prahlāda Mahārāja said: My dear sir, you undergo no endeavor to earn your livelihood, but you have a stout body, exactly like that of a materialistic enjoyer. I know that if one is very rich and has nothing to do, he becomes extremely fat by eating and sleeping and performing no work.
Purport: 

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura did not like his disciples to become very fat in the course of time. He would become very anxious upon seeing his fat disciples becoming bhogīs, or enjoyers of the senses. This attitude is herewith confirmed by Prahlāda Mahārāja, who was surprised to see a saintly person adopting ājagara-vṛtti and becoming very fat. In the material world also, we generally see that when a man who is poor and skinny gradually endeavors to earn money through business or some other means and he then gets the money, he enjoys the senses to his satisfaction. By enjoying the senses one becomes fat. Therefore in spiritual advancement becoming fat is not at all satisfactory.