The following verse shows that fasting leads to accumulation of merit (Punya or good Karma).
Manu 2.188. He who performs the vow (of studentship) shall constantly
subsist on alms, (but) not eat the food of one (person only); the
subsistence of a student on begged food is declared to be equal (in
merit) to fasting.
And verses like the ones given below show ...