Futurama Episodes

When Fry eats an egg-salad sandwich from a vending machine at a gas station, he begins to have strange side-effects — he becomes stronger and smarter. Professor Farnsworth makes a diagnosis and concludes that Fry had ingested “intelligent worms” that have set up shop in his body. Because these worms are so smart, the regular means of flushing them out will not work. The Planet Express crew must shrink themselves to microscopic form and enter Fry’s body to fight off the intruders. Meanwhile Leela is left to divert Fry’s attention, but finds herself more and more attracted to the new man Fry has become.
wikipedia.org summary:
When Fry becomes infested with parasitic worms that make him stronger and smarter, he finally finds the perfect way to profess his feelings to Leela. Meanwhile, the rest of the crew goes on a Fantastic Voyage-esque journey into Fry’s body to eradicate the worms.
imdb.com summary:
After Fry eats a bad egg-salad sandwich, he begins acting strange. Parasites from the sandwich begin making him smarter and stronger, causing Leela to look at Fry in a new light.