Lucien PÃ©rot, 69, who had been drinking, choked on a 44g (1.5oz) beef rib he could not chew, reportedly because he had several teeth missing.
Olivier Boudin, 38, who had a pre-existing genetic heart condition, had a heart attack seeing his friend die.
There had been intense speculation over what had happened after their bodies were discovered last Thursday.
The men had been sharing a meal in Perot's garden in Authon-du-Perche, south-west of Paris, and drinking heavily. PÃ©rot was found to have 2.4g/l of alcohol in his blood.
One was found sitting on a chair and the other lying down, prosecutors said.
The two men had grown close and developed a "father-son" relationship, local residents said.
Many were relieved to discover that they had died of natural causes, reports said.
"It's clear that it did not involve an external intervention," one neighbour told Le Parisien newspaper.
"They did not have enemies, lived simple lives and were not types who would get themselves killed by the mafia," she added.
Post-mortems in France have explained the mystery of how two men found dead together after a meal perished.