What started as the dubious drug bust of a beloved, elderly Mill Valley merchant — a case that rattled many in this bucolic burb — is morphing into a clash about vegetarian rights. Dave McDonald, 70, of Mill Valley, has been a vegetarian for 42 years. But when he was jailed recently for 99 days on drug-related charges (most of which were later dropped), Mr. McDonald was denied vegetarian meals.

He refused to eat anything that he did not know was animal-free, and as a result, his weight plummeted nearly 50 pounds to 155.

“I don’t want animal corpses on my plate,” said Mr. McDonald, who is now free on bail. “My belief in not hurting animals is more powerful than any religious belief.”

Had Mr. McDonald said he was a vegetarian for religious reasons, or because of a medical condition, the county would have been legally required to comply. But Marin County officials said that simply believing in the sanctity of animal life was not enough.