Still, some have attributed Jackson's apparent low weight to the strenuous schedule he adopted for his upcoming concert tour.
"He was always thin, but he was also in the middle of a very stressful time, getting ready for the tour," said LaPerruque, who noted that he last saw Jackson about four weeks ago at a Beverly Hills restaurant. "I even said to him, 'Michael, this is the skinniest I've ever seen you.' He said, 'Well, I've been rehearsing.'
"It was always a running joke with us, that I needed to put meat on his bones."
During his appearance on "Good Morning America," Ferrigno's statements appeared to support that explanation.
"He might have been a little thin because he was under a lot of stress training for the tour," Ferrigno said. "But when I put him through the routine and everything, I mean, it was just fine -- I mean, very energetic."
Meanwhile, the singer's representatives have said Jackson passed a four-hour physical in preparation for his London concerts.
But Ayoob said he harbors doubt about the veracity of the physical.
"I'm very concerned about all these pseudo-reports that Michael received a 'clean bill of health' to do these concerts," he said. "I don't know who examined him but, at reports of 5'10" and a reported 125 pounds, his body mass index was 17.9. That spells wasting.
"He may have been allowed to do a concert in Spain, but he could not have walked a fashion runway there," Ayoob added. "They have laws about models being too thin to work."
Ayoob said that if the reports that Jackson was only 112 pounds are true, his health situation could have been even more dire than many of his acquaintances knew.
"In terms of his weight, if was still at 125, he was emaciated," he said. "If he was at 112 -- if those reports are true -- he's cachexic."
Whether or not Jackson himself had an eating disorder, research has shown that men, too, can suffer from them -- albeit at a rate about 10 percent of that seen in women.
However, certain eating disorders are more common than others among men, research suggests. In a 2007 study, Harvard University researchers found that men account for 25 percent of Americans with anorexia or bulimia and 40 percent of those with binge-eating disorder.
Still, Jackson's acquaintances say that even despite the star's apparent preference for healthy food, he was not always so particular. On rare occasions, LaPerruque said, Jackson would send his assistants out for an order from Roscoe's House of Chicken and Waffles, or an order of hot wings -- another of his junk food favorites.
He believes the rumor that Jackson suffered from an eating disorder is based on "something that someone made up.
"Now, was his appetite the same as mine?" he asked. "Absolutely not."
ABC News' Imaeyen Ibanga contributed to this report.