(William Fernando Martinez/AP Photo)

Bill Clinton is cheating - on his vegan diet.

Clinton's doctor let the secret out in New York Times that sometimes the former president cheats on his healthy diet.

But two of the nation's leading vegan and vegetarian organizations say they're willing to give Clinton a pass since he is mostly adhering to the tenants of the diet.

Why does Clinton continue to call himself a vegan?

"There is some latitude … he is primarily a vegan," said Len Torine, Executive Director of the American Vegetarian Association.

"Whatever amount of vegan you are, I support it. I support him. He's bringing enlightenment to a huge population because of his popularity."

Over the weekend, Clinton family doctor, Mark Hyman, revealed in the New York Times interview that he has advised Clinton to "occasionally eat fish and lean protein."

"It's hard being a vegan to eat enough good, quality protein and not have too much starch," Hyman told The Times. "I know a lot of fat vegans."

If he follows his doctor's advice, Clinton is not a vegan "according to strict definitions," American Vegan Society President Freya Dinshah points out. But "people want to aspire to something … we applaud everyone doing the best they can."

Though indulging in animal products, once in a while, appears to be just what his doctor ordered, the former president continues to embrace the vegan label - doing so in over and over again in recent interviews.

Appearing on ABC's "Jimmy Kimmel Live" less than two weeks ago, Clinton didn't dispute the host's claim that the former hamburger-lover was a practicing vegan.

"You, being a vegan, you only get half a pizza really," Kimmel said.

Clinton responded: "One of the few things I miss about this diet is I loved hard cheese - I miss that. But I feel a lot better."

Just last month, former first daughter Chelsea Clinton called her father "the world's most famous vegan."

"It's not even really discipline now, because it's just part of his life," Chelsea said on the web series, Mondays with Marlo.

The former president - once famous for his love of the McDonald's Big Mac - made headlines when he first adopted a vegan diet following his 2010 angioplasty. He shed 30 pounds, championed healthy eating, and was even named PETA's "Person of the Year."

Some vegan purists might raise a ruckus over the way Clinton bends the rules from time to time, but this isn't the first time he's owned up to it.

In a September 2013 AARP Magazine profile, Clinton revealed that he eats fish and eggs "once a week or so" in order "to maintain iron, zinc and muscle mass."

Clinton has also admitted to snatching a single bite of turkey on Thanksgiving.