David Attenborough's diet change he credits to long life as he celebrates 100th birthday

Sir David Attenborough is now officially a centenarian, with the British broadcasting legend attributing his longevity to a little-known diet change.

Today (8 May), Attenborough celebrated his 100th birthday - a milestone moment which the BBC have honoured with a slate of new shows.

Making Life on Earth - Attenborough’s Greatest Adventure, Secret Garden and David Attenborough's 100 Years on Planet Earth are all set to air during a week-long celebration of the star’s work and legacy.

The latter, a 90-minute special hosted by Kirsty Young at the Royal Albert Hall in London, is set to take audiences on an ‘extraordinary journey through a century of exploration and discovery in the natural world, seen through the prism of David’s remarkable life and work’, as per a press release.

Despite his lifelong adoration for wildlife, Attenborough is not a staunch vegetarian and does not follow a vegan diet.

David Attenborough turned 100 on Friday (Dave Benett/Getty Images)

And even though he consumes dairy products and fish, the naturalist has admitted he’s become much more plant-based in recent years.

In a 2017 interview with The Sun, he claimed he was drawn to vegetarianism in a way that he never thought he would be.

Because of this, the Blue Planet star now very rarely eats red meat, including beef and pork.

While red meat is considered a good source of iron, zinc and B vitamins, too much of the protein is linked to increased chronic diseases, including bowel cancer, heart disease and type 2 diabetes, the NHS warns.

People who choose to consume lamb, venison, and other red meats should eat no more than 70g per day.

The father-of-two, who said the slight shift in eating habits was not done in ‘a great sort of dramatic way’, has also previously spoken about his aversion to heaped portions.

He revealed in an interview with the Radio Times: “I’ve never really been one for eating enormous meals and I’m not particularly a gourmet either, so I can’t pretend that I’m feeling deprived in any way or that it’s cost me all that much.”

The father-of-two said he rarely eats meat and enjoys small portion sizes (BBC)

The British Heart Foundation has warned that if your portion sizes are too big, your weight and your blood glucose control will be harder to manage.

Having too much on your plate can also impact weight loss efforts and cause side effects such as acid reflux, bloating, heartburn and stomach pain, as per the Cleveland Clinic.

In a previous interview, Attenborough spoke about the idea of him turning 100, claiming he saw ‘no reason whatsoever’ that he wouldn’t make it to the milestone and beyond.

“Earth has enough wonders to make more than three Planet Earth series.”

David Attenborough's 100 Years on Planet Earth will air on BBC iPlayer and BBC One on Friday 8 May from 8.30pm.

The broadcaster's birthday special will air on BBC One and iPlayer (BBC)

The show will feature the BBC Concert Orchestra playing iconic tracks from Planet Earth, Blue Planet, and Frozen Planet, alongside special performances by Bastille, Sigur Rós and Sienna Spiro.

Contributions from those who have worked alongside the national treasure over the years will also be aired, with the BBC confirming it celebrates not only Attenborough but a ‘century long relationship between audiences and nature’.