The PM has apologised for blowing up at the woman after he did not receive the non-red-meat meal he had requested on a VIP flight from the Pacific Islands Forum in Port Moresby in January.

Yesterday, Karen Inge, head of nutrition at the Victorian Institute of Sport, said: "If you cut down on red meat it can reduce your iron levels.

"The major role of iron is to carry oxygen in the blood.

"If you have low oxygen it makes you tired.

"It's not rocket science. You only have to look at a child who is tired to see how cranky they are.

"When you are tired you don't often react in the best way possible."

Opposition agriculture spokesman John Cobb said a lack of red meat explained the Prime Minister's "toddler tantrum" and why he was "as weak as a limp lettuce".

"Without iron in their diet a person will become pale, insipid, wishy-washy, anaemic and prone to outrageous outbursts," Mr Cobb said.

"A lamb chop or steak would put colour in his cheeks and iron in his soul.

"If you denied me a chop, I'd have serious anger management issues."

Mr Rudd took time out from the G20 summit in London to apologise for the outburst.

"All of us are human, I'm human, I'm not perfect," he said.

But yesterday - as he met with the Prime Minister of Singapore, Lee Hsien Loong, during a brief stopover on his way home - he found support from one of his inner circle.

The Housing Minister and member for Sydney, Tanya Plibersek, said Mr Rudd was "absolutely not" bad-tempered.

"He's a great person. He is very hard-working, he's very dedicated to his job," Ms Plibersek said.

"It's never appropriate for any of us to lose our temper but unfortunately many of us do on a regular basis - me included."

The controversy has boiled to the surface as the Meat and Livestock Association begins an advertising push - including a supplement in The Sun-Herald today.

In the past Mr Rudd has denied he is anti-lamb.

Late last week his office said he was not on a meat-free diet, but "follows a healthy, balanced diet including red meat, other meats and of course plenty of fruit and vegetables".