A Christian author has come to the defence of US mega-church leader Joel Osteen against critics who say the megapastor's messages are "theology lite" and void of the central Christian message of the cross.

"Critics say Osteen lacks biblical references in his books and claim that he preaches prosperity gospel," said Richard Young, author of The Rise of Lakewood Church and Joel Osteen. "However, I found nearly 130 scriptural references in 'Become a Better You,' Osteen's newest book."

Three million copies of Become a Better You, published by Free Press - a division of Simon & Schuster - released in America on Monday along with a resurfacing of criticism as Osteen went on a media tour this week.

"How do you react to the critics who call your message 'theology lite?'" CNN's Larry King asked Osteen, who pastors Lakewood Church in Houston - the largest church in the country.

"I talk about forgiveness and how to have faith when bad things happen and how to overcome and love your enemies and things like that," said Osteen, alluding to situations such as those suffering with cancer or marriage troubles. "So when they say it's gospel lite, I think, you know, we're helping people where the rubber meets the road."

"We give them hope. We pray for them," Osteen emphasised. "We say God's going to give you strength."

"But, you know, how can that be gospel lite to me?" he asked. "That's why I come back to saying I'm helping people."

To critics, Osteen's latest work, which is mainly based off his sermons, is another self-help book. But Osteen says it's the principles of God's words and his book aims to reach outside church walls to those who normally don't go to church.

"I don't think you have to shove it down people's throat. You have to just present it to them. Just, you know what? The Bible is full of common sense that can help us in our everyday lives," said the megapastor Tuesday night.

Although Osteen says he believes in hell and the afterlife, he doesn't preach "fire and brimstone" and his messages often leave out the traditional Christian teachings of sacrifice, the cross of Jesus Christ, and the word "sinners."

Backing Osteen, Young acknowledged that not everyone agrees with Osteen's style, but said the megapastor encourages people to live better lives through faith in God and following Biblical principles.

"Few individuals have been as successful as Joel in spreading God's word," stated Young. "Joel understands today's culture and that messages of damnation and of a vengeful God no longer resonate with an overstressed society that already believes they are living in Hell daily.

"Instead, Joel tells people that if they draw closer to God that their lives will be better. This is a message that our society is eager to embrace. Who doesn't seek a fuller life on earth?"

Osteen calls himself a motivator who preaches a message of hope and tells people they can live a good life no matter what's happened.

And his message resonates.

His first book, Your Best Life Now, sold nearly 5 million copies, and he draws some 47,000 people to his church every weekend. Futhermore, he has 10 million television viewers tuning in every Sunday.

Regarding his lack of formal seminary training, he pointed to Jesus' 12 disciples - some of whom were fishermen without any formal training.

"The Bible says that God chooses people that are not the most educated or the smartest, to confound other people," said Osteen on Larry King Live on Tuesday.

Osteen is currently in New York for a two-night speaking engagement at the Madison Square Garden. His Lakewood Church in Houston was ranked the largest church in the USA by Outreach magazine in its annual list of America's largest and fastest-growing churches.