Once upon a time, before the infiltration of the internet and cable television, the sauciest age-inappropriate viewing available to a teenage girl featured sofas, pot plants and roving mikes.

Back in the gentler times of the early 1990s, my friends and I spent many sick days and school holidays relishing the adult themes of daytime chat. We marvelled at the white supremacists, abuse victims and sufferers of multiple personality disorder on Oprah, Donahue and Sally Jessy Raphael.

Then everything changed. Jerry Springer (''Midgets Fight''), Ricki Lake (''My Sister Has No Class She's a Hoochie'') and Maury Povich (''Is My Man the Father of My Sister's Baby?'') arrived. The genre skewed gutter, Oprah skewed inspirational and the rest was history.

This month Kitty Kelley, noted shoveller of celebrity dirt, published a biography of Oprah Winfrey - inspirational leader, media mogul, world's richest black woman. It charts her ascent from her Mississippi roots, roots which are depicted as modest but not quite as modest as Oprah has made out, with her claims to having nought but a pair of cockroaches named Melinda and Sandy as pets.

The biography is no masterpiece. The great wordsmith the book uncovers is the Nashville barber Vernon Winfrey, the man who raised Oprah as his daughter: ''I felt like my daughter dusted her shoes with my white hankie and stuffed it back in my pocket''; ''Listen, girl, if I say a mosquito can pull a wagon, don't ask me no questions. Just hitch him up.'' (Compare this to the lacklustre imagery of Kelley who at one stage describes platters of ''shrimp the size of iPods'' at an event in 1993.)

Still it is an illuminating read for anyone interested in unpicking the tenets of the self-help gospel that Oprah espouses. Kelley notes Oprah's frequent attacks on welfare mothers from the earliest days of her talk show. In one episode she tells the assembled guests: ''I was a welfare daughter, just like you . . . How did you let yourselves become welfare mothers? Why did you choose this? I didn't.'' Then there are the comments Oprah made when visiting her home town in 1998. Speaking of her wealth and power: ''You receive in proportion to how big your heart is and how willing you are to extend yourself to other people.''

Years later in 2007 when Oprah discovered The Secret, a self-help book that is to psychology what The Da Vinci Code is to literature, she told CNN's Larry King: ''The message of The Secret is the message that I've been trying to share with the world on my show for the past 21 years.''

The Secret is about the supposed law of the universe that positive attracts positive and negative attracts negative, which will come as a surprise to anyone with even the most rudimentary knowledge of the habits of electrons and magnetic fields. The ''law of attraction'' means that if you send out positive vibes, you succeed. If you send out negative vibes, you fail.

It comes very close to laying the credit for all success, and the blame for all failure, at the feet of the individual, ignoring luck and circumstance. This gospel is in many ways the opposite of Christianity; it is about blaming victims rather than lauding them, or even providing them with comfort. It is a philosophy that suits the successful.

This is not to say Oprah does not do good. She has championed victims of sexual abuse and racism; she has been a generous philanthropist and promoter of reading among those who wouldn't ordinarily. Ultimately though, disappointing as it is for a closet fan like myself to admit, Oprah is not the messiah, just a very successful businesswoman.

The Oprah Winfrey Show winds up in September next year after 25 years. Already it is a relic of a time past. Now that I have reached the target demographic for such shows - a mother at home - better distractions are on offer, like podcasts and Facebook.

But I will always have a soft spot for her brand of inspirational daytime television, in which motivation serves as a kind of sensory thrill rather than a precursor to action, in which all the talk about marathons and living your best life is just enough to spur a flurry of leg lifts on the couch, until the ads come on and it is time to head to the kitchen for more ice-cream.