There's a lot to look at in Jenny Saville's new painting, Fulcrum, on show at the Saatchi Gallery's exhibition "Ant Noises". For one thing, Fulcrum is the kind of billboard-sized work that cruel critics maintain appeals to Charles Saatchi's ad-man's eye. At five metres by three, it is about bigness. Which is fair, given that the picture's subject is a trio of enormously fat women, tied together naked on what looks like a mortuary slab. Vast breasts shear across the canvas like tectonic plates, an effect made more powerful by Saville's planar brushwork. Her palette - a mottling foxblood, cellulite yellows and subaqueous blues - suggests dead meat. At Fulcrum's centre, the thighs of the two lower women lock like clasped fingers. So dense is the painting that the figures become a single, illegible mass: a cumulo-nimbus of flesh that floats out at you with that lightness-on-its-feet of the very fat.
And it is beautiful. The thing that strikes you about Fulcrum is its delicacy, that same perverse juggling with massiveness that allows you to see a two-ton Richard Serra as fragile or a wall-sized Rothko as frail. On the one hand, the painting's construction makes you worried that it is about to collapse under its own weight, thundering out of the picture-space in an avalanche of avoirdupois. Saville, who appears as the top figure in the picture, says that she had to paint it from polaroids because "you just can't ask people to lie on top of each other like that for long." There are delicacies in Fulcrum's narrative as well. A mother and daughter feature: "The mother's sixty and they'd never seen each other naked before," says Saville.
But is the picture intentionally grotesque? Had Fulcrum been painted by Lucian Freud - comparisons of the two artists' styles are made more frequently than Saville likes - you would have felt that its premise was unkind. As it is, Saville has placed her subjects in a pose that is plainly painful on account of their weight, tied them together with ligatures that cut into their arms and splattered them with a clotted red pigment that reads ambiguously as either shadow or blood. The echo is less of Freud than of Francis Bacon, humanity on the butcher's hook.
Saville's answer is uncompromising. "I don't think Bacon pushed it as far as he could have done," she says, drawing on the compulsory Britpack Marlboro. "His mark-making retained an interest in the subject, that's what gave it its charge. I want a different pivot: areas of painting where you lose yourself and only see what they are when you step back."
So there are more pivots at work in Fulcrum than meet the eye. Saville admits that she is fascinated by "bodies that are extreme, bodies that are transgressive, narrative.
"You see someone really huge and you think, 'heart attack'," she says. "You see a pregnant woman and you think, 'life'." Her taste for fat lies in its story of change. So huge is Fulcrum's canvas, so mountainous the figures on it, that they can't be taken in in a single glance. "To read it, your eye has to move across it, like a landscape", says Saville.
Bound up in this is a double self-portrait, of Saville as both feminist and painter. The idea of the female body as a landscape of sexual sites (as opposed to the phallocentricism of the male) owes itself to the writings of Luce Irigaray and Seventies Ecriture FÃ©minin. The oddness of Saville's bodies forces you to see them as a narrative in time. Best of all, Saville likes plastic surgery. "When the surgeons talk about moving flesh - donor sites, mattresses - it's a recipe for how to paint. I sometimes feel I have this tin of liquid flesh in my studio, and that surgery manuals are kind of how-to-do books."
Which makes the title of one of her other works in the show, Ruben's Flap, intriguing. Critics have seen it as a reference to Saville's feminist repossession of the female nude, a quick jab at Rubens and his phallus-bearing kind. It is actually a clinical term for the incision made in a thigh before a skin-graft. What this suggests is a movement away from Irigaray towards a more visceral understanding of painting. Saville's blood-splashes, her hills of flesh, don't just tell the story of her subjects: they also tell her own. "People say my work is less feminist," muses Saville, in front of another new work, called Hyphen. "I don't know. I do know that I can pinpoint the moment I made this or that particular mark, how it tied the surface down, whether it was a nightmare day or not. I'm a lot more open to paint now, it really used to freak me out. I've got this suspicion that painting's kind of over, but I like it too much to stop doing it."
'Ant Noises', Saatchi Gallery, NW8 (020 7328 8299), from Thursday to 20 August