The novel for which Lionel Shriver is best known, We Need to Talk about Kevin (2003), generated endless discussion across the spectrum of readers, from buzzing suburban home-based reading groups to the pages of the Guardian and the New York Times. Much of this discussion circled around the question of the first-person narrator and mother, Eva Khatchadourian, and her relationships with her uncomprehending husband and her psychopathic son.

Ten years later, here is another ‘issues novel’, again told in the first person by a woman with a singularly multicultural name, a close male relative who has something dreadfully wrong with him, and an unravelling marriage to a bewildered husband whose name begins with F. It’s as though Shriver has worked out what sort of narrative template will best suit her exploration of the various pathological conditions that bedevil contemporary American society, and is sticking with it.

One difference, however, is that few readers conflate Eva Khatchadourian with her creator, despite the fact that a first-person narrator is often taken by readers as an invitation to read a novel as autobiographical. But that is problematic in Big Brother because Shriver, like her narrator, really did have a morbidly obese brother, who died at fifty-five of complications arising from his condition. Many will have seen her recent article on the subject, and may have been as disturbed as I was by the fact that her own attitude to food and fat seems less than healthy. All of this complicates a reading of her novel, sometimes beyond interpretation.

The narrator, Pandora Halfdanarson, has not seen her brother Edison for some years, so when he arrives for a visit she is profoundly shocked at the airport as she realises that the human mountain being pushed towards her in a wheelchair by two flight attendants is her brother. Formerly a jazz pianist of note but now on the skids largely because of his weight, Edison is an uneasy fit in his sister’s house with her husband and two teenage stepchildren, for Pandora’s husband, Fletcher, is what Manning Clark would have called a ‘punisher and straightener’: a skinny, dour perfectionist and extreme exerciser whose views on food and fitness are in their own way almost as warped as Edison’s, and whose tolerance of Edison is predictably minimal.

Eventually, Pandora decides that she must stage an intervention to save her brother’s life: she and he will take an apartment together, and together they will diet. For Pandora herself, who vaguely believes that she has gained about twenty pounds since her marriage, has actually gained twice that amount. We hear about these siblings repeatedly in terms of the number of calories they consume and the number of pounds they weigh – American dieting culture seems never to have embraced the decimal system; perhaps the meanings attached to numbers of pounds and calories have sunk too deep for change – and Edison, at the start of their disgusting but effective protein-shake diet, weighs 386 pounds. That’s 180 kilos, or twenty-eight stone.

Shriver turns the fierce light of her intelligence onto the question of how and why a person’s relationship to food can go so wildly awry, and onto the casual, open expression even by total strangers of unambiguous, self-righteous fat hate: ‘Landlords refusing to rent to lard-asses was perfectly legal.’ She pays particular attention to the insistent association of fat with moral failure, and her characterisation of Fletcher is in itself an eloquent critique of the usual corollary, that thinness equals virtue: ‘Following Edison’s arrival, my husband’s fare had grown only more viciously nutritious. We were drowning in bulgur and quinoa.’ There is also an implicit comparison with the moral ambiguity of the strange little business by which Pandora has gained a measure of money and fame, the production of custom-made dolls as gifts physically resembling those destined to receive them: eerie and rather nasty little voodoo poppets whose ‘talkie’ function repeats their recipients’ characteristic utterances according to scripts provided by the giver, usually smacking of passive-aggressive ambiguity. One of these has been made for and presented to Fletcher, whose catch-cries include ‘I want DRY toast! I want DRY toast!’ and ‘I’m sorry, but I don’t eat daaaaaaairy!’

The book is full of Shriver’s characteristically unforgiving observations, finely tuned and finely turned: ‘I could have tolerated Edison’s garrulousness if it weren’t for the fact that he never said anything … Edison could talk all day, at the end of which no one knew him any better than before.’ The physical descriptions are too vivid and pointed to make for anything but reader unease: ‘His gut had shifted downward to center around his groin, and sloshed independently of his gait.’

As will be clear by now, this is not a novel for the easily grossed-out. Managing your body and all of its functions at 180 kilos must occasionally take you places where nobody wants to go, and there is one episode in particular that may be the most disgusting scene I’ve ever read in literary fiction, redeemed only by its acknowledgment of the things that siblings are capable of doing for each other. The novel is worth reading for its frankness about the problems of obesity and for Shriver’s characteristic intelligence and verbal flair, but for many reasons – including the ending, which is a cheap cop-out – it is a horror from which, as with a train wreck, the reader may find it hard to look away.