On the first page of the first chapter of his unauthorised and unflinching new biography of Anthony Bourdain, Charles Leerhsen paraphrases George Orwell’s remark that saints should be considered guilty until proven innocent. Later, Leerhsen makes a more explicit case for pursuing an unvarnished portrait of the beloved chef, writer, and television host. “[W]hen we try to pick and choose the lessons to take from a life,” he argues, “we begin to construct a lie – in this case, a lie about a man singularly devoted to truth and opposed to pretension and public relations.”

If Leerhsen sounds a bit defensive, it’s not out of nowhere. Down and Out in Paradise – which contains unflattering details about Bourdain and quotes private communications from the final days, and hours, before his suicide in 2018 – has been the subject of a nasty controversy that started before it even came out. Bourdain’s younger brother, Christopher Bourdain, has accused the book of being defamatory, and many of Bourdain’s friends and colleagues declined to speak to Leerhsen.

Enough did speak, however, to provide the material for an engrossing, penetrating, but often bleak book whose candour crosses the line into something uncomfortable. For example, Leerhsen uses Bourdain’s final messages with Asia Argento, the Italian actor with whom he had an unhappy and increasingly one-sided romance at the time of his death, as an epigraph, which feels tasteless.

The title Down and Out in Paradise is, of course, a nod to Orwell’s Down and Out in Paris and London, a favourite book of Bourdain’s and the model for his bestselling memoir Kitchen Confidential, but also an encapsulation of the question that has haunted his legacy from the time the news first broke of his death in a French hotel room. How could someone loved and admired by millions, and who had what has often been described as the best job on earth (“I travel around the world, eat a lot of shit, and basically do whatever the fuck I want,” Bourdain once said), be so unhappy as to take his own life?

Leerhsen deftly sketches Bourdain’s childhood as a would-be rebel in suburban New Jersey, his unhappy period at Vassar College before switching to cooking school and falling in love with the pirate-crew atmosphere of professional kitchens, and his early career as a very average chef who came to realise that he enjoyed writing about food as much as cooking it. After he published the New Yorker essay that became Kitchen Confidential, Bourdain was transformed from a slightly dorky recovering addict – whose finances were so bad that he couldn’t qualify for a credit card – to an iconoclastic, world-traveling television celebrity.

Along the way, however, things began to fall apart. Armed with research drawn from confidential interviews and, apparently Bourdain’s phone and laptop, Leerhsen describes a man who, at the end of his life, was on difficult terms with his mother and brother and not particularly present in the life of his 11-year-old daughter; had become a “boss-from-hell” whose “increasing obnoxiousness” had alienated the few longtime friends he hadn’t already unceremoniously ditched; and who, although he had quit heroin and other drugs years earlier, was a “very active alcoholic”. Bourdain was meeting prostitutes, we are told, and leaning heavily on Viagra, steroids, and human growth hormone to impress the two-decades-younger Argento.

Leerhsen speculates that Bourdain was grappling with a sense that he’d materially achieved everything a younger him craved but had become a person – rich, prickly, lonely, in need of constant validation – he despised.

Leerhsen, who has a background in magazine writing, approaches biography not as a dry accumulation of facts but as something ruminative, chatty, and essayistic. He’s a stylist with a knack for winding sentences, and a nice eye, or ear, for the vivid: Bourdain’s face was “a big, beautifully cragged-out Easter Island mask through which he somehow both eagerly and warily surveilled the world”.

For all its perceptiveness, Down and Out in Paradise is marred by its tendency to constantly tie Bourdain’s life to the circumstances of his death: the book returns frequently to the subject, constantly foreshadows it, and closes, somewhat abruptly, with his funeral. That short-changes Bourdain. His suicide may have been the final act of his life, but it was hardly, by a long shot, the most interesting.

• Down and Out in Paradise: The Life of Anthony Bourdain is published by Simon & Schuster.