In the Victorian era, the boiled root (or a paste made from the powdered root and water) was often served as an easily digestible food for children and the sick. This practice was widespread, not only in the West Indies but also in Britain, as it was wrongly believed to be very nutritional. Mrs Greenlow eats it for its nutritional properties in Anthony Trollope's Can You Forgive Her? and the invalid Richard Swiveller receives a hamper of arrowroot and other 'delicate restoratives' in Dickens's The Old Curiosity Shop. In fact, it is almost entirely carbohydrate, and has very little nutritional value at all. For more information, and for Napoleon's claim that the British enthusiasm for arrowroot was merely a way of propping up their colonial empire, click here.
Although I don't recommend it (not only is it ineffective, it also apparently tastes like bland gruel), the recipe can be found here.