The world is affected by an obesity epidemic, but why is it that not everyone is succumbing? Medical science has been obsessed with this subject and is coming up with some unexpected answers. As it turns out, it is not all about exercise and diet. At the centre of this programme is a controversial overeating experiment that aims to identify exactly what it is about some people that makes it hard for them to bulk up.

The honey badger looks like something you might buy in pet shop and give to children, but turns out to be one of the most violent and determined creatures ever to scuttle across the face of the earth. Nothing in the badger’s world-not even the badgers themselves-are safe from its remarkable ability to create havoc and cause harm. Like a meter long skunk with the brain of a shark the Honey Badger’s metabolism compels it to eat constantly and live on the run. Its diet is admirably inclusive ranging from insects to its own young. If an animal is too big to eat then the badger will fight it anyway, indeed it is this almost supernatural tenacity that compels you respect it, as well as yielding some of the most spectacular sequences in the film. Five foot long cobra sleeping in the top of tree? No problem, the badger scoots up and bites its head off. When an ailing badger is attacked by a full size leopard it takes the leopard over an hour to finish it off. When one is bitten in the face by a snake that can kill a man, it just lies down for a while and sleeps it off.

What would happen if you ate nothing but fast food for an entire month? Filmmaker Morgan Spurlock does just that and embarks on the most perilous journey of his life. The rules? For 30 days he can't eat or drink anything that isn't on McDonald's menu; he must wolf three squares a day; he must consume everything on the menu at least once and supersize his meal if asked.
Spurlock also treks across the country interviewing a host of experts on fast food and an equal number of regular folk while chowing down at the Golden Arches. Spurlock's gruelling drive-through diet spirals him into a physical and emotional metamorphosis. Find out in 'Super Size Me' a look at the legal, financial and physical costs of America's hunger for fast food.

The plant eaters take on the largely indigestible, spiny and poisonous defences of plants with some spectacular physical adaptations to diet. Plant Predators demonstrates the particular (and often peculiar) adaptations of herbivores

The next instalment focuses on dietary needs and how different species have evolved beaks to suit their individual requirements. The latter come in a multitude of forms. Blue tits and goldfinches have beaks akin to tweezers, with which to extract seeds, while the hawfinch's razor-like bill can deal with a cherry-stone. However, the crossbill is the only finch that can twist its mandibles in opposite directions. Jays store acorns for winter by burying them in the ground, whereas woodpeckers can keep up to 60,000 of them in one tree trunk. Sap is also desirable, and there are a variety of methods used to obtain it. The hoatzin is the only specialised leaf-eater, and accordingly has a digestive system more akin to that of cattle. Plants recruit birds to aid pollination, and offer nectar as a reward. Hummingbirds eat little else, and the sword-bill's beak is the longest of any bird in relation to its body. Insects are also highly prized, and Galapagos finches are shown to possess some ingenuity as they not only strip bark, but also use 'tools' to reach their prey. Crows are hailed as being among the most intelligent birds, and one is shown using a twig to spear a grub within a fallen log. The robin is an opportunist, and Sir Attenborough observes one seizing morsels as he digs a patch of earth. In South America, a cattle tyrant sits atop an obliging capybara and uses its vantage point to spot passing food that may be dislodged by its grazing partner.

The fifth programme explores the alliances formed between the animal and plant worlds. Attenborough dives into Australia's Great Barrier Reef and contrasts the nocturnal feeding of coral, on microscopic creatures, with its daytime diet of algae. Some acacias are protected by ants, which will defend their refuge from any predator. Besides accommodation, the guards are rewarded with nectar and, from certain species, protein for their larvae as well. Fungi feed on plants but can also provide essential nutriment to saplings (Mycorrhiza). The connection is never broken throughout a tree's life and a quarter of the sugars and starches produced in its leaves is channelled back to its fungal partners. Meanwhile, fungi that feed on dead wood leave a hollow trunk, which also benefits the tree. Orchids enjoy a similar affiliation. Lichens are the product of a relationship between fungi and a photosynthetic associate, usually algae. They are extremely slow-growing, and a graveyard is the perfect location to discover their exact longevity. Mistletoe is a hemiparasite that obtains its moisture from a host tree, while using own leaves to manufacture food. Its seeds are deposited on another by the mistletoe tyrannulet, following digestion of the fruit. The dodder (Cuscuta) is also parasitic, generally favouring nettles, and siphons its nourishment through periodic 'plugs' along its stem. The rafflesia has no stem or leaves and only emerges from its host in order to bloom — and it produces the largest single flower: one metre across.