What's worse for us: sugar or fat? To answer the hottest question in nutrition, twin doctors Chris and Xand Van Tulleken go on month-long high-fat and high-sugar diets. The effects on their bodies are shocking and surprising. But they also discover that in the debate about fat and sugar, the real enemy might have been hiding in plain sight.

Western countries are the most sleep-deprived countries in the world. Insomniac Michael Mosley finds out what happens if we don't get enough sleep and looks at surprising solutions to help us get more.

Roses are red, violets are blue but according to the latest understanding these colours are really an illusion. One that you create yourself. Horizon reveals a surprising truth about how we all see the world. You may think a rose is red, the sky is blue and the grass is green, but it now seems that the colours you see may not always be the same as the colours I see. Your age, sex and even mood can affect how you experience colours. Scientists have unlocked the hidden power that colours can have over your life - how red can make you a winner, how blue makes time speed up. Watch an experiment where for people in a blue pod, a minute lasts 11 seconds shorter.

Raging Teens follows a group of young boys and girls throughout their teenage years and captures the changes that the body undergoes through puberty. Its main focus, however, is on Beatrice and the changes she undergoes such as shopping, growing breasts, pubic hairs and her first period (her mother bought her some Chocolate Éclairs to help celebrate which must be a British thing). The boy's side covers testosterone and what changes it spurs in a lad's body such as facial hair, their voice cracking at the wrong time, and parts of the body that have until now lain dormant. You also learn that a pubic hair only grows for 6 months, which keeps it short, and is actually flat oval and not round which is why they curl.

The world stood in fear of an emerging new disease that threatened to kill millions. A new flu variant H1N1 had arrived. If this latest pandemic has taught anything, it is just how little is understood about the invisible world of viruses. But that has not stopped scientists trying. Horizon follows the leading researchers from across the world, who are attempting to unravel the many secrets of viruses to understand when and why they kill.

In recent years, close study of the aging process has opened up new ways that could help us all live healthier for longer. Can we move beyond treating individual diseases, and instead treat the aging process itself? But would a longer life necessarily be a better life? A loose-knit group of researchers believe the real breakthrough is extending our health span - the period of life spent free of disease". Hear from Laura Deming, who dropped out of M.I.T. at the age of 14 and committed herself to finding and funding projects that can expand the human health span, and Dr. Brian Kennedy, whose work in the basic biology of aging has been crucial to the development of countless other researchers' work.