Why is food advice so confusing? Up for debate is the role of fat in our diet. Adrian Golberg takes a look at the methods behind determining what food is good for us and what food is bad for us, and asking why is it so hard to be certain. He speaks to Nina Teicholz, who tells the story of Ancel Keys, the researcher whose work laid the foundation for many dietary guidelines today, as well as Gary Taubes, a journalist who wants to improve the way nutritional studies are carried out. Ayela Spiro of the British Nutrition Foundation says that nutrition, like all science, is ever evolving, and not always exact.

(Photo: Woman holds up a hamburger in one hand and an apple in the other. Credit: Thinstock)