Take a reporter passionate about nutrition. Then take a group of people with deficient eating habits and illnesses caused by these who are willing to take part in an experiment.
The Truth About Food, a mini-series broadcast on BBC about how food can make you ill or cure you, features an episode in which journalist Fiona Bruce tries to discover first hand what is good and what is not good for eating.
She splits subjects in four groups: one group will eat mainly raw fruit and vegetables like our early ancestors, one group will eat fiber-rich food, one group will test what foods are good for increasing the level of good and infection resistant bacteria in our body, and the last group will test the effect of garlic on our body.
See the results in the film at this link.