My interest in barefoot running has over the last couple of years taken me on a journey that led me to Crossfit and a Paleo diet. In the process I became more aware of what constitutes fitness and a healthy diet. But in particular I began to realise that we have been influenced towards a diet that is heavily based upon cheap constituents that the food industry finds it profitable for us to eat, namely cereals and sugar. Along the way fat has been cast as the bogeyman and a healthy diet has been defined as a low fat diet.
The reality as I now understand it is that fat is not inherently bad for us and sugar is the cause of problems with overweight and obesity. The Guardian published a great article Why our food is making us fat which I recommend you read that summarises the key facts on this suject.